WO2009102228A3 - Planar capacitive proximity sensor - Google Patents

Abstract

Planar capacitive sensor consists of two electrodes, which are in the same plane, and most often, are carried out on a printed circuit board as two surfaces of a conductive material. In case there is no object of detection and since the distance between the electrodes is relatively long, capacitance that is made between the electrodes approximately equals zero. Because the electrodes are extremely thin less than 0.1mm and the area between them relatively large about 1cm, the capacitance which these electrodes make can be considered as 0. When there is no object the surface of the equivalent capacitor is somewhere near 1cm therefore C, proportionally 0.0001 times dialectic air constant plus parasitive capacitor made of two plates in the same plane which have isolator on one side (printed plate), and on the other thin varnish which coats conductor and the air. When the object is near electrodes of size about 1cm or less a capacitor is formed between the first electrode E1 and the object as well as between the object and the second electrode, E2. Total capacity between E1 and E2 is serial connection of these two capacitors. Since the surface between the electrodes and the object is now about 1 cm x 1 cm and the distance is 1 cm, capacity of the equivalent capacitor is proportional to 0.01 times dialectic air constant or some other isolator, in case electrodes are in an isolator. From the picture 1 it is seen that amplification of the capacity is about 100 times.