WO2000058687A1

WO2000058687A1 - Magnetoelastic device for providing a useful electrical signal

Info

Publication number: WO2000058687A1
Application number: PCT/IL2000/000189
Authority: WO
Inventors: Oleg Michailov
Original assignee: Elfor Smart Sensors Ltd.
Priority date: 1999-03-31
Filing date: 2000-03-27
Publication date: 2000-10-05
Also published as: IL129282A0; AU2000234521A1

Abstract

A magnetoelastic device (10) for providing a useful electric signal, which includes a unitary ferromagnetic element (12) having at least first and second generally planar substrates (20 and 22), at least one of the substrates being formed of ferromagnetic material, and wherein the substrates have different magnetically inductive association with the ferromagnetic element, operative, in response to a force applied thereto, which may or may not cause a displacement thereof, to provide a useful electrical signal.

Description

MAGNETOELASTIC DEVICE FOR PROVIDING A USEFUL ELECTRICAL

SIGNAL

FIELD OF THE INVENTION

The present invention relates to magnetoelastic devices.

BACKGROUND OF THE INVENTION

Magnetoelastic sensor operation is based on the magnetoelastic effect in which the magnetic parameters of a ferromagnetic core change under elastic stresses. Such sensors are powerful, simple in design and highly reliable. They are very effective in industrial and building applications, and it is possible to use them in war materiel and other equipment designed to operate in heavy field conditions.

Many magnetoelastic sensors known in the art have a large ferromagnetic core and high mechanical stiffness, and can be used for measuring high loads and pressures. The design and fundamentals of operation of such sensors are described in many patents and articles, some of which are cited below.

US Patent entitled 03,932,112 entitled "Magnetic, Remanent, Hysteretic Devices" describes a magnetoelastic switch using the inverse Wiedemann effect. The Wiedemann effect is the resulting twist produced in a wire that exhibits magnetostriction when the wire is placed in a longitudinal magnetic field and has an electric current flowing therethrough. In the inverse Wiedemann effect, axial magnetization is produced by a magnetostrictive wire that carries current therethrough when the wire is twisted.

US Patent 4,137,512 entitled "Contactless Magnetic Switch" to Sidor, describes a switch that is not based on the magnetoelastic effect. In this patent, a permanent magnet moves with respect to a magnetometric sensor. The magnetic circuit of sensors such as the one described include an air gap, and the output power is relatively lower than in devices where the comparative units (usually two in number) are in actual physical contact.

US Patent 5,747,986 entitled "Array Sensors Based on the Magnetostrictive Delay Line Technique" to Hristoforou teaches a sensor operating under bending conditions. Two equal magnetostrictive ribbons are glued on two sides of an elastic bending beam and constitute a delay line having parameters which change under elastic stresses. The configuration and function of this device are very different from those of the present invention.

Bimetallic plates are temperature sensitive, so the temperature variation causes an extra bending to occur and to generate additional elastic stresses within the bimetallic body. This introduces the risk of encountering an undesirable temperature error affecting the operation of the smart switch.

US Patent 4,541 ,289 to Valdemarsson entitled "Temperature-Compensated Magnetoelastic Force Measuring Means" describes a system where the temperature effect in ferromagnetic materials is taken into consideration. However, that system utilizes spring-loaded stress forces on the metallic elements and requires complicated and lengthy calibration.

SUMMARY OF THE INVENTION

The present invention seeks to provide an improved magnetoelastic device which may be used for various functions, and which employs a dual-layered, integral ferromagnetic element, having predetermined magnetostrictive properties, so as to overcome disadvantages of known art.

The present invention further seeks to provide an improved magnetoelastic device which can be used as a smart, contactless switch, or as a force or displacement measurement device, which is characterized by providing as an electrical signal a relatively high voltage which corresponds to an applied force or displacement. The required accuracy of such a device is determined by its intended use, and is regulated by appropriate selection of materials for the ferromagnetic element.

A further aim of the present invention is to provide an accurate magnetoelastic device in which the construction thereof, while ensuring an output signal of a relatively high voltage, eliminates error due to differential thermal expansion of the different layers within the device.

There is thus provided, in accordance with a preferred embodiment of the present invention, a magnetoelastic device for providing a useful electrical signal, which includes a unitary ferromagnetic element having at least first and second generally planar substrates, at least one of the substrates being formed of a ferromagnetic material, and wherein the substrates have different magnetostrictive properties; and a coil arrangement arranged in magnetically inductive association with the ferromagnetic element, operative, in response to a force applied thereto, which may or may not cause a displacement thereof, to provide a useful electrical signal.

