A Novel Cross-Capacitive Sensor for Noncontact Microdroplet Detection

In this paper, a novel capacitive sensor for noncontact microdroplet detection has been developed and tested successfully. For an accurate and highly repeatable droplet detection, the sensor makes use of a cross-capacitive structure, which is an extension of the Thompson and Lampard theorem. The sensor consists of four identical copper electrodes with infinitesimally small gaps etched out of double-sided copper-cladded polyimide substrate by screen printing and chemical etching process. The sensor prototype has been tested for different sizes of the droplets as well as the droplets from liquids having different dielectric constants and conductivities. The response characteristics of the presented sensor are very accurate, significant, fast, highly repeatable (±0.13%), and drift free. The achieved characteristics of the presented sensor are suitable for employing it for the noncontact microdroplet detection.