WO1997044911A1

WO1997044911A1 - Method and device for local elimination or restriction of a radio-frequency radiation field

Info

Publication number: WO1997044911A1
Application number: PCT/FI1997/000286
Authority: WO
Inventors: Heikki RYHÄNEN; Mikael Ottelin
Original assignee: Ryhaenen Heikki; Mikael Ottelin
Priority date: 1996-05-17
Filing date: 1997-05-16
Publication date: 1997-11-27
Also published as: AU2776897A; FI962091A0

Abstract

The invention relates to a method and apparatus for locally eliminating or reducing a radio-frequency radiation field, particularly in telephones from the antenna in the direction of a user, when using a dipole antenna consisting of at least two antenna elements, said elements being supplied from a transmitter generator (5) with an alternating current. Some of the alternating current supplied to the first antenna element (1) is delivered by means of a safety conductor (3) directly to the proximity of the point of the second antenna element (2), that the safety conductor (3) is throughout its length spaced from the second antenna element (2).

Description

Method and device for local elimination or restriction of a radio frequency radiation field

The present invention relates to a method and apparatus for locally eliminating or reducing a radio-frequency radiation field, particularly in mobile telephones from the antenna in the direction of a user, when using a dipole antenna consisting of at least two antenna elements, said elements being supplied from a transmitter generator with an alternating current matching the applied frequency.

It is generally known that radio frequencies e.g. within the range of 30-3000MHz have an effect, for example a warming effect, on polar molecules, such as a living tissue. The radiation sources operating on these frequencies include e.g. radiophones, mobile or cellular phones, mobile communicators, satellite phones, cordless phones, as well as mains-connected computer equipment. The frequencies applied in these are within the range of 125-2450MHz. The most obvious examples of these are NMT/GSM mobile phones, whose transmitting and receiving antenna is often just a few centimeters away from the head of a user.

The human-affecting effect of a radiation field depends on the field strength, i.e. the antenna of an apparatus, and the power supplied therein, as well as on the applied frequency. This power diminishes exponentially relative to distance, having its starting point at the centre of an antenna. The maximum outputs used in NMT450-900 as well as GSM telephones are 2-9W, depending on the age of a phone. This transmitter output depends substantially also on the quality of a receiving area in which the phone is used. In favorable mains conditions, a telephone operates on low power. This power is controlled by a base station according to a signal-to-noise ratio. In future, the applied frequencies will be increased as the preceding ones run out of "space". Furthermore, the telephone operating times are on the rise. This will further emphasize the hazards that people may be exposed to as a result of a high-frequency radiation field. Thus far, however, no practical solutions have been disclosed for the reduction of radiation, especially such that would be compatible with already existing phones.

The radio field in a dipole antenna or its multiples may consist of elements between oppositely charged points - points of an antenna - the voltage and polarity thereof reversing at a given frequency. The field depends on the excitation of an antenna with respect to the transmitter and the ambient space.

In mobile phones, the antennae are in fact asymmetric split dipoles. In current telephones, the field developes between the points of a dipole, i.e. between the box and the points of an antenna probe. The visible parts of an antenna are available in two different types, extensible as well as fixed antennae. These have a dissimilar vertical radiation pattern, but both are horizontally circular radiators.

The audibility of a telephone in a base station has an effect on the transmission power used by the phone. The reason is often a shadow region formed by the head from the antenna relative to the base station or the distance from a base station to a telephone. Short radio waves no longer progress well through the head since, for example at a frequency of 900MHz, the head induces a suppression of about -15dB in the field strength. This causes rattle or breaks in phone connections. At the same time, the phone also raises its output unnecessarily. This head- bound power is mostly absorbed in internal head tissues as slight warming. Thus, the head-bound radiation can be considered both technically and physically unnecessary and harmful.

An object of the invention is to provide an effective, simple and inexpensive method and apparatus for producing an asymmetric radio field around a transmission antenna.

This has been resolved according to the invention and a method of the invention is characterized by the characterizing features set forth in the characterizing clause of claim 1.

An apparatus of the invention is characterized by the characterizing features set forth in the characterizing clause of claim 2.

Preferred evolutions of the invention are set forth in the non-independent claims.

The invention will now be described in more detail with reference made to the accompanying drawings, in which:

Figs. 1-8 depict various embodiments for an apparatus of the invention in schematic representation.

Fig. 9 is a schematic section, showing a fixed-antenna telephone which is fitted with an apparatus of the invention.

Figs. 9A-D show a section X-X in fig. 9, illustrating various exemplary embodiments of the invention for a safety conductor connectable to a telephone.

Fig. 10 shows a schematic section of an adjustable- antenna telephone which is fitted with an apparatus of the invention. Fig. 11 illustrates a vertical field produced when using an apparatus of the invention.

Fig. 12 illustrates a horizontal field produced when using an apparatus of the invention.

