JPS5478949A - Electrode for surface acoustic wave element - Google Patents

Abstract

PURPOSE:To establish the electrode less in loss and not subject to the effect of the end surface reflection, by providing two comb type electrodes placed by shifting the surface wave in the center frequency of the surface acoustic waves by 1/4 wave length and the common electrode placed at the clearance of the comb type electrodes. CONSTITUTION:The wave length of the center frequency of the surface acoustic waves is taken as lambdao, and the comb type electrodes 13 and 14 are placed shifted by 1/4lambdao toward the propagation of surface acoustic waves. The distance of finger between the electrodes 13 and 14 is set to lambdao, and the common electrode 15 is placed so that the distance with the edges of the both electordes can be equal to the clearance of the both electrodes. When an AC input is fed to the voltage terminal 16 and the common electrode 18, the surface acoustic waves are excited on the piezoelectric substrate 3 with the AC electric field between the electrodes 13 and 15. When a signal delayed for the phase by 90 deg. is fed between the terminals 17 and 18, the phase is shifted by 90 deg. with the surface acoustic waves excited with the electrodes 13 and 15, and it is excited at the position shifted by lambdao/4 spacingly, then the waves are only the progressive waves toward right direction. Accordingly, the electrode not having harmful tripple transient echo can be obtained.