A new NSPUDT configuration using coupled piezoelectrics

Natural single-phase unidirectional transducer (NSPUDT) behavior in layer systems consisting of two coupled piezoelectrics is studied. The concept is characterized by combining those substrates and layers, the distances between the transduction and reflection centers of which differ by ±λ/4 or ±3λ/4 (λ=wavelength). A criterion making it possible to find those crystal materials by general symmetry considerations and the layer thickness required for an optimal NSPUDT effect is formulated. The NSPUDT behavior is achieved, if the wave vector is parallel directed to a crystal rotation axis of the substrate and perpendicular to a mirror plane of the layer (or vice versa). These directions are pure mode ones for the substrate and the layer alone, but in general no longer for the layer system. There is even the chance to realize opposite forward directions on one and the same sample. The NSPUDT effect is experimentally demonstrated with the layer configuration ZnO/IDT/STX quartz