Design and Simulation of Capacitive Pressure Sensor for Monitoring Lead-Acid Battery Charge

Abstract

In the present study, we have proposed a design of a novel, graphene-based micro-capacitive pressure sensor to measure minute variation in differential pressure developed in the air-purge system of lead-acid battery. Online state of charge (SOC) monitoring of lead-acid batteries using a sensor is a critical problem. The key principle is that specific gravity of the acid solution interlinks the amount of charge or discharge of the acid solution and the differential pressure of the air-purge system. We have obtained results from the analytical model, which are benchmarked with the numerical model of Comsol Multiphysics commercial software. The proposed graphene-based capacitive MEMS sensor has been designed for the range of 0–1 kPa differential pressure variation. The gap between the two capacitive plates is maintained at 3 μm and the thickness of the circular diaphragm is 10 μm. It is found in this study that the minuscule range of small changes in the specific gravity (or pressure) is consistent with the sensitivity of the newly designed MEMS sensor. In a nutshell, it can measure a tiny pressure drop in the air-purge system. On the contrary, the micro-piezo resistance sensor is observed to be less accurate on the account of its temperature sensitivity. Through this study, it is observed that the graphene-based MEMS sensor shows greater accuracy compared to the silicon-based sensor. The change in capacitance of graphene is linear compared to silicon. In case of the graphene, capacitance changes from 4.875 × 10−12 to 4.955 × 10−12 pF whereas in silicon, capacitance changes from 2.3 × 10−12 to 3.5 10−12 pF.