High-Quality Wide-Band Mechanical Filters Theory and Design

Abstract

Filters using wire coupled ultrasonic resonators and equipped with electromechanical transducers are recently favored by telecommunication techniques in an increasing degree due to their superiority over conventional LC filters in dissipative losses, temperature stability, and in small geo- metric dimensions. At frequencies <l00 kHz, flexural reso- nators have specific advantages: they resonate in the lowest modes; the consequence is a minimum of unwanted spurious modes. The particular integrals of differential equations of flexure which are important for this application can be closely approximated by functions of electrical networks. The result- ing analog networks, however, cannot be designed by con- ventional methods. An approach to a solution is made by an iterative procedure, which is based on the multidimensional Newton method, and finding starting values from image param- eters. It is suitable for the design of filters with attenuation poles and Ijnearized phase response.