Electronic packaging of sensors for lower limb prosthetics

Millivolt level signals generated in residual muscles can be used to control sophisticated upper limb prosthetics. The low level voltages known as surface-electromyogram (sEMG) signals have seldom been applied in lower limbs due to moisture, large pressure, and shear forces which induced anomalies, and in particular triboelectric interference. An electronic module, known as a multi-sensor unit or MSU incorporates a multiplicity of sensors which promises to overcome the problems with sEMG in lower limbs. By incorporating a multiplicity of signals from what is physically happening in terms of pressure, temperature, and surface shear, it is anticipated that the sEMG signals can be corrected. Testing of the MSU with able bodied personnel and amputees is currently under way at Clarkson University. The MSU, which is totally potted is soft silicone rubber, measures sEMG, pressure, axial and tangential shear, and temperature. The 35×65×6.5mm electronic module is thin enough to be comfortably inserted between the liner of the prosthetic and the residual lower limb. As part of the program, a unique MEMS shear sensor, capable of being totally encased in silicone rubber, was developed. The temperature and pressure sensor are based on commercial off-the-shelf sensors. The design of the shear sensors is based on bonding a glass ball to a commercial off-the-shelf pressure sensor, thus avoiding the costly development of a custom shear sensor. The final MSU is both waterproof and rugged. Preliminary test results are briefly presented.