DE2065828B2 - Marking element with high magnetic permeability for object detection by generating harmonics when interrogated by an alternating magnetic field - Google Patents

Description

The invention relates to a marking element for use in a device for detecting a Object in an interrogation zone, in which the object is a periodically changing electromagnetic Field is exposed, with a section made of a material of high magnetic permeability whose magnetic properties are such that in the presence of a marking element carrying Object in the interrogation zone with an applied alternating magnetic field of a predetermined Frequency the magnetization of the element is reversed in order to generate an external magnetic Pulse containing harmonics of a predetermined frequency

From FR-PS 7 63 681 a device emerges in which dynamic magnetic phenomena to determine the presence of an object, eg. A book carried through the door of a library. This known device is based on the discovery that the action of a sinusoidal alternating magnetic field on a piece of metal induces a voltage which is characteristic of the metal composition and which is induced in two balanced coils in the vicinity of the generated magnetic field. An analysis of this characteristic voltage therefore enables a classification of the generated magnetic field.

metal. A book can therefore be identified to which a piece of metal of a special class has been attached

From FR-PS 7 63 681 there is a class of Metals in which there is a magnetic saturation strong magnetic field must be generated. The voltage induced by a metal from the class mentioned In addition to a basic component, it has a certain number of harmonic components, namely should such a metal, namely iron, a tension ι ο generate which contains a third harmonic and a small proportion of the fifth harmonic

Furthermore, highly permeable metals, e.g. those metals that are in a weak magnetic field saturate, induce a voltage that is contrary to the voltage induced by iron contains higher order harmonics A highly permeable metal is according to FR-PS 7 63 681 Permalloy (according to Webster, Permalloy has approx. 8% Ni, 20% Fe and is light magnetizable and demagnetizable) and the characteristic voltage induced by Permalloy contains harmonics of the named and as components eleventh order in contrast to metals such as copper, iron or aluminum, which produce practically no harmonics of such a high order.

Only the composition of a metal is intended to determine the order of the harmonics contained in the characteristic stress. Furthermore, the size of the metal piece and its outer shape should Affect the amplitudes of the harmonics proportionally. The ratio of the two would be accordingly individual harmonics for a particular metal are the same regardless of the size and shape of the Metsllstückes. Furthermore, the ratio should be at least be characteristically different between selected components for different metals, however the size of the metal piece to be used as a marking element should not only be important for determining the order of the harmonic present, but rather for the generation of a signal that is responsible for the Determination is strong enough

FR-PS 7 63 681 thus shows that metals with a high permeability and in particular permalloy can be distinguished from other classes of magnetizable metals by the fact that harmonics of the ninth and eleventh order are present, and by the ratio of some characteristic harmonics Components to each other. Therefore Permalloy is a suitable material for insertion of a special metal marker in v> books a library because normally hardly anyone such a metal carries with him!

In FR-PS 7 63 681 various devices for generating an electromagnetic field are specified. One of these devices has an 8-shaped coil. That from such a coil The generated field has only one direction at one point, while the total number of directions only a part of all possible directions amounts to Another device is equipped with two coils, the μ are excited at the same time, but in which there is no phase equality, so that a rotating field is generated will. Such a field has a different direction at different times, which different However, directions always only form a part of all possible directions. Furthermore, the size of a soft Rotating field small compared to the size of the coil. By creating a field with a large In contrast to a minimum intensity, intensity can reduce the unreliability that The result is that there is no field in some directions. Such a strong field would have more vector components with sufficient intensity than a field with a minimum intensity A field with a minimum intensity is a field that is one Marking element supplies sufficient energy if the latter is geared towards the "greatest sensitivity"

Here, the directions are increased, which in the Field are possible. However, as the intensity of the field increases, the cost of the the field generating agent and the risk increases the use of other facilities is hindered or disrupted.

With the devices of the above type can only be achieved with difficulty that each Marking element receives enough energy when entering an interrogation zone, although "energy" one The function of time and intensity is intended to simplify the description with the hereafter The term "energy" only means its intensity. The by a marker at one point in Energy received in a zone depends both on the intensity of the feathers at that point and on the Orientation of the marking element in relation to the direction of the field at this point. For the definition the orientation of a marking element is suitably the plane, the axis or the length of a marking element used. Known marking elements point to a flat receiving coil, an axial electric dipole or a piece usually in the form of an elongated strip of an isotropic magnetizable material that has at least one long dimension The orientation of such geometric features (plane, Axis, length) in relation to the direction of the field generally determines the proportion of the energy of the field at this point, which is received by the marking element. With that in the present Description used expression "direction or intensity of the field" is intended to indicate the direction or the Intensity of the field at one point can be designated, and this point is usually the point at which there is a marking element. A marking element that has only one such geometric Feature, there is an orientation where the Marker receives the most energy Any other orientation will receive a smaller amount of energy. The orientation at which the greatest Amount of energy is received is the "alignment of greatest sensitivity". In general, the Alignment of the greatest sensitivity of a receiving coil or other flat receiving means the orientation at which the direction of the field perpendicular to the plane of the coil or of the receiving means, and is at an axial electric dipole it is the orientation in which the direction of the field is parallel to the axis of the dipole during in the case of a magnetizable metal piece, it is the orientation of the metal piece in which the direction of the Field runs parallel to the longest straight line dimension of the metal piece With »Alignment or Direction of a marking element «should be named the direction of the geometric feature of the marking element, which is used to define the orientation with the greatest sensitivity.

In some cases the direction of a marker in a zone can be quite random, or the direction changes as the marker is moved through the zone. This applies to those cases in which theft should be prevented. In most areas of use, a Marking element take every possible direction, which can also change constantly. Is located for example a marking element on an object conveyed on a conveyor belt, so it is very likely that the marking element only takes a few of all possible directions and this does not change when running through the zone. These considerations and the one desired in the establishment Reliability are important factors in determining field requirements; H. to the Determine if a field component is along each

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Direction at some points in the zone or along only certain directions must be provided in one or most places in the zone. With the The term “field component” naturally means a vector component, the intensity of which supplies the marking element with “sufficient” energy

The requirements to be placed on the field also depend on the external shape of the marking element. These requirements are less stringent for one "Multi-dimensional" marking element than for a "one-dimensional" one. The multi-dimensional marking element has two or more geometric ones Features, each of which has a different direction One-dimensional marking elements are flat coils, foils and electrical dipoles. One-dimensional markers are generally preferable to multi-dimensional markers because of their cost and potential for damage. In some applications, other considerations make one-dimensional markers highly desirable are, such as B. when such marking elements are arranged hidden for theft protection should.

In a very reliable system for detecting an object by generating fields in several directions, the peak intensities of the field must be chosen so that one for activation a marking element sufficient field component is generated in almost every direction. The fields are generated as a train of pulses, each pulse in the train having a different direction

For detecting an object in an interrogation zone, ζ. B. at the exit of a library, must be at everyone to be detected object a marking element can be attached, which consists of a ferromagnetic !! Material with a total magnetic saturation moment of at least 0.1 electromagnetic Units consists The marking element is chosen so that its magnetization in one orientation for the highest sensitivity with respect to a 60 Hz test magnetic field changing sinusoidally with a predetermined peak intensity of

less than about 1600 - each time the

Test field is reversed.

Strictly speaking, it is a complete reversal the magnetization from one to the other saturation state of opposite polarity is not necessary. With reversal of magnetization is a periodic change in magnetization of at least 0.2 electromagnetic units per cm ³ with a change in the acting field meant. In the interrogation zone there is an electromagnetic Alternating field generated, the at least the mentioned has a predetermined peak intensity and is substantially free of frequency components that exceed a predetermined frequency of at least 1000 Hz. Will be one with a marker element provided in the generated field introduced, and if the marking element and a vector component of the generated field are oriented, the magnetization of the marking element is reversed with each change in the field. at

every reversal of magnetization becomes an impulse generated by the external polar magnetic field. Means are provided with which to close the

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components of the magnetic flux can be monitored. the

> o lower limit frequency of this band is higher than that predetermined frequency, while the bandwidth is at least 600 Hz. There are means of determining a signal is provided which corresponds to a polar magnetic field pulse, and which is used to detect the Object is used, the amplitude and the time characteristic of at least one of the signals ermitteH will.

For a specific marking element, this is the predetermined peak intensity of the test field

jo minimum field, which is a reversal of magnetization of the marking agent can cause.

