Gang Jing

Pseudo-LFE study in AT-cut quartz for sensing applications

Lateral field excitation (LFE) AT-cut quartz devices have recently been investigated for liquid sensing applications. However, previous studies concentrate on LFE device with Psi = plusmn90deg due to the maximum theoretical LFE coupling coefficient. Here Psi represents the angle between the lateral electric field and the crystallographic X-axes in the plate surface. In the present study, AT-cut LFE devices with different electric field directions were studied and a TSM (Thickness shear mode) was observed in the LFE device with Psi = 0deg, where the calculated LFE coupling coefficient is zero. This indicates that the observed TSM may not be excited by the lateral field but the thickness field with the liquid acting as an analog electrode, and the device is in fact a pseudo-LFE device. Moreover, experiments have also shown that LFE devices with different electric field directions are of similar sensitivities to liquid viscosity, relative permittivity and conductivity.

Novel electrode configurations of lateral field excited acoustic wave devices on (yxl)-58° LiNbO 3

In the present study, Several 4.5 MHz LFE devices with different electrode configurations, including the dual-gap electrode, single-turn Archimedes spiral electrode, two-turn Archimedes spiral electrode and two-turn symmetric spiral electrode, were fabricated and tested. A common LFE device with the single-gap electrode is also fabricated for comparing their performances. A major resonance peak was observed in all devices in air. However, devices with the single-gap electrode and the two-turn symmetric spiral electrode offer higher Q value than other devices. The device with the dual-gap electrode shows the maximum frequency change compared to other devices when the sensing surface of these devices is exposed to water and 0.06 wt% NaCl water solution. Theoretical analysis for these phenomena is given.

Three operation modes of acoustic wave devices with a lateral field exictation structure

Through theoretical calculations using the extended Christoffel-Bechmann method and experiments, three operation modes of the LFE devices, which were referred to as the pure-LFE, quasi-LFE and pseudo-LFE modes, were presented. Several about 5 MHz LFE devices with similar geometry using the (yxl)-58deg LiNbO3, (yxl)-16.51deg LiTaO3 and AT-cut quartz crystals were fabricated for analyzing three LFE operation modes. Their piezoelectric coupling factors and acoustic wave phase velocity for LFE and TFE were calculated for designing LFE devices. The motional resistance at resonance was theoretically derived from the device geometry and material constants and was well corresponding to the measured results for analyzing three modes.