SYSTEM AND METHOD FOR AN ACOUSTICALLY DRIVEN FERROMAGNETIC RESONANCE SENSOR DEVICE

1 . A method for electromagnetic (EM) field measurement using an acoustically driven ferromagnetic resonance (ADFMR) sensor comprises:

generating, at an oscillator, an electrical signal;

converting the electrical signal to an acoustic wave at an ADFMR sensor;

propagating the acoustic wave across a magnetic material at the ADFMR sensor, thereby altering the acoustic wave in proportion to an external EM field magnitude; and

converting the altered acoustic wave to an altered electrical signal at the ADFMR sensor.

2 . The method of claim 1 , wherein converting the electrical signal to the acoustic wave comprises activating a pair of interdigitated transducers arranged to drive a piezoelectric element of the ADFMR sensor.

3 . The method of claim 1 , wherein propagating the acoustic wave across the magnetic material comprises directing the acoustic wave into a magnetostrictive element configured to mechanically respond to the acoustic excitation.

4 . The method of claim 3 , wherein converting the altered acoustic wave to the altered electrical signal comprises detecting a change in the magnetostrictive element or a change in the acoustic wave using a readout circuit.

5 . The method of claim 1 , wherein generating the electrical signal includes applying an electrical drive that induces surface acoustic waves within the ADFMR sensor.

6 . The method of claim 1 , wherein the acoustic wave is guided or modified using an acoustic surface-wave device.

7 . The method of claim 1 , wherein the magnetic material comprises a thin-film magnetostrictive layer acoustically coupled to a piezoelectric element.

8 . The method of claim 1 , further comprising detecting a change in absorption or resonance characteristics of the magnetic material as the acoustic wave interacts with the external EM field.

9 . The method of claim 1 , wherein generating the electrical signal includes operating the oscillator at a frequency selected to drive the ADFMR sensor at or near its acoustic resonance.

10 . The method of claim 1 , wherein converting the altered acoustic wave to the altered electrical signal includes monitoring variations in amplitude or phase of the altered electrical signal to determine changes induced by the external electromagnetic field.

11 . A method of measuring an external electromagnetic field, comprising:

driving an acoustically driven ferromagnetic resonance (ADFMR) circuit with an electrical test signal;

acoustically exciting a ferromagnetic element within the ADFMR circuit to produce ferromagnetic resonance responsive to the external electromagnetic field;

monitoring a perturbation of the electrical test signal through the ADFMR circuit produced by the external electromagnetic field;

applying a calibration magnetic field to the ADFMR circuit; and

adjusting the calibration magnetic field in a closed loop to maintain a predetermined operating point of the ADFMR circuit while extracting a measurement of the external electromagnetic field from the monitored perturbation.

12 . The method of claim 11 , wherein the perturbation is demodulated using phase-sensitive detection to obtain in-phase and quadrature components.

13 . The method of claim 11 , wherein applying the calibration magnetic field comprises driving an on-chip field generator integrated with the ADFMR circuit.

14 . The method of claim 11 , wherein adjusting the calibration magnetic field comprises nulling the perturbation to a target value and reporting the external electromagnetic field as a function of the calibration magnetic field used to maintain the target value.

15 . The method of claim 11 , further comprising time-division multiplexing a plurality of ADFMR circuits onto a common readout bus and generating a spatial map of the external electromagnetic field from perturbations associated with the plurality of ADFMR circuits.

16 . The method of claim 11 , wherein the predetermined operating point corresponds to a target phase shift between the electrical test signal and the monitored perturbation.

17 . The method of claim 11 , wherein monitoring the perturbation comprises sampling a complex transfer function of the ADFMR circuit and computing a field estimate using a predetermined linearization around the operating point.

18 . The method of claim 11 , further comprising compensating temperature-induced drift of the operating point using a temperature sensor co-located with the ADFMR circuit and a correction applied to the calibration magnetic field.

19 . The method of claim 11 , wherein the closed loop is implemented by a controller configured to update the calibration magnetic field at a rate greater than a specified fraction of the acoustic resonance bandwidth.

20 . The method of claim 11 , wherein the ferromagnetic element comprises a magnetostrictive film acoustically coupled to a piezoelectric substrate.