GB2137820A - Magneto-electric pulse generating device - Google Patents

Abstract

Magneto-electric devices producing an electrical signal in response to a change in a magnetic field may preferably produce uniform pulses independent of the rate of change of the magnetic field. Devices of this type have been made using the so-called Wiegand effect, but such devices are not as sensitive as those used having amorphous magnetic material. Devices made of ferromagnetic metallic element (13) usually have essentially amorphous structure which has been plastically deformed by cold deformation, are more likely to prevent a device from responding to strong magnetic fields such that these devices are more sensitive. Among those devices having a ferromagnetic element are keys, credit cards and proximity sensors.

Description

SPECIFICATION Magneto-Electric Pulse Generating Device 1. Field of the Invention The invention is concerned with magnetoelectric devices for generating an electrical signal in response to a change in a magnetic field, such as sensors and control devices.

Background of the Invention Magneto-electric pulse generating devices play a role, e.g., as switches, flowmeters, tachometers, automotive ignition distributors, and proximity sensors in a variety of commercial and industrial applications. Electrical pulses generated by such devices may depend on the rate of change of magnetic flux or, as may be preferred in certain applications, pulses may be velocity-independent.

Among devices of the latter type are devices based on the so-called Wiegand effect, i.e., on the fact that a suitably processed magnetic wire possesses a cylindrical, magnetically hard outer region and a magnetically soft core portion.

Such a wire may be in one of two stable magnetic states, one in which magnetization in outer and inner portions is parallel, and the other in which such magnetizations are antiparallel. Switching between states is triggered by a suitable change in an ambient magnetic field, resulting in a large change of magnetic flux in the wire, and inducing a voltage pulse in a pickup coil. Such devices have received considerable attention as shown, e.g., by the following papers and patents: R. F. Stengel, "Pulse Generator Produces Rate Independent Voltage", Design News, April 18, 1977; G. M. Walker, "Wiegand Effect Getting Practical", Electronics, April 28, 1 977; U.S. Patent 3,774,180, "Ferromagnetic Memory Readout Device", issued November 20, 1973 to J. R. Wiegand; U.S.Patent 3,774,179, "Ferromagnetic Storage Medium", issued November 1973 to J. R. Wiegand; U.S. Patent 3,780,313, "Pulse Generator", issued December 18, 1973 toJ. R. Wiegand; U.S. Patent 3,783,249, "Coded Magnetic Card and Reader", issued January 1, 1 974 to J. R.

Wiegand; U.S. Patent 3,818,465, "Traveling Magnetic Domain Wall Device", issued June 1 8, 1 974 to J.

R. Wiegand; U.S. Patent 3,866,193, "Asymmetric Bistable Magnetic Device", issued February 11, 1 975 to J.

R. Wiegand; and U.S. Patent 3,892,118, "Method of Manufacturing Bistable Magnetic Device", issued July 1, 1975 to J. R. Wiegand.

In another line of development, metallic materials have been produced in which, in contrast to the customary crystalline structure, an essentially amorphous or glassy structure predominates. Such materials have been produced in ribbon or wire form, and they have been found to have high tensile strength especially when wire drawn as disclosed by T.

Masumoto et al., "Production of Pd-Cu-Si Amorphous Wires by Melt Spinning Method Using Rotating Water", Scripta Metallurgica, Vol.

15, pp.293-296(1981).

Furthermore, amorphous metallic materials have been found to have useful soft-magnet properties as disclosed in U.S, Patent 4,187,128, "Magnetic Devices Including Amorphous Alloys", issued February 5, 1 980 to R. T. Billings et al., and, recently, amorphous metallic ribbons have been proposed for substitution in place of Wiegand type wire as disclosed by: K. Mohri et al., "Sensitive Magnetic Sensors Using Amorphous Wiegand-Type Ribbons", IEEE Transactions on Magnetics, Vol. MAG-17, pp.

3370-3372 (1981); and K. Mohri et al., "Sensitive Magnetic Sensors Sensors Using Twisted Amorphous Magnetostrictive Ribbons Due to Matteucci Effect", Journal ofApplied Physics, Vol. 53, pp. 8386- 8388(1982).

Due to low coercive force of the amorphous magnetic material, the resulting devices are extremely sensitive and, in fact, are considered to be too sensitive for many applications where stray magnetic fields may be expected.

According to the present invention, there is provided a magneto-electric device for generating an electrical signal in response to a change in a magnetic field, said device comprising a magnetic element comprising a body of metallic, ferromagnetic material having a substantially amorphous structure, said device further comprising an electrically conducting element in proximity to said body, wherein said body is plastically deformed at a temperature which is less than the recrystallization temperature of said material.

