New Optical Approach of SAW Delay Line Characterization

Surface acoustic wave devices are usually characterized solely through their electrical parameters. Mechanical displacements can also be numerically computed using finite element software. In this paper, we show that this characterization can be supplemented using an interferometer system capable of measuring out-of-plane mechanical displacement over the entire sensor structure. Conventionally, interferometer imagery is limited to 20MHz, but this work reports the results of the characterization of Rayleigh wave-based SAW sensors operating at a frequency of 78.8MHz using ultrahigh-frequency scanning laser vibrometry. An overview of the conventional methods used to characterize SAW devices is presented here, as well as a comparison between the results obtained using these methods and laser vibrometry. It is shown that the latter technique also provides access to time-resolved ultrasonic fields over the entire rsubstrate surface and provides an insight into important reflection and divergence phenomena. Comparison with standard network analyzer measurement is shown to assess the performance of Laser Doppler Vibrometry system. Mechanical and electrical characterization and comparison with a model results are presented and discussed. The purpose of this article is to review these latest developments tools in the SAW sensor measurement and present an outlook of the future of these characterizations in the next generation piezo-sensors.