P1I-4 Relationship Between Permittivity of Piezoelectric Ceramic and Electrical Impedance Measurement in Proposed Touch Sensor

This paper presents the relationship between permittivity of piezoelectric ceramic and capacitance measured by the proposed touch sensor. The proposed touch sensor uses a pair of piezoelectric ceramics and measures not only the ultrasonic property of the material and but also the electrical property by using each electrode on the surface of the piezoelectric ceramic. From these data, the quality of material including the thickness is discriminated. In the experiment, capacitance values at several frequencies were measured by using piezoelectric ceramics with three kinds of relative permittivity such as 2130, 510 and 215, and their capacitance values were compared. As the measurement material, four kinds of materials such as acrylic resin, silicone rubber, aluminium and agar, which thickness of each material was 10mm, 20mm or 40mm, were prepared. From results, it was presented that capacitance measured by using electrode of piezoelectric ceramic was influenced by relative permittivity of piezoelectric ceramic. It was also found that measurement accuracy of capacitance became better as relative permittivity of piezoelectric ceramic was smaller. In addition, discrimination of four kinds of materials including detection of thickness from 10mm to 40mm was demonstrated from capacitance and propagation time measured by the proposed sensor