Non-reflective electrode cell for SAW with quarter-wavelength electrodes

Non-reflective interdigital transducers (IDTs) for surface acoustic waves (SAWs) are important elements for development of SAW devices with precise frequency responses. Until now a common way to have a non-reflective periodic cell of IDT at the resonance frequency is to use split electrodes with periodicity P/4 and finger width P/8, where P is the IDT period equal to the SAW wavelength. But for 2.45 GHz (ISM frequency band), standard lithography allows electrode (and gap) widths only to be about quarter-wavelength. Thus, a new structure solution for non-reflective IDT is required for high frequencies. A novel solution for non-reflective cell with two quarter-wavelength electrodes per one-wavelength period is based on 2D-periodic structure consisting of alternating active IDT tracks and passive reflector tracks. If tracks have equal apertures and if electrodes in adjacent tracks are shifted to each other by P/4, SAWs reflected from electrodes in adjacent tracks have equal amplitudes but with phases shifted by a half wavelength. So the reflected waves cancel each other and the total reflection from the structure should be equal to zero.