WO1999008263A1

WO1999008263A1 - Magnetic flux processing apparatus and method

Info

Publication number: WO1999008263A1
Application number: PCT/US1998/016639
Authority: WO
Inventors: Jerry J. Conley; Gary B. Mortensen
Original assignee: Itron, Inc.
Priority date: 1997-08-12
Filing date: 1998-08-11
Publication date: 1999-02-18
Also published as: AU8902598A

Abstract

The present invention provides methods and apparatus' relating to the use of GMR materials (206) and the biasing of the GMR material (206) into the Barkhausen effect area. Specifically, the present invention utilizes a GMR bridge (204) to sense and monitor changing magnetic flux (214) such that sensing and signal processing can be effected relative to chances in magnetic flux density (214). As the GMR materials (206) in the GMR bridge (204) are directed to enter into the Barkhausen effect area by a magnetic field generator (210), the GMR material (206) becomes especially sensitive to changes in flux (214) such that a small change in flux (214) can produce a large change in the output of the GMR bridge (204). The various devices herein that take advantage of the GMR materials (206) and the Barkhausen effect include a magnetic coupler (20), an amplifier, a frequency multiplier, a speed/position indicator and an adjustable oscillator.

Description

MAGNEΗC FLUX PROCESSING APPARATUS AND METHOD

CLAIM TO PRIORITY This application claims priority to United States provisional application having serial no. 60/055,686, filed August 12, 1997.

FIELD OF THE INVENTION The present invention relates to a method and apparatus for implementing magnetic flux elements in electronic and signal processing systems. Specifically, the invention relates to the use of giant magnetoresistive (GMR) materials to sense and harness magnetic flux while operating under the Barkhausen effect for providing reliable devices to be used in electronic and signal processing.

BACKGROUND OF THE INVENTION Magnetoresistive materials have been widely used in magnetic recording heads for magnetic tape storage systems and magnetic disk memories. In the late 1980's and early 1990's development of giant magnetoresistive (GMR) materials further enhanced the capabilities of magnetic recording heads.

Giant magnetoresistance is present in heterogeneous magnetic systems with two or more ferromagnetic components and at least one nonmagnetic component. The spin-dependent scattering of current carriers by the ferromagnetic components results in a modulation of the total resistance of the GMR by the angles between the magnetizations of the ferromagnetic components. An example of a GMR material, is the trilayer permalloy/copper/permalloy, where GMR operates to produce a minimum resistance for parallel alignment of the permalloy magnetizations, and a maximum resistance for antiparallel alignment of the permalloy magnetizations. The GMR ratio or coefficient for a multilayer system is defined as the fractional resistance change between parallel and antiparallel alignment of the adjacent layers, i.e., ratio = ΔR/R, where ΔR is the total decrease of electrical resistance as the applied magnetic field is increased to saturation and R is the resistance as measured in the state of parallel magnetization. This ratio can be as high as 10% for trilayer systems and more than 20% for multilayer systems. This is in comparison to magnetoresistive ratios of 2-4% thus indicating the improved sensitivity of GMR materials.

While the application of GMR materials in magnetic recording heads is commonplace, the application of GMR materials, and the advantages they provide, especially when the GMR material is directed into the Barkhausen effect area (the area in which the ferromagnetic material of the GMR exhibits jumps in magnetic flux density in the presence of an increasing magnetic field, also see the Detailed Description of the Preferred Embodiments), is relatively unexplored and unexploited in relation to electronic and signal processing systems.

SUMMARY OF THE INVENTION The present invention provides methods and apparatus' relating to the use of GMR materials and the biasing of the GMR material into the Barkhausen effect area. Specifically, the present invention utilizes a GMR bridge to sense and monitor changing magnetic flux such that sensing and signal processing can be effectuated relative to changes in magnetic flux density. As the GMR materials in the GMR bridge are directed to enter into the Barkhausen effect area by a magnetic field, the GMR material becomes especially sensitive to changes in flux such that a small change in flux can produce a large change in the output of the GMR bridge. The various devices described herein that take advantage of the GMR materials and the Barkhausen effect include a magnetic coupler, an amplifier, a frequency multiplier, a speed/position indicator and an adjustable oscillator.

DESCRIPTION OF THE DRAWINGS Figure 1 depicts a typical magnetization curve and a Barkhausen effect area.

Figure 2 depicts a magnetic coupler.

Figure 3 depicts an amplifier.

Figure 4A depicts a frequency multiplier. Figure 4B depicts a transfer function of a GMR bridge of the frequency multiplier.

