Multiple film microwave acoustic transducers

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Abstract
It has been previously demonstrated by Foster and DeKlerk that oriented thin films of cadmium sulfide can be fabricated using proper vacuum deposition techniques. These CdS films form the basis for practical high efficiency transducers of electromagnetic energy to acoustic energy at microwave frequencies. We describe some further investigations of the deposition of CdS films for this purpose and some investigations of the use of, multiple film assemblies in which quarter wave films of various materials are used to transform acoustic impedances for the purpose of increasing the conversion efficiency. Using these methods low conversion losses of 4.5 dB at 800 MHz and 5 dB at 1600 MHz have been achieved experimentally. The lowering of the conversion loss by a significant amount as predicted removes a major obstacle in the technology for the further development of the many devices utilizing acoustic waves at microwave frequencies. The following are described in detail: the vacuum deposition techniques for the CdS film; the formulation of the problem and the calculations which give the transducer conversion loss as a function of frequency for multilayer films; and the comparison of calculated and measured conversion loss as a function of frequency from 500 to 4000 MHz.