SYSTEMS AND METHODS TO RECORD BIOMAGNETIC SIGNALS AT AMBIENT CONDITIONS
Described herein are methods and apparatuses to provide accurate measurement of relatively small magnetic fields under ambient conditions while being worn on an ambulatory subject. These methods and apparatuses may allow accurate and reliable detection of biomagnetic fields from organs such as the brain, heart, and muscles, using a magnetometer, and in particular, using an Acoustically Driven Ferromagnetic Resonance (ADFMR) sensor. These methods and apparatuses may incorporate one or more of: a synthetic gradiometer, flexible and/or thin-film/foil shielding, and/or denoising.
1 . A method of sensing a biomagnetic field under ambient conditions in an ambulatory subject, the method comprising:
receiving a primary signal from one or more primary acoustically driven ferromagnetic resonance (ADFMR) sensors worn on the subject;
receiving a secondary signal from one or more secondary ADFMR sensors worn on the subject;
weighting the secondary signal by a weighting factor;
periodically adjusting, at a tuning frequency, the weighting factor;
generating a corrected biomagnetic sensor signal by subtracting the primary signal from the weighted secondary signal; and
outputting the corrected biomagnetic sensor signal.
2 . The method of claim 1 , further comprising estimating a level of noise from a spectral density of the primary and/or secondary signal and weighting the secondary signal to minimize the estimated noise.
3 . The method of claim 2 , wherein weighting the secondary signal to minimize the estimated noise comprises using a gradient-based and/or stochastic technique to minimize the estimate noise.
4 . The method of claim 1 , wherein receiving the secondary signal comprises receiving the secondary signal from the one or more secondary ADFMR sensor that is flexibly connected to the one or more primary ADFMR sensors.
5 . The method of claim 1 , wherein outputting comprises continuously outputting.
6 . The method of claim 1 , wherein outputting comprises outputting in real time.
7 . The method of claim 1 , wherein the one or more secondary ADFMR sensors comprises three or more secondary ADFMR sensors that are arranged orthogonal to each other.
8 . The method of claim 1 , wherein the tuning frequency is adjusted based on input from a motion sensor.
9 . The method of claim 1 , wherein the tuning frequency is between 0.1 Hz and 10 Hz.
10 . The method of claim 1 , further comprising converting the primary signal and the secondary signal into the digital domain before generating the corrected biomagnetic signal.
11 . The method of claim 1 , further comprising shielding the one or more primary and one or more secondary ADFMR sensors.
12 . The method of claim 11 , wherein shielding comprises shielding under a mumetal foil.
13 . The method of claim 1 , further comprising denoising the corrected biomagnetic sensor.
14 . A method of sensing a biomagnetic field under ambient conditions in an ambulatory subject, the method comprising:
receiving a primary signal from one or more primary acoustically driven ferromagnetic resonance (ADFMR) sensors worn on the subject;
receiving a secondary signal from one or more secondary ADFMR sensors worn on the subject;
estimating a level of noise from a spectral density of the primary and/or secondary signal;
weighting the secondary signal by a weighting factor to minimize the estimated noise using a gradient-based and/or stochastic technique;
periodically adjusting, at a tuning frequency, the weighting factor;
generating a corrected biomagnetic sensor signal by subtracting the primary signal from the weighted secondary signal; and
outputting the corrected biomagnetic sensor signal.
15 . A method of sensing a biomagnetic field under ambient conditions in an ambulatory subject, the method comprising:
placing an acoustically driven ferromagnetic resonance (ADFMR) sensor on a region of a subject's body;
shielding, using a flexible foil shield, the ADFMR sensor by at least partially covering the ADFMR sensor with the flexible foil shield;
receiving a signal from the shielded ADFMR sensor worn on the subject;
generating a biomagnetic sensor signal from the signal; and
outputting the biomagnetic sensor signal.
16 . The method of claim 15 , further shielding comprises partially shielding the ADFMR sensor.
17 . The method of claim 15 , wherein the flexible foil shield comprises a mumetal foil.
18 . The method of claim 15 , wherein the flexible foil shield is between 0.01 and 0.2 mm thick.
19 . The method of claim 15 , wherein the flexible foil shield is approximately 0.1 mm thick.
20 . The method of claim 15 , wherein the flexible foil shield comprises between 1-4 layers of foil.