Design and comparative material analysis of a capacitive type pressure sensor for measurement of knee pressure distribution of rodents

Abstract

Rodents are commonly used in biomedical and biomechanical research because of their genetic and biological characteristics closely resemble those of humans. Rodents have similar knee joint structures to human beings, and are commonly used as models for human osteoarthritis. Biomechanical factors influencing the patterns of pressure distribution within the joint are very important in the pathogenesis of osteoarthritis at the knee joints. The pattern of pressure distribution of the femoral condyles of weight bearing knee joints is therefore of great interest. A flexible and biocompatible Polymer based Micro-Electromechanical (MEMS) pressure sensor was designed for this purpose with capacitive sensor array embedded inside the structure. The sensor structure comprises of a 4x16 arrays of sensors embedded inside the Polymer structure with air gaps and insulation layers to provide a suitable dielectric medium to achieve better capacitive sensitivity. A three dimensional model of the sensor was created using ANSYS Workbench Design Modeler and analyzed with two different types of polymers and metals as potential structural materials of the sensor. A suitable clean-room fabrication process was proposed and analyzed for the sensor and corresponding mask designs were created with a CAD (Computer Aided Design) program. Residual stresses due to mismatch of thermal coefficient of expansion were calculated along with proposing a schematic readout circuitry for high gain and signal to noise ratio and failure analysis of the sensor.