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-electro-mechanical system (MEMS) technology has been chosen for the design because of the low cost, small size and adaptability to this application. In this paper, the finite element method (FEM) package ANSYS has been employed for the stress analysis of the micro shear-stress sensors. The sensors contain two transducers that will transform the stresses into an output voltage. In the developed sensor, a 3000x 3000x300 μm³ square membrane is formed by bulk micromaching of an n-type (100) monolithic silicon. The piezoresistive strain gauges were implanted with boron ions with a dose of 10¹⁵ atoms/cm². Static characteristics of the shear sensor were determined through a series of calibration tests. The fabricated sensor exhibits a sensitivity of 0.13 mV/mA-MPa for a 1.4 N full scales shear force range and the overall mean hysteresis error is than 3.5 %. In addition, the results simulated by FEM are validated by comparison with experimental investigations.