The object of the invention is to provide a marking element of the type mentioned at the beginning with a combination of shape and magnetic properties

js, which if the Markinguiigselementes on an object at the same time enables the latter to be reliably detected in an interrogation zone According to the invention, this object is achieved by

a) an elongated strip or wire with a length to square root ratio the cross-sectional area of at least 150,

b) with a layer of normally tacky, very strong, self-adhesive on at least one side

of the strip or wire,

c) by a removable backing material attached to the Adhesive layer is attached, the adhesive layer after removal of the carrier material for

Attachment of the strip or wire ar dem

Object serves and the combination of shape and magnetic properties of the so formed Marking element is such that at a maximum rate of change of the attached placed magnetic alternating field of more than

24,000 - per second that in the generated pulse

containing signal comprises a frequency band whose lowest limit is above the 16th harmonic the predetermined frequency and the width of which is at least 10 times the predetermined frequency

With ferromagnetic materials we mean both & 3 conductive and non-conductive materials, For example, iron and its alloys with nickel are to be mentioned as conductive materials and ferrites as non-conductive materials.

! .hurried materials are generally preferable, because they can generate ten times stronger external magnetic fields than the non-conductive materials. A Lean agent made of conductive material can therefore be measured smaller than that of a non-conductive, Material. Small markings are also cheap. -: and can be attached more hidden. This is especially important in preventing theft.

It has been shown that a long strip n> from a ferromagnetic !! Material, if it is sufficiently thin in relation to the dimensions of it ■ 'geometrical characteristic' is measured, a characteristic impulse of an external polar magnetic field generated when its magnetization iimge- ι, and with the action of a changing field.

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de exceeds. In contrast to the Markieningsclcinent according to IK PS 7 636Hl this can be a n elongated stripes pointing towards the invention Maikicrungselemenl cannot be reliably distinguished by means of a single frequency or a \ ■ rhiiltni'.scs of two frequencies to each other. Fs shark It has been shown that the amplitude of a particular I lamionic depends on the amplitude and frequency of the depends on the relevant field and on the orientation of the marking elements in relation to this Field Reqiicnieren suitable for a selected band can ^ edoi h with a ! iiiif a signal would be selenient, the distinguishing one Has features that are essentially iinab are often of the nature of the marking element as well as the amplitude and the efficiency of the acting field. The inventive market;, ι Auxiliary element is frequency-independent to the extent that that it generates the chaakicistic signal for him, solerii is not used instead of a Siniisw echseifeldcs other. /. B. a pulsed field is used v, ird

If the long-grained spreading is to be carried out a migcs i eld a. in this way an extremely polar impulse is generated, which can be distinguished by the entire interconnection in a band, the lower limit of which (the correct frequency) exceeds 1000 Hz and the width of which is at least ten times the lcldfrequcnz, so that with certainty a statistically representative group of frequencies is obtained. A signal of the total time change of the flux components within the band, for example, the 7th, corresponds in a nested with the flow Spuie, n induced voltage is very narrow and is less than 0.1 ms at half amplitude.

The signal generated by the elongated strip has still another distinguishable feature, namely occurs at a particular - the amplitude peak ■, =, composition and at a specific size and shape of the material of the signal under the action of an alternating field with a specific waveform, a predetermined Time after each change of field. This characteristic of the signal e> o can also be defined by the absolute instantaneous value of the acting field at the point in time at which the net magnetization of the elongated strip has the value zero. According to the hypothesis, the "reversal" of the magnetization takes place at this point in time, which corresponds to the peak point of the magnetization reversal signal Properties of the material depends, but also on the waveform of the acting field. However, this expression is found to be useful in comparing the response of different elongated strips subject to the action of the same field.

The elongated strip of the according to the invention Marking elements can be made from a thin tape or wire of a ferromagnetic material with a magnetic moment of at least 0.1 electromagnetic Einheil exist. With circumstances below the value of the ratio of length to square root of the cross-sectional area of at least 150 can the inner self-confidence MciuiigMciiiciiekiL 'at iiociiiMeigiieiiM-iieii "viaici iaiicn

increase the acting field beyond 1600 Bei

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below the ratios below 150, the amplitude decreases of the Magrictisicrungsumkchrungssignals decreases sharply and is noticeably dependent on the orientation of the elongated strip in the acting suffering.

The corresponding criterion for a thin, flat disk made of a magnetic material would be a Ratio of the geometric characteristic dimension to the thickness of at least 6000. Leading hand or disc-shaped marking elements should have a thickness of approximately 0.1 to 130 ini, while diahtförniigc conductive marking elements Diameter from 10 to 30 (1 μm should be at larger dimension, η decreases the amplitude of the magnetic reversal signal. and the hurry becomes larger at half the amplitude and can ultimately no longer be distinguished from reverse signals. those of ferromagnetic metal objects !! that people may carry with them.

A thin, flat and narrow marking clamp is particularly suitable for books in libraries, as the marking clcmcnt is in the spine of the book used or inserted between two book pages and thus remains hidden. A book is in generally provided with two pairs of flyleaves, one over the entire length running fold are connected to each other. These folds are usually wider than an open one Strip, so that a marking element can be easily hidden in this fold. It will Maikierungselement provided on both sides with an adhesive coating and a pad, see above this can be used close to the dressing between two sides.

The preferred number and relative orientations of the geometric characteristic dimensions of the marking element depend on the characteristics of the active field in a still explanatory manner. An idealized marking element has a single major dimension. while a marker with two to each other main vertical dimensions, e.g. B. in the form of an "L", "T", "+", and a marker with three main dimensions perpendicular to each other are common

The elongated strip can be entirely inorganic or made of a ferromagnetic one Laminate that is made with an organic adhesive

is held together, or the strip may also consist of a dispersion of ferromagnetic particles in an organic binder, e.g. B. vinyl chloride exist. The marking element can also consist of several ferromagnetic strips separated from one another by a small distance, the position of which is fixed to one another, or which are embedded in a non-magnetic material ^{1, e.g.} B. as very fine wire threads or ribbons in a piece of paper.

A further embodiment of the marking element according to the invention consists of two or more elongated strips with different alternating current coercive forces, which are used as a unit. Even if such united, elongated strips are in contact with one another, they do not influence one another magnetically so strongly that each strip can generate its own characteristic impulse.

Another embodiment of the marking element according to the invention has one or more elongated strips and at least one control element made of ferromagnetic material, its

Coercive force is at least 400, and that at

remanent magnetization has a static exterior Magnetic field of at least 60 on at least one

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Part of the strip is generated, the amplitude and the /.eitcharakterisük one of the strips below Effect of the field of action generated signal clearly differs from the corresponding signal, when the control is demagnetized.

A possibility of preventing or changing the reversal of magnetization of the marking element is thus to effectively bias the field acting on the elongated strip by using a remanently magnetizable material as the control element. In the case of remanent magnetization, the field of the control element alternately strengthens or weakens the acting field in successive half-periods. If a sufficiently strong remanent field is generated on an elongated strip, the net field in the half-period in which the remanent field counteracts the external field is not sufficient to reverse the magnetization of the elongated strip in the characteristic way. The reversal of the magnetization of the elongated strip for each change in the alternating field need not be completely prevented. Rather, it is sufficient to modify the inversion in such a way that the resulting signal is not characteristic of a marking element. Accordingly , such a magnetic control element need not completely cover the area of the elongate strip. For example, a magnetized control on only a central portion of the elongate strip will cause the segments on either side to behave approximately like two independent strips. The part located in the middle should therefore be sufficiently large and arranged in such a way that none of the segments satisfies the aforementioned ratio criterion

The remanent magnetization of the control element need not be uniform, and indeed are unevenly magnetized controls are generally desirable because they are less of a use is costly

A non-uniformly magnetizable control element has, for example, a series of retentive bands Magnetization, with adjacent bands being oppositely polarized. About internal demagnetization effects should be kept low and to generate a strong external magnetic field the directions of magnetization of the bands of such a magnetized control element parallel to the length of the Control element run.

To demagnetize the marking element, the control element can be in the conventional manner be magnetized. For example, in order to magnetize the control element evenly, the element could exposed to the action of the field of a strong permanent magnet. For a ribbon-like Uneven magnetization of the control element could be the element of exposure to a number of Permanent magnets are exposed, adjacent permanent magnets are polarized in opposite directions. Care must be taken when removing the magnetizing magnets Movement of the magnetizing magnets along an axis parallel to the magnetic poles would result in a Change of the desired magnetization lead with the consequence that the magnetic influence of the control element is reduced to the extent smaller than that to demagnetize the elongate Strip required extent. When using a single pulsed magnetic field, its field distribution is similar to the field distribution generated by permanent magnets, for magnetizing marking agents, the difficulties mentioned could be avoided, since in this case none are controlled Movement is required between the leaning agent and the magnetization source. Facilities for generating such errors are known per se. As an example, the "overdamped" discharge is a Capacitor led by a coil.