In an embodiment of the invention there is provided a device for generating an electrical signal in response to a change in a magnetic field, and the device comprises a magnetic element which is substantially a body of a metallic ferromagnetic material having a substantially amorphous structure and having been plastically deformed. The device further comprises an electrical conductor in proximity to the magnetic element, typically in the form of a pickup coil surrounding or adjacent to the magnetic element.

In the course of device operation a voltage signal is available at electrical conductor terminals.

Brief Description of the Drawing Fig. 1 is a schematic of a magneto-electric device in accordance with an embodiment of the invention; Fig. 2 is a schematic of an alternate magneto electric device in accordance with another embodiment of the invention; and Figs. 3-6 are graphs depicting magnetic hysteresis loops realized by magnetic elements of embodiments of the invention.

Fig. 1 shows permanent magnet or electro magnet 11 on shaft 12, amorphous magnetic element 13, and pickup coil 14 having terminals 1 5 and 1 6. When shaft 12 is rotated as indicated, voltage pulses are produced at terminals 1 5 and 16. Such pulses are attributed to one or severai large Barkhausen jumps which, in turn, may be due to a re-entrant loop magnetic effect in magnetic element 1 3. (This effect is characterized in that field strength required to propagate a magnetic domain is less than field strength required to nucleate a domain.Accordingly, once an element is exposed to a field which is sufficient to nucleate a magnetic domain, speed of domain expansion is independent of field strength, and uniform electrical pulses are induced independent of the rate of change of the magnetic field.) Fig. 2 shows platform 21 attached to shaft 22 and supporting permanent magnets 23 and 24.

Magnetic element 25 is inside pickup coil 26 which has terminals 27 and 28. When shaft 22 is rotated as indicated, voltage pulses are produced at terminals 27 and 28. (In Fig. 1, one and the same magnet serves for setting and resetting the magnetic element 13; in Fig. 2 these functions are performed by separate magnets 23 and 24.) Magnetic elements 13 and 25 are made, in the embodiments, as bodies of a metallic, ferromagnetic, substantially amorphous material which is plastically deformed, preferably in a preferred direction such as, e.g. by wire drawings, swaging, or rolling. Preferred plastic deformation results in cross-sectional area reduction of 1 percent or greater; in the interest of enhanced magnetic squareness and coercive force of the material, such deformation preferably results in 10 percent or greater area reduction.

(Alternatively, deformation may be by flattening, in which case preferred thickness reduction is at least 1 percent and preferably at least 10 percent.) Resulting enhanced coercive force is desirable for the sake of safeguarding against accidental switching due to stray magnetic fields.

Preferred coercive force is greater than or equal to 39.789 A/m (0.5 oersted) and preferably greater than or equal to 11 9.366 A/m (1.5 oersted).

Compositions suitable for the manufacture of magnetic elements in accordance with the embodiments can be substantailly represented by the formula (CoaFebT) jXj, cobalt content being specified by values of a parameter a greater than or equal to 0 and less than or equal to 1, iron content being specified by values of a parameter b greater than or equal to O and less than or equal to 1, one or several transition elements being represented by T and selected from Ni, Cr, Be, Mn, V, Ti, Mo, W, Nb, Zr, Hf, Pd, Pt, Cu, Ag, Au, Ta, Ir, Ru, and Rh and included in the composition in an amount specified by values of the parameter c less than or equal to 0.6 and such that a plus b plus c substantially equals 1.Further in the formula, X represents one or several glass forming elements selected from the group P, Si, B, C, As, Ge, Al, Ga, In, Sb, Bi, and Sn. The parameters i andj are such that i plusj equals 1.

Magnetic elements of the embodiments are conveniently made in the form of ribbon or wire by quenching from a melt, e.g. by roller quenching or by pressure expulsion into a quenching bath, in contrast to conventional wire making by extensive processing starting with an ingot. Cold deformation of the resulting ribbon or wire is conveniently effected by drawing, rolling, swaging, or flattening, or by any combination thereof; preferred deformation is carried out at temperatures below the recrystallization temperature of an alloy and preferably at a temperature which is less than or equal to 400 degrees C depending on alloy composition.

As compared with processing involving torsional deformation, described processing is relatively simple, and relatively small amounts of ordinary wire drawing are sufficient in many instances for desired magnetic squareness and coercive force. Moreover, high saturation magnetization as is desired in the interest of a strong electrical output signal is readily realized depending on alloy composition, and values greater than or equal to 0.2, 1.0 or even 1.4T (1000, 10,000, or even 14,000 gauss, respectively) can be realized.

While no torsional deformation is required, such deformation is not precluded and may be used in the interest of further enhancing device performance. Simiiarly, magnetic treatment of the magnetic element is not precluded either alone or in combination with torsional deformation.

