Interaction of surface acoustic waves and particles

Abstract

In this paper, we present interaction of a shear horizontal surface acoustic wave (SH-SAW) and particles. The detection mechanisms of the SH-SAW sensor are mechanical and electrical perturbations. The SH-SAW sensor based on the electrical perturbation can detect particles in liquid. On the other hand, the SH-SAW sensor based on the mechanical perturbation cannot detect particles in water environment. We estimate that the water thin layer exists between the sensor surface and the particles and its thickness is larger than the viscous penetration depth. To increase the viscous penetration depth, high viscous solution is used as reference solution. The SH-SAW sensor is influenced by the particles in 80wt.% glycerol/water mixture. However, the results indicate that the detection mechanism is not based on the mass loading. Moreover, particle measurements are performed in gas phase. The results indicate that the SH-SAW is influenced by static stress due to particle loading on the surface. perturbation cannot detect those. In this paper, we discuss interactions SAW with particles. Especially, particle detection based on the mechanical perturbation is discussed. In section III, the results of pigment measurements based on mechanical and electrical perturbations are described. Then, polymer particle measurements based on the electrical perturbation are described. In section IV, the discussions of the measurements of the particles based on the mechanical perturbations are entered into details. II. EXPERIMENTAL The SH-SAW sensor was fabricated on 36o rotated Y-cut, X-propagating LiTaO3 (Yamaju Ceramics, Aichi Japan). As a SAW on the piezoelectric material is a coupling wave on mechanical displacements and electrical static potential, the SAW is influenced by mechanical and electrical perturbations. The three-channel SH-SAW sensor was proposed for simultaneous measurements of those perturbations (3). Figure 1 shows the SH-SAW sensor pattern in this study. The center frequency was 50 MHz. The liquid cell was placed on the propagation surface. The propagation surface was used as sensing area, where the SH-SAW interacts with an adjacent liquid. The mechanical perturbation was obtained from differential signals between channels 1 and 2 and the electrical perturbation was obtained from differential signals between channels 2 and 3. The measurement system is shown in Fig. 2. A 50 MHz signal from a signal generator (Anritsu MG3601A) was fed to the three-channel SH-SAW sensor. The channels were selected using VHF switching unit (HP 3488A). Phase difference and amplitude ratio between two channels were measured using a vector voltmeter (HP 8508A). Velocity shift