An apparatus according to the invention, by means of which the radio-frequency radiation, for example from a portable phone towards a user, can be locally eliminated or it can be significantly reduced, is shown schematically in fig. 1 in terms of its main electrical components.

In fig. 1, reference numerals 1 and 2 designate antenna elements included in a dipole antenna which is symmetrical in terms of its elements. A safety conductor of the invention is shown with reference numeral 3. Reference numeral 4 designates a junction, included in each antenna element 1 , 2 for connecting the antenna elements 1 , 2 therefrom through the intermediary of a symmetrical transmission wire 7 to a component representing the transmitter and receiver of a phone and designated with reference numeral 5 and connected, in turn, through the intermediary of wires 8 to a power source, e.g. a battery pack, designated with reference numeral 6.

Along the supply wires 7 travels from the transmitter generator 5 an alternating current, adapted to the applied frequency and matched in terms of its symmetry, to the antenna elements 1, 2. The voltages reverse their polarity according to the operating frequency of a phone, e.g. 900 000 000/s. The power emitted by the antenna 1, 2 depends on the power delivered by the transmitter generator 5 through the intermediary of the transmission wire 7 to the antenna excited of tuned to the applied frequency. For example, in a symmetrically supplied ^-wave dipole, this power is distributed from the base point 4 uniformly to both antenna elements 1 and 2, whose points experience a momentary maximum voltage while the maximum current lies at the base point 4. Some of the power supplied to the antenna 1 , 2 dissipates in order to overcome various internal resistances, but in the end, some of this power is emitted from the antenna into space.

In order to produce an asymmetric radio field around an antenna, the junction 4 of the antenna element 1 is provided in fig. 1 with a safety conductor, designated with reference numeral 3. The safety conductor 3 is adapted to extend to the proximity of the point of the second antenna element 2, such that the safety conductor lies throughout its length at a distance, i.e. an appropriate insulation away, from the second antenna element 2.

The safety conductor 3 has a task of carrying some of the current and voltage passing into the first antenna element 1 directly to the vicinity of the point of the second antenna element 2. The point of the conductor 3 has a voltage peak oppositely phased to that at the point of the element 2. Thus, if considering the power emitted by the elements 1 and 2 into ambient space, the radiation power shielded by the conductor 3, from some horizontal space sector, hence progresses in the conductor 3. The lower, unprotected radiation of this sector occurs now between the conductor 3 and the second antenna element 2 and it advances there in certain cases the same way as in the antenna transmission wire 7, thus resulting in no power losses.

The safety conductor 3 may be made of any electrically conducting material as well as structural combinations of wires and insulations as well as also materials absorbing radio radiation. An improved reflection of radio waves is achieved from the safety conductor 3 to the actual antenna element 2, if the material of the safety conductor 3 includes some reflection enhancing material in addition to a wire. Between the safety conductor 3 and the antenna element 2 may be some material having a high dielectricity or permeability. This contributes favorably to the reception and transmission capability of the antenna elements 1, 2, 3 from the direction in which the antenna is emitting. The combination of materials has also a slightly focusing effect on the emitting power of the antenna.

The safety conductor 3 can be shaped either like a plate or it may consist of one or more thin wires. The most preferred geometry for the safety conductor 3 can be considered a plane section matching the antenna element 2 and a plate-like body made concave towards the element 2. This reduces the development of a high-frequency alternating current field on the surface of said safety conductor 3 furthest away from the antenna element 2. Part of the structure of the safety conductor 3 may be comprised of electronic components or semi-conductors.

The reduction of a field strength behind the safety conductor 3 depends on its shape, electrical properties, as well as on the relative adaptation thereof to the antenna elements 1, 2. With a correct adaptation the field strength is reduced behind the safety conductor 3 to a fraction of the original - yet without weakening the field in front. The safety conductor 3 may extend from the junction 4 of the antenna element 1 or 2 to the proximity of the point of the second antenna element.

Fig. 2 illustrates an asymmetric dipole, supplied asymmetrically from a base point 4 by means of a transmission wire 7 and adapted to an operating frequency by means of elements 1 , 2 as well as a safety conductor 3. The safety conductor 3 may extend from the junction 4 of the antennal element 1 or 2 to the proximity of the point of the second antenna element.

Fig. 3 depicts a split or divided asymmetric dipole antenna 1 , 2 which is adapted at a base point 4 to a transmission wire 7, supplied asymmetrically with an L/C circuit at an operating frequency. The safety conductor 3 may extend from the junction 4 of the antennal element 1 or 2 to the proximity of the point of the second antenna element.

In fig. 4, the current and voltage for antenna elements 1, 2 and a safety conductor 3 are produced directly from a transmitter generator. In an ideal case, the current at a point 4.2 is equal to what it is at points 4.1 and 4.3 in total, or such that, in accordance with the invention, some safety conductor 3 is capable of achieving the elimination or reduction of a radiation field.