Figure 4C depicts a waveform of an input signal to the frequency multiplier and a resulting waveform of an output signal of the frequency multiplier. Figure 5 A depicts a speed /position indicator.

Figure 5B depicts a profile of a magnetic field and ferromagnetic domains of the speed /position indicator.

Figure 6A depicts an adjustable oscillator.

Figure 6B depicts a transfer function of a GMR bridge of the adjustable oscillator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Each of the electronic and sensing signal systems disclosed hereinbelow preferably utilizes a GMR material or equivalent. Specifically, each of the apparatus' use a GMR bridge sensor of the type supplied by Nonvolatile Electronics Inc., (NVE) or equivalent. The NVE type bridge sensors use a wheatstone bridge arrangement with two pairs of giant magnetoresistors which employ permalloy 80 as their ferromagnetic material. Each identical leg comprises opposite legs of the bridge. When there is no applied magnetic field, the giant magnetoresistors are designed to be equal. The current flowing in the opposite halves of the bridge are equal, regardless of the magnetic field, and the output from the bridge is thus dependent on the match in resistance values. The bridge circuit is of a straight-forward design and preferably includes a temperatures compensation feature. The GMR bridge is designed with one pair of opposite legs to respond differently to an applied field relative the response of the other two legs. In each of the electronic and sensing signal systems, a magnetic field generating means, e.g. a biasing electro magnetic circuit, magnet, permanent magnet, or rotary magnet generates a magnetic field which is collected, as magnetic flux, by the giant magneto-resistors in the GMR bridge. As the magnetic field increases, the ferromagnetic material within two legs of the GMR bridge enters the Barkhausen effect area at a predetermined flux density (entry and exit points of the Barkhausen effect area are determined by the type of ferromagnetic material present within the giant magnetoresistive material, e.g. permalloy 80). In explaining the Barkhausen effect area, it is key to understand that ferromagnetic materials consist of small magnetic regions resembling individual bar magnets called domains. Each domain is magnetized along a certain crystallographic easy direction of magnetization. Domains are separated from one another by boundaries known as domain walls. Magnetic fields will cause domain walls to move back and forth. In order for a domain wall to move, the domain on one side of the wall has to increase in size while the domain on the opposite side of the wall shrinks. The result is a change in the overall magnetization of the ferromagnetic material. The first electrical observation of domain wall motion was made by professor Heinrich Barkhausen in 1919. He proved that the magnetization process, which is characterized by the hysteresis curve, in fact is not continuous, but is made up of small, abrupt steps caused when the magnetic domains move under an applied magnetic field. Referring to Figure 1, a typical magnetization curve, with B, the flux density, appearing to be a continuous function of H, the magnetic field, is depicted. However, if the curve is examined more closely, it can be seen that the B-H curve consists of small discontinuous changes of B as H varies. These discontinuous changes are a result of the Barkhausen effect. Each abrupt jump produces a brief burst of magnetic noise, Barkhausen noise, which can be detected. Each ferromagnetic material has specific flux density parameters that define entry and exit from the Barkhausen area. Once the GMR has entered the Barkhausen effect area, as indicated by the detected Barkhausen noise, only a small change in magnetic field is required to effect a large change in resistance in the GMR, e.g. only approximately 0.1 gauss is required to effect a change in resistance of a permalloy 80 GMR operating in the Barkhausen effect area while other types of magnetoresistive materials not operating in the Barkhausen effect area can require up to 10,000 gauss to effect a change in resistance. Because the current within the GMR bridge remains the same, the large change in resistance correspondingly produces a large change in the output of the GMR bridge. The electronic and sensing systems described below advantageously use this feature.

Magnetic Coupler

FIG. 2 depicts a magnetic coupler 20 that utilizes the GMR bridge and Barkhausen effect as described above. In this instance, a voltage potential is connected to two opposing nodes of GMR bridge 204, which comprises four giant magnetoresistors 206. The other two opposing nodes of GMR bridge 204 are connected to signal output 208. An electromagnetic device 210, e.g. inductor, is connected to input signal 212. The assembly comprising electromagnetic device 210 and input signal 212 generates a magnetic field. GMR bridge 204 forms a magnetic coupling due to its inherent sensitivity to the magnetic field; magnetic flux 214 indicates this coupling formed between GMR bridge 204 and electromagnetic device 210. Increased sensitivity by GMR bridge 204 can be achieved by biasing GMR bridge 204 in the Barkhausen effect area, wherein entry into the Barkhausen effect area is caused due to an increased magnetic field supplied by electromagnetic device 210 and input signal 212.

