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Surface acoustic waves: theory and application
A detailed investigation is undertaken in order to determine the potential usefulness of acoustic surface-waves in implementing various signal processing functions. The propagation of elastic, vibrational energy on the surface of an isotropic solid is determined, and the surface-localized particle motion and velocity characterized. The requirement for the generation and reception of surface-waves is then developed, utilizing the interdigital electrode structure on a piezoelectric substrate. Emphasis is on the selection of the substrate (lithium niobate) and on the design of efficient transducers. The theory developed is utilized to design several acoustic surface-wave signal processing devices. Acoustic bi-phase and linear FM coded matched filters are designed and evaluated for their usefulness in future communication and radar systems. Of particular importance is the performance of an electronically code-alterable bi-phase modulation generator. An acoustic surface-wave compressive receiver is breadborded or possible electronic intelligence receiver applications in the detection of unknown signals in a dense environment and the accurate determination of intercept frequencies. Also developed are an electronically variable tapped delay line (electronic warfare deception techniques) and a contiguous bank of bandpass filters (signal sorting techniques) both of which may find eventual use in electronic warfare signal processors. Each application's area is discussed in concept, as well as with respect to the role played by the respective surface-wave devices. In closing, the future of these microminiature signal processing devices is assessed with respect to what exists today and, even more important, what is needed to make the technology useful tomorrow.