Systems and methods for acoustically driving a ferromagnetic resonance sensor device

Abstract

A system and method for an acoustic driven ferromagnetic resonance (ADFMR) based sensor, comprising: a power supply to provide an electrical signal to power the system; and an ADFMR circuit sensitive to an electromagnetic field, wherein the ADFMR circuit comprises an ADFMR device. The function of the system is to detect and measure an external electromagnetic (EM) field by measuring the perturbation of the electrical signal through the ADFMR circuit due to the EM field.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application No. 62 / 948,146, filed on December 13, 2019, the entire contents of which are incorporated herein by reference into this disclosure. Technical Field

[0003] The present invention relates generally to the field of ferromagnetic resonance-based sensors and, more particularly, to a new and useful high-sensitivity and low-noise sensor readout system and method for acoustically driven ferromagnetic resonance. Background Art

[0004] Ferromagnetic resonance (FMR) can measure the magnetic properties of materials by detecting the precession of magnetization in ferromagnetic samples. Different types of FMR include externally driven FMR and current-driven FMR. FMR can be excited using a variety of techniques, such as cavity excitation, stripline excitation, spin transfer torque, and spin-orbit torque. These applications are generally incompatible with device applications. They require large cavities, high-power drives, and the use of large sample volumes to be effective. Therefore, the use of FMR is mainly limited to large laboratories and research projects. Currently, FMR is not available in production-ready systems. In addition, systems for circuit integration are not available in current implementations.

[0005] Other types of magnetic sensors exist, but they have various limitations. For example, SERF and SQUID magnetic sensing methods can achieve high sensitivity, but at the expense of bulk, complexity, and difficulty in system integration. Hall effect sensors and magnetoresistive sensors may offer smaller solutions, but at the expense of sensitivity. Therefore, in the field of magnetic field sensors, there is a need for an acoustically driven ferromagnetic resonance sensor device. The present invention provides such a new and useful system and method. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a simplified schematic diagram of the system of the preferred embodiment.

[0007] Figure 2 is a schematic diagram of the interferometer system.

[0008] Figure 3 is a schematic diagram of a one-dimensional gradiometer system.

[0009] Figure 4 is a schematic diagram of the low-energy interferometer system.

[0010] Figure 5 is a schematic diagram of an interferometer system that achieves noise reduction.

[0011] Figure 6This is a schematic diagram of a large-gap electromagnetic field interference instrument.

[0012] Figure 7 This is the general circuit schematic diagram of the interferometer system.

[0013] Figure 8 This is the general circuit schematic of the system.

[0014] Figure 9 It is a schematic diagram of two test circuits and a two-dimensional interferometer.

[0015] Figure 10 The second schematic diagram shows two test circuits and a two-dimensional interferometer.

[0016] Figure 11 It is a schematic diagram of a test circuit and a two-dimensional interferometer.

[0017] Figure 12 It is an explanatory diagram of an example of an interdigitated transducer (IDT). Figure 13 is a schematic diagram of a surface acoustic wave (SAW) device.

[0018] Figures 14 to 18 It is a schematic diagram of the alternating changes of the SAW device.

[0019] Figure 19 This is an example of how the ferromagnetic absorption spectrum changes with the applied field strength.

[0020] Figure 20 This is the circuit diagram of the gradiometer.

[0021] Figure 21 It is a schematic diagram of the vector modulator circuit.

[0022] Figure 22 This is the schematic diagram of the IQ mixer circuit.

[0023] Figure 23 is a schematic diagram of the linearization circuit.

[0024] Figure 24 This is the schematic diagram of the amplifier circuit.

[0025] Figure 25 This is the schematic diagram of the detection circuit.

[0026] Figure 26 This is a circuit diagram of an interferometer system including analog subtraction.

[0027] Figure 27 This is a circuit diagram of an interferometer system including a linearization circuit.

[0028] Figure 28 This is a simplified interferometer schematic.

[0029] Figure 29 This is the circuit diagram of the interferometer.

[0030] Figure 30 is a schematic diagram of an example interferometer including subassemblies.

[0031] Figure 31 This is the circuit diagram of the gradiometer.

[0032] Figure 32 This is a circuit diagram of an interferometer with a vector modulator circuit.

[0033] Figure 33 This is a circuit diagram of an interferometer having an IQ mixer circuit.

[0034] Figure 34 This is a circuit diagram of an interferometer with a linearization circuit.

[0035] Figure 35 is a flow chart of the method of the preferred embodiment.

[0036] Figure 36 is an exemplary system architecture that can be used to implement the system and / or method.

[0037] Figure 37 is a glossary of example circuit subcomponents. DETAILED DESCRIPTION

[0038] The following description of the embodiments of the invention is not intended to limit the invention to these embodiments, but rather to enable any person skilled in the art to make and use the invention.

[0039] 1. Overview

[0040] A system and method for an acoustically driven ferromagnetic resonance (ADFMR) sensor device facilitates the design and operation of chip-scale ADFMR devices that can be used to measure electromagnetic (EM) fields. The system and method preferably uses magnetic resonance to measure the EM field and then uses this information to determine the amplitude and / or gradient of the field. The system and method preferably include: a voltage oscillator operating in the MHz-GHz range to generate an oscillating signal; a power splitter that separates the oscillating signal into a test signal and a reference signal; and an ADFMR circuit including an acoustically driven ferromagnetic resonance (ADFMR) device. The ADFMR device modifies the test signal relative to a magnetic field. A detector uses the modified test signal and the reference signal to determine the amplitude and / or gradient of the magnetic field. The ADFMR device may include: a base piezoelectric substrate; at least two acoustic transducers on the piezoelectric substrate; and a ferromagnetic body on the piezoelectric substrate between the at least two acoustic transducers. An acoustic wave is generated from the test signal at a first of the at least two acoustic transducers. An acoustic wave propagates along a ferromagnet, exciting the ferromagnet to resonance or near resonance. The ferromagnet modifies the acoustic wave by absorption; the modified acoustic wave is converted back into a modified signal at a second of at least two acoustic transducers. In some variations, the ADFMR device is a surface acoustic wave (SAW) device, where the SAW is the acoustic wave used to drive the transducer, but any general type of acoustic wave can be implemented using the system and method.

[0041] The system and method can provide many potential benefits. The system and method are not limited to always providing such advantages, and the system and method are presented only as exemplary representations of how the system and method can be used. This list of benefits is not exhaustive, and other benefits may exist in addition or in lieu thereof.

[0042] One potential benefit of the system and method is that the system and method can provide a field sensor device that is compact relative to comparable solutions. Where the typical implementation is a large benchtop laboratory setup, such a field sensor device can utilize magnetic resonance to measure the magnetic field without the general space requirements. More specifically, the system and method can utilize ferromagnetic resonance. This advantage enables the system and method to be implemented in many situations that were previously impossible. The system and method can preferably provide a chip-level solution that can be integrated into a circuit design printed circuit board (PCB). The resulting sensor device can enable CMOS compatible processing, which can make the sensor device cheaper and scalable. The system and method can use ADFMR devices to make magnetic sensors that are more easily integrated.

[0043] Another potential benefit of the system and method is that ADFMR sensors can have enhanced sensitivity compared to other magnetic sensor technologies. The system and method can be sensitive to fields across a wide frequency spectrum (0-10 GHz). This can enable the system and method to be implemented in a wide range of sensor devices.

[0044] Combined with the potential advantages of a compact form factor, the system and method can provide a magnetic sensing device that exhibits the high sensitivity desired for specific applications while being significantly easier to integrate in terms of size and device packaging design. In an exemplary application area, such as a magnetoencephalography system for measuring brain activity, the system and method can meet the sensitivity requirements needed to monitor neuronal fields while enabling a chip-based solution.

[0045] Another potential benefit of the system is that the system and method may require very little power. Compared to other FMR devices, the system and method can be implemented using significantly less power. The low power requirement may have the additional benefit of generating less heat. The low heat generation allows the system and method to be implemented in temperature-sensitive environments.

[0046] The system and method can be applied to virtually any field requiring field measurement. Its small size, low power consumption, and high dynamic range allow it to be incorporated almost anywhere. The system and method are particularly useful for mechanical sensor devices, magnetic imaging, SQUID device replacement, and integration with any device requiring field measurement.

[0047] The system and method can provide many potential benefits. The system and method are not limited to always providing such advantages, and the system and method are presented only as exemplary representations of how the system and method can be used. This list of benefits is not exhaustive, and other benefits may exist in addition or in lieu thereof.

[0048] 2. System

[0049] like Figure 1 As shown, a system for an acoustically driven ferromagnetic resonance (ADFMR)-based sensor includes a power supply 110 that provides an electrical signal to power the system, and an ADFMR circuit 120 that is sensitive to electromagnetic fields, i.e., a first "test" circuit. The ADFMR circuit includes an ADFMR device 122 and a detector circuit including an analog-to-digital converter. The system functions to detect and measure external electromagnetic (EM) fields by measuring the perturbations of the electrical signal passing through the ADFMR circuit caused by the electromagnetic field. In some preferred embodiments, the system may include at least one additional circuit (e.g., an additional test circuit or a reference circuit). The system also includes at least one power splitter 130 that splits the electrical signal to the at least one circuit, and at least one power combiner 132 that combines the potentially perturbed electrical signal output from the ADFMR circuit 120 with other electrical signals.

