Capacitive Sensing of Surface EMG for Upper Limb Prostheses Control

Active upper limb prostheses can be controlled by surface electromyography (EMG) signals. State of the art sensors are based on conductive electrodes which measure local voltage differences at the surface of the skin due to muscle activity. The current project deals with non-conductive measurement of EMG signals. For this purpose a sensor was designed as multi-layered composite of conducting and insolating materials. The different layers were used for signal sensing as well as active and passive guarding. The low amplitude EMG signal was detected by differential capacitive sensors. Electronic circuits were developed for the special requirements of these capacitive sensors. Basic requirements were high input impedance, high amplification and filters, e.g. for suppression of power supply hum and its harmonics. For the differential signal high common mode rejection ratio is essential. The electronics comprise rectification and smoothing of the output signal. A standard prosthesis is controlled successfully with the prototype output signal. When placing the sensors on the human forearm, the prosthesis follows the desired hand movement.