LiNbO3基片溶液成分测试声传感器

利用准纵波模式在 Ｌｉ Ｎｂ Ｏ３ 基片上制作了能有效地检测溶液成分的实验性声传感器．准纵波模式的优点是声波速度快，波长长，声波能量能透入基片深处，因此可以从基片背面检测液体，简化了通常 Ｓ Ａ Ｗ 传感器复杂的封装结构，有利于实用化．

ACOUSTIC SENSORS ON LiNbO 3 SUBSTRATES FOR DETECTING CONCENTRATION OF LIQUID SOLUTIONS

The characterization of acoustic wave propagating at the surface of a piezoelectric substrate depends on the properties of substrate materials and the surface boundary condition of mechanical and electrical properties; therefore it is very sensitive to the adjoined liquids with various dielectric constants,viscosities and conductivities.This sensitivity has been successfully utilized for sensing the properties of adjoined liquids by measuring the variation of velocity,phase and attenuation of different acoustic wave modes.This paper presents a novel prototype sensor with compact package structures,for detecting the concentration of lliquid solution,utilizing quasi longitudinal wave mode(QLWM) sensor on LiNbO 3 substrates.The outstanding advantage of QLWM sensor is that the sensing face could be at the back face of the substrate,due to QLWM with high piezoelectric coupling constant and high propagation velocity,etc.Therefore it enhances the sensitivity of the sensor to the variations of the dielectric constant or the conductivity of liquid solution adjoining the sensing surface, and the sensors can be easily packaged.Moreover,in general SAW sensor,the wave energy will be seriously absorbed by the adjoined liquids;it causes an unstability in measurement circuits.However the propagation attenuation is uninfluenced by the adjoined liquids,because the particle displacement of quasi-longitudinal wave is nearly parallel to the direction of waveguide and the surface of the crystal substrate.In the experimental system,the quasi-longitudinal wave is generated and received by interdigital transducers(IDT).The variations of the center frequency of IDT will be caused by the changes of the liquid adjacent to the back of the substrate,because of the liquid solutions,such as dilute electrolytes and metal ion solution or organic liquid solution,with various conductivity or dielectric constant respectively.The experiment results show good agreement with the theoretical prediction.