[0050] In some variations including at least one additional circuit, such as Figure 2 As shown, at least one additional circuit includes a first signal processing circuit that is connected in parallel with the ADFMR circuit 120 and serves as a "reference" for the ADFMR circuit. This system variant, an interferometer variant, is used to detect and measure external electromagnetic (EM) fields by comparing a perturbed electrical signal passing through the ADFMR circuit 120 with an undisturbed electrical signal passing through the first signal processing circuit, a first reference circuit. That is, in the interferometer variant of the system, the power signal passing through the ADFMR circuit 120 is perturbed by the external field, which is then perturbed by an undisturbed reference signal from the reference circuit. A detector circuit can then use the interference (e.g., destructive interference) distribution between the test signal and the reference signal to determine the field strength.

[0051] In another variation, Figure 3 As shown, the system can be used to measure changes (i.e., gradients) in an external EM field, i.e., functioning as a gradiometer. In gradiometer variations, at least one circuit can include an additional ADFMR circuit 120, i.e., a second test circuit sensitive to EM fields. In these variations, the difference in measurements between the first test circuit and the second test circuit can be used to determine the gradient of the EM field. That is, in the gradiometer variation of the system, the power signals passing through the two ADFMR circuits 120 are perturbed by the external field. By accounting for the positional dependence of the two circuits, the field gradient can be measured by measuring the interference (e.g., destructive interference) between the two signals.

[0052] In some variations, the system may additionally or alternatively include subcomponents to increase and / or modify system capabilities. Examples include: additional ADFMR devices 122 (e.g., to enable multi-dimensional field measurements), amplifiers (e.g., to amplify power / electrical signals), filters (e.g., to reduce internal and background noise), matching networks (e.g., to match signal power between parallel circuits), attenuators, phase shifters (e.g., to change the interference pattern between test and reference signals), mixers (e.g., to mix signal frequencies), magnetic field coils (e.g., to shift signal frequency bands), and any other desired components. Potential system subcomponents include: signal amplifiers (A), bandpass filters (F), attenuators (I), inductors (L), phase shifters (γ), couplers (C), mixers (X), matching networks (M), analog-to-digital converters (ADCs), digital-to-analog converters (DACs), and comparators (≥), logic circuits, and field coils. The system may include any other applicable desired components. The implementation of some of these components will be discussed further. Figure 37 Includes a glossary of terms and symbols for subcomponents implemented in some variants of the system.

[0053] These subcomponents can implement many additional variations. For example, the system may include: Figure 4 A variant optimized for low energy consumption is shown in an example in ; Figure 5 A noise-reducing variant as shown in one of the examples in ; and Figure 6 The system may additionally or alternatively include any combination or additional variations as desired.

[0054] The system may include circuits and circuit segments connected in parallel or in series as part of the system. These circuits may include any circuit subassemblies (e.g., the aforementioned subassemblies) that provide the desired functionality. As used herein, the term "circuit" will generally refer to an entire circuit or a circuit segment. That is, a circuit itself does not necessarily constitute a closed loop, but rather, in combination with additional circuits, the circuit may function as part of a closed loop. These additional circuits may or may not be explicitly indicated herein.

[0055] like Figure 7 and Figure 8As shown, the circuit number refers to the number of the test circuit (indicated by a subscript number with a superscript symbol (')), and the circuit includes: an ADFMR device subassembly; and a signal processing circuit (indicated by a subscript number). The test circuit may also be referred to as an ADFMR circuit or a sensor circuit. In addition, the first test circuit may also be referred to without a number, such as a test circuit or an ADFMR circuit. Although the circuit is shown in the figure only in a parallel manner, variations of the system may include test circuits and / or signal processing circuits in other non-parallel configurations within the circuit (e.g., as shown in FIG. Figure 6 shown).

[0056] like Figure 8 As shown, in the general circuit layout of the system, the system may include "n" test circuits and "N" signal processing circuits, where n and N are arbitrary integers determined by the specific implementation. Circuit subcomponents, that is, components on a particular circuit, can be represented by subscripts representing the circuit number, where subscripts with a superscript symbol (') will be used for test circuit subcomponents (e.g., L 2’ denoting an inductor on the second test circuit), while subscripts without a superscript symbol (') will be used for signal processing circuit subcomponents (e.g., L2 denoting an inductor on the second signal processing circuit). In some variations, certain subcomponents may appear in areas where it is unclear to which circuit they belong. These subcomponents may be left without any subscripts, or may include a subscript connecting them to the desired circuit (e.g., when the subcomponent has a function complementary to the desired circuit).

[0057] As part of circuit identification, circuit subcomponents can be described as being upstream or downstream relative to one another. Here, "upstream" and "downstream" are used to refer to the direction of power propagation through the circuit. That is, subcomponent 'A' downstream of subcomponent 'B' means that power propagates from subcomponent 'B' to subcomponent 'A', with or without other components in between. Subcomponent 'A' upstream of subcomponent 'B' means that power propagates from subcomponent 'A' to subcomponent 'B', with or without other components in between.

[0058] A system can include a power supply 110. The power supply serves as an energy source, providing an electrical signal to the system. In some variations, the power supply 110 is an electronic oscillator. The function of the electronic oscillator is to provide an oscillating voltage, i.e., an alternating current (AC) power signal, to the system, where the power from the oscillator is used to activate the sensor circuit. Alternatively, other types of current, such as direct current (DC), can be used.

[0059] In some variations, the electronic oscillator is a voltage-controlled oscillator (VCO). Preferably, the oscillator has a frequency in the gigahertz range, more preferably 2 GHz. The high-frequency pulses of the oscillator can enable faster turn-on and turn-off times for the sensor. Fast turn-on / off times can be on the order of microseconds or faster. Since the ADFMR device 122 can operate at MHz oscillation, the oscillator can optionally be in any range that allows ADFMR operation, i.e., in the MHz to GHz range.

[0060] The system may include at least one ADFMR circuit 120. The ADFMR circuit 120 serves as a "test" circuit that includes an ADFMR device that implements the sensor capabilities of the system. The ADFMR circuit 120 may also be referred to as a sensor circuit or a test circuit. Depending on the variant, the system may include one or more ADFMR circuits 120. Each ADFMR circuit may share multiple ADFMR devices 122 between them, have one ADFMR device per ADFMR circuit, or have multiple ADFMR devices. In some variants, the system may include a group of ADFMR circuits. Multiple ADFMR circuits 120 may be used for gradient field measurements, multi-dimensional field measurements, and / or to improve field measurement accuracy (e.g., by overlapping measurements). The ADFMR circuit 120 is located downstream of the power supply 110 so that the electrical signal provided by the power supply can be implemented as a test signal along the ADFMR circuit.

[0061] In some variations, the system may include multiple ADFMR devices 122 distributed across multiple ADFMR circuits 120. In one variation, multiple ADFMR circuits 120 measuring one or more dimensions may be implemented on a single chip, as in the example of FIG. Figure 9 or Figure 10 The layout shown is very similar. Depending on the desired implementation, each dimension function can be activated or deactivated.

[0062] In one variation, a single ADMR circuit 120 measuring one, some, or all desired dimensions may be implemented on a single chip, as in the example Figure 11 The layouts shown are very similar. Depending on the desired implementation, each dimension function can be activated or deactivated.

[0063] The ADFMR device 122 is preferably a component of the system and is additionally a subcomponent of the ADFMR circuit 120. The ADFMR device 122 is used as a device that "measures" EM fields by modifying a radio frequency (RF) carrier signal (i.e., a test signal) using acoustically driven magnetic resonance. In some variations, the magnetic resonance is achieved using ferromagnetism (i.e., ferromagnetic resonance), but the magnetic resonance can be achieved using any magnetic material. Examples of other types of magnetic materials include non-ferromagnets, ferrite magnets, and the like. That is, although the device is referred to as an ADFMR device 122, the ADFMR device can actually be, for example, a ferrite magnetic resonance device. The ADFMR device 122 may include: at least one acoustic transducer that generates and / or absorbs acoustic waves; an acoustic resonator that provides a medium for acoustic wave propagation; and a magnetic material that uses magnetic resonance to perturb the acoustic waves caused by the EM field.

[0064] The ADFMR device 122 preferably includes an acoustic transducer. The acoustic transducer is configured to convert a test signal into an acoustic wave and / or convert an acoustic wave into an RF signal (e.g., a modified test signal). The acoustic transducer is configured to generate and / or absorb an acoustic wave (or pressure wave) from an electrical signal propagating along an acoustic resonator (e.g., a piezoelectric substrate).