To sensitize the marking element, a conventional degaussing device can be used, with which a relatively high-frequency magnetic field with a decreasing amplitude is applied to the marking element. ELs can e.g. For example, a device can be used which causes an "underdamped" discharge of a capacitor through a coil, ie an interconnection of a coil with a capacitor in the same way as the circuit that is used to magnetize a control element, but which has a high t? Value (quality ) having. On the other hand, it is also possible to use a degaussing device with a series of permanent magnets which are polarized in opposite directions. If a control element is moved with respect to such a demagnetization device along a coordinate common to the row of magnets, an alternating magnetic field acts on the control element. With a suitable choice and arrangement of the magnets, a field with a decreasing amplitude can be generated in the demagnetization device. If magnets of different strengths are used and are arranged in such a way that their fields are gradually weaker one after the other in the direction of movement, the amplitude of the magnetic field apparently disappears when the arrangement is moved over a control element. The same result could also be achieved if magnets of equal strength are arranged in a staircase or in an inclined plane, so that the amplitude of the

Magnetic field gradually becomes smaller.

Since the external magnetic field of a control element changes depending on the pattern of magnetization; a can, a demagnetization of the control element in the strictest sense is generally not necessary, but the magnetic influence of the control element need only be reduced to the extent that it is be that the acting field can magnetize the elongated strip.

To simplify manufacture, the control element can consist of a thin, magnetic and uniform coating of a gamma iron oxide powder in a vinyl chloride section on one side of the elongated strip.

With other types of demagnetization, the elongated strip deformed or torn so that its resulting longest linear section is smaller than the length that for the said ratio length to Square root of the cross section is required. The marking element can also be demagnetized as a result "'ground that the elongate strip is stretched to make it magnetically responsive change. The elongated strip can e.g. B. together with a heat sensitive bimetal strip or used as an element of such a bimetal strip.

If the marking element is passed through the field of action, then -_ 's must go through during the movement the interrogation zone can be influenced in at least one and preferably in several places so that the elongated strips of the marking element is remagnetized. An absolutely safe orientation would be achieved with a one-dimensional Effective field together with a marking element with three main dimensions perpendicular to one another, where the strength of the field of action at every point in the interrogation zone is at least t.4 times of the .Schaltfeldes of the marking element would be. As a one-dimensional field becomes a field in which all magnetic lines of force in the interrogation zone run parallel to each other.

A one-dimensional field has two mutually perpendicular directions, which also run perpendicular to the direction of the field, in which directions there are actually no components of the effective field. Likewise, a two-dimensional field has only one direction in which no components of the effective field actually run, while in a three-dimensional field no field components run in any direction. From this it can be seen that with a combination of a marking element having one main dimension with a three-dimensional field and also a marking element having two mutually perpendicular main dimensions with a two-dimensional field and a marking element having three mutually perpendicular dimensions with a one-dimensional field, an absolute orientation at every point in the query zone will be reached with certainty.

With such combinations, the path of the marking element through the interrogation zone can be very great be short and only slightly longer than an elongated strip. If the path is lengthened, it is one ideal combination in which the marking element can be safely oriented at every point reached in the query zone is not required. To ensure that when moving an elongated Strip through the interrogation zone over a

moderately long distance at least one Ummagneiisie It is only necessary that the vectors of the magnetic field components are greater than the switching field of the marking element in each direction at some points in the interrogation zone.

This condition can be met in that three one-dimensional fields are generated in chronological order at each point in the interrogation zone, each field being oriented according to a different coordinate axis in space. On the other hand, the required condition can also be met in that several areas are provided in the movement path through the Abiragezone, in which the orientation of the effective field does not change, while the fields in successive areas have a different orientation.

In addition to the length of the zone through which the elongate strip is to move, there are Structure of a certain facility still other important and interdependent variables, with which is assured that upon movement of the elongate strip through the interrogation zone at least one remodeling has taken place. These variables are the speed of the elongated Strip, the number and orientation of the characteristic geometric dimensions of the elongated strip, the frequency of the effective alternating field, the peak intensity of the field, and the Vector component;) of the field at any point in the interrogation zone at any point in time.

The alternating magnetic field can after a conventional methods can be generated, for example by supplying an air core coil or the coil an electromagnet with alternating current and by moving a permanent magnet so that its Magnetic field in the interrogation zone changes polarity.

A flux monitoring device and a detector circuit can serve to monitor the magnetic flux changes in the interrogation zone and to distinguish the magnetic flux changes produced by the marking element from all external magnetic flux changes. External changes in the flow include the acting field, a noise generated by electric motors, noise etc. generated when an Au holder is operated, the effect on the flow monitoring device being essentially dependent on the strength of the effects and on the distance from the interrogation zone. There are monitoring devices for the magnetic flux, which display the frequency of the change in the field directly, and other devices which display the momentary strength of the field, from which display the alternating frequency can be derived. The last-mentioned devices include magnetoresistive devices in which the Hall effect is used, and magnetic-diode sensors. Either type of device can be used with flow collection devices to improve sensitivity. In such a device, at least one coil is provided with which the magnetic flux is determined inductively. A large coil with a few turns can be used and even with only a single turn, or several small coils can be used, each coil having relatively more turns. Small coils have the advantage of being less sensitive to magnetic noise caused by electric motors and circuit breakers. On the other hand, speaks

a large spool more evenly on the marking element at various points in the interrogation zone as individual small coils. It can be any number of Coils which are in opposition to one another are provided so that magnetic noise from a distant source can be kept low, while detecting a marker which is closer to one coil than to another. at If several coils are used, these can be provided with individual detectors, or the coils are connected in sequence to a common detector.

The signal detector assigned to the flow monitoring device shows in the simplest embodiment the Presence of the marking element in the interrogation zone by determining the time and the amplitude characteristics a signal corresponding to a single magnetization reversal of the marking element. As already stated, the marking element according to the invention generates an unusually narrow signal and a signal that occurs for a particular field of action while the marker field with a certain AC coercive force outputs a signal at a predetermined point in time after a change of the effect generated. By finding signals that are within a predetermined interval occur and have a minimum amplitude, and which begin during a minimum interval and end, the detector distinguishes between noise, the signals generated by the marking device and external signals from other objects that act on a address magnetic interchangeable cld.

The advance determination of the point in time at which the characteristic generated by the marking element Signals occur, also enables the detector circuit clwiis to be more richly equipped than Security feature set false alarms. The reference means for measuring successive signals can be a previous signal, phase or time of the field of action and may be suitable for this purpose can be used at the alternating point of the field of action. 1 front man can enter the interrogation zone Marking elements are permanently arranged, which generates the reference signal. The time intervals between the signals and the individual signal features therefore reliably show the detection of the marking element at. If both options are provided, a system free from false alarms can be be achieved.

In the case of a system to prevent theft, a prescribed measure must be initiated as soon as an apparently stolen item is discovered. The special ones to be met Measures depend on the operation of the invention Marking element together. These measures can be taken from photographing the exist in the interrogation zone person, or there will be an automatic device to open the doors are out of order.

The determination device may consist of a circuit that responds to at least one signal that has a minimum amplitude and a width less than the maximum. The circuit can additionally the time of occurrence of the detected signal in relation to the time characteristic of either the effective magnetic field or monitor for a reference signal that is correlated with the magnetic field signal. The same circuit can be used for a marking element with one or more elongated Strips without a control element as well as for a marking element with one or more elongated ones Stripes and one or more controls can be used. As stated, the generated by an elongated strip when demagnetizing an associated control element Signals have essentially the same amplitude and width as those from a strip that does not contain any Control has generated signals. However, if the control element is magnetized, the shape, the amplitude and time of occurrence of the signals generated by the elongated strip changed will. The detector circuit can therefore essentially determine the magnetization of the control element.

If the marking element according to the invention is used to prevent books from being stolen used in a library, the use of a marking element with at least a control element as suitable, the latter being demagnetized during a check, so that the book can be taken from the library. When the book is returned, the control element are magnetized, so that an unauthorized removal of the book from the library is prevented.

With such magnetization and demagnetization, a precise assembly point of the marking component is required not to be known per se. By dnc clever and hidden arrangement of an or several marking impsclcmentc on one object can be a theft of the item or a impermissible removal of the marking clamps can be safely avoided.