Magnetic coupler 20 is specially suited to provide magnetic coupling for high voltage isolation systems. GMR bridge 204 in the present structure operates like a bridge rectifier. However, unlike the conventional bridge rectifier, GMR bridge 204 is able to sense high magnetic fluxes at electromagnetic device 210 and is able to transmit flux signals at output 208. Further, unlike the conventional bridge rectifier, GMR bridge 204 is not directly connected to electromagnetic device 210. The coupling is made via the magnetic flux which is sensed by the GMR bridge 204 when the orientation of the flux relative to the sensor is optimal, i.e. parallel.

Amplifier

FIG. 3 depicts a GMR amplifier 30 that utilizes the GMR bridge and Barkhausen effect as described above. Here, GMR bridge 304 has two of its opposing nodes connected to a voltage potential. The other two opposing nodes of GMR bridge are connected to the inverting 306 and noninverting 308 inputs of an amplifier 310. A field generating means 312, in this instance a magnet or electromagnet, is moved to a position relative GMR bridge 304 such that entry into the Barkhausen effect area occurs. In this manner, the output, V₀, is increased by a sensitivity factor of 5, i.e. from 2 mV operating in a non-Barkhausen effect area to 10 mV in the Barkhausen effect area (the sensitivity factor of 5 is due to the type of ferromagnetic material present within the GMR bridge namely, permalloy 80; other ferromagnetic materials will produce a different sensitivity factor. The impressive gain is due to the increased movement of the magnetic domains with only small changes in flux. GMR amplifier 30 can be combined with magnetic coupler 20. Note, that while the above embodiment utilizes a permanent magnet as field generating means 312 numerous other field generating means may be used without departing from the spirit or scope of the invention.

Frequency Multiplier

FIG. 4A depicts a GMR multiplier 40 that utilizes the GMR bridge and Barkhausen effect as described above. Here, GMR bridge 404 has two of its opposing nodes connected to a voltage potential while the other two opposing nodes are connected to a voltage output, V₀. An electromagnetic device 410, e.g. inductor, is connected to input signal 412. The assembly comprising electromagnetic device 410 and input signal 412, having drive voltage e(t), generates a magnetic field and corresponding flux which is collected by GMR bridge 404. Similar to magnetic coupler 20, the sensitivity of GMR bridge 404, and thereby, GMR multiplier 40, can be increased by biasing GMR bridge 404 in the Barkhausen effect area, wherein entry into the Barkhausen effect area is caused due to an increased magnetic field supplied by electromagnetic device 410 and input signal 412.

The structure describe above may be exploited as a multiplier by using the non-linear voltage transfer and saturation characteristics of

GMR bridge 404. Figure 4B is a graphical depiction of the nonlinear voltage transfer curve of multiplier 40. As indicated, the output voltage,

V₀, is a function of the applied magnetic field, H. The drive voltage e(t), where e(t) = E cos (cot+a) (for the Exciting voltage assume a=0), creates the field, H, which serves to operate GMR bridge 40 along the linear slopes V₀₁ and V₀₂, driving the output waveform of GMR bridge 40 to have twice the fundamental frequency of the input signal 412 frequency. This result is shown in FIG. 4C as a waveform with both halves of the sinusoidal cycle on the same side of the zero axis, resulting in a period of one-half of the input signal of the original driving function, i.e. original driving function has a period of T and multiplier has a period of T/2. As such, the above provides a multiplier of input frequency of magnetic drive by providing harmonic output due to the nonlinear bimodal transfer function of GMR bridge 404. GMR multiplier 40 has numerous applications. As described above, multiplier 40 may be used to multiply the basic frequency of a sinusoidal signal(or other appropriate signal with a periodic content) due to the nonlinear transfer characteristic of multiplier 40. This is in reference to the bimodal voltage output as a function of the applied magnetic field, resulting in a frequency output that is double the frequency input. Additionally, multiplier 40 may be used to process two input signals through nonlinear mixing action, resulting in an output similar to that of amplitude modulation, through the multiplication of two signals. For example, the multiplication of cosωt and msin(ωt+l), resulting in cosωt + k(sinaωt + cosωt) + k(sinaωt - cosωt), the fundamental equation for amplitude modulation. Moreover, multiplier 40 units may be cascaded with DC leveling interfaces such as capacitive coupling devices to allow for DC offset while continuing the multiplication process. And, multiplier 40 may be biased with a magnetic field to allow preferential detection of an incoming signal for the purposes of radio wave detection via the non- linear method.