[0065] Preferably, the acoustic transducers are implemented in pairs, with one transducer generating an acoustic wave that then propagates to another acoustic resonator and is then absorbed by the second transducer. That is, the first acoustic transducer converts a test signal propagating through the ADFMR circuit 120 into an acoustic wave, where the acoustic wave propagates within or along the ADFMR device 122 to the second acoustic transducer, which then converts the acoustic wave into an electrical signal. Alternatively, a single acoustic transducer can convert an RF test signal into an acoustic wave and then convert the acoustic wave back into an RF signal. For example, an acoustic transducer can convert an electrical signal into an acoustic wave, which propagates outward and then reflects back to the acoustic transducer, whereupon the acoustic transducer converts the acoustic wave back into an electrical signal. In other examples, multiple acoustic transducers can be implemented to both generate and absorb acoustic waves. That is, each ADFMR device 122 can implement multiple acoustic transducers. Single or multiple RF signals can be converted into acoustic waves once or multiple times, and / or acoustic waves can be converted into RF signals once or multiple times.

[0066] The acoustic transducer preferably generates acoustic waves of a type suitable for the ADFMR device 122. Examples of acoustic waves generated may include: surface acoustic waves (SAWs), bulk acoustic waves (BAWs), and Lamb waves. The specific acoustic transducer may be specifically implemented. The type of acoustic transducer may depend on the electrical signal (e.g., signal frequency, signal power) and / or the type of acoustic wave generated (e.g., surface acoustic wave, bulk acoustic wave). For example, in a variant where the system uses Lamb waves, the acoustic transducer may include electromagnet-acoustic transducers (EMATs). In a variant where the system uses surface acoustic waves, the acoustic transducer may include interdigital transducers (IDTs). Alternatively, other types of transducers (e.g., thin film bulk acoustic wave resonators, high-overtone bulk acoustic wave resonators) that generate surface acoustic waves or other types of acoustic waves may be implemented. The acoustic waves are preferably generated at or near the resonant frequency of the ferromagnet. The acoustic waves preferably propagate through the ferromagnet in or along the acoustic resonator. Thus, the acoustic waves can cause the ferromagnet to operate at or near resonance.

[0067] In some variations where the system uses surface acoustic waves, the acoustic transducer may include an IDT. An IDT can be used to generate a SAW from an electrical signal (or vice versa) using the piezoelectric effect. An IDT is a device comprising an array of interlocking comb-like metal electrodes formed into a periodic structure on a piezoelectric substrate (e.g., quartz, lithium niobate). The IDT can have any desired configuration / shape. Figure 12 An example IDT configuration is shown. For this pair of IDTs, one is preferably used as an input IDT and the other as an output IDT. The input IDT can convert radio frequency (RF) electrical signals into surface acoustic waves (SAWs) using the piezoelectric effect. The output IDT operates by absorbing the SAWs and converting them back into electrical signals.

[0068] The ADFMR device 122 may include an acoustic resonator. The acoustic resonator acts as a medium, enabling acoustic waves to propagate. The acoustic resonator may allow waves to propagate through a volume (e.g., BAWs), along a surface of a medium (e.g., SAWs), or through a cavity of a medium (e.g., acoustic waves propagating through an air cavity of an acoustic resonator). The acoustic resonator may be composed of any material capable of achieving the desired type of acoustic wave propagation. In some variations, the acoustic resonator is composed of a piezoelectric substrate (e.g., quartz). In some variations, the acoustic resonator may comprise the "body" of the ADFMR device 122, with all other components located on or around the acoustic resonator.

[0069] In some variations, the acoustic resonator is a piezoelectric substrate. The piezoelectric substrate is capable of forming and propagating acoustic waves through the piezoelectric effect. The piezoelectric substrate can be composed of any desired piezoelectric compound (e.g., most crystals or ceramic compounds). In a preferred variation, a Y-cut lithium niobate substrate is used as the piezoelectric substrate. In some variations including two acoustic transducers, the space between the two acoustic transducers (i.e., delay lines) is 1-3 mm in length. In one example, a piezoelectric substrate (e.g., zinc oxide) is deposited below or above two IDTs on an ADFMR substrate (e.g., a diamond substrate material).

[0070] ADFMR devices may include magnetic materials, preferably magnetostrictive materials. Magnetostrictive properties enable magnetic materials to convert strain into magnetic changes, or vice versa. The only limitation on the magnetic material is that it can achieve resonance on a macroscopic scale (i.e., beyond the resonance of individual molecules and / or atoms). Examples of magnetic materials include ferromagnets, ferrite magnets, non-ferromagnets, paramagnets, diamagnets, and the like. In some variations, the magnetic material may include ferromagnets and / or ferromagnetic mixtures. The function of the magnetic material is to absorb acoustic waves, where, at resonance, the absorption is very sensitive to magnetic fields. Preferably, the magnetic material is positioned in the path of the acoustic wave (along the delay line) such that the local magnetic field sets the resonant frequency of the magnetic material to the acoustic wave frequency or close to it—thus enabling the magnetic material to effectively absorb the acoustic wave and, therefore, alter the propagating acoustic wave relative to the amplitude of the field. In a preferred variation, the ferromagnet is positioned between two acoustic resonators (e.g., as a magnetic film), where the thickness and length of the magnetic material play an important role in the absorption, and thus the magnetic material may have varying thicknesses and lengths depending on the implementation. For the ferromagnetic variant, examples of ferromagnetic materials include iron, nickel, and cobalt, but any suitable type of ferromagnet can be used. In some variations, the system can be implemented with other magnetic materials, such as paramagnets, diamagnets, ferrite magnets, or any combination of these materials. Similar to the ferromagnetic variant, the magnetic material can be implemented at or near resonance to absorb the magnetic field.

[0071] In some variations, the ferromagnet has a spatial orientation. That is, the ferromagnet can be constructed and oriented so that an EM field having one spatial direction (e.g., the x-direction) can affect the interaction between the magnet and the acoustic wave, while fields from other directions can leave the ferromagnet unaffected. In this way, depending on the ferromagnet implemented, the ferromagnet (and therefore the ADFMR device 122) can be sensitive to one, two, or three spatial dimensions.

[0072] In some variations, the ADFMR device 122 may include a signal detector. The signal detector is configured to measure the output power signal from the ADFMR device 122. Because the output power signal may have been perturbed by the applied field, the output power signal can be used to determine the field strength. The signal detector may also additionally include a noise reduction function. In one variation, the signal detector may perform a Fourier transform to separate the desired output signal from other extraneous electromagnetic (EM) waves. For example, the input acoustic transducer may additionally generate extraneous EM waves. The signal detector may perform a fast Fourier transform to isolate and remove these extraneous waves from the desired signal. Due to the time delay of acoustic wave propagation compared to EM wave propagation, other time-dependent methods may be employed to separate acoustic and EM waves. For example, in one embodiment, an electronic oscillator may be cycled on and off over a fixed time period, enabling measurement of the propagating acoustic wave during the electronic oscillator's off period, thereby potentially eliminating undesired signals.

[0073] In some variations, such as the example Figure 13 As shown, the ADFMR device 122 can be a SAW device. That is, in one SAW device example, the ADFMR device 122 may include: two IDTs, an input IDT and an output IDT, positioned along the piezoelectric substrate. The magnetic film is positioned between the two IDTs along the piezoelectric substrate. The specific configuration and shape of the SAW device can vary depending on the implementation. Example variations include: each ADFMR circuit 120 has a single SAW device (e.g., Figure 13 SAW devices); such as Figure 14 and Figure 15 As shown, a multi-dimensional field sensor having a spatially oriented ferromagnet (one or more) on a SAW device; Figure 16 As shown, a single SAW device having a single ferromagnetic body is used between multiple ADFMR circuits 120; Figure 17 As shown in FIG, a single SAW device with multiple ferromagnets is used as an interferometer or gradiometer; Figure 18 As shown, there are multiple distinctly oriented ferromagnetic bodies connected in series (eg, as part of a series multi-dimensional sensor). Certain variations may include fewer or additional components as desired or necessary.

[0074] In some variations, the ADFMR device includes a field coil (FC). The field coil can be a direct current (DC) coil and / or any suitable coil or system for generating a magnetic field. Any other suitable component capable of creating a field to shift the power output can be used. The field coil is used to generate a magnetic field bias to shift the output of the ADFMR device 122 positively or negatively. In one variation, the field coil reduces the power output by inducing a reduced external field to which the ADFMR device 122 is exposed. The field coil can be implemented to shift the power output to a small output state where the circuit components function linearly, thereby reducing system errors due to nonlinearities. For example, an amplifier may have a much smaller linear amplification range than the output of the ADFMR device 122. Therefore, reducing the range of the sensor output will enable the amplifier to function linearly. The field coil can potentially apply a magnetic field at any frequency (or combination of frequencies) as desired. For example, if the system is exposed to a large, unwanted signal from the power line (e.g., 60 Hz) in addition to the earth's field, both the unwanted alternating power line field and the earth's field can be canceled. The field coil can be used to apply any suitable type of canceling magnetic field.