Devices of the embodiments typically include the metallic, ferromagnetic, substantially amorphous, plastically deformed element in the form of a wire inside a pickup coil as shown in Figs. 1 and 2. Such wire has high tensile strength (typically in the range of 200--500 kg/mm2), high stiffness, and high electrical resistivity (typically in the range of 100--300 micro-ohm-cm, thus being relatively free of eddy currents as may be induced especially when a device operates at high frequency.

Enhanced mechanical strength and stiffness of the deformed amorphous alloy facilitates device handling and manufacturing involving coil winding and results in ruggedness of a device in operation.

EXAMPLE 1 An amorphous metallic wire having a diameter of approximately 0.13 mm was made by pressure expulsion of a melt through an orifice into water; the melt material had an approximate composition represented by the formula Fe75Si10B1s. The coercive force of the quenched wire was approximately 3.98 A/m (0.05 oersted).

A section of the wire was drawn at room temperature to effect an area reduction of approximately 20 percent, resulting in a diameter of approximately 0.11 5 mm. A hysteresis loop was determined using a variable magnetic field having a maximum strength of 4464.3 A/m (56.1 oersteds); the resulting hysteresis graph is shown in Fig. 3. Coercive force was 912 A/m (19 oersteds). The element was tested in a coil having 500 turns. Exposure to a field of approximately 15,91 5.4 A/m (200 oersteds) produced a voltage pulse of approximately 1 30 mV at the terminals of the coil, corresponding to a voltage per crosssectional area per turn of approximately 2.5 V/cm2.

EXAMPLE 2 Another section of the wire made as described above in Example 1 was wire drawn to effect an area reduction of 80 percent, resulting in a diameter of approximately 0.06 mm. The corresponding hysteresis loop is shown in Fig. 4.

Coercive force was 832.4 A/m (18 oersted).

Testing in the coil gave approximately 6.4 V/cm2 per turn.

EXAMPLE 3 An amorphous metallic wire having a diameter of approximately 0.1 3 mm was made by pressure expulsion of a melt through an orifice; the melt material had an approximate composition as represented by the formula Co72,5Si12 5B15 The quenched wire had a coercive force of approximately 1.59 A/m (0.02 oersted). A section of the wire was drawn to effect an area reduction of approximately 20 percent, resulting in a diameter of approximately 0.11 5 mm. A hysteresis loop was recorded using a variable magnetic field having a maximum strength of 439.27 A/m (5.52 oersteds). The resulting hysteresis graph is shown in Fig. 5. Coercive force was 135.28 A/m (1.7oersted).

The element was tested-in a coil having 500 turns. Exposure to a field of approximately 15,915.4 A/m (200 oersteds-) produced a voltage pulse of approximately 200 mV at the terminals of the coil, corresponding to a voltage per crosssectional area per turn of approximately 3.8 V/cm2.

EXAMPLE 4 Another section of the wire made as described above in Example 3 was wire drawn to effect an area reduction of 60 percent, resulting in a diameter of approximately 0.8 mm. The corresponding hysteresis loop is shown in Fig. 6.

The coercive force was approximately 278.52 A/m (3.5 oersteds). Testing in the coil gave approximately 4.8 V/cm2 per turn.

Claims (11)

1. A magneto-electric device for generating an electrical signal in response to a change in a magnetic field, said device comprising a magnetic element comprising a body of metallic, ferromagnetic material having a substantially amorphous structure, said device further comprising an electrically conducting element in proximity to said body, wherein said body is piastically deformed at a temperature which is less than the recrystallization temperature of said material.

2. Device according to claim 1, wherein the magnetic field necessary to propagate a magnetic domain in said body is less than the magnetic field necessary to nucleate a magnetic domain in said body.

3. Device according to claim 1, or 2, wherein said body is plastically deformed by drawing, swaging, or rolling by an amount which corresponds to a cross-sectional area reduction which is greater than or equal to 1 percent.

4. Device according to claim 3, wherein said cross-sectional area reduction is greater than or equal to 10 percent.

5. Device according to claim 1, or 2, wherein said body is plastically deformed at a temperature which is less than or equal to 400 degrees C.

6. Device according to any one preceding claim, wherein said body has a coercive force which is greater than or equal to 39.8 A/m (0.5 oersted).

7. Device according to claim 6, wherein said coercive force is greater than or equal to 11 9.4 A/m (1.5 oersted).

8. Device according to any one preceding claim, wherein said body has a saturation magnetization which is greater than 0.2T (2000 gauss).

9. Device according to claim 8, wherein said saturation magnetization is greater than or equal to 1 AT (14,000 gauss).

10. A magneto-electric device, substantially as hereinbefore described with reference to any one of the Figs. of the accompanying drawings.

11. A magneto-electric device, substantially as hereinbefore described with reference to Example 1,2,3 or 4.