A more specific application of multiplier 40 relates to the need to pass information through power lines or other medium which resist frequency doubling characteristics, e.g. frequencies used in the communications or power industries. This difficulty is in particular shown by the need to pass information through energy transfer devices and impedance transfer devices, such as transformers. These devices have a great variation of permeability and internal capacitance that can resist the flow of various waveforms therethrough. And, as such, the devices act to literally attenuate the information flow by the combination of resistance, inductance, and capacitance, as well as through the power line parameter constituents themselves. Therefore, it is of interest and practical use to apply a method or methods which bypass or apply in an alternative manner the information transfer method which will successfully achieve the passage of data or other desirable quantified attributes. A mathematical example and description of achieving the above with multiplier 40 is described below:

Assume an initial signal of 1,048,576 cycles/unit time, divided by 2 for 20 times, giving 1 cycle/unit time. This results in a reduction of frequency by the ratio of 1/1048576. The signal is now in condition for easy transmission by a power line. To insert information into the signal, the transmission is shifted by 1048.576 cycles/unit time, which creates a shift in the original 1 cycle/unit time of approximately 1/1001. This illustrates the compressive nature of the shift, which will flow easily within the power line domain. GMR multiplier 40 stands ready at the receiver end of the signal, where the receive signal is multiplied with data shift information and then multiplied (with GMR multiplier) by 2 for 20 times, thereby providing the original signal with no shift. However, considering the aforementioned shift, the signal will be approximately 1,048,576 - 1048.576 cycles/unit time. Thus, providing the means of information transfer through the medium of interest, such as the power line.

The result here is that a very small shift attributed to a base band carrier may be expanded to a large shift upon receipt. This can be performed in a rapid manner, using a variety of shifts, depending upon the number of

GMR multipliers 40 used and can provide complete information transfer at the end of one cycle of sampling.

Speed or Position Indicator FIG. 5A depicts a GMR speed or position indicator 50 that utilizes the GMR bridge and Barkhausen effect as described above. Here, GMR bridge 504 is in close proximity to magnet 542 which is set to generate magnetic fields so as to cause GMR bridge 504 to enter into the Barkhausen effect area. Two of the opposing nodes of GMR bridge 504 are connected to a voltage potential. The other two opposing nodes of GMR bridge 504 are connected to amplifier 544. Further, amplifier 544 is connected to capacitor 545 and capacitor 545 is serially connected to amplifier 546. Ground contact 547 and capacitor 548 are serially connected to output 549. Points 1, 2 and 3 are established as reference points and are discussed below in reference to FIG. 5B.

FIG. 5B shows a profile of the magnetic field and the ferromagnetic domains thereof. Point 1 marks the establishment of a magnetic field within indicator 50. The waveforms between points 2 and 3 show relaxing, or decaying, ferromagnetic domains within the GMR; point 2 indicates the entry into the Barkhausen effect area while point 3 indicates exit from the Barkhausen effect area. The flux density at points 1, 2 and 3 is at definite levels for a particular magnetic material. Accordingly, knowing the type of magnetic material and the magnitude of the magnetic flux, it is possible to locate points 1, 2 and 3. The sensitivities of GMR bridge 504 at points 1, 2 and 3 provide signals which, after amplifications, can be used as reference locations to determine, speed, position and other similar parameters in, for example, a detection and scalar/nonscalar observations systems. For example, the elapsed time from entering and exiting the Barkhausen effect area determines the speed of passing magnet 542, or alternatively, in the instance of a rotating part, the angular position of the part.

Oscillator

FIG. 6A depicts a GMR oscillator 60 that utilizes the GMR bridge and Barkhausen effect as described above. In basic terms, GMR oscillator 60 is a device which provides an output signal through the means of electromagnetic feedback. The electromagnetic feedback is achieved by utilizing GMR bridge 604 as a reception device and further by utilizing a means of magnetic field generation, such as a coil, wire, permanent magnet attached to a vibrating piezoelectric membrane or other appropriate electromechanical or electrical transfer function method, as magnetic generation device. The reception device and the magnetic generation device combine to provide the feedback loop that is necessary to create an oscillator of electromagnetic means.