The invention will now be described in detail In the drawings is the

Fig. 1 is an overview of a system for preventing theft or an impermissible Removal of objects from a building, with the system at the exits of the building is arranged.

F i g. 2 is an illustration of two long, straight and parallel conductors and dci lines of force generated by a current flowing in the conductors.

F i g. 3 is an illustration of four long, straight and parallel conductors and the lines of force leading from the in electricity flowing through the conductors is generated,

4 50t is a schematic representation of two generally rectangular »ow coils. and 503 one Diagram of 501 and a zone in which the field lines of the coils run almost at right angles to each other

5, 503 a representation of a grid formed by three superimposed coils, which consists of two generally rectangular "8" coils and one generally rectangular "o" coil, 507, 509 and 511 each a representation of the coils of the grid 505 ,

F i g. 6 502 a representation of two coils according to FIG. 5 and a cross section through a zone in which vectors represent the fields which are generated by the "horizontal" sections of the coils shown in FIG. 5, 504 a representation of the in FIG F i g. 5, not shown in FIG. 502, and a cross-section through a zone in which vectors represent the field extending from the "vertical" central portion of a coil shown in FIG. 5, the "8" coil shown is generated,

Fi g. 7 is a front view of a preferred embodiment of the device according to FIG

the field generating device used,

F i g. 8 is a schematic representation of the windings of part of the FIG. 7 field-generating device shown,

F i g. 9 and 10 each show the magnetic fields generated by the device shown in FIG be generated,

F i g. 11 shows the superposition of two Groups of magnetic field lines which are determined by the one shown in FIG. 7 are generated,

Fig. 12 is a circuit diagram for a device with the a plurality of electromagnetic field generating devices in sequence with electrical energy to be taken care of,

13 is a circuit diagram for a preferred embodiment of the device monitoring the magnetic flux and of the signal detector in the system according to FIG Fig. 1,

F i g. 14 is a perspective view of a book with a marking element according to the invention and

15 is a perspective view of a book; in which a part of the outer cover is placed over the spine for the purpose of showing the otherwise covered, Marking element according to the invention is removed

A preferred embodiment of the marking element according to the invention, which can be used particularly to protect the book inventory of a library, consists of an elongated strip of annealed permalloy tape with the composition of 4% molybdenum, 79% nickel and 1% iron and with a thickness of 25 μπι, a length of 18 cm and a width of 0.6 cm. A gamma iron oxide strip control element is provided which is the same width and length as the open strip. Such a control element can be made by first dispersing 100 parts by weight of a gamma iron oxide pigment used for audio tapes and 2 parts by weight of a wetting agent in a solvent such as toluene to form a 25% solids mixture. To this mixture, 50 parts by weight of a resin composition are added, e.g. B. 75% of a copolymer of 89 parts vinyl chloride and 11 parts vinyl acetate (VYHH) and 25% dioctyl phthalate. A small amount of a mixture of equal parts of methyl ethyl ketone and toluene can be added as required to prepare a solution which can be applied in the form of a layer. The solution is applied by means of a doctor blade to a removable paper sheet-like base w coated with silicone. After the solution has dried, the base is peeled off and strips with a uniform thickness of 230 μm are produced for use as a control element. If the thickness of the elongated strip is more than 230 μm, the elongated strip can be desensitized if the control element is operated by a magnetron -Magnet is magnetized with a gap of 25.4 mm. These controls are then layered together to form the elongated strip. For the production in large quantities, the mixture may _Μ of the elongated strip to be applied to a wide film of the material from which film then 0.6 cm wide strips are cut out.

The F i g. 1 shows three units 10A, 10B and 10q which are arranged so that they form two access paths, the spaces between the opposing units 104 and JOS and between 10/7 and lOCje form an interrogation zone.

The unit HM is partially cut open so that two electromagnets 12Λ and 12B, an air core coil 14 and four smaller coils 16/4, 16B, 16C and 16D can be seen. The electromagnets and the air-core coil form a device that generates an effective field with a connection contact (referred to as input contact), which is connected to the ungrounded (hot) conductor 18 of a filtered alternating current source, and with an "output contact" which is connected via conductors 22, 24 and 26 is connected to a field sequence circuit 20, of which only the conductors 22/4, 24A and 26/4 connected to the unit IQA are shown. The units 10/4 and IOC have the same structure, while the unit lOfl differs from the other units in that it is not equipped with the four smaller coils. 1 mm have a diameter of 10 cm and form a magnetic flux monitoring device labeled 23. These coils are connected in series with an RG 58 A / U coaxial cable, placed in separate locations on one side of the surveillance zone and carefully oriented to filter out as much of the magnetic noise generated by the field generating device and other sources as possible . In the illustrated embodiment, the upper coils 16/4 and 16ß are oriented vertically, while the lower coils 16C and 16D are oriented horizontally. Each coil is covered with a 12.7 μm thick aluminum foil, not shown, which shields against electrostatic noise, but allows the passage of magnetic signals. These shielding foils are connected to the shielding of the connecting coaxial cable.

A signal detector 32/4 is connected to the magnetic flux monitoring device of the unit 10/4 via a coaxial cable 28, and an identical signal detector 32b is connected to the magnetic flux monitoring device of the unit IOC via a coaxial cable 30. If a book 31 provided with a sensitized marking element 33 is carried through the effective field in an interrogation zone, the marking element is magnetized with each change in the effective field and generates a pulse of an external polar magnetic field. The flow monitoring device in this zone responds to this change in the magnetic flux in the zone and generates a signal which corresponds to the pulse and which is sent to the associated detection circuit 32. The detector circuit generates a signal based on the particular amplitude and time characteristics of the marker signal which sets an alarm and display circuit 34 into operation

The F i g. 1 shows generally the spatial arrangement of the field generating device and the flow monitoring device, which devices form monitoring zones which are arranged in a library are whose books are equipped with a marking element according to the invention. The field generating Facility can e.g. B. also consist of a grid-like or other arrangement of conductors, of which an arrangement is shown in Figure 2 to generally show the field that of long straight lines Ladders is generated.

The F i g. FIG. 2 shows in section two long, straight and parallel conductors 512 and 314 with the lines of force leading from FIG the current flowing in each conductor in different

Time intervals are generated. The circular line 513 represents represents only one line of force of a series of circular lines of force from the one flowing in conductor 512 Electricity can be generated while the circular line 515 is just a line of force of a series of concentric and represents circular lines of force generated by the current flowing in conductor 514. For the purpose of Simplification of the representation are shown in FIG. 2 only the magnetic flux lines shown. For the same reasons, only the magnetic properties are shown hereinafter of the electromagnetic field

As can be seen from Fig.2, run in the the area 510 enclosed by the broken line 517 is the field lines of the two conductors 512 and 514 although curved, but essentially at right angles to one another at the crossing points. District 510 represents a cross-section through an interrogation zone and is therefore shown at right angles, since this is often the The shape of the cross-section of a passage is in which the Inquiry zone generated by an electromagnetic field Such a cross-section should generally have entrances and exits, corridors and the like Passages on.

Assuming that the dimension 519 of the area 510 corresponds to the width of a passage, and that conductors 512 and 514 are oriented perpendicularly, dimensions 519 and 521 correspond to FIG Latitude or longitude of the query zone. The considerations in determining the actual length of the Interrogation zone have already been explained. It is well known that the intensity of the field changes directly with the Amplitude of the current flowing in the conductor and vice versa in relation to the distance from the conductor. For a special passage nu. of width 519, when conductors 512 and 514 are spaced apart, js which corresponds to dimension 523, and its distance from the edge of the passage is equal to distance 525 is, and for a particular sufficient energy Each of the fields at their intersection points at the most distant point in the district (near the Dimension 521) determine the amplitude of the current flowing in conductors 512 and 514 must have.

