Natural single-phase unidirectional transducers on a LiNbO3 substrate for SAW sensor applications

LiNbO3 is the substrate most often used in wireless identification tags because of its large electromechanical coupling constant. A single-phase unidirectional transducer (SPUDT) on LiNbO3 is attractive to realize a wireless SAW sensor with reduced size, low insertion loss, low passband ripple, and high degree of linearity of phase. A natural single-phase unidirectional transducer (NSPUDT) produces the directivity even when the geometry is symmetrical. The NSPUDT is good for high frequency sensor applications because of its simple structure with wide electrode width. In this paper, NSPUDT orientations on a LiNbO3 substrate are described. Analytical results of transduction characteristics and COM parameters of the NSPUDT using coupled-mode and perturbation theories are shown. A useful orientation on Euler angle (0deg, 38deg, psi ) cut is obtained for aluminum and copper electrodes.