Sounding of SAW devices insertion loss by means of photoacoustic method

The insertion loss of SAW devices is one of the important parameters determining the applicability of these devices as frequency selective components in modern telecommunication systems. A new method for localizing the signal energy absorption areas in SAW devices is described. The method is based on the well-known fluctuation-dissipative theorem. In accordance with this theorem, thermal radiation (in the case of SAW devices it is thermal acoustic radiation registrated as electric signal at the output interdigital transducer) at the output of a system is formed by partial radiations of its consisting parts. These partial radiations being proportional to these parts contributions to the absorption of useful signal in the system. Experimentally the thermal electrical fluctuations at the output of the SAW device transducer were registered under device local irradiation by an intensity modulated focused laser beam. These preliminary experiments were carried out for SAW filters with lithium niobate as a substrate and show the potential of using this method in practice.