3 shows four long, straight and parallel conductors 516, 538, 520 and 522 and two groups of magnetic field lines which could be generated by the current flowing in the conductors. One group of flow lines is shown in solid lines and the other group in broken lines. The solid lines are the lines of force that would be created if currents were to flow in opposite directions with the same strength in conductors 516 and 518 while in conductors 520 and 522, no current flows, the broken lines ss dargestell- th field lines are generated at a reverse current flow, d. That is, the conductors 516 and 518 are currentless, while in the conductors 520 and 522 currents of the same strength but in opposite directions flow. It should be noted that, given the same dimensions, _{M in} FIGS. 2 and 3 the field in FIG. 3 has a greater length (521), but both fields can be generated in the same period of time (in both cases only two "field pulses" need to be generated). The analysis to determine the current requirement of the two conductors in FIG. 3 is performed generally in the same manner as with respect to FIG. 2 described. Another "sentence" becomes a Such an arrangement of ladders is provided, and these two sets of ladders are combined into one closely spaced parallel planes arranged so that the heads of the sets concerned run perpendicular to each other, a three-dimensional device is created. With such a Facility exists at essentially every location in district 510 at least once during each pulse sequence of the four pulse fields each of the three Magnetic fields that are almost perpendicular to each other. The "end" head of the other set of heads mentioned is shown in Fig.3 with broken lines and denoted by 527

4 shows a two-dimensional field generating device, which is labeled 501 and has two "o" coils 524 and 526. For the purposes an analysis, the perpendicular sections of the coils can be viewed as long, straight, and parallel conductors will. The coils 524 and 526 are located essentially in the same plane, but overlap one another in such a way that that the distance between the adjacent sections 528 and 530 belonging to different coils from each other is much smaller than the distance between the vertical sections of the same coil from each other. In this way, the field lines between the vertical sections on the inside roughly resemble those in FIG. 2 field lines shown. At 503, one of such is unequal spaced Coils formed zone shown, which has the length 521, the width 519 and the height 534 If the coils equidistant from each other, d. h if the distance between the interior sections would be equal to half the distance between the vertical sections of the same coil, fields with those in the F i g. 3 field lines shown are generated. It has been shown that with such, an unequal distance having coils with a length of 105 cm of the vertical sections and with .'20 cm long horizontal sections, which coils of 10 turns a strand of wire No. 10 A.W.G. (like both # 30,610), an essentially two-dimensional field can be generated in an interrogation zone that is approximately 90 cm high, 90 cm wide and had a length of 150 cm when a pulsating underdamped sinusoidal current through the coils an initial peak amplitude of 180A.

5 shows a device generating a three-dimensional field. The device shown at 505 has a grid-like structure 539 which consists of three coils. In the preferred embodiment, the coils are located in parallel planes with a small spacing. The coils are shown individually at 507, 509 and 5_M. The grid has three vertical components 540, 542 and 533 and five horizontal components 546,548,550,552 and 554. As will be seen from the following description of these components, each of these components consists of at least a portion of a coil, and most of these components comprise portions of a plurality of coils. It should be noted that those fields which are generated by the coil sections forming the components 540 and 544 are not required. However, these fields are created and shorten the "length" of the zone when components 540 and 544 are sufficiently close to component 542 ((. In those cases where a

Part of a section of more than one coil is only the field is a section requires following are therefore of the individual coils only the required fields treated in the Figure 5 at 507 and an upright generally rectangular "" - illustrated coil 555! The coil consists of a conductor wound in an "I" shape defining two generally rectangular and serially connected portions of nearly equal size, indicated generally at 558 and 560, having substantially parallel top and bottom lengths. The portion 558 has an upper length 572 and a lower length 574 , while the portion 560 has an upper length 576 and a lower length 578. The lower length 574 of the loop 558 and the upper length 576 of the loop 560 together form the central portion of the "8" coil 555. The upper and lower lengths of the parts 558 and 560, namely the upper length 572 and the lower length 578, form the end sections of the "8" coil 555. Energy impulses can be sent to the coil via the attachment cap sockets 580 and 582 are fed. The arrows shown in the two loops, one of which is labeled 584 , indicate the direction of current flow through the various sections of the loop for direct current. From the sub-figure 507 it can be seen that the length 572 corresponds to the horizontal component 546 , that the length 572 corresponds to the horizontal component 546 , that the lengths 574 and 576 correspond to the horizontal component 550, and that the length 578 corresponds to the horizontal component 554 The sub-figure 509 shows an "o" coil 557, the horizontal sections of which are denoted by 586 and 588, and which correspond to the horizontal components 548 and 552 of the grid 539 (sub-figure 505). In the sub-figure 5JJ a j>&<coil is shown turned to the side. The lengths of the coil labeled 594 and 596 correspond to the vertical component 542 of the grid 539 (505 ), while the lengths 5Γ3 and 592 correspond to the components 540 and 544, respectively correspond.

FIG. 6 shows vector representations of the magnetic lines of force for the fields which are generated by the device generating a three-dimensional field (coils 555, 557 and 559 according to FIG. 5). In the lower figure 502 field vesors are shown in a plane -r, which runs parallel to the "perpendicular" lengths (e.g. 594 and 596) of the coil as well as perpendicular to the plane of the coils, and a side view of the lengths of the coils 555 and 557. The coil 559 is not shown. A region 539 is shown in broken lines with a cross-section. Field vectors are shown at three arbitrarily chosen points 610,612 and 614. The vectors labeled "a" vectors correspond to the field generated by lengths 572,574, 576 and 578 of coil 555 , while the vectors labeled "6" vectors correspond to the field generated by conductors 586 and 588 of coil 557. The field vectors of the field generated by the third coil 559 are shown at 504 at points 610, 612 and 614 , the field being viewed in a plane parallel to the horizontal lengths of the coils and perpendicular to the plane of the coils The coils 555 and 557 are not shown. The area 510 is shown again with broken lines and the vectors of the field of the coil 559 are a'-. "C" - denotes vectors The sub-figure 504 shows the centrally located lengths 594 and 596 and the end lengths 590 and 592 of the coil

559. The dimension 521 of the district 510 runs only part of the distance from the two middle sections 594 and 596 to the end conductor 590 and 59Z. This is a consequence of the fact that in the end conductors 590 and 592 the current flows in the opposite direction than in conductors 594 and 596. In conductors 594 and 596 , the current flows in the same direction so that the two conductors can be treated as a single conductor. In such a "•" coil, the distance between the conductors 594 and 596 of the central section and the end conductors 590 and 592 can be changed by changing the dimension 521. The dimensions shown in FIG. 6 field vector diagrams shown at 5Q2 show that coils 555 and 557 create a two-dimensional field at points 610, 612 and 614, while the field vectors shown at 504 show that the field of coil 559 has added a "third" dimension to the field

In one embodiment of the device according to FIG. In 5, an interrogation zone consisting of a district leading to a passageway was created with a height of at least 150 cm, a width of 60 cm and a length of 75 cm (dimensions 534, 519 and 521). The grid formed by coils 555,557 and 559 had the following dimensions: the vertical components 540, 542 and 544 were 180 cm long, while the horizontal components 546,548, 550 and 554 were 150 cm long. The "o" coil was centered around the intersection of the center sections of the "8" coils, and their lengths 586 and 588 were spaced 53 cm from lengths 574 and 576 of coil 555. All coils 555, 557 and 559 were made from vinyl insulated wire # 10 (both # 30610). Coil 555 consisted of 6 turns, coil 557 of 10 turns, and coil 559 of 7 turns.

It should be noted that the one shown in FIG. 5 is flat structure shown without great cost to manufacture and can be clad so that it is a Has a pleasing appearance Such a structure can easily be attached to one side of a door leading passage can be arranged. The structure described has the further advantage that the coils can easily be "balanced" in such a way that between an excited coil and the There is therefore little or no inductance occurring in the other two non-energized coils actually the energy generated by a coil is available for the generation of a field, which in a Query zone is in effect

The F i g. 7 shows a front view of a field generating and flow monitoring device according to FIG. 1. The electromagnets 12 of the field generating device consisted of iron bars with a cross section of 5.1 cm ² , which were surrounded by coils. The Standen products from sheets having a thickness of 0.45 mm ⁷ of transformer steel Type M-19 together and had a length of 142 cm and a width of 5.1 cm. Each coil consisted of two windings with 125 turns of enamelled wire with a diameter of 0.2 cm, which were distributed evenly on the rod, as well as two further windings with 60 turns of enamelled wire with a diameter of 0.259 cm at each end of the The two additional windings with 60 turns each were connected to the am

60 turns at the end of the 125 turns existing windings bifilar wound. In FIG. 8 the type of winding is shown schematically.

As can be seen from FIG. 8, the 60 turns of the windings 36/4 and 36 ß are connected in series with one another and with the parallel connection of the windings 38/4 and 385 comprising 125 windings. This combination of windings is hereinafter referred to as “coil winding”, which is provided with an input contact 35 and an output contact 37. The poles of the magnets were found to be 7.5 cm from the ends of the rods. Two such devices, which are arranged at a distance of approximately 1 m from one another and have the dimensions mentioned, are suitable for setting up a surveillance zone with dimensions of approximately 100 cm × 200 cm × 200 cm.

