CAPACITIVE CONTACTLESS SENSOR SYSTEM FOR LIQUID DROPLETS IN THE AIR CHANNEL DETECTION

Abstract

This paper presents of design, fabricate and survey the performance of a non-contact capacitive sensor is used to detect the presence of droplets of conductive and weak electrical conductive liquid in the air channel. The sensor structure consists of two signal pick - up electrodes and a  excitation electrode. The electrodes are directly bonded on the PCB with built - in differential amplifier and signal processing circuit in order to reduce the parasitic capacitors component and common noise. The fluid is weak conductive, the output voltage changes to 1.58V corresponding to a pure water droplet with a volume of 10.32mm³. The conductive liquid, the output voltage varied by 1.74V corresponding to a saline droplets (NaCl, concentration of 0.009) with a volume of 16,35mm³, and corresponding to a glucose water droplet (concentration of 0.05) with a volume of 42.12mm³. When liquid droplets appear in the channel the capacitance value of the capacitor is changed. The output voltage of the capacitance readout circuit is used to evaluate the volume of the liquid droplets and to calculating the velocity of the droplet in the conduit. This proposed  sensor  can  be  used  for  medical  devices  and  systems and applied in biomedical.