[0075] The field coils can shift the power output to any desired range. In some variations, the field coils can shift the external field to a position close to zero. In other variations, the field coils can alternatively or additionally shift the magnetic field to a range where the ADFMR sensor operates optimally. For example, in embodiments where the system functions as a gradiometer, the field coils can shift the magnetic field to a state where the region of change in the external field results in the greatest change in power output (e.g., an inflection point in the output power spectrum). Figure 19 The absorption spectrum of the sample as a function of the external field is shown. Thus, for a given frequency, the field coils can enable the external field to be modified so that the activity is concentrated around the inflection point of the curve.

[0076] The system may include a detector circuit. The detector circuit is used to acquire the output of the ADFMR circuit 120 (i.e., the potentially disturbed electrical signal) and any other components and determine the EM field strength. In some variations, the detector circuit includes an analog-to-digital converter (ADC). The function of the ADC is to convert an analog signal into a digital signal. In some variations, the ADC can be used to convert the output signal into a digital signal for analysis. In some variations, an ADC can be implemented for each circuit (including the ADFMR circuit 120). In these variations, the ADC converts the signal output of the circuit into a digital output before combining the circuit signals. All circuit digital outputs can then be combined into a digital output signal.

[0077] In variations including parallel circuits, the system may also additionally include a power splitter 132 and / or a power combiner 134. Power splitter 132 is used to split the power signal into multiple components, thereby enabling the connection of additional parallel circuit components. Power combiner 134 is used to combine multiple circuits. In some variations, power splitter 132 is capable of separating the original power signal into a test signal and a reference signal. Additionally or alternatively, the power splitter can separate the power signal into multiple test signals and / or multiple reference signals. Among other features, the power splitter / combiner assembly can also function as an interferometer for performing field measurements. That is, the power signal can be separated into two components (e.g., a test signal and a reference signal), one (or both) of which can be altered (e.g., by the power absorption of the field by the ADFMR device). The field can then be measured by examining the interference pattern generated by the combination of the two signals. The system may include a pair of power splitters / combiners for each parallel circuit included in the system. Alternatively, the system may include more or fewer power splitter / combiner pairs for each parallel circuit included in the system. In some variations, the system may include an unequal number of power dividers 132 and power combiners 134 (eg, a split power signal may be connected to ground and no power combiner is required).

[0078] For some multi-dimensional field detection implementations, the system may include additional power dividers / combiners to allow the addition of ADFMR circuitry 120. For example, Figure 9 As shown, for an implementation capable of measuring fields in a plane, the system may include: a power divider 132 that divides the circuit into a first test circuit and a second test circuit; and a power combiner 134 that combines the first ADFMR circuit 120 that measures the field in the "x direction" and the second ADFMR circuit that measures the field in the "y direction." The system may also have a second pair of power dividers / combiners (instead of the couplers shown) where the power signal is initially separated into a reference signal and a test signal. Alternatively, as shown Figure 11 As shown, a single test circuit can have multiple ADFMR devices 122 in series (eg, with different orientations) such that their orientations can measure fields in multiple dimensions. In some variations, these ADFMR sensors in series can operate simultaneously, and they can replace other variations.

[0079] As previously mentioned, the system can also include a combination of various subcomponents. Example subcomponents include: signal amplifiers, bandpass filters, attenuators, inductors, phase shifters, couplers, mixers, matching networks, field coils, and comparators. Subcomponents can be integrated into the test circuit, signal processing circuit, or any other part of the system.

[0080] In some variations, the system includes at least one amplifier (A). The amplifier is used to increase signal strength. The amplifier can help offset the effects of power consumption and the reduced power resulting from splitting the original power. The amplifier can be an active or passive amplifier.

[0081] In some variations, the system may include an attenuator (1). The function of the attenuator is to reduce the power of the signal without affecting the signal waveform. In some variations, the attenuator is implemented to reduce noise. In addition, the attenuator can match the power signal size between parallel circuits (for example, between a test circuit and a reference circuit). The attenuator can be digital or analog. In some variations, a digital attenuator is used to minimize the elimination of 1 / f "pink" noise; the noise is proportional to the power. An analog attenuator can also reduce 1 / f noise, but depends on the noise signal of its control voltage. In some variations, the ADFMR circuit 120 may include an attenuator.

[0082] In some variants, the system includes at least one bandpass filter (F). The bandpass filter works by narrowing the frequency band of the electrical signal, thereby narrowing the frequency band of application and / or analysis. This may also be the case once the signal is amplified, which may naturally broaden the signal spectrum.

[0083] In some variations, the system includes at least one inductor (L). The function of the inductor is to store energy in a magnetic field. The matching inductor can match the impedance of the transducer to any circuit components adjacent to the transducer. In some variations, the system can include a matching inductor that matches the acoustic transducer to the mixer input.

[0084] In some variations, the system includes at least one phase shifter (γ). A phase shifter works by "shifting" the phase of an electrical signal. A phase shifter can be implemented to impose constructive or destructive interference between parallel circuits that are then combined. This is particularly important when implementing an interferometer.

[0085] In some variations, the system may include at least one mixer (i.e., mixer (X)). The mixer's function is to combine two electrical signals into one. The mixer can multiply the frequency of the signal, thereby achieving frequency mixing. In some variations, the mixer can reduce the ~1 GHz frequency of the ADFMR device 122 to zero frequency DC. In addition, the mixer can mix the original power supply 110 signal with the ADFMR device 122 output to remove electronic oscillator noise.

[0086] In some variations, the system includes at least one coupler. The function of the coupler is to couple power transmitted from one circuit to another circuit, allowing the same signal to be used in the other circuit. In some variations, a coupler can be used instead of a power splitter to maintain the same power level in both paths. In some variations, the system may additionally include a hybrid coupler. A hybrid coupler can couple two input sources to two output sources. In some preferred variations, the hybrid coupler is implemented as two separate input sources and shifts the phase of the output sources.

[0087] In some variations, the system includes at least one matching network. The matching network may include a combination of inductors and capacitors. The function of the matching network may be to match the impedance between the acoustic transducer and adjacent circuit components (e.g., a mixer input) and to allow the transducer impedance to appear high so that it can be connected to a high-efficiency (low-power) oscillator. In some variations, the matching network may match the impedance of the transducer to any circuit components adjacent to the transducer. In some variations, the system may include a matching network that matches the acoustic transducer to the mixer input.

[0088] In some variations, the system includes at least one comparator (≥). The function of the comparator is to detect the sign of the output signal, i.e., positive, negative, or zero. The comparator can be used with a logic circuit to implement incremental changes to the output signal.

[0089] As previously described, the system includes at least one ADFMR circuit 120 (i.e., a first ADFMR circuit), which includes at least one ADFMR device 122. Each ADFMR circuit includes an ADFMR device subassembly and / or shares an ADFMR device subassembly with other ADFMR circuits (e.g., Figure 10 ). ADFMR circuit 120 is used to measure an external magnetic field. Depending on the variant, each ADFMR circuit 120 may be identical or different. ADFMR circuit 120 may have additional subcomponents depending on the implementation. For example, in one implementation, ADFMR circuit 120 may include a matching network. In other variants, ADFMR circuit 120 may include an inductor and / or an attenuator. ADFMR circuit 120 may additionally or alternatively have other components, such as an amplifier or a phase shifter.

[0090] In a "low power" variation, the ADFMR circuit 120 includes a matching network. In this variation, the matching network can be used to match the impedance of the ADFMR circuit to another circuit. In this variation, the system can include a high impedance power source (e.g., an oscillator), and the acoustic transducer of the ADFMR device can be low impedance.

[0091] In another variation, ADFMR circuit 120 includes a digital attenuator upstream of ADFMR device 122 and two matching inductors, one upstream and one downstream of the ADFMR device. Compared to analog attenuators, the digital attenuator reduces power and helps reduce 1 / f noise. The matching inductors can match the impedance between the IDTs in ADFMR device 122 and other components, such as a mixer.

[0092] In some variations, the system may include multiple ADFMR circuits (e.g., a first ADFMR circuit, a second ADFMR circuit, etc.). Multiple ADFMR circuits 120 may be used to implement additional and / or improved sensing functionality of the system. In some system embodiments, multiple ADFMR circuits 120 (e.g., a first test circuit and a second test circuit) may be located in parallel at different spatial locations, such that the system may function as a gradiometer. Thus, as Figure 20 As shown in the example schematic of FIG, any reference to a gradiometer will refer to at least two ADFMR circuits 120 connected in parallel, and a set of power dividers / combiners that split and combine the original power signal into two test signals. Additional circuits (e.g., additional test circuits and / or signal processing circuits) and additional subassemblies can generally be added depending on the desired implementation, wherein, for an implementation, the additional subassemblies can still be connected in series or in parallel as desired.

