A simple and effective method to compensate the thermal drift of implantable blood pressure sensors

Abstract

This article presents a study of implantable blood pressure sensors based on a probe made up of four piezoresistors. An original method combining both measurements and calculations allows extracting the values of each piezoresistor without degrading the probe is developed. This study made it possible to create a simulation model in Cadence/Pspice electronic simulation software, considering the variation of the piezoresistor according to the temperature and the pressure. To our knowledge, no simulation model considering both the variation of the temperature and the pressure of each piezoresistor exists in the literature. So, the simulation of the sensor allows to quickly test the efficiency of the compensation circuit before its realization. Once the thermal drifts of the sensor have been quantified, a circuit based on PNP transistors is developed to compensate this thermal drift. This analog compensation technique ensures low cost, compactness and low power consumption. It proved experimentally effective in reducing thermal drift of the sensor. For example, the experimental thermal drift of the sensor is reduced from 9.97 mmHg/°C without compensation to 2.12 mmHg/°C after compensation at the pressure of 300 mmHg. This method has been validated with 3 pressure levels (0, 100, 200 and 300 mmHg).