Design Considerations of Capacitive Sensors for Micro-Droplet Detection

The flexible capacitive sensors are employed for micro-droplet detection in drug delivery systems. The structures of capacitive sensors such as interdigitated electrode and parallel plate types possess certain geometrical properties which are greatly influencing the accuracy, sensitivity, and stability. These properties are improved in semi-cylindrical type, whereas it is nullified in cross-capacitive sensor. In this paper, the semi-cylindrical and cross-capacitive sensor designs are analyzed for the suitability of micro-droplet detection. The proposed simulation studies include the change of capacitance due to variation in liquid droplet size and free-flying liquid droplet position sweep, electric field distribution between sensing and working electrodes. Moreover, the guard electrodes and metal shielding effects are analyzed for further improvement in sensor performance by eliminating the effects of stray capacitance. The COMSOL Multiphysics based simulation studies reveal the suitable sensitivity and change in capacitance for the sensor design.