Additionally in accordance with a preferred embodiment of the present invention, the substrates are joined via a common interface such that, in response to flexing of the unitary element, a plane of zero stress occurs in the region of the interface, and wherein, due to the substrates having different magnetostrictive properties, a non-zero, useful electrical signal is induced in the coil arrangement.

Further in accordance with a preferred embodiment of the present invention, the first and second substrates are formed of ferromagnetic materials. The first substrate is formed of a material having a magnetostriction of a first value, and the second substrate is formed of a material having magnetostriction of a second value, different to the first value.

Additionally in accordance with a preferred embodiment of the present invention, one of the first and second substrates may have a magnetostriction value equal to zero. Alternatively, the first substrate is formed of a material having positive magnetostriction properties and the second substrate is formed of a material having negative magnetostriction properties.

In accordance with a further embodiment of the invention, the first and second substrates are formed of materials having similar magnetoanisotropic magnetostrictive properties, but wherein, in the ferromagnetic element, the substrates are formed so as to be oriented in mutually perpendicular directions vis-a-vis the respective magnetostrictive magnetoanisotropic properties of the substrates.

Additionally in accordance with a preferred embodiment of the present invention, the ferromagnetic element is arranged for bending in a predetermined bending plane, and the coil arrangement includes one or more coils wound about the ferromagnetic element in a direction transverse to the bending plane.

Further in accordance with a preferred embodiment of the present invention, the two coils are arranged, together with the ferromagnetic element, as a transformer, wherein the coils include a first, primary coil having thereacross an electrical voltage, and a second, sensing coil, operative to provide an electrical signal having an increased voltage, in response to deflection of the ferromagnetic element.

Alternatively, each of the coils may be connected with a different electrical circuit, so as to provide thereto a useful electrical signal in response to deflection of the ferromagnetic element.

In accordance with a further embodiment of the invention, the first and second substrates have similar thermal expansion properties, such that no differential bending of the ferromagnetic occurs in response to a temperature change. Preferably, the first and second substrates are connected to each other via an intervening, electrically insulating substrate.

In this arrangement, the first and second substrates are arranged for bending in a predetermined common bending plane, and the coil arrangement includes at least one coil wound about each of the first and second substrates in a direction transverse to the bending plane.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more fully understood and appreciated from the following detailed description, taken in conjunction with the drawings, in which:

Fig. 1 is a pictorial view of a magnetoelastic device constructed and operative in accordance with a first embodiment of the present invention;

Fig. 2A is a side view of the device of Fig. 1 , showing flexure thereof in response to a bending force;

Fig. 2B is a stress distribution diagram of a predetermined cross-sectional portion of the unitary ferromagnetic element of Fig. 1 , induced by the flexure illustrated in Fig. 2A;

Fig. 2C is a graphical representation of induced voltage in the unitary ferromagnetic element of Fig. 1 , induced by the flexure illustrated in Fig. 2A;

Fig. 3A is a side view of a magnetoelastic device, having a pair of coils thereon, constructed and operative in accordance with a second embodiment of the present invention, , showing flexure thereof in response to a bending force;

Fig. 3B is a voltage output diagram for the magnetoelastic device of Fig. 3A;

Fig. 4A is a side-sectional views of a contactless magnetoelastic switch constructed in accordance with the present invention;

Fig. 4B is a plan view of the switch of Fig. 4A;

Fig. 5 is a pictorial view of a contactless magnetoelastic device similar to the switch of Figs. 4A and 4B, but employing a triple-substrate ferromagnetic element;

Fig. 6 is a pictorial view of a shear type contactless magnetoelastic device, constructed an operative in accordance with an alternative embodiment of the invention; Fig. 7 is a pictorial view of a buckling type contactless magnetoelastic device constructed and operative in accordance with a further embodiment of the invention;

Fig. 8A is a side view of a ferromagnetic element for use in a magnetoelastic force measurement device; and

Fig. 8B is a schematic diagram of the force measurement device in which the element of Fig. 8A is used.

DETAILED DESCRIPTION OF THE INVENTION Referring now to Figs. 1 and 2A, there is seen a magnetoelastic device, referenced generally 10, for providing a useful electrical signal. As will be appreciated from the following detailed description, the magnetoelastic device of the invention may be used either as a contactless switch, or, alternatively, as a force or displacement measurement device.