The air core coil 14 consists of a simple closed loop with several turns. at the one shown in FIG. 7, the loop 14 is designed to be circular, the diameter of which is equal to the distance between the poles of the electromagnets 12, while the loop of 80 Turns of enamelled wire with a diameter of 2.05 mm is formed. Had the electromagnets not the same length, the loop would be curved, but designed so that the circumference of the Loop runs close to the poles of both magnets. The reasons for such a measure result from the Relationships between the magnetic fields of the electromagnets and the air core coil, explained below.

Figs. 9 and 10 show the characteristic Magnetic fields of an electromagnet and an air core coil are the same as the coil shown in FIG. 7 free space, with the lines of force running in the plane of the drawing. According to the illustration, the Field of the vertically oriented electromagnet and perpendicular components (parallel to the V-axis) important horizontal components close to the poles (parallel to the X-axis). Likewise contains the magnetic field the air-core coil components that run parallel to the A "axis and parallel to the K-axis.

If the air coil is moved past the poles of the electromagnet, the two forms of the field-generating means complement each other. This is best seen in FIG. 11, in which the superposition of two magnetic fields in free space is shown, which are generated by the devices 12/4 and 12ß and 14 in a zone unit. For the sake of clarity, the lines representing the field generated by the device 12A are drawn with uniform dashed lines, while the lines representing the field generated by the device 12B are drawn by alternating short and long lines. The lines representing the field generated by the device 14 are solid. As can be seen from the illustration at 2, one group of lines of force intersects at point M and the other group of lines of force intersects at point N. At 4, the angular relationship of the magnetic field strengths at point M and at 6 at point W is shown (vectors) . At 4, the components provide τ, s and t is the thickness of the magnetic fields at the point M is generated by the devices 14 and HB ₁ YiA, while at 6 the components R *, S 'f'die strength of the respective magnetic fields at the Represent point N by vectors. As can be seen, they run

Components of each group almost perpendicular to each other, although the directions of the components r, s and I are different from the directions of the components r ', s' and /'. It can be seen from FIG. 11 that the vector components of the points of intersection of other groups of lines of force likewise run almost perpendicular to one another. By selecting the individual magnetic field strengths accordingly, the devices 12/4, 12fl and 14 could produce an almost exemplary field.

Are fields of not less than 1.4 times (square root of 2) the field of the elongated If the strip is generated, such fields are even at the ends of the interrogation zone at the ends of the polar ones Magnets on which the relevant directions of the fields change rapidly, almost exemplary or "Three-dimensional". An absolutely uniform three-dimensional field is not required because it is impossible is to pass a marking element through an entire zone without the marking element is aligned at least once to a component of the field of action that is larger than the switching field of the marking element.

The fields shown in FIGS. 9, 10 and II are generated, unless an external magnetic one Influence exists. In the case of the one shown in FIG Setup with three zone units, the middle zone unit interacts with the two outer zone units together to form two interrogation zones, se that in turn all nine field-generating means in Operation would have to be set so that the displayed fields are generated. Because of the proportionate long distance is the generation of the nine fields in sequence for the reasons already explained not mandatory. This can be undesirable as the peak amplitude of the through the windings of the Electromagnets and currents flowing through the air core coil and therefore the cost of the circuit as a result can be reduced that a field is generated simultaneously in each zone unit.

12 shows a circuit diagram for a device with an energy supply part 670, with three energy transmission sections 672/4, 672B and 672C and with a sequence control signal generator 683. The circuit is not limited to exactly three transmission sections 672, but this number has only been made for simplification the description of a circuit for a field generating device with three coils according to FIG. 5 or 7 chosen. Only a portion of the transmission section 672 is shown in detail, since all of these sections have the same structure Energy have the same duration and frequency, other values can be selected for some circuit elements. The energy supply section 670 suitably has an AC voltage source 674 , which can consist of the conventional mains connection 617 and a conventional voltage doubler rectifier 676. This generates a DC voltage With a potential of approximately zero and minus 200 volts, what voltage is applied across conductors 678 and 680 of power transmission sections 6724, 6725 and 672i.

An electrical circuit is provided which ir a conductor (e.g. in the winding of the electromagnet

th according to Figures 7 and 8, in the air core after the F i g. 7 and in the heads of the field-generating means according to FIGS. 2, 3, 4 and 5) generates an alternating current, the first half-cycle of which generates an electromagnetic field, which in turn is a determinable characteristic Signal generated The electrical circuit educated therefore in an interrogation zone an attenuated sinusoidal electromagnetic field. The circuit has a parallel resonance circuit, its inductive Component consists of a conductor that generates the electromagnetic field. They are means provided with which a source of electrical energy is intermittently connected to the resonant circuit, so that a predetermined amount of electrical energy is supplied to the resonant circuit. Will the If the energy source is switched off by the resonance core, free vibrations consume the multiple resonance the first-mentioned circuits can be used to sequentially several field-generating To supply means with electrical energy.

It should be noted that in the circuit according to the F i; G. 12 the transmitted from the energy source Energy primarily in the capacitive element and is not stored in the inductive element of the resonance circuit. The capacitive element of the resonance circuit therefore has a double function, and first of all, this element provides energy transmitted, and secondly, a resonance circuit is formed together with the inductive element, which the The rest of the transmitted energy is consumed as free vibrations. Because of this dual function, this capacitive element hereafter sometimes as a component of the resonance circuit as well as a part of the Energy transmission section and therefore

flowing damped sinusoidal current, so that in the sequence a damped sinusoidal electromagnetic Field is generated. The transmitted energy can either be capacitive or inductive Component of the resonance circuit are stored. Should the energy be stored in the inductive element the time required to generate sufficiently strong currents results in much longer Pulses are generated than when the energy is stored in the capacitive element.

In a preferred embodiment, the mer is in each case the electrical relayed to the resonance circuit Energy limited approximately to a value at which the rate of dissipation of the energy from the resonance circuit exceeds the speed at which the energy is stored in the resonance circuit will. This can be achieved with the help of a controllable silicon rectifier with which the resonance circuit is intermittently connected to the energy source. Used with the rectifier and the resonance circuit an appropriately selected inductor is connected in series, so no further means for Blocking the rectifier and disconnecting the resonance circuit from the energy source is required. the The inductance of the inductor should be at least 4.7 times the inductance of the conductor used to generate it of the electromagnetic field is used. This inductance should preferably be 4.7 to 25 times and ideally be about 6 times the inductance of the conductor. The difference is less than that 4.7 times, the controllable silicon rectifier cannot be blocked.

In another embodiment, the inductor forms the primary winding and the inductive part of the The secondary winding of a transformer. To be sure of an effective coupling of the two windings with each other, the transformer can consist of an autotransformer (autotransformer) exist. In a further alternative embodiment, instead of an inductor, rwischen the connecting means and the resonance circuit switched a resistor

As is known per se, the amount of energy supplied to a resonance circuit can thereby be determined be that either the charge on the capacitive element or in the inductive element of the resonance circuit flowing electricity is regulated.

With reference to the F i g. 12 hereinafter becomes a Execution of an electrical circuit described with which a further circuit cooperates so that

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Section represents the means for connecting the energy source to the resonance circuit.

