A contact-type piezoresistive micro-shear stress sensor for above-knee prosthesis application

A prototype contact-type micro piezoresistive shear-stress sensor that can be utilized to measure the shear stress between skin of stump and socket of above-knee (AK) prosthesis was designed, fabricated and tested. Micro-elec tro-mechanical system (MEMS) technology has been chosen for the design beca use of the low cost, small size and adaptability to this application. In th is paper, the finite element method (FEM) package ANSYS has been employed f or the stress analysis of the micro shear-stress sensors. The sensors conta in two transducers that will transform the stresses into an output voltage. In the developed sensor, a 3000x 3000x300 mum(3) square membrane is formed by bulk micromaching of an n-type (100) monolithic silicon. The piezoresis tive strain gauges were implanted with boron ions with a dose of 10(15) ato ms/cm(2), Static characteristics of the shear sensor were determined throug h a series of calibration tests. The fabricated sensor exhibits a sensitivi ty of 0.13 mV/mA-MPa for a 1.4 N full scales shear force range and the over all mean hysteresis error is than 3.5%. In addition, the results simulated by FEM are validated by comparison with experimental investigations.