In the present embodiment, device 10 includes an elongate, unitary ferromagnetic element 12 having first and second ends, respectively referenced 14 and 16; first end 14 is supported in any suitable support 18, while second end 16 is a free end, such that element 12 is capable of flexure in response to an applied mechanical force. Element 12 has at least first and second generally planar substrates, respectively referenced 20 and 22, which define therebetween an interface 23 along which they are bonded, welded, soldered or otherwise securely fastened together, so as to form a composite, integral mechanical unit. It _. will be appreciated that first and second substrates 20 and 22 may have a thickness extending between that of a foil and that of a thin plate, typically in the range 50 - 500 μm, although they may be of thicknesses exceeding this range, as long as they are both self-supporting and flexible. Preferably, the substrates 20 and 22 have respective thicknesses hi and h₂ which are evaluated by the following expression: hι/h₂ = V(E₂/Eι), in which Ei and E₂ are Young's modulus of elasticity for first and second substrates 20 and 22, respectively. Device 10 also includes a coil 24, wound about element 12 so as to be in magnetically inductive association therewith. It will be appreciated that, even though a single coil only is shown, two or more coils may be provided.

Ferromagnetic element 12 is arranged for bending in a predetermined bending plane, generally coincident with interface 23, and coil 24 is wound about element 12 in a direction transverse to the bending plane. There may also be provided an electrically insulative covering 26 (Fig. 1 ), disposed between element 12 and coil 24, thereby to electrically insulate therebetween. In other embodiments of the invention, this may be otherwise provided by coating element 12 with an insulating material, or by providing an electrically insulating coating on coil 24.

Referring now particularly to Fig. 2A, when undergoing flexure, as in response to an applied force F (Fig. 2A), ferromagnetic element 12 is operative to induce an electrical voltage in coil 24. Due to the fact that first and second substrates 20 and 22 are bonded or otherwise fastened together so as to act as a single mechanical unit, bending stresses therein are as appear in Fig. 2B, being equal and opposite at the top and bottom surfaces of element 12, and being substantially zero at the interface 23 between the first and second substrates.

In order to receive an electrically induced voltage from the bending of element 12, and in accordance with a preferred embodiment of the invention, the two substrates, 20 and 22, have different magnetostrictive properties. From the voltage diagram seen in Fig. 2C, it is clear that the induced voltage in each half of the element 12 is equal, but of the same sign, such that, rather than canceling each other out, the voltages ΔB_T and ΔB₂ are added together so as to provide a voltage increase ΔB. This voltage increase is received when element 12 is formed as a bimetallic element, such that first and second substrates are made either of first and second ferromagnetic materials having positive and negative magnetostriction properties, respectively; or wherein the first and second substrates are formed of materials having similar magnetoanisotropic magnetostrictive properties, but wherein the substrates are formed so as to be oriented in mutually perpendicular directions, vis-a-vis their magnetoanisotropic magnetostrictive properties. Typically these will be formed from a single sheet of material.

Various other ways of receiving useful electrically induced signals by combining various materials in element 12 include:

A. use of ferromagnetic materials such that the first substrate is formed of a material having a magnetostriction of a first value, and the second substrate is formed of a material having magnetostriction of a second value, different to the first value; and

B. use of only one of the substrates made of a magnetostrictive ferromagnetic material; the other being made of a neutral or a non-metallic material, such as phosphor bronze, or plastic, so as to have a magnetostriction equal to zero, and such that the element 12 is essentially a composite element.

Referring now to Fig. 3A, there is seen a magnetoelastic device, referenced generally 30, which is generally similar to device 10, shown and described above in conjunction with Figs. 1-2B. Accordingly, for the sake of conciseness and simplicity, like components are denoted in Fig. 3A by like reference numerals. Device 30, having two coils, may be a transformer type device, and includes first and second coils, respectively referenced 34 and 35. In this arrangement, coil 34 is connected to an alternating current supply, and thus constitutes a primary winding, while coil 35 is a secondary, sensing coil.

Referring now also to Fig. 3B, the output voltage of element 12 when in an at rest position, indicated in solid lines, is indicated by portion 38 of the voltage graph. Deflection of free end 16 of element 12 to the position illustrated in broken-lines, however, causes a sharp increase in the magnetic permeability thereof, represented in the graph by ramp portion 40, to a value indicated by upper graph portion 42.

The above-described transformer-type arrangement is useful for providing a device with increased sensitivity. In accordance with an alternative embodiment of the invention, however, coils 34 and 35 may be connected to different electrical circuits, such that device 30 provides control signals thereto simultaneously. It is clear that further coils may be provided on the same device, thereby affording the opportunity of controlling a corresponding number of electrical circuits simultaneously, by use of a single device.

