You searched for: “surface acoustic wave
surface acoustic wave, SAW (s) (noun); surface acoustic waves; SAWs (pl)
A technology used for automatic identification in which low power microwave radio frequency signals are converted to ultrasonic acoustic signals by a piezoelectric crystalline material in the transponder: Surface acoustic waves were first described by Lord Rayleigh in 1885.

Variations in the reflected signal can be used to provide a unique identity.

SAW appliances are applied in television and radio.