The energy transmission section 672 contains a switch in the form of a transistor 682/4, which is switched to the conductive state when a control signal from the sequence control signal generator 683 is fed to the connection point 684/4. If the transistor 682Λ is conductive, the section 672.4 forwards an energy pulse to the coil of the associated field-generating device. In FIG. 12, the coil belonging to the energy transmission section 672/4 is shown schematically as an inductor 686. If the transistor 682 is conductive, a capacitor 688 stores an energy pulse which is passed on to the field-generating device as a damped energy pulse. The circuit for charging the capacitor 688, which later causes this charge to be passed on to the field-generating device or to the inductor 686, comprises an inductor 690, a controllable silicon rectifier 692 and a circuit shown at 694 for triggering the rectifier 692 normally non-conductive transistor 696, the base electrode of which is connected to one end of the two resistors 698 and 700. The resistor 698 is connected at the other end via a blocking capacitor 704 and a diode 706 to the collector electrode of the transistor 682/4. One layer of the capacitor 704 and the cathode of the diode 706 are connected together with one conductor of a resistor 708, the other conductor of which is connected to the conductor 678, to which a reference voltage of zero volts is applied. When the transistor 682 non-conductive, so normally the voltage across the capacitor 704 is about 200 V, so that the base electrode of the transistor 696 no current can flow, wherein the transistor remains in the normal non-conductive state, the transistor 682 conductive, the capacitor 704 charged, and the current flowing through the capacitor 704 charging current enables the transistor 696 in the conductive state has to the voltage across capacitor 704 reaches the level of 212 V the remaining part of the trigger circuit 694 includes the emitter and collector resistors 710 and 712 of the transistor 696 , a capacitor charging network with a resistor 714, a Zener diode 716 uno. with a capacitor 718. The grid conductor of the rectifier 692 is connected both to the emitter electrode of the transistor 696 and to the emitter resistor 710 , so that at the other end of the resistor 710

and a voltage of approximately minus 200 V at the cathode of the diode 692, the rectifier is rendered conductive or triggered, and only if the transistor 696 is conductive. Transistor 6% becomes conductive when a pulse is applied to junction 684 which forward biases transistor 682. A current flows from the emitter electrode to the collector electrode of the transistor 682 via the diode 706, the capacitor 704 and the resistor 698, the transistor 696 being put into the conductive state. In this case, the capacitor 718 is discharged via the resistor 712 and the transistor 6%, so that the grid electrode of the controllable silicon rectifier 692 is supplied with a current pulse which puts the rectifier in the conductive state, so that the capacitor 688, the Inductor 690 and through rectifier 692 a current flows with the result. Hatred on Hem capacitor 688 energy is stored. In order for the energy to be stored sufficiently quickly, the value of inductor 690 must be chosen so that it is no more than approximately ¹ A of the value of inductor 686. Most of the current from capacitor 688 therefore flows through inductor 690 and not through inductor 686. When capacitor 688 charges to approximately minus 200 volts, the current flowing in inductor 590 is at its maximum. This current flow continues until the energy in the inductor 690 is consumed, with the result that the capacitor is charged to a voltage of approximately -300 V jo. This highest voltage depends in part on the ratio of the inductances of inductors 686 and 690 and the losses caused by the resistance in inductor 690 and other circuit elements through which the ts current flows. If the voltage across the capacitor 688 has reached its maximum value and no more current flows in the inductor 690, the controllable silicon rectifier 692 becomes non-conductive. The capacitor 688 is now discharged into the field-generating inductor 686, a current with a characteristic damped and sinusoidal waveform flowing in the coil. A resistor 691 with a very small value is connected between one end of the inductor 686 and the conductor 678, on which the reference voltage of nr'i volts is located. The voltage drop across resistor 691 is exactly proportional to the current flowing in inductor 686 and can therefore be used as a synchronization signal for a detector device. In such Einrich- vt tung shows a detector the presence of a responder in if a characteristic signal is detected at a certain time relative to the time base of the electromagnetic field.

The sequence control signal generator 683 has the task of applying a control signal to the connection points 684/1, 684S and 684C in sequence so that the coils of sections 672Λ 672A and 672C generate field pulses, one of which is shown as inductor 686 number of monostable multivibrators are made in a ring circuit, so that with a changeover of each multivibrator from the unstable to the stable state a reversal of the operating states of the following multivibrators in the Ringschaitung ti If the outputs of the individual multivibrators have the connection points are supplied to the 684th Another possibility is to connect the connection points 684 ma to the individual stages of a simple flip-flop counter which is operated by a free-running multivibrator.

FIG. 13, which consists of two drawings a and b is a circuit diagram for one of the two and the same construction combination of the magnetic flux monitoring device 29 with the signal detector circuits 32 of the system according to FIG. 1. As from the F i g. 13 shows the coils 16 / 1.16 pounds 16C and 16D of the magnetic flux monitoring device 29 via a coaxial cable 28 to the input of Detector circuit 32 in connection.

The detector circuit 32 comprises a signal shaping and amplification section (SSAS) 128, a signal discriminating section (SDS) 130, and eiron Output section 132, the output of which is via the conductor 134 to the alarm and display device 34 of the system according to Her F i g. 1 is directed by H.

The SSAS section 128 comprises in sequence an input filter 136, a preamplifier 138 in the first stage, a preamplifier 140 in the second stage, a preamplifier 142 in the third stage, which is connected via a coaxial cable to a further filter (144) , a further amplifier 146 and a limiter stage (148), which circuit elements consist of designs known per se. The two twin T filter elements of the filter 136 have a very high transmission impedance at 60 Hz, which frequency is the frequency of the field-generating device in the embodiment according to FIG. 7. These filters consist of a cheap design with a tolerance of 10%, do not require tuning, almost completely eliminate the very strong 60 Hz interference and weaken other interfering signals up to 1000 Hz just as well. In the input filter 136, the capacitors 201, 202, 204 and 206 have a value of 0.01 μΩ, the capacitors 208 and 210 each have a value of 0.022 μ ^, the resistors 212,214,216 and 218 each have a value of 270 Ω. and the resistors 220 and 222 have a value of 120 kn each. A transistor with very low inherent noise is used in the preamplifier stage 138, since it is to be avoided that additional inherent noise occurs in the amplified signal at the output.

The second and third amplifier stages 140 and 142 cause signal amplification with good linearity. The interposed coupling capacitors attenuate frequencies below approximately 1000 Hz. Between the preamplifiers 140 and 142 is a variable resistor 150 switched on, with which the system can be set so that no wrong Alarms are triggered by randomly occurring signals in the vicinity of the system concerned may occur frequently. The best setting is made by increasing the on the collector electrode of the transistor 152 lying AC voltage to a value at which the detector 130 a signal determined, although it is known that there is no signal characteristic of a responder in the interrogation zone The value of this alternating voltage at the collector electrode is determined, after which the Variable resistor 150 is set so that the Collector electrode of the transistor 152 lying AC voltage is half of the determined value

The filter 144 also consists of a high-pass filter an additional band filter, the mean value of which is matched to the fundamental frequency of the effective field, which latter filter consists of a twin T-fil-

ternetzwerk exists, which is connected between the high-pass filter capacitors. The twin T-filter network has a high transmission impedance at the fundamental frequency of 60 Hz of the effective field, while the high-pass filter capacitors essentially attenuate signals whose frequency is between 60 and 1000 Hz, the frequency of which in the currently preferred embodiment is the predetermined frequency Im Filter 144 , capacitors 224 and 266 each have a value of 0.01 μΩ, resistors 228 and 230 each have a value of 270 kΩ, resistor 232 has a value of 120 kΩ and capacitor 234 has a value of 0.022 μΩ. The amplifier 146 effects an additional amplification, while the limiting stage 148 effects a further amplification and represents a high input impedance for the amplifier 146 and the signal discriminator 130

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The signal discriminator 130 generates an output signal that puts the alarm and display device 34 into operation whenever three signals with an amplitude at least twice as high as that of the noise and with a duration of less than ^{one another in successive intervals of approximately 16 2 / a ms} than approximately 03 ms occur. Each of these signals corresponds to the characteristic signal of a responder of the embodiment described above. Furthermore, the 16 ² / 3ms um'issende interval corresponds to the period of a 60 Hz signal and therefore represents the reversal of magnetization of a sensitized marking element Time span of approximately 1.5 ms or within a time window that immediately follows a change in direction of the field of activity. Upon detection of such a signal, a signal is fed to output section 132 via conductor 154. Upon receipt of three signals over conductor 154 at successive intervals of 16 ^2/3 ms each, output section 132 feeds a signal to alarm and display device 34. After receiving a first signal, the output section 132 blocks the counter during the following 13 ² Λ ms, and if no further signal is received in the following 6 ms, the counter is reset to the state zero

The signal discriminator 130 has a blocking transistor 156, which together with the trigger circuit 158, the delay timer 160 and the coercive gate 162, the passage of an output signal from the limiting stage 148 to the combination of a signal shaper 164 and a signal width discriminator 166 during most of each period In operation, the trigger circuit 158 changes its state approximately at the point in time at which the AC mains voltage exceeds the value zero. In this transition from the positive to the negative value, the same transition occurs at the output of the trigger circuit, with a pulse being generated triggers the delay timer via a capacitor 168 and sets the monostable multivibrator into the unstable state.The delay timer remains in this state for approximately 4 ms, after which it is switched off approximately at the point in time when the field of action crosses the value zero (the we kungsfeld has a lag of a little less afc 90 ° or approx. 4 ms compared to the mains voltage). When the delay timer takes effect, it passes a negative going pulse through capacitor 170 which triggers the coercive gate and unstable a monostable mid-vibrator by holding the multivibrator for approximately 1.5 ms until it returns to steady-state In the unstable state, there is a low voltage across the resistor 172 , so that there is no current to the base electrode of the blocking transistor 156

κι flows. If the gate 162 is in the unstable state, the transistor 156 is therefore non-conductive, during which time the signal shaping device is put into operation. At the same time, the resistor 174 is supplied with a high voltage, so that the base electrical

r, de of transistor 176 receives current and the transistor becomes conductive, with the result that the signal width discriminator is put into operation. If the multivibrator of the coercive gate returns to the stable state, the opposite is the case. A high voltage is applied to resistor 172 , so that transistor 156 conducts a current through resistor 177, with the result that transistor 179 is continuously conductive, the signal shaping circuit being put out of operation. At the same time the resistor 174 becomes a low one

> -, voltage is supplied so that the transistor 176 receives no current and the signal width discriminator is switched off. A signal can therefore only be received during the brief unstable state of the coercive gate 162 in each 60 Hz period. In

The characteristic signal pulse from a marking element falls in this short time interval of the invention is generated.

