Signal processing in acoustic surface-wave devices

The Rayleigh surface-wave mode propagates on the surface of suitable elastic solids with velocity independent of frequency at about 10-5 times the speed of light and an attenuation of about 1.5 dB for 104 wavelengths. Thus as a delay line it is far more compact, has much less attenuation, and can be much cheaper than electromagnetic delay lines. Piezoelectric elastic solids permit the launching and detection of the waves by electrodes on the surface. Fabrication technology is similar to that used for monolithic semiconductors and amplification is possible by interaction with carriers in a semiconductor surface layer. Parametric interactions can be used to perform convolution of two signals. The feasibility of deflecting and modulating light beams also has been demonstrated. This rapidly developing art can today produce delay lines, filters, pulse compressors and expanders, and pulse-sequence generators and decoders, and in the future may perform convolution, correlation, and light-beam manipulation in small, economical, low-power structures.