Fig. 5 depicts a symmetrical dipole 1, 2 similar to that of fig. 1 and provided with a safety conductor 3, wherein the antenna element 1 is spirally shortened to operate at an applied frequency.

Fig. 6 depicts a symmetrical dipole 1, 2 similar to that of fig. 1 and provided with a safety conductor 3, wherein all elements 1, 2, 3 are spirally shortened to operate at an applied frequency.

Fig. 7 illustrates a solution, wherein the current and voltage for a safety conductor 3 are picked up from an antenna wire 7 from between an antenna element 1 and a transmitter generator 5.

Fig. 8 illustrates a solution, wherein the current and voltage for a safety conductor 3 are picked up from an antenna element 1. Fig. 9 shows an exemplary embodiment, wherein a safety conductor 3 of the invention is attached to a fixed- antenna telephone. The phone includes antenna elements 1, 2 which are secured to a junction 4. The safety conductor 3 is connected at its bottom end to the junction 4 of the bushing-like antenna element 1. The safety conductor 3 is at least unilaterally insulated and it may further include the above-mentioned, antenna reception and transmission improving materials. The second, wire-like antenna element 2 of the antenna is surrounded by an insulation designated with reference numeral 9. On the other hand, the antenna element 1 comprises a member, which is bushing-like at its base point 4 and surrounds the bottom end of the antenna element 2 and which otherwise serves as a housing for telephone electronics. The antenna element 2 extends through the bushing formed by the antenna element 1.

Figs. 9a-D illustrate a number of various embodiments for a safety conductor 3.

Fig. 10 shows a telephone, wherein an antenna element 1 comprises a movable, extensible member lb and a fixed coil 1a. When the member 1b is in an extended position, the current passes through the coil 1a and the base point 4 over a surface 1b' to the point of the element lb. The second antenna element 2 is fixedly inside the telephone casing and provides at least partially a housing for telephone electronics. The safety conductor 3 is attached to the base point 4 of the element 1a. The safety conductor 3 comprises a conductive film, having a width equal to that of the element 2 and insulated with a thin layer of plastics. The safety conductor 3 is attached throughout its length to the telephone housing. Some of the current travels from the base point 4 of the coil la to the safety conductor 3, regardless of whether the antenna is up or not. Figs. 11 and 12 illustrate the effect of an apparatus of the invention on the vertical field and, respectively, the horizontal field of a telephone.

The invention can be applied to all portable phones, since the antennae thereof are principally split dipoles. Thus, the conductor 3 which provides the protection can be readily installed so as to develop a necessary contact as described and illustrated above.

The invention applies not only to refittings but also to new production, wherein an apparatus of the invention can be used in the antenna equipment of a telephone as a built-in component. Furthermore, it is obvious for a skilled person that the invention has numerous applications in all areas of antenna technology, which are based on split-dipole technology as antenna groups or galvanic combinations thereof, one example of such being a folded dipole.

The undisputed benefits of the invention include its structural simplicity and small outer dimensions. The radiation coil for an antenna can be readily designed to avoid excessive sharpness. In a preferred design, the shield does not increase the power losses, either. Also, the transmission powers of a telephone can be raised without exceeding the SAR standard.

Claims

1. A method for locally eliminating or reducing a radio- frequency radiation field, particularly from an antenna, when using a dipole antenna consisting of at least two antenna elements (1, 2), said elements being supplied from a transmitter generator (5) with an alternating current, c h a r a c t e r i z e d in that some of the alternating current supplied to the first antenna element (1) is delivered by means of a safety conductor (3) directly to the proximity of the point of the second antenna element (2), that the safety conductor (3) is throughout its length spaced from the second antenna element (2).

2. An apparatus for locally eliminating or reducing a radio-frequency radiation field, particularly in telephones from the antenna in the direction of a user, when using a dipole antenna consisting of at least two antenna elements (1, 2), said elements being supplied from a transmitter generator (5) with an alternating current to a base point (4) by way of a transmission wire (7), c h a r a c t e r i z e d in that some of the alternating current supplied to the first antenna element (1) is adapted to be delivered by means of a safety conductor (3), which is in a galvanic contact with the first antenna element (1), directly to the proximity of the point of the second antenna element (2) in such a manner that the safety conductor (3) is throughout its length spaced from the second antenna element (2).

3. An apparatus as set forth in claim 2, c h a r a c ¬ t e r i z e d in that the safety conductor (3) includes a member substantially parallel to the second antenna element (2) and a member extending therefrom over to the side which includes said antenna element (2).

4. An apparatus as set forth in claim 1 or 2, c h a r - a c t e r i z e d in that the safety conductor (3) consists of one or more electrically conductive wires.

5. An apparatus as set forth in claim 1 or 2, c h a r ¬ a c t e r i z e d in that the safety conductor (3) consists of a plate-like electrically conductive body.

6. An apparatus as set forth in claim 5, c h a r a c - t e r i z e d in that the safety conductor (3) is made concave towards the second antenna element (2).