Development and Experimental Study of Miniature Two-plate Electrical Capacitance Sensor to Detect Dielectric Material

Electrical capacitance sensing technique is used in many industrial applications. It is being used through the tomography technique in the non-destructive test, process monitoring and control systems and also as proximity sensors. In this paper, electrical capacitance sensor to detect dielectric material has been constructed and experimentally studied. The miniature two plates of electrical capacitance sensor (ECS) is designed using COMSOL Multiphysics software to see the electric field and contour of the electric potential of the system. The capacitance value of the sensor is measured based on AC circuit concept. The alternating current from the sensor flows to the detector circuit providing the voltage corresponding to the capacitance between a pair of electrode. The voltage from the detector has been amplified by amplifier circuit before sending to the lowpass filter to filter out any unwanted signal of the fringe effect. A signal conditioning circuit will process the signal before it is processed by a computer. The LabVIEW software is used as a graphical user interface (GUI) to display the type of dielectric material of paper, plastic or FR4 in the computer system. The experiment process has shown promising results to prove this concept work. When a dielectric material is placed between the parallel plates, each type of dielectric material produces different readings. Furthermore, there are significant results with regards to the size and the permittivity of the object. From the studies, there are two factors that will influence the reading of the sensor, which are the distance between the two sensor plates and the number of electrodes being used on the sensor plates. The results revealed that the sensor can distinguished dielectric material, namely paper, plastic and FR4. These results further support the idea of establishing a parallel plate ECT system to inspect the defect on a composite material. Further work needs to be done to establish whether parallel ECT can distinguish the type of defect which appear on a composite material, such as delamination or crack.