If such a characteristic signal is received in a timely manner by the limiting stage 148 , the

π State of the waveform shaping circuit changes when the level of the amplitude exceeds the value of approximately 8 V, while transistors 179 and 181 are switched from the normally conductive state to the non-conductive state. Here, the

4n capacitor 178 and the diode 180 a pulse is passed, which puts the multivibrator 182 of the signal width discriminator in the unstable state.

The transistors 179 and 181 remain in their new states for as long as the received signal

4-, exceeds the value of approximately 6 V, which time for characteristic marking signals is less than approximately 03 ms. Since during this time no current flows through the collector electrode of transistor 179 , transistor 184 remains blocked, which again

, ο is blocked if either one or both transistors! 76 and 186 are non-conductive. The non-conductive state of the first transistor has already been described in the description of the coercive gate 162. The transistor 186 is non-conductive during the steady state of the signal width multivibrator 182. The transistor 184 is therefore only conductive when the coercive gate and the signal width multivibrator are in the unstable state and during a normal state of the signal fcrmer 164 when the collector current of the transistor 179 is with its base electrode The unstable state of the multivibrator 182 must therefore last longer than the width of the characteristic signal

If the transistor 184 is switched to the conductive state by a characteristic signal, a negatively directed signal is fed to the input conductor of the output section 132 via the conductor 154

The output section has a counter 188 Period timer 190, a consecutive pulse gate 192 and a counter clear gate 194.

The period timer 190 simply consists of a monostable multivibrator which is connected to the input conductor s 154 and which is placed in the unstable state by a negative-going signal. At each transition of the periodic timer from the stable in the unstable state, the counter 188, switching transistor 196 to a step indexed The unstable state of the period timer takes about 13 ^J / 3 ms, so that the speed of the counter to one count per 13 ^2/3 ms or to approximately one count in a 60 Hz period. The counter is prevented from being erased or reset to zero during this ISVa ms duration by the forward bias voltage present at connection point 198, since transistor 200 is blocked in this case returns to the steady state. In the approximately 6 ms unstable condition, gate 192 prevents the counter from being reset to zero by applying a forward bias to the base electrode of counter clear gate 194. If the period timer has not yet been reset to the unstable state when the consecutive pulse gate 192 has returned to the stable state, the counter is reset to the setting zero

A relay drive circuit 133 generates when the Counter counted to three has an output signal on conductor 134 which the alarm and display device 34 puts into operation. r,

14 shows a perspective view of a book 850 with a marking element 852 with "n" individually arranged open strip members 854, 856, 858 and 860 made of ferromagnetic material in the vicinity of the rear cover of the book. At least three members 854, 858 and 860, labeled "1", "n-1" and "n", are required to produce at least three separate magnetic pulses and to accommodate the necessarily equally spaced intervals. The term 856 shown in dashed 4-: lines is determined to represent a number by the value of "n"

Limbs used

15 shows a perspective view of a book 852 with a concealed marking element 864 in multiple states. Part of an outer cover 866 over the spine of the book is shown broken away for the purpose of showing the marking element 864. The marking element 264 has “n” links 868, 870, 872 and 874. The terms 868, 872 and 874 represent the numbers "1", "n- 1" and "na", respectively. Link 870 shown in dashed lines represents optional links, the number of which depends on the value before "a" . Links 868, 870 and 872 are comprised of elongated strips 876 on which control elements 878 are stacked and extend the entire length of each elongated strip . The Gliec 874 consists of an elongated strip 880, au! The controls 882 and 884 are stacked each only over part of the open strip! 880 extend.

The arrangement and selection of the marking elements elements according to FIGS. 13 and 14 is arbitrary and can be changed in any way.

The marking element according to the invention can be used except for protection against theft from librarians or used from warehouses for other purposes, such as B. for sorting Objects. The objects belonging to a class can be marked with a marking element are equipped, the elongated strip has a certain alternating current coercive force while providing objects belonging to a different class with a marking element whose elongated strips have a different AC coercive force, etc.

The marking element according to the invention could also be used as a fraud-proof closure the integrity of which can be determined without direct contact by facilities, e.g. B. on one Railroad car driving past an inspection point Such a marking element can consist of a strong adhesive on a length of an elongated strip of ferromagnetic Material. The adhesive can consist of the design described in US-PS Re 24 906, while the elongated strip of Permalloy with a width of 6 mm, a thickness of 25 μπι and one Length of 18 cm.

In addition 9 sheets of drawings

Claims (8)

Patent claims: 1. Marking element for use in a device for detecting an object in an interrogation zone in which the object is exposed to a periodically changing electromagnetic field is exposed, with a portion of a material of high magnetic permeability, the Magnetic properties are such that in the presence of a marking element carrying Object in the interrogation zone with an applied magnetic alternating field of a predetermined The magnetization of the element is reversed in order to generate a frequency external magnetic pulse containing harmonics of a predetermined frequency, characterized by a) an elongated strip or wire (854 - SSO; 876, 880) with a length to square root ratio of cross-sectional area of at least 150, b) through a layer of a normally sticky, very strong self-adhesive on at least one side of the strip or wire, c) by a peelable carrier material which is fastened to the adhesive layer, the adhesive layer after removal of the carrier material serves to fasten the strip or wire to the object (31; 850; 862) and the combination of shape and magnetic properties of the 3 formed Marking element (33; 852; 864) is such that at a maximum change ^ speed of the applied magnetic alternating field of more than 24,000 - per second that in the m generate pulse-containing signal comprises a frequency band, the lowest limit of which is above the 16th harmonic of the predetermined frequency and its width is at least is 10 times the predetermined frequency 2. Marking element according to claim 1, characterized by π strips or wires (854-860; 876; 880), where π is an integer greater than 1 and the strips or wires are chosen so that they are in after a change of direction of the field of action same time intervals reverse their magnetization in the 3c series, each time interval equal to or less than -; - with T equal to the period of the Field of activity is, and in such a way that with each Ummagne listening a magnetic impulse is generated that has a characteristic frequency occurs by a simple device (Fig. 1) is clearly detectable 3. Marking element according to claim 2, characterized by a coding by number and & o dimensioning of the strips or wires (834-860; 876; 880 ) which are assigned to each object (31; 850; 862) and are provided by a corresponding device ( Fig. 1), and by means of decrypting and recording this encoding. 4. Marking element according to claim 1, 2 or 3, characterized by at least one control element (878, 882, 884) made of ferromagnetic material, the coercive force of which is at least 400 - and which, with remanent magnetization, has a static external magnetic field of at least 60 - generated on at least a part of the strip (876; 880) , the amplitude and the time characteristic of a signal generated by the strip under the action of the active field clearly differing from the corresponding signal when the control element is demagnetized. 5. Marking element according to claim 4, characterized in that the control element (878 ) has a static external magnetic field with a value of over the entire length of the strip (876) at least 60 - generated
m 6. Marking element according to claim 4, characterized in that each of a plurality of control elements (882, 884) generates a static magnetic field on a different part of the strip (880) 7. Marking element according to claim 6, characterized in that the control elements (882, 884) have different coercive forces. 8. Marking element according to one of claims 4, 6 and 7, characterized in that at least one control element (884) is arranged substantially shorter than the strip (880) and in the vicinity of the central part of the strip, the remanent magnetization of the control element causing that the parts of the strip which are not in the vicinity of the at least one control element behave as independent strips in which the ratio of the length to the square root of the cross section is less than necessary to generate the characteristic impulse.