[0093] The system can include at least one signal processing circuit, such as a first signal processing circuit. The signal processing circuit can be connected in parallel with the ADFMR circuit 120. Alternatively, the signal processing circuit can be connected in series with the ADFMR circuit 120. The signal processing circuits can be the same or different and can play a variety of functional roles as part of the system, depending on the implementation. In some variations, the first signal processing circuit is connected in parallel with a reference circuit of the ADFMR circuit 120.

[0094] According to this embodiment, the first signal processing circuit, i.e., the reference circuit, can work together with the ADFMR circuit 120 so that the two circuits together act as an interferometer. In these embodiments, the reference circuit can include a phase shifter and an attenuator. Thus, as Figure 4As shown in the example schematic of FIG, any reference to an interferometer refers to the ADFMR circuit 120, the reference circuit, and the power splitter / combiner that splits and combines the original power signal into the test signal and the reference signal. Additional circuits (e.g., additional test circuits and / or signal processing circuits) and additional subcomponents can generally be added depending on the desired implementation, wherein, for one implementation, the additional subcomponents can still be connected in series or in parallel as desired. A reference circuit phase shifter can be used to change the phase of the reference signal so that the reference circuit can destructively interfere with the ADFMR circuit 120.

[0095] In some variations, the system includes a signal processing circuit, such as Figure 21 The vector modulator circuit is shown in an example schematic diagram of . The vector modulator circuit is preferably connected in parallel with the ADFMR circuit 120, although it can be connected in series with the ADFMR circuit. The vector modulator circuit acts as a reference circuit, which forms an interferometer in combination with the test circuit. The vector modulator circuit can additionally act to reduce noise (for example, as an analog subtraction circuit), although it can have other or additional functions. The vector modulator circuit preferably includes at least one attenuator. In a preferred example, the vector modulator circuit includes an upstream attenuator, and a hybrid coupler feeds the output of one upstream attenuator into two downstream attenuators, the outputs of which are then recombined. The two downstream attenuators can achieve any desired phase shift in the power signal. The vector modulator circuit can achieve any desired phase while using only attenuators, thereby minimizing noise due to phase shift. In certain variations, such as Figure 32 As shown, the vector modulator circuit can be used as the only reference circuit and, together with the test circuit, as an interferometer circuit. The vector modulator circuit can additionally or alternatively function in conjunction with a different interferometer circuit or a gradiometer circuit, wherein the vector modulator circuit reduces the magnitude of signals that do not originate from the signal of interest.

[0096] In some variations, such as Figure 22As shown in the example schematic, the system includes a signal processing circuit that is an IQ mixer circuit. The IQ mixer circuit can be connected in parallel with the ADFMR circuit 120. Alternatively, it can be connected in series with the ADFMR circuit 120. The IQ mixer can include: a power divider 134 for splitting the power in half; a mixer connected to a hybrid coupler downstream of the power divider to shift the phase of half of the power signal; and a mixer downstream of the power divider connected to the non-shifted output of the hybrid coupler, which mixes the other half of the power signal without shifting the signal. The IQ mixer can achieve better measurement of the magnitude and phase of the power signal by creating a linear combination of an "in-phase" power signal and a 90-degree "out-of-phase" power signal. In addition, the IQ mixer circuit can be used to center and normalize the test signal, but may also include other or additional functions. The IQ mixer circuit can be implemented in conjunction with an interferometer circuit or a gradiometer circuit.

[0097] In some variations, such as Figure 23 As shown in the example schematic of FIG, the system includes a signal processing circuit that is a linearizer circuit. In some variations, the linearizer circuit is connected in series with the ADFMR circuit 120, although it can be connected in parallel with the ADFMR circuit. In one example embodiment of the linearizer circuit, the linearizer circuit may include at least one comparator and a logic circuit. The linearizer circuit minimizes the nonlinear output of the system subcomponents by reducing the output voltage of the system to a smaller, "more" linear region. The linearizer circuit can be used as a feedback loop controlled by the logic circuit in conjunction with the magnetic field coil. The logic circuit uses the input information from the comparator to guide the magnetic field coil current. The linearizer circuit can be implemented with any desired ADFMR circuit 120.

[0098] The linearizer circuit can be configured to operate in a "setup" mode prior to a final measurement of the field. The setup mode is used to bring the voltage output of the ADFMR circuit 120 and / or the external field applied to the ADFMR circuit to an optimal desired measurement / output state (i.e., a desired active state). Through the setup mode, the linearizer circuit can incrementally modify the magnetic field with the field coil voltage. Through cycling, the field coil voltage can be increased or decreased until the desired field active state is achieved. Once the desired state is achieved, the setup mode can be stopped and a measurement of the effective field can be taken. By considering the current or voltage supplied to the field coil, the actual field strength can be determined. Alternatively, the linearizer circuit can include a simpler field detector to determine the approximate desired voltage and enable the field coil to reach the desired active region in one or just fewer incremental cycles (e.g., an implementation of a field programmable gateway array).

[0099] In one example utilizing a linearizer, the desired active state for the external field is 0 (or close to 0), and the field coil is a DC coil. In this example, during the setup mode, the voltage across the DC coil can be increased or decreased until the effective field across the sensor approaches 0. Once the effective field is close enough to 0, the ADFMR circuit can make a "final" measurement of the effective field. Using the voltage across the DC coil, the system can then calculate the actual field strength.

[0100] In some variations, such as Figure 24 As shown in the example schematic of FIG, the system may include a signal processing circuit as an amplifier circuit. The amplifier circuit can be connected in series with the ADFMR circuit 120 and is used to amplify the power signal (e.g., a test signal). The amplifier circuit preferably includes at least one amplifier. In some variations, the amplifier circuit includes bandpass filters upstream and downstream of the amplifier to maintain a narrow power spectrum. The amplifier circuit can be implemented to compensate for power loss and / or power reduction caused by circuit separation.

[0101] In some variations, such as Figure 25 As shown in the example schematic diagram of , the system can include a detection circuit. The detection circuit is used to "read" the output voltage of the system as an applied field. Generally, this requires normalizing the output signal and converting it into a quantity that can be analyzed by the detection circuit. The detection circuit preferably operates in conjunction with the IQ mixer circuit, but can be implemented independently of the detection circuit. Any general-purpose detection circuit capable of operating within the desired range can be used for this function. In a preferred variant, the detection circuit includes an amplifier and an analog-to-digital converter (ADC). In addition, the detection circuit can include an inductor.

[0102] The above-described circuit components can be used in any desired manner with the basic interferometer / gradiometer components. Generally speaking, any embodiment can be used as an interferometer or gradiometer as described above. In a first example of a general interferometer application, the basic system additionally includes a vector modulator circuit, an IQ mixer circuit, an amplifier circuit, and a detection circuit. Figure 26 This example is shown implemented as an interferometer. In this example, an amplifier circuit amplifies the outputs of the "internal" and "external" interferometers. A vector modulator circuit is then connected to an IQ mixer circuit. All signals are ultimately combined and output to a detection circuit. This example is generally used to measure a desired field. This example can also or alternatively be implemented as a gradiometer system.

[0103] In the case of large gaps that may include large gaps in field strength, e.g. Figure 27As shown, the previous general application examples can additionally include linearization circuitry. The large-gap example is used to accurately measure fields that may have large variations in amplitude. While the general application examples can operate over a wide range, the large-gap example includes a feedback loop that reduces the nonlinear effects caused by the wide variations in field amplitude, thereby making field measurements more accurate.

[0104] In a third low-power example, the system may include only a mixer and detection circuitry. The low-power example can detect fields at very low power consumption (less than 25 μW). In variations where the ADFMR device includes a SAW device, the system may additionally include matching networks before and after the interferometer. The matching networks can provide high resistance and match the IDT impedance to the electronic oscillator and mixer impedance, thereby matching their voltages.

[0105] 3. System Example

[0106] In this section, variations of a sample system are presented. The details of the variations described can be used in combination with or in place of other system variations described herein. The description of these examples is not intended to limit the system to these embodiments.

[0107] In the first system variant, as Figure 1 As shown, a system for a sensor based on acoustically driven ferromagnetic resonance (ADFMR) includes a power supply including an electronic oscillator that provides an electrical signal; at least one circuit including a first ADFMR circuit including an ADFMR device, wherein the first ADFMR circuit enables the electrical signal to be perturbed by an electromagnetic (EM) field; and a detector circuit that determines the EM field based on the perturbation of the electrical signal. In many variations, the detector circuit includes an analog-to-digital converter. The system functions as a sensor capable of detecting the EM field.

[0108] In the first interferometer example of the first system variant, as Figure 28 As shown, at least one circuit includes an interferometer circuit. In some variations, the at least one circuit includes: the aforementioned first ADFMR circuit (also referred to as a first test circuit) and a first signal processing circuit as a first reference circuit. The first reference circuit is connected in parallel with the first ADFMR circuit, so that the first ADFMR circuit and the first reference circuit form an interferometer circuit in combination. The interferometer circuit is used to measure the EM field by interfering with a disturbed electrical signal passing through the first test circuit and interfering with an unperturbed signal passing through the first reference circuit. In some variations, the interferometer circuit may include multiple test circuits and / or reference circuits, wherein the test circuits and reference circuits, in combination, enable EM field measurements through interference.