Specifically, the circuit comprises GMR bridge 604 having two opposing nodes connected to an operational amplifier 652. Amplifier 652 also includes connections to a voltage source and a ground. Electromagnetic device 654 is disposed close to GMR bridge 504 and produces a magnetic flux 656. Amplifier 652 is connected to a variable resistor 658 at the output. Variable resistor 658 is also connected to electromagnetic device 654. Further, GMR bridge 604 and electromagnetic device 654 are individually grounded.

Oscillator 60 is operative when current through electromagnetic device 654 increases. This creates magnetic flux 656 and because GMR bridge 604 is sensitive to flux variations, the voltage, V„, increases. Note that as the magnetic field is increased, entry into the Barkhausen effect area occurs, whereby GMR bridge 604 has increased sensitivity to flux and increased domain mobility; a small change in flux creating a great change in voltage, V_g. The voltage increase in V_g operates to decrease output voltage V₀ because of polarity. Thus, the phase is reversed in amplifier 652. Because of phase reversal, magnetic flux 656 falls. Ultimately, this interaction results in the decrease of V_g accompanied by an increase in V₀ and magnetic flux. This sequence of balanced increase and decrease in the related parameters is implemented thereby yielding GMR oscillator 60. The circuit is adjustable based on changes of the related parameters discussed hereinabove. Thus, for example, an adjustable oscillation frequency dependent upon the values of electromagnetic device 654, amplifier 652, output voltage V₀, voltages V_} and V₂ and magnetic flux 656 can be generated. Further, GMR oscillator 60 may also be adjusted by varying magnetic flux or by change the values of variable resistor 658. Specifically, the oscillation frequency is related to the loop phase constant, involving the electromagnetic device 654 value, the gain value and the position of the inductor field with relation to the GMR bridge 604. The Q of electromagnetic device 654 is also a factor.

Figure 6B depicts the non-linear voltage transfer curve of oscillator 60. As indicated, the output voltage, V₀, is a function of the applied magnetic field, H. The drive voltage e(t), where e(t) = E cos (cot+a) (for the

Exciting voltage assume a=0), creates the field, H, which serves to operate GMR bridge 604 along the linear slopes V₀₁ and V₀₂- As indicated, the polarity of the circuit is generally oriented such that feedback is positive. However, should the feedback be negative, the circuit will also function as a variable magnetically controlled amplifier that is capable of adjustable amplification without oscillation. The feedback concept related to the feedback equation, A' = 1/(1+AB), where B is the feedback voltage ratio occurring at the input of summing node at the amplifier; if AB (loop in phase feedback component) is less than 1, and the amplifier phase shift is 180 degrees, the system will provide a condition for oscillation.

GMR oscillator 60 has numerous applications. For example, the oscillator may be used to detect various materials. Due to the presence of a permeable material, or a material capable of presenting a permeable situation, the output frequency of oscillator 60 will shift, indicating the effect of loading and the sensing of the material. As such, oscillator 60 may used within an instrument to detect and locate metals of a magnetically permeable nature or those of a conductive nature capable of generating a circulating current within the conductor.

Additionally, oscillator 60 relates to the field of the earth, and responds to such fields as the field of the earth, as well as tellurian currents underground (due to recent sunspot activity) relating to the value of underground materials /objects such as oil, iron, etc. Moreover, proximity devices, such as fuses, slow crash detectors on cars, stairs in houses, rest homes, and associated location devices including burglary detectors (guns, etc.) can be detected and interpreted by oscillator 60 as frequency shifts. And, if operated in the negative feedback mode, oscillator may perform amplification changes sufficient to achieve detection of various objects also.

The present invention may be embodied in other specific forms without departing from the spirit of the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.

Claims

What is claimed: 1. An output adjustment circuit for use in an electronic circuit, comprising: a giant magnetoresistive (GMR) bridge; and a magnetic field generator for generating a magnetic field having a corresponding flux, the GMR bridge being disposed relative to the magnetic field generator such that the corresponding flux causes the GMR bridge to operate in a Barkhausen effect area.

2. The circuit of claim 1, wherein the GMR bridge employs a ferromagnetic material and wherein the ferromagnetic material comprises permalloy 80.

3. The circuit of claim 1, wherein the electronic circuit comprises a magnetic coupler.

4. The circuit of claim 1, wherein the electronic circuit comprises an amplifier.

5. The circuit of claim 1, wherein the electronic circuit comprises a frequency multiplier.

6. The circuit of claim 1, wherein the electronic circuit is selected from the group consisting of a speed indicator and a position indicator.

