| 20120032554 | TRANSDUCER HAVING NATURAL UNIDIRECTIONALITY FOR SURFACE ACOUSTIC WAVES - The invention relates to a transducer having natural unidirectionality for surface acoustic waves, wherein an interdigital electrode structure is arranged on a piezoelectric crystal substrate and is constructed with interdigital transducers comprising collecting electrodes and fingers, wherein at least two of the fingers form a transducer cell, which comprises at least one excitation center for exciting an electrical potential wave and at least one reflection center for reflecting electrical potential waves. The invention is based on the problem of finding materials, material sections, and propagation directions for transducers having natural unidirectionality that result in a low insertion loss even in broadband transducers, and for which the frequency position is not affected or is affected only slightly by errors in the orientation of the electrode structure on the substrate despite the unidirectional characteristics of the transducers. According to an essential characteristic of the invention, the fingers are oriented perpendicularly to a direction R, wherein the direction R is directed parallel to a 1- or 3-fold rotational axis of the substrate crystal and the derivative dv/dθ=0 applies to R, wherein v is the phase velocity of the surface wave and θ is an angular deviation of the perpendicular to the finger direction from the direction R. According to a further characteristic of the invention, the electrode materials and the layer thicknesses thereof are selected in such a way that the phase shift Φs between the excitation center and a reflection center in each transducer cell, given by the equation sin | 02-09-2012 |