[0109] In the second interferometer example of the first system variant, as Figure 29As shown, the at least one circuit further includes a first signal processing circuit, which is a first reference circuit connected in parallel with the first ADFMR circuit. Furthermore, the system includes a power splitter located upstream of the first ADFMR circuit and the first reference circuit, such that the power splitter splits the electrical signal into a test signal that passes through the first ADFMR circuit and a reference signal that passes through the first reference circuit; and a power combiner located downstream of the first ADFMR circuit and the first reference circuit, such that the power combiner combines the test signal output from the first ADFMR circuit and the reference signal output from the first reference circuit. The first ADFMR circuit and the first reference circuit can operate together as an interferometer circuit to measure EM fields.

[0110] The first ADFMR circuit of the interferometer variant can also have a low energy / minimal embodiment. In a "low power" embodiment, such as Figure 4 As shown, the ADFMR circuit may include: an upstream matching network located upstream of the ADFMR device; and a downstream matching network located downstream of the ADFMR device.

[0111] In a second embodiment of the interferometer circuit of the first system, as shown in FIG. Figure 30 As shown in the example of , the ADFMR circuit includes: the aforementioned ADFMR device and an attenuator. In some variations, the attenuator can be located upstream of the ADFMR device. Alternatively, the attenuator can be located downstream of the ADFMR device. Optionally, the ADFMR device can have an upstream inductor located upstream of the ADFMR device and a downstream inductor located downstream of the ADFMR device. The reference circuit can have many different variations. In one variation, the reference circuit includes a phase shifter and an attenuator. The phase shifter can be used to shift the phase of an unchanged reference signal by 180 degrees so that if combined with an unchanged test signal, the test signal and the reference signal will completely destructively interfere with each other.

[0112] The system can also be used as a gradiometer. The gradiometer function can be an additional or alternative function of the system, depending on the embodiment. In a first gradiometer variant of the first system, as Figure 31As shown, the system includes: a power supply; at least one circuit; and a detector circuit including an analog-to-digital converter. The at least one circuit preferably includes a set of ADFMR circuits, the set including at least a first ADFMR circuit and a second ADFMR circuit, wherein the second ADFMR circuit is connected in parallel to the first ADFMR circuit. Furthermore, the first ADFMR circuit and the second ADFMR circuit can be spatially positioned such that a vector displacement between the two ADFMR circuits is known. The system also includes a power splitter located upstream of the first test circuit and the second test circuit, such that the power splitter splits an electrical signal into two test signals: a first test signal passing through the first ADFMR circuit and a second test signal passing through the second ADFMR circuit; and a power combiner located downstream of the first and second ADFMR circuits, such that the power combiner combines the first test signal output from the first ADFMR circuit and the second test signal output from the second ADFMR circuit. A gradiometer variant of the system can measure an EM field gradient by measuring a perturbation difference between the altered first test signal passing through the first ADFMR circuit and the altered second test signal passing through the second ADFMR circuit. Depending on the implementation, additional test circuits may be added to the system, for example to enable full three-dimensional field gradient measurements.

[0113] In one example of a gradiometer variation of a first system, a first ADFMR circuit includes: a first ADFMR device and a first attenuator. In some variations, the first attenuator may be located upstream of the first ADFMR device. Alternatively, the first attenuator may be located downstream of the first ADFMR device. Additionally, a second ADFMR circuit may include: a second ADFMR device and a second attenuator. In some variations, the second attenuator may be located upstream of the second ADFMR device. Alternatively, the second attenuator may be located downstream of the second ADFMR device. The first ADFMR device may optionally have a first upstream inductor located upstream of the first ADFMR device and a first downstream inductor located downstream of the first ADFMR device, and the second ADFMR device may optionally have a second upstream inductor located upstream of the second ADFMR device and a second downstream inductor located downstream of the second ADFMR device.

[0114] ADFMR devices of all variants may take different forms. In some variants, the ADFMR device comprises a surface acoustic wave (SAW) device. In particular, in interferometer variants and gradiometer variants, the ADFMR device may comprise a SAW device. SAW devices are used to generate and utilize SAWs to achieve ferromagnetic resonance, thereby measuring EM fields (and EM field gradients) via SAW waves. Other types of ADFMR devices may be used, depending on the implementation. Other examples include F-bar and BAW devices.

[0115] Due to the magnetostrictive properties of the ferromagnets embedded in the SAW device, in some variations, a SAW device is generally sensitive to EM fields in a single direction (e.g., the field can be measured along the "x-direction"). Depending on the desired implementation, more complex (e.g., Figures 14 to 18 ) SAW devices, or multiple SAW devices can be implemented for multi-dimensional field and field gradient measurements. In one embodiment of a three-dimensional interferometer, the system can include three ADFMR test circuits, wherein each test circuit includes ADFMR devices positioned in orthogonal directions. In one embodiment of a three-dimensional gradiometer, the system can include 12 ADFMR test circuits, wherein each group of four test circuits has ADFMR devices in the same orientation, and wherein each group of four test circuits will define a three-dimensional space of positions (e.g., measuring the x-direction gradient of the EM field in the x, y, and z directions).

[0116] In some variations, the system can be implemented as a multi-dimensional function. The multi-dimensional function can be implemented using any variation of the system including the interference measurement and gradient measurement embodiments. In a multi-dimensional embodiment, such as Figure 9 As shown, the ADFMR device of the first ADFMR circuit includes a first ADFMR device, and at least one circuit includes a second ADFMR circuit, the second ADFMR circuit including a second ADFMR device, wherein the second ADFMR device has a different sensing direction than the first ADFMR device. In this two-dimensional embodiment, the system can have two-dimensional functionality to measure EM fields in a plane.

[0117] In another multi-dimensional embodiment, multi-dimensional sensing can be arranged in series. Figure 11 As shown, the first ADFMR circuit may include two ADFMR devices, wherein each ADFMR device has a different sensing direction.

[0118] In some variations, the system may be implemented with noise reduction and / or cancellation capabilities. The noise reduction functionality may be implemented with any variation of the system including both interferometry and gradient measurement implementations. In one noise reduction interferometer variation, such as Figure 32 As shown, the interferometer system may further include a vector modulator circuit connected in parallel with the first ADFMR circuit, and the interferometer system may be used as an "external" interferometer. Depending on the implementation, the vector modulator circuit may be used as an analog subtraction circuit to reduce ambient noise and / or 1 / f noise.

[0119] In some variations, the system can be implemented using an IQ mixer circuit. The IQ mixer circuit can improve signal measurement by separating a perturbed electrical signal into a linear combination of orthogonal waves. The IQ mixer can be implemented in any system variation including both interference measurement and gradient measurement implementations. In one IQ mixer interferometer variation, such as Figure 33 As shown, the interferometer system further includes an IQ mixer circuit, wherein the IQ mixer is located upstream of the detector circuit such that the IQ mixer receives an electrical signal output from the interferometer circuit and another electrical signal input. In some embodiments, the other signal input includes an input derived from the original electrical signal. Depending on the desired implementation, the original electrical signal to the IQ mixer may not be altered or modified (e.g., by including an amplifier circuit between a power supply and the IQ mixer).

[0120] The system can be modified so that the applied external EM field is measured within a desired field amplitude bandwidth so that the ADFMR device operates optimally or near optimally. In these variations, the system can be implemented with a linearizer. The linearizer can normalize the external EM field to the desired field amplitude bandwidth. Linearization can be implemented in any system variation, including interferometry and gradiometric implementations. In one interferometry system implementation of the linearizer, such as Figure 34 As shown, the system further includes a linearizer circuit, wherein the linearizer circuit includes an EM field source, a comparator, and a logic circuit for the first ADFMR circuit. The linearizer circuit can be configured to operate in a set mode such that the EM field source modifies the EM field applied to the first ADFMR circuit such that the applied EM field is in an improved measurement state. Thus, the set mode can provide incremental improvements in the measurement state and, therefore, can incrementally enable the system to reach an optimal or near-optimal measurement state.

[0121] 3. Methods

[0122] like Figure 35 As shown, the method for measuring an electromagnetic field using an acoustic driven ferromagnetic resonance (ADFMR) sensor includes: S110, an oscillator generates an electrical signal; S120, the ADFMR sensor converts the electrical signal into an acoustic wave; S130, the ADFMR sensor propagates the acoustic wave through a magnetic material, thereby changing the acoustic wave in proportion to the EM field affecting the magnetic material; S140, the ADFMR sensor converts the changed acoustic wave into a changed electrical signal; S150, measuring the EM field using the changed acoustic wave.