7. The circuit of claim 1, wherein the electronic circuit comprises an oscillator.

8. The circuit of claim 1, wherein entering the Barkhausen effect area causes the GMR bridge to have an increased sensitivity to changes in the magnetic field.

9. The circuit of claim 8, wherein the sensitivity is increased by a factor of between 1.5 and 5.

10. A method of adjusting the output of an electronic circuit, wherein the electronic circuit comprises a giant magneto-resistive (GMR) bridge and magnetic field generator: generating a magnetic field with the magnetic field generator; collecting the flux corresponding to the generated magnetic field with the GMR bridge whereby the GMR bridge enters the Barkhausen effect area; and adjusting the output of the electronic circuit by biasing the GMR bridge with the magnetic field while the GMR bridge is operating in the Barkhausen effect area.

11. The circuit of claim 10, wherein the GMR bridge employs a ferromagnetic material and wherein the ferromagnetic material comprises permalloy 80.

12. The circuit of claim 10, wherein the electronic circuit comprises a magnetic coupler.

13. The circuit of claim 10, wherein the electronic circuit comprises an amplifier.

14. The circuit of claim 10, wherein the electronic circuit comprises a frequency multiplier.

15. The circuit of claim 10, wherein the electronic circuit is selected from the group consisting of a speed indicator and a position indicator.

16. The circuit of claim 10, wherein the electronic circuit comprises an oscillator.

17. An output adjustment circuit for use in an electronic circuit comprising: a giant magneto-resistive (GMR) bridge, wherein the GMR bridge produces an output; a magnetic field generator wherein the magnetic field generator produces a magnetic field having a corresponding flux being collected by the GMR bridge, and wherein the magnetic field generated by the magnetic field generator and the flux collected by the GMR bridge causes the GMR bridge to enter into a Barkhausen effect area, the magnetic field generator for biasing the GMR bridge within the Barkhausen effect area to adjust the output of the GMR bridge, the output useable within the electronic circuit.

18. The circuit of claim 17, wherein the GMR bridge employs a ferromagnetic material and wherein the ferromagnetic material comprises permalloy 80.

19. The circuit of claim 17, wherein the electronic circuit comprises a magnetic coupler.

20. The circuit of claim 17, wherein the electronic circuit comprises an amplifier.

21. The circuit of claim 17, wherein the electronic circuit comprises a frequency multiplier.

22. The circuit of claim 17, wherein the electronic circuit is selected from the group consisting of a speed indicator and a position indicator.

23. The circuit of claim 17, wherein the electronic circuit comprises an oscillator.

24. The circuit of claim 17, wherein entering the Barkhausen effect area causes the GMR bridge to have an increased sensitivity to changes in the magnetic field.

25. The circuit of claim 24, wherein the sensitivity is increased by a factor of between 1.5 and 5.

26. A frequency multiplier comprising: an input signal having a fundamental frequency; a giant magnetoresistive (GMR) bridge operationally coupled to the input signal, the GMR bridge having an output; a magnetic field generator for generating a magnetic field having a corresponding flux, the GMR bridge being disposed relative to the magnetic field generator such that the corresponding flux causes the GMR bridge to produce an output that is a multiple of the input signal's fundamental frequency.

27. The frequency multiplier of claim 26, wherein the multiple is a multiple of two.

28. The frequency multiplier of claim 26, wherein the GMR bridge is disposed relative to the magnetic field generator such that the corresponding flux causes the GMR bridge to operate in a Barkhausen effect area, the GMR bridge producing an output that is a multiple of the input signal's fundamental frequency while operating in the Barkhausen effect area.

29. An output adjustment circuit for use in an electronic circuit, comprising: a giant magnetoresistive (GMR) bridge having an output; and a magnetic field generator for generating a magnetic field having a corresponding flux, the GMR bridge being disposed relative to the magnetic field generator such that a change in the corresponding flux causes a corresponding change in the output of the GMR bridge, the output of the GMR bridge useable within the electronic circuit.

30. The circuit of claim 29, wherein the GMR bridge employs a ferromagnetic material and wherein the ferromagnetic material comprises permalloy 80.

31. The circuit of claim 29, wherein the electronic circuit comprises a magnetic coupler.

32. The circuit of claim 29, wherein the electronic circuit comprises an amplifier.

33. The circuit of claim 29, wherein the electronic circuit comprises a frequency multiplier.

34. The circuit of claim 29, wherein the electronic circuit is selected from the group consisting of a speed indicator and a position indicator.

35. The circuit of claim 29, wherein the electronic circuit comprises an oscillator.