SAW Delay Line for Vibration Sensors

Abstract

The paper presents an analysis of surface acoustic wave delay line. The line consists of two simple interdigital transducers placed on a ST-cut quartz plate. Mid-band operation frequency of the line is 74 MHz. The line will be applied for surface acoustic wave vibration sensor. At the immovable end of the plate there are electric signal feeds to both transducers. This is the cause of increase in signal value going directly between the transducers and the cause of line losses. By means of equivalent electric model of interdigital transducer a loss analysis of the line has been made at 50 Ω load. The analysis allows to minimize line losses by matching the transducers to 50 Ω impedance. This has been practically achieved by a design of transducer geometry and conguration matching 50 Ω impedance, by means of inductance. An analysis of repeated operation characteristics of two interdigital transducers has been made. A