New SPUDT cell structures

The present paper describes single-phase unidirectional transducers (SPUDT) cells with all fingers wider than A/S while maintaining the unidirectional effect. The first solution is related to a SPUDT consisting of /spl lambda//4 and /spl lambda//2 wide fingers arranged in two tracks. Each track has no significant unidirectional effect. Both tracks form a wave-guide, and the waveguide coupling generates the interaction of the tracks. As a result of that interaction, a unidirectional effect arises as verified by experiment. This transducer type is called double-track (DT) SPUDT. A second solution is suggested that includes, in contrast to distributed acoustic reflection transducer (DART), electrode width control (EWC), and Hunsinger cells, SPUDT cell fingers with one and the same width only. Cell types with /spl lambda//6, /spl lambda//5, and /spl lambda//3 wide fingers called uniform width electrode (UWE) cells are considered. One of these cell types, including exclusively /spl lambda//5 wide fingers, is experimentally investigated and a unidirectional effect is found. Moreover, a filter example using the /spl lambda//5 cell type has been designed for reducing SPUDT reflections. The echo suppression expected could be verified experimentally. No wavegiiide coupling is required for this cell type.