| 摘要 |
PROBLEM TO BE SOLVED: To increase a convolver output signal by decreasing the angle of a normal of a wave front of a surface acoustic wave with respect to a lengthwise direction of a guide path so as to enhance the impedance matching efficiency. SOLUTION: The surface of a piezoelectric substrate is covered by a metallic thin film 14 to allow a circular-arc IDT(inter digital transducer) 12 with a larger size as possible to stimulate the surface acoustic wave between an output electrode 13 and the IDT 12 of an input transducer consisting of interdigital electrodes. The IDT 12 is formed in a circular-arc shape with a concave shape with respect to the output electrode 13, the end face of the metallic thin film 14 of the circular-arc IDT 12 is formed in a circular-arc with the same radius of curvature as electrode fingers of the IDT 12 and the end face toward the output electrode 13 is formed to be a recessed circular-arc shape. In this case, while an aperture angle of the output electrode 13 is nearly 28 deg., the center angle of the circular-arc IDT 12 is selected to be 30 deg. or over by the wave front relax action of the metallic thin film. Thus, it is possible to reduce the inductance for impedance matching, the loss is reduced and harmonics of the surface acoustic wave are reduced. |