[0123] The method utilizes the sensitivity of a ferromagnetic mass to EM fields at or near resonance to measure EM fields. In preferred variations, the method may include additional steps to optimize the field measurements, which may include reducing signal bandwidth, reducing signal noise, and optimizing field absorption. The method may additionally and / or alternatively include other steps to improve the field measurements. The method is preferably used with the system described above, but may be implemented with any desired applicable system. The method is particularly useful for implementing an ADFMR sensor as an interferometer, such that a modified electrical signal is recombined with an unmodified reference signal to measure the EM field. The method is also particularly useful for implementing an ADFMR sensor as a gradiometer, such that spatial multi-field measurements can be used to determine changes in the EM field.

[0124] In some variations, the method can be implemented to perform an interferometer function. In these variations, the method can further include: separating the electrical signal into a test electrical signal and a reference electrical signal before the ADFMR sensor; combining the altered electrical signal with the reference electrical signal after the ADFMR sensor; and determining the EM field strength using the reference signal.

[0125] In some variations, the method may be implemented to implement a gradiometer function. In these variations, the method may further include: separating the electrical signal into a plurality of test signals prior to the ADFMR sensor.

[0126] Block S110 includes generating an electrical signal for providing power to the ADFMR function. Generating the electrical signal S110 may generate direct current (DC) or alternating current (AC). In some variations, the electrical signal is alternating current (AC), and generating the electrical signal S110 occurs at a voltage oscillator. In some variations, the AC frequency may be in the MHz-GHz range. Alternatively, the AC frequency may be higher or lower. In preferred variations, the AC frequency is of a magnitude such that the electrical signal is complementary to the acoustic transducer, such that all or part of the electrical signal may be converted into acoustic waves.

[0127] In many variations, the method can include splitting the electrical signal. Splitting the electrical signal is used to separate a single current (e.g., AC or DC) into two currents. In interferometer variations, these currents can include: a test signal to an ADFMR sensor and a reference signal. Splitting the current can enable a comparative measurement between the test signal and the reference signal as part of the interferometer variation. For gradiometer embodiments, splitting the signal can separate the electrical signal into two test signals (e.g., a first test signal and a second test signal) that are sent to different ADFMR sensors. Depending on the embodiment, all method steps that refer to or apply to a test signal or ADFMR sensor will also refer to or apply to all ADFMR sensors and / or all test signals.

[0128] In addition to interferometer and gradiometer variations, separation of electrical signals can be implemented in a number of variations to enhance or improve the ability to measure EM fields. Depending on the implementation, separation of the electrical signals may occur zero, one, or multiple times. For example, separation of the electrical signals can be implemented in conjunction with specific circuits and components to: amplify the desired signal, perform multi-dimensional field measurements, filter noise (e.g., reduce 1 / f noise), optimize field detection (e.g., through field normalization), and / or improve field measurements. In variations that include separation of the electrical signals, the method can also include the supplementary step of combining the electrical signals into a single signal.

[0129] Block S120 includes converting the electrical signal into an acoustic wave, for converting part or all of the electrical signal into an acoustic wave. Converting the electrical signal preferably occurs at the ADFMR sensor. More specifically, block S120 occurs at an acoustic transducer at or on the ADFMR sensor, where the electrical signal is absorbed to generate an acoustic wave of a desired type, frequency, and amplitude.

[0130] The acoustic waves generated can be of any desired type, as long as they work with the ADFMR sensor. Examples of acoustic waves that may be generated include surface acoustic waves (SAWs), bulk acoustic waves (BAWs), Fbars, Lamb waves, or any other type of acoustic wave. In preferred variations, the acoustic wave frequency and amplitude are proportional to the converted electrical signal. That is, a relatively large electrical signal can generate a relatively large acoustic wave, and / or a relatively high-frequency electrical signal can generate a relatively high-frequency acoustic wave.

[0131] In some variations, converting the electrical signal into an acoustic wave S120 includes generating a SAW from the electrical signal. In these variations, the ADFMR sensor may include a SAW device. In these variations, generating the SAW may include generating the SAW from the electrical signal using a piezoelectric body. In a preferred variation, the electrical signal is converted into a radio frequency (RF) field, which is then converted into a SAW by an input interleaved transducer (IDT), but other methods may also be implemented. In this variation, the input IDT is preferably a component of a SAW device that additionally includes a piezoelectric substrate base, an output IDT, and a ferromagnetic material along the piezoelectric substrate between the input IDT and the output IDT. Generating the SAW preferably generates a SAW having a frequency at or near the resonant frequency of the ferromagnetic material.

[0132] Block S130 includes propagating an acoustic wave through the magnetic material of the ADFMR sensor so that the acoustic wave is perturbed in proportion to the effect of the electromagnetic field on the magnetic material. The external EM field can bias the magnetic material, causing the acoustic wave to change in proportion to the amplitude of the electromagnetic field. In variations of SAW devices, when the SAW propagates along a ferromagnetic body, the ferromagnetic body may be excited to resonate. This may cause the ferromagnetic body to absorb a portion of the incident acoustic wave. Near resonance, the amount of acoustic power absorbed varies significantly with changes in the external magnetic field. In some variations, the ferromagnetic body may be magnetostrictive, so that the propagating acoustic wave generates an effective RF magnetic field within the ferromagnetic body (at the frequency of the acoustic wave or an integer multiple thereof). In other variations, the ferromagnetic body may have other properties that perturb the propagating acoustic wave. The perturbation of the acoustic wave can be of any desired type, with the limitation that the perturbation is proportional to the amplitude and direction of the electromagnetic field. In this manner, Block S130 may include sensing the external EM field via the altered acoustic wave.

[0133] Block S140 includes converting the altered acoustic wave into an altered electrical signal so that the field can be measured using the altered electrical signal. Converting the altered acoustic wave into an altered electrical signal can occur at the ADFMR sensor, preferably at the acoustic transducer. In variations where the ADFMR sensor includes a SAW device, the acoustic transducer can include an output IDT. Thus, converting the altered acoustic wave into an altered electrical signal S140 can occur at the output IDT on the piezoelectric substrate of the SAW device. Thus, in a manner similar to the altered acoustic wave, the altered electrical signal includes information about the external electromagnetic field.

[0134] Block S150 includes measuring the field for determining the EM field strength at the detector. Preferably, this is accomplished by combining the modified electrical signal with a reference signal and utilizing interference (e.g., destructive interference) to determine the field strength. In some variations utilizing destructive interference, measuring the field S150 may include phase shifting the reference field by half a cycle so that the reference signal and the original electrical signal cancel each other. In alternative preferred variations for measuring the field gradient, measuring the field S150 includes determining the field strength difference between the modified electrical signals (e.g., determining the difference between a modified first test signal and a modified second test signal).

[0135] Measuring field S150 can include converting the signal into a digital signal. Converting the signal into a test signal can have two variations: the test signal and reference signal can be first combined and then digitized, or they can be digitized separately and then combined. That is, measuring field S150 can include combining the altered electrical signal and the reference signal and then converting the combined signal into a digital output signal; or converting the altered electrical signal into an altered digital electrical signal, converting the reference signal into a digital reference signal, and then combining the digital test signal and the digital reference signal.

[0136] Highly sensitive measurements, noise, and other environmental issues may affect the accuracy of field measurements made using this method. The method may include additional steps to improve field measurements. Among other potential improvement steps, the method may include: reducing signal bandwidth; reducing signal noise; and optimizing field absorption.

[0137] Reducing the signal bandwidth has the effect of producing a thin, coherent signal band rather than a large signal spectrum. Preferably, this occurs at the bandpass filter, but other filters may be used in addition or as an alternative. Reducing the signal bandwidth can reduce signal noise. Furthermore, reducing the signal bandwidth can improve the size and spacing of the wave groupings, minimizing interference between different wave groupings.

[0138] Signal noise reduction is used to reduce system noise that can affect field measurements. 1 / f (i.e., pink noise) can be a major factor in inhibiting accurate field measurements. Signal noise reduction can include reducing the power of the signal and filtering the signal to reduce noise. Signal noise reduction can include passing the electrical signal through an attenuator. Digital attenuators can be implemented to remove all activity below a certain threshold. Analog attenuators can also be implemented to reduce power and minimize noise. 1 / f noise can also be minimized by using an interferometer or bias coil to minimize the signal power input to any amplifier or other active components.

[0139] In certain variations, the method may include optimizing field absorption. Optimizing field absorption is used to increase field absorption by a ferromagnet. The ferromagnet may have an optimal field strength at which the absorption amplitude is most sensitive to the external field. Optimizing field absorption may include modifying the applied field strength to improve field measurement. In one example, optimizing field absorption may include determining an optimal field absorption strength range and applying a field to the ADFMR sensor such that the total applied field is within or near the optimal field absorption strength range.

[0140] 4. System Architecture

[0141] The systems and methods of the above-described embodiments may be embodied and / or implemented, at least in part, in conjunction with a computing system comprising at least one machine configured to receive a computer-readable medium storing computer-readable instructions. ADFMR devices enabled by the above-described systems and methods may be integrated into a computing system, enabling programmatic control of such devices, wherein the computing system may utilize sensor inputs providing EM field sensor data. The computing system may include one or more system-enabled ADFMRs. The instructions may be executed by a computer-executable component integrated with a user's computer or mobile device, wristband, smartphone, application, applet, host, server, network, website, communication service, communication interface, hardware / firmware / software elements, or any suitable combination thereof. Other systems and methods of the present embodiments may be embodied and / or implemented, at least in part, in a machine configured to receive a computer-readable medium storing computer-readable instructions. The instructions may be executed by a computer-executable component integrated with the aforementioned types of devices and networks. The computer-readable medium may be stored on any suitable computer-readable medium, such as RAM, ROM, flash memory, EEPROM, optical devices (CD or DVD), hard drives, floppy drives, or any other suitable device. The computer-executable component may be a processor, but any suitable special-purpose hardware device may (alternatively or additionally) execute instructions.

[0142] In one variation, a system includes one or more computer-readable media storing instructions that, when executed by the one or more computer processors, cause a computing platform to perform operations comprising the systems or methods described herein, such as: generating an electrical signal; converting the electrical signal into an acoustic wave; propagating the acoustic wave through a magnetic material; converting the altered acoustic wave into an altered electrical signal; and measuring a field.

[0143] In one variation, a non-transitory computer-readable medium storing instructions that, when executed by one or more computer processors of a computing platform, can cause the computing platform to perform the operations of the systems or methods described herein, such as: generating an electrical signal; converting the electrical signal into an acoustic wave; propagating the acoustic wave through a magnetic material; converting the altered acoustic wave into an altered electrical signal; and measuring a field.

[0144] Figure 36 is an exemplary computer architecture diagram of one embodiment of the system. In some embodiments, the system is implemented in multiple devices that communicate via communication channels and / or networks. In some implementations, elements of the system are implemented in separate computing devices. In some embodiments, two or more system elements are implemented in the same device. The system and portions of the system can be integrated into a computing device or system that can be used as a system or integrated into a computing device or system within a system.

[0145] Communication channel 1001 interacts with processors 1002A-1002N, memory (e.g., random access memory (RAM)) 1003, read-only memory (ROM) 1004, processor-readable storage medium 1005, display device 1006, user input device 1007, and network device 1008. As shown, a computer infrastructure can be used to connect a power source 1101, and ADFMR circuit 1102, detector circuit 1103, and / or other suitable computing devices. Alternatively, the above system can be implemented as a self-contained system connected to the computer infrastructure.

[0146] Processors 1002A-1002N can take many forms, such as central processing units (CPUs), graphical processing units (GPUs), microprocessors, machine learning / deep learning (ML / DL) processing units such as tensor processing units, field programmable gate arrays (FPGAs), custom processors and / or any suitable type of processor.

[0147] Processors 1002A-1002N and main memory 1003 (or some subset) may form a processing unit 1010. In some embodiments, the processing unit includes one or more processors communicatively coupled to one or more of RAM, ROM, and machine-readable storage media; the one or more processors of the processing unit receive instructions stored by one or more of the RAM, ROM, and machine-readable storage media via a bus; and the one or more processors execute the received instructions. In some embodiments, the processing unit is an application-specific integrated circuit (ASIC). In some embodiments, the processing unit is a system-on-chip (SoC). In some embodiments, the processing unit comprises one or more elements of a system.

[0148] The network device 1008 may provide one or more wired or wireless interfaces for exchanging data and commands between the system and / or other devices such as devices of an external system. Such wired and wireless interfaces include, for example, a universal serial bus (USB) interface, a Bluetooth interface, a Wi-Fi interface, an Ethernet interface, a near field communication (NFC) interface, etc.

[0149] Computer and / or machine-readable executable instructions comprising configurations for software programs such as operating systems, applications, and device drivers may be stored in memory 1003 from processor-readable storage media 1005 , ROM 1004 , or any other data storage system.

[0150] When executed by one or more computer processors, the various machine-executable instructions may be accessed by at least one of the processors 1002A-1002N (of the processing unit 1010) via the communication channel 1001 and then executed by at least one of the processors 1001A-1001N. Data, databases, data records, or other storage forms of data created or used by the software program may also be stored in the memory 1003 and such data may be accessed by at least one of the processors 1002A-1002N during execution of the machine-executable instructions of the software program.

[0151] The processor-readable storage medium 1005 is one or a combination of two or more of a hard disk drive, a flash drive, a DVD, a CD, an optical disk, a floppy disk, a flash memory, a solid-state drive, a ROM, an EEPROM, an electronic circuit, a semiconductor memory device, etc. The processor-readable storage medium 1005 may include an operating system, software programs, device drivers, and / or other appropriate subsystems or software.

[0152] As used herein, first, second, third, etc. are used to characterize and distinguish various elements, components, regions, layers and / or parts. These elements, components, regions, layers and / or sections should not be limited by these terms. The use of numerical terms can be used to distinguish an element, component, region, layer and / or part from another element, component, region, layer and / or part. The use of these numerical terms does not mean sequence or order unless the context clearly indicates. Such numerical references can be used interchangeably without departing from the teachings of the embodiments and variations herein.

[0153] As those skilled in the art will recognize from the foregoing detailed description and from the accompanying drawings and claims, modifications and changes may be made to the embodiments of the present invention without departing from the scope of the invention as defined in the claims.

Claims

1. A system for a sensor based on acoustically driven ferromagnetic resonance (ADFMR), comprising: a power supply comprising an electronic oscillator for providing an electrical signal; a set of ADFMR circuits, the set of ADFMR circuits comprising a first ADFMR circuit and a second ADFMR circuit, the first ADFMR circuit comprising an ADFMR device, wherein the first ADFMR circuit enables the electrical signal to be perturbed by an electromagnetic (EM) field, the second ADFMR circuit being connected in parallel to the first ADFMR circuit; a power splitter located upstream of the first ADFMR circuit and the second ADFMR circuit, such that the power splitter splits the electrical signal into two test signals: a first test signal passing through the first ADFMR circuit and a second test signal passing through the second ADFMR circuit; a power combiner located downstream of the first ADFMR circuit and the second ADFMR circuit such that the power combiner combines the first test signal output from the first ADFMR circuit and the second test signal output from the second ADFMR circuit; as well as A detector circuit determines the EM field based on the electrical signal disturbance.

2. The system according to claim 1, wherein: The set of ADFMR circuits includes an interferometer circuit.

3. The system according to claim 2, wherein: The set of ADFMR circuits further includes a first signal processing circuit as a first reference circuit, wherein the first reference circuit is connected in parallel with the first ADFMR circuit such that the first ADFMR circuit and the first reference circuit form the interferometer circuit in combination.

4. The system according to claim 1, wherein: The first ADFMR circuit further includes: an upstream matching network located upstream of the ADFMR device; and A downstream matching network is located downstream of the ADFMR device.

5. The system according to claim 1, wherein: The first ADFMR circuit further includes an attenuator.

6. The system according to claim 5, wherein: The first ADFMR circuit further includes a phase shifter.

7. The system according to claim 6, wherein: The ADFMR device includes a surface acoustic wave device.

8. The system according to claim 1, wherein: The ADFMR device includes a first ADFMR device, and wherein the first ADFMR circuit includes: the first ADFMR device and a first attenuator.

9. The system according to claim 8, wherein: The second ADFMR circuit includes a second ADFMR device and a second attenuator.

10. The system according to claim 9, wherein: The first ADFMR device includes a first surface acoustic wave device, and the second ADFMR device includes a second surface acoustic wave device.

11. The system according to claim 1, in, The ADFMR device of the first ADFMR circuit includes a first ADFMR device; Wherein, the second ADFMR circuit includes a second ADFMR device; The second ADFMR device has a different sensing direction than the first ADFMR device.

12. The system according to claim 1, wherein: The first ADFMR circuit includes a first ADFMR device and a second ADFMR device, wherein the second ADFMR device has a different sensing direction than the first ADFMR device.

13. The system according to claim 3, wherein: The set of ADFMR circuits further includes a vector modulator circuit connected in parallel with the first ADFMR circuit.

14. The system according to claim 3, in, The set of ADFMR circuits also includes an IQ mixer circuit, The IQ mixer is located upstream of the detector circuit, so that the IQ mixer receives an electrical signal output of the interferometer circuit and another electrical signal input.

15. The system according to claim 14, wherein: The further electrical signal input comprises an input of the electrical signal from the electronic oscillator.

16. The system according to claim 3, wherein: The set of ADFMR circuits further includes a linearization circuit including an EM field source, a comparator, and a logic circuit for the first ADFMR circuit.

17. The system according to claim 16, wherein: The linearization circuit is configured to operate in a set mode such that the EM field source modifies the EM field applied to the first ADFMR circuit such that the applied EM field is in a desired measurement state.

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