Optimization of the signal-to-noise ratio of silicon-embedded microphones for mechanomyography

Soft silicon sockets enhance mobility and comfort of artificial limbs for below-elbow amputees compared to acrylic resin laminated hard sockets. However, standard electromyographic (EMG) sensor attachment issues prevent their use with electrically powered prostheses. Mechanomyography (MMG) may facilitate the use of soft silicon sockets with electrically powered prostheses. Unlike EMG sensors, MMG sensors can be reliably placed distally over the patient´s stump, by embedding them into the silicon socket. Our experiments focused on maximizing the signal-to-noise ratio (SNR) of silicon-embedded microphones for MMG. Optimal dimensions were obtained for the cylindrical air chamber enclosed within the embedding capsule (13mm diameter, 2mm height). Furthermore, shores 20A and 65A were identified as the optimal silicon hardness values for the embedding case and driving membrane, respectively. Embedded microphones provided, on average, a 6dB SNR enhancement over previously reported embedded accelerometers.