Many of the recently discovered characteristics and applications to electronics of surface elastic waves are discussed. First the propagation of various elastic waves at the surfaces of solids is considered, followed by descriptions of the many ways which have been demonstrated for transduction between surface elastic waves and electromagnetic waves. Surface-wave amplification, primarily in semiconductors, and wave guiding, focusing, and reflection are examined. The properties of these waves suit them for use in a number of applications, which are discussed, ranging from realization of electronic amplifiers, frequency and analog time-domain filters, and coding devices, to the modulation of light beams and the measurement of surface properties of solids. Many references to the recent surface-wave literature are included.

Surface elastic waves

Delay lines with a variety of delay versus frequency characteristics are obtained by fabricating the delay line apparatus from multilayer materials In one modification, the delay line is of rod construction and in another, of strip design

Ultrasonic delay lines

The recent progress of the digital and the surface acoustic wave (SAW) technologies have made them compatible; and it is now possible to design signal-processing modules which benefit from the flexibility of the digital techniques and the very high computation speed of the SAW techniques. Very fast signal processors can now be built which are able to process several tens of megasamples per second and whose volume and power consumption are limited. This paper shows the compatibility of these technologies and the advantages yielded by their joint use. Several examples are described which relate to one- and two-dimensional Fourier and correlation processors.

Very Fast Signal Processors As a Result of the Coupling of Surface Acoustic Wave and Digital Technologies

Signal processors incorporating dispersive delay lines can be designed for matched filters in active sonars, for spectrum analyzers in passive listening, and for generators of frequency‐modulated codes. Depending upon its bandwidth and its duration, the signal to be processed is fed into a dispersive delay line that is matched to it in the case of wide‐band systems, or matched to an homothetic signal (a signal having the same modulation characteristics, the same time‐bandwidth product as the original signal, but having a frequency scale multiplied or divided by a factor k and a time scale divided or multiplied by the same factor k) with a larger bandwidth in the case of narrow‐band systems. In this last case, the signal is previously time compressed with an appropriate unit, such as a recirculating memory or a magnetic recorder.

J. Bertheas

Papers

Use of Dispersive Delay Lines for Signal Processing in Underwater Acoustics