It is therefore, clear that the present invention provides a device which can provide a useful electrical signal in response to a deflection, and that, furthermore, the output of the electrical signal is proportional to the deflection, for any given device construction.

Accordingly, the device of the invention may thus be used as a contactless switch, in which either a single ON/OFF control signal is required, or different levels of signal intensity are provided, rendering it a "smart" switch. Alternatively, as the output of the electrical signal is proportional to the deflection, the device may be used as a force or displacement measurement device.

Referring now to Figs. 4A and 4B, there is seen a contactless switch, referenced generally 50, constructed and operative in accordance with an embodiment of the present invention.

In the present embodiment, switch 50 has a unitary ferromagnetic element 52 having a first end 54 mounted in a suitable support 58, and a second, free end 56. Save for the fact that element 52 is illustrated as having formed therein a window 53 (Fig. 4B), element 52 is generally similar to element 12, shown and described above in conjunction with Figs. 1 and 2A, and is thus not specifically described again herein, in detail. There is also provided a pair of ferromagnetic coils 64, each wound about one of the two parallel, elongate portions 51 and 55 of element 52, and so as to be in magnetic association therewith. Each coil 64 is further attached to a switch circuit (not shown).

Switch 50 further includes an actuator element 60 which is affixed to free end 56 of element 52, and which, in the present example, is retained within a support member 62 so as to be axially deflectable with respect thereto. In operation, depression of actuator element 60, in a manner analogous to depression of a regular, contact switch, causes flexure of element 52, thereby inducing a voltage in coils 64. This voltage is provided across a switching circuit, (not shown) thereby to operate the circuit, or a device associated therewith.

It will be appreciated that, as the switching device of the present invention is not dependent upon electrical contact between a pair of electrodes, such as is required in contact electrical switches, but on deflection alone, it is highly reliable, and can be used in hostile environments, including mud, dust, and water. Furthermore, in view of the fact that there are no moving contacts, there are, accordingly, no electrodes which can wear down, and no sparking occurs.

Referring now to Fig. 5, there is seen a contactless switch, referenced generally 70, constructed and operative in accordance with yet a further embodiment of the present invention.

In the present embodiment, switch 70 has a unitary ferromagnetic element 72 having a first end 74 mounted in suitable clamp-like supports 77 and 79; and a second, free end 76. Element 72 is generally similar to element 52 (Figs. 4A and 4B), and is thus not specifically described again herein, in detail, except to state the fact that element 72 is formed of a plurality of substrates, thereby to augment the electrical signal output produced thereby, when compared to that provided by the more basic, dual-substrate element 52 (Figs. 4A and 4B). In the present embodiment, there are provided top, middle, and bottom substrates, respectively referenced 80, 81 and 82. Among the three substrates, some of them may have similar magnetostrictive properties, as long as adjacent substrates have magnetostrictive properties which are different, as described hereinabove with regard to element 12, in Fig. 1. It will, of course, be appreciated, that more than three substrates may be used in alternative constructions.

Element 72 also has a one or more ferromagnetic coils, seen schematically at 78. Switch 70 further includes an actuator element 83 which is arranged for selectable impingement on a reinforced portion 75 of element 72, such as a suitable metal or plastic pad, affixed to free end 76 of element 72. In the present example, actuator element 83 is retained within a support member 85 so as to be deflectable with respect thereto.

Operation of switch 70 is similar to operation of switch 50, shown and described above in conjunction with Figs. 4A and 4B, and thus is not described again herein.

Referring now to Fig. 6, there is seen a shearing or "snap-through" action contactless switch, referenced generally 90, constructed and operative in accordance with yet a further embodiment of the present invention.

In the present embodiment, switch 90 has a unitary ferromagnetic element 92 having first and second ends 94 and 96, respectively mounted in resilient supports 97 and 98 formed within a switch housing 100. Element 92 is generally similar to element 12 (Figs. 1 and 2A), and is thus not specifically described again herein, in detail.

Element 92 also has a coil 104, mounted thereon in a manner as shown in Figs. 1 and 2A. Switch 90 further includes an actuator element 110 which is retained within an opening 105 of housing 100, so as to be deflectable with respect thereto. Actuator element 110 is thus arranged to apply a snap action, as via a reinforced portion 95 of element 92, such as a suitable metal or plastic pad, affixed to a mid-section thereof.

Operation of switch 90 is generally similar to operation of switch 50, shown and described above in conjunction with Figs. 4A and 4B, although the actuation time of this switch is independent of the time taken for the actuator element 110 to move, due to the snapping action.

Referring now to Fig. 7, there is seen a buckling action contactless switch, referenced generally 120, constructed and operative in accordance with yet a further embodiment of the present invention.

In the present embodiment, switch 120 has a unitary ferromagnetic element 132 having first and second ends 134 and 136, mounted resiliently within a switch housing 140. Element 132 is generally similar to element 12 (Figs. 1 and 2A), and is thus not specifically described again herein, in detail. Element 132 also has a coil 134, mounted thereon in a manner as shown in Figs. 1 and 2A. Switch 120 further includes an actuator element 142 which is retained within an opening 145 of housing 140, so as to be deflectable with respect thereto. Element 132 is supported between first and second, mutually opposing generally groove-like mountings, respectively referenced 150 and 152, which respectively support first and second ends 134 and 136 of ferromagnetic element 132. First groove-like mounting 150 is formed in an inward-facing portion 151 of switch 120, and second groove-like mounting 152 is formed in an opposing portion 153 of housing 140. Mountings 150 and 152 are spaced apart such that, when actuator element 142 is in an at rest, non-depressed position, ferromagnetic element 132 is held therebetween in a generally non-stressed position.

It will be appreciated, however that depression of actuator element 142, as indicated by arrow 154, causes element 132 to buckle, as indicated by the broken-line profile, thereby to induce an electrical charge in coil 134.

While the devices shown and described above in conjunction with Figs. 4A-7 have been exemplified as switches, they may also be used as force measurement devices, particularly in domestic appliances in which very accurate measurements are not required, or in thermally stable environments.

As stated above, the value of the output voltage produced by flexure of the ferromagnetic element corresponds to the applied force. While this is certainly true, the effect of differential thermal expansion of different materials from which the substrates of the element are formed must be taken into account when seeking to use the device of the invention as a high accuracy force measurement device. This is particularly so for scientific, industrial or military tools, for example, while for purposes which generally do not require highly accurate measurements, such as domestic weighing devices, it may not be necessary to consider the effects of differential thermal expansion.

Referring now to Figs. 8A and 8B there is provided a ferromagnetic element 212, in which the effects of thermal compensation are inherently neutralized. This is achieved by forming the element 212 of first and second substrates, respectively referenced 214 and 216, of materials which have the same thermal expansion coefficient.

However, in order to produce a ferromagnetic element which produces a voltage when flexed, first and second substrates 214 and 216 are provided with separate coils, these being referenced 215 and 217, respectively, and the substrates are separated by means of an intermediate substrate 218. Intermediate substrate 218 is formed preferably of an insulating adhesive, thereby to electrically isolate the ferromagnetic substrates 214 and 216 from each other, while ensuring that they behave as an integral unit, such that opposite and equal stresses are obtained at the outside edges of element 212, when flexed. Preferably, the thickness of the intermediate substrate 218 is no greater than the diameter of the wire from which coils 215 and 217 are formed.

Referring now particularly to Fig. 8B, ferromagnetic element 212 may be employed in a measuring device in the following manner. Coils 215 and 217 are connected in series with first and second resistors, respectively referenced 221 and 223 so as to form therewith a bridge circuit. A supply voltage is applied across a first pair of terminals, A_s and B_s and an output voltage V_out is measured across another pair of terminals A and B₀.

It will be appreciated that, when ferromagnetic element 212 is at rest, i.e. when no bending force is applied thereto, a zero voltage across the circuit results, such that V_out = 0. When, however, a bending force is applied to ferromagnetic element 212, , this results in an output voltage across the circuit, such that Vout > 0, where V_out provides a direct indication of the bending force.

It will be appreciated by persons skilled in the art that, while the ferromagnetic elements shown and described in conjunction with any of the above devices are generally flexible, they also have an inherent stiffness, and that a displacement of an element of the invention occurs only when a force which is sufficient to overcome this stiffness is applied. However, in the presence of a force which is less than that required to overcome the stiffness of a ferromagnetic element in a device of the invention an output voltage, indicative of the force applied, is, nonetheless, produced.

It will be yet further appreciated by persons skilled in the art that the scope of the present invention is not limited by what has been shown and described hereinabove. Rather the scope of the present invention is limited solely by the claims, which follow.

Claims

1. A magnetoelastic device for providing a useful electrical signal, which includes: a unitary ferromagnetic element having at least first and second generally planar substrates, at least one of said substrates being formed of a ferromagnetic material, and wherein said substrates have different magnetostrictive properties; and a coil arrangement arranged in magnetically inductive association with said ferromagnetic element, operative, in response to a displacement thereof, to provide a useful electrical signal.

2. A device according to claim 1 , wherein said unitary element is a flexible element, and said device includes a support for said element so as to permit flexure thereof in the presence of a displacement thereof.

3. A magnetoelastic device for providing a useful electrical signal, which includes: a unitary ferromagnetic element having at least first and second generally planar substrates, at least one of said substrates being formed of a ferromagnetic material, and wherein said substrates have different magnetostrictive properties; and a coil arrangement arranged in magnetically inductive association with said ferromagnetic element, operative, in response to application thereto of an external force, to provide a useful electrical signal.

4. A device according to claim 3, wherein said unitary element is a flexible element, and said device includes a support for said element so as to permit flexure thereof in the presence of a mechanical force applied thereto.

5. A device according to either of claims 1 or 3, wherein said substrates are joined via a common interface such that, in response to flexing of said unitary element, a plane of zero stress occurs in the region of said interface, and wherein, due to said substrates having different magnetostrictive properties, a non-zero, useful electrical signal is induced in said coil arrangement.

6. A device according to claim 5, wherein said first and second substrates are formed of ferromagnetic materials.

7. A device according to claim 6, wherein said first substrate is formed of a material having a magnetostriction of a first value, and said second substrate is formed of a material having magnetostriction of a second value, different to said first value.

8. A device according to claim 7, wherein at least one of said at least first and second substrates has a magnetostriction value equal to zero.

9. A device according to claim 7, wherein said first substrate is formed of a material having positive magnetostriction properties and said second substrate is formed of a material having negative magnetostriction properties.

10. A device according to claim 6, wherein said first and second substrates are formed of materials having similar magnetoanisotropic magnetostrictive properties, but wherein, in said ferromagnetic element, said substrates are formed so as to be oriented in mutually perpendicular directions vis-a-vis the respective magnetostrictive magnetoanisotropic properties of said substrates.

11. A device according to either of claims 1 or 3, wherein said ferromagnetic element is arranged for bending in a predetermined bending plane, and said coil arrangement includes at least one coil wound about said ferromagnetic element in a direction transverse to said bending plane.

12. A device according to claim 11 , wherein said coil arrangement includes at least two coils.

13. A device according to claim 12, wherein said at least two coils are arranged, together with said ferromagnetic element, as a transformer, wherein said coils include a first, primary coil having thereacross an electrical voltage, and a second, sensing coil, operative to provide an electrical signal having an increased voltage, in response to deflection of said ferromagnetic element.

14. A device according to claim 12, wherein each of said at least two coils is connected with a different electrical circuit, so as to provide thereto a useful electrical signal in response to deflection of said ferromagnetic element.

15. A device according to either of claims 1 or 3, wherein said ferromagnetic element includes a plurality of connected, elongate, parallel elongate ferromagnetic portions, each having said first and second substrates, said ferromagnetic portions being arranged for bending in predetermined parallel bending planes.

16. A device according to claim 15, wherein said coil arrangement includes at least one coil wound about each said ferromagnetic portion in a direction transverse to said bending plane thereof.

17. A device according to either of claims 1 or 3, wherein said first and second substrates have similar thermal expansion properties, such that no differential bending of said ferromagnetic occurs in response to a temperature change.

18. A device according to claim 17, wherein said first and second substrates are connected to each other via an intervening, electrically insulating substrate.

19. A device according to claim 18, wherein said first and second substrates are arranged for bending in a predetermined common bending plane, and said coil arrangement includes at least one coil wound about each of said first and second substrates in a direction transverse to said bending plane.

20. A device according to any of claims 1-19, wherein said magnetoelastic device is a force or displacement switch, and said useful electrical signal is a control signal.

21. A device according to any of claims 1-19, wherein said magnetoelastic device is a displacement measuring device, and the value of said useful electrical signal corresponds to a displacement of said ferromagnetic element.

22. A device according to claim 19, wherein said magnetoelastic device is calibrated so as to measure a force applied to said ferromagnetic element.

23. A device according to any of claims 1-20, and substantially as shown and described in conjunction with any of Figs. 1-8B.

24. A device according to any of claims 1-20, and substantially as shown in any of Figs. 1 -8B.