Systems, articles, and methods for electromyography sensors
Systems, articles, and methods for surface electromyography (“EMG”) sensors that combine elements from traditional capacitive and resistive EMG sensors are described. For example, capacitive EMG sensors that are adapted to resistively couple to a user's skin are described. Resistive coupling between a sensor electrode and the user's skin is galvanically isolated from the sensor circuitry by a discrete component capacitor included downstream from the sensor electrode. The combination of a resistively coupled electrode and a discrete component capacitor provides the respective benefits of traditional resistive and capacitive (respectively) EMG sensor designs while mitigating respective drawbacks of each approach. A wearable EMG device that provides a component of a human-electronics interface and incorporates such capacitive EMG sensors is also described.
1. A method comprising:
at a wearable device that includes a sensor electrode and a circuit associated with the sensor electrode for processing muscular activity signals from a wearer of the wearable device:
receiving, via the sensor electrode and while the circuit is tuned to operate using a first impedance, a first muscular activity signal;
in response to detecting a variation in impedance at an interface between the sensor electrode and a skin portion of the wearer, electrically tuning the circuit to operate using a second impedance, distinct from the first impedance; and
receiving, via the sensor electrode and while the circuit is tuned to operate using the second impedance, a second muscular activity signal.
2. The method of claim 1 , wherein the wearable device further includes an electrically conductive pathway that communicatively couples the sensor electrode and the circuit through a first capacitor and a first resistor.
3. The method of claim 2 , wherein the first sensor electrode is configured to resistively couple to the skin portion of the wearer.
4. The method of claim 3 , wherein the first capacitor comprises a discrete component capacitor configured to provide a fixed capacitance.
5. The method of claim 4 , wherein the circuit is tuned to the fixed capacitance provided by the discrete component capacitor.
6. The method of claim 2 , wherein the first capacitor is configured to galvanically isolate the circuit from the skin portion of the wearer.
7. The method of claim 6 , where the first resistor is configured to dominate impedance of the resistive coupling between the first sensor electrode and the skin portion of the wearer.
8. The method of claim 2 , wherein the circuit includes at least a portion of a circuit selected from the group consisting of: an amplification circuit, a filtering circuit, or an analog-to-digital conversion circuit.
9. The method of claim 2 , wherein the wearable device further comprises a ground electrode to resistively couple to another skin portion of the wearer, wherein the ground electrode includes a plate of electrically conductive material, and wherein the ground electrode is communicatively coupled to the circuit.
10. The method of claim 2 , wherein the wearable device further includes:
a second sensor electrode configured to resistively couple to a second skin portion of the user;
a second capacitor configured to galvanically isolate the circuit from the second skin portion of the wearer, the second capacitor being electrically coupled in series between the second sensor electrode and the circuit; and
a second resistor configured to dominate impedance of the resistive coupling between the second sensor electrode and the second skin portion of the wearer, the second capacitor being electrically coupled in series between the second sensor electrode and the circuit.
11. The method of claim 10 , wherein the circuit comprises a high-pass filter that includes the first capacitor and the second resistor.
12. The method of claim 11 , wherein the circuit comprises a low-pass filter that includes the first resistor and the second capacitor.
13. A wearable device comprising:
a sensor electrode configured to receive muscular activity signals from a wearer of the wearable device;
a circuit associated with the sensor electrode, and tuned to operate using a first impedance, configured to process muscular activity signals from a wearer of the wearable device; and
a tuning component configured to electrically tune the circuit to operate using a second impedance, distinct from a first impedance in response to detecting a variation in impedance at an interface between the electrode and a skin portion of the wearer.
14. The wearable device of claim 13 , further comprising an electrically conductive pathway that communicatively couples the sensor electrode and the circuit through a first capacitor and a first resistor.
15. The wearable device of claim 14 , further comprising:
a second sensor electrode configured to resistively couple to a second skin portion of the wearer;
a second capacitor configured to galvanically isolate the circuit from the second skin portion of the wearer, the second capacitor being electrically coupled in series between the second sensor electrode and the circuit; and
a second resistor configured to dominate impedance of the resistive coupling between the second sensor electrode and the second skin portion of the wearer, the second capacitor being electrically coupled in series between the second sensor electrode and the circuit.
16. The wearable device of claim 14 , wherein the first resistor has a magnitude of at least 1 kΩ.
17. The wearable device of claim 13 , wherein the sensor electrode has a first layer of a first electrically conductive material, and the first layer of the first electrically conductive material comprises copper.
18. The wearable device of claim 17 , wherein the sensor electrode includes:
a second layer of a second electrically conductive material that includes a material selected from the group consisting of: gold, steel, stainless steel, silver, titanium, electrically conductive rubber, or electrically conductive silicone.
19. The wearable device of claim 18 , further comprising:
a housing, wherein the circuit, the first capacitor, and the first layer of the sensor electrode are all substantially contained within the housing, the housing including a hole, and
wherein at least a portion of the second layer of the sensor electrode extends out of the housing through the hole.
20. A wearable electromyography (“EMG”) device, comprising:
an EMG sensor electrode configured to receive muscular activity signals from a wearer of the wearable device;
a circuit associated with the EMG sensor electrode, and tuned to operate using a first impedance, configured to process muscular activity signals from a wearer of the wearable device; and
a tuning component configured to electrically tune the circuit to operate using a second impedance, distinct from a first impedance in response to detecting a variation in impedance at an interface between the electrode and a skin portion of the wearer.
21. The method of claim 1 , wherein the muscular activity signals are associated with hand gestures where the user touches their thumb to at least one portion of their hand, and
the hand gestures, when detected, are configured to control a user interface on the wearable device or a head-wearable device.
22. The wearable device of claim 13 , wherein the muscular activity signals are associated with hand gestures where the user touches their thumb to at least one portion of their hand, and
the hand gestures, when detected, are configured to control a user interface on the wearable device or a head-wearable device.
23. The wearable EMG device of claim 20 , wherein the muscular activity signals are associated with hand gestures where the user touches their thumb to at least of one portion their hand, and
the hand gestures, when detected, are configured to control a user interface on the wearable EMG device or a head-wearable device.