Device and method for sensing electrical activity in tissue
An exemplary embodiment providing one or more improvements includes apparatus and methods for sensing electrical activity in tissue of a person in a manner which is substantially limits or eliminates interference from noise in a surrounding environment.
1. A headset comprising:
a sensor electrode structured to be placed on skin of a user at a first point, the sensor electrode structured to sense electrical activity in a tissue of the user and to produce a signal of interest, an undesired signal and noise;
a reference electrode structured to be placed on the skin of the user at a second point, the second point being spaced apart from the first point; and
an electronics module, the electronics module including:
a front end amplifier structured to (1) amplify the signal of interest and the undesired signal occurring in a first frequency range while (2) attenuating the noise occurring in a second frequency range, the sensor electrode electrically coupled to a first input of the amplifier and the reference electrode electrically coupled to a second input of the amplifier, an output of the amplifier electrically coupled to the second input of the amplifier via a parallel resistor and capacitor circuit;
a filter electrically coupled to the output of the amplifier and structured to receive an output signal from the amplifier containing the signal of interest and the undesired signal, the filter structured to isolate the signal of interest by attenuating the undesired signal; and
a processor programmed to receive the signal of interest from the filter for analysis.
2. The headset of claim 1 , wherein the electronics module is proximate the reference electrode.
3. The headset of claim 1 further including a power source having a power source reference terminal communicatively coupled to the reference electrode.
4. The headset of claim 1 , wherein the signal of interest is from 4 Hz to 12 Hz.
5. The headset of claim 1 , wherein the signal of interest includes Alpha band and Theta band brain waves, and the filter is structured to attenuate 60 Hz signals and harmonics of 60 Hz signals.
6. The headset of claim 1 , wherein the first point is on a forehead of the user and the second point is on an ear of the user.
7. The headset of claim 1 , wherein the sensor electrode is mounted to a frame, the frame structured to be supported by ears and a nose bridge of the user.
8. The headset of claim 7 , wherein the electronics module is supported by the frame.
9. The headset of claim 1 , wherein the filter further includes an averaging circuit structured to remove 60 Hz signals and harmonics of 60 Hz signals from the signal of interest.
10. The headset of claim 1 , wherein the filter is structured to attenuate signals below 4 Hz and above 12 Hz.
11. The headset of claim 1 , wherein the output signal of the amplifier is an analog output signal, the headset further including a converter structured to convert the analog output signal to a digital output signal, and wherein the processor is programmed to transform the digital output signal using a Fourier transform to determine an energy spectrum of the digital output signal, the energy spectrum including a plurality of bins representing energy in corresponding frequencies of the digital output signal.
12. The headset of claim 11 , wherein the processor is programmed to sum the energy in the bins corresponding to frequencies of from 4 Hz to 8 Hz to create a Theta band energy signal.
13. The headset of claim 12 , wherein the processor is programmed to sum the energy in the bins corresponding to frequencies of from 8 Hz to 12 Hz to create an Alpha band energy signal.
14. The headset of claim 13 , wherein the processor is programmed to determine a ratio of the Alpha band energy signal and the Theta band energy signal.
15. The headset of claim 13 , wherein the processor is programmed to compute (Theta band energy signal−Alpha band energy signal)/(Theta band energy signal+Alpha band energy signal).
16. The headset of claim 1 , wherein a local reference potential in the electronics module and a potential of the second point on the skin are approximately equal to allow a surface of the reference electrode to be in direct contact with the skin of the user at the second point without having to prepare the skin or use a material that decreases a contact resistance between the surface of the reference electrode and the skin.
17. The headset of claim 1 , further including a pocket, the electronics module disposed in the pocket such that when the headset is worn by the user, the electronics module is disposed at a temple of the user.
18. The headset of claim 17 , further including a clip, the reference electrode coupled to the clip, the clip structured to attach to an ear of the user near the temple of the user where the electronics module is disposed when the headset is worn by the user.
19. The headset of claim 18 , wherein, when the headset is worn by the user, the sensor electrode is disposed on a forehead of the user.
20. The headset of claim 1 , wherein the electronics module includes a wireless transmitter programmed to transmit the signal of interest, after being analyzed by the processor, to a wireless receiver of an electronic device.