A tunable surface wave resonator is disclosed comprising a substrate of piezoelectric material having acoustic surface wave absorbing extremities, a pair of spaced acoustic surface wave gradient reflectors positioned adjacent to the absorbing extremities of the substrate, a pair of spaced multiphase...http://www.google.es/patents/US4028648?utm_source=gb-gplus-sharePatente US4028648 - Tunable surface wave device resonator
