Effects of longitudinal wave on the resonance behavior of an electrode-separated piezoelectric sensor in liquids

An electrode-separated piezoelectric sensor (ESPS) was constructed and its operation in the liquid phase was characterized. When the surface of the se parated-electrode reflects the weak longitudinal wave (LW) back to the surf ace of the quartz disc where it was generated, the interaction of the refle cted LW with the main thickness-shear wave of the quartz disc is a potentia l error source. In this study, the influence of the LW effect on the respon se of the ESPS was investigated by an impedance analysis method. It was sho wn that all the impedance response parameters shift periodically as a funct ion of the distance between the separated-electrode and the quartz crystal. The LW effect depends markedly on the surface conditions, including the sh ape, area, position, angle and roughness, of the separated-electrode. When a rough, non-parallel or ball electrode was used, the influence of the LW c ould be decreased greatly. The influence of the air/liquid interface on the reflection of the LW was efficiently screened in the ESPS. (C) 2001 Elsevi er Science B.V. All rights reserved.