Phase-sensitive absolute-amplitude measurements of surface waves using heterodyne interferometry. We describe a novel heterodyne interferometer for scanning surface-acoustic waves at high frequencies, up to 6 GHz. The heterodyne operation facilitates the measurement of the absolute amplitude of the surface waves without calibration. It simultaneously also enables measuring the phase. The amplitude and phase information allows a precise characterization of the surface acoustic waves. Moreover, the wave motion can be visualized in the form of animations to gain insight. The interferometer has been tested by measuring a 167 MHz SPUDT device and a 374 MHz fan-shaped SAW filter.

Phase-sensitive absolute-amplitude measurements of surface waves using heterodyne interferometry

Scanning laser interferometry has proven useful in the identification of novel acoustic loss phenomena. However, it remains challenging to provide a rigorous physical interpretation of the details of the optically measured acoustic field distribution. With the help of our powerful FEM/BEM finite transducer model, we can make a direct comparison between the measured and simulated acoustic field distributions. This enables us to search and correct for unwanted acoustic phenomena which can deteriorate the filter performance. Here we focus on the modeling of the stress at the interface between the electrodes and the substrate. We describe the FEM/BEM tool for finite transducers that we have developed and its validation with optical Michelson interferometer scans. We show how it is possible to evaluate and optimize the power-handling properties of a SAW device structure.

SAW device analysis using a combination of FEM/BEM calculations and scanning interferometer measurements

Acoustic field profiles within a dual-track fan-shaped SAW filter on a 112/spl deg/ LiTaO/sub 3/ substrate have been studied in detail with our heterodyne laser interferometer. The experimental results are compared to extensive numerical simulations utilizing discretization of the filter into elementary cells. The experimental results and simulations show the existence of a phase difference between the acoustic main beam and its side lobes. Also, the wave fronts are tilted with respect to the propagation direction. The unidirectionality of the launching transducer and the absorption at the receiving transducer are determined experimentally. The simulations reproduce not only the amplitude fields, but also the phase fields with excellent accuracy when compared with the phase sensitive laser interferometric measurements.

Phase sensitive optical measurements and numerical simulations of a fan-shaped filter

PROCEEDINGS Donald E. Yuhas

We have investigated the surface-acoustic wave field variation in a fan-shaped filter on a 112/spl deg/ LiTaO/sub 3/ substrate as a function of position and frequency. The acoustic field has been measured with the help of a scanning laser interferometer and the SAW-field distribution in the complete filter has also been numerically simulated in detail. Our modelling scheme utilizes a discretization of the filter into elementary cells. The simulations serve to render features of the acoustic-field distribution in astonishing quantitative agreement with the laser-interferometric detections.

L. Kopp

Papers

Acoustic-field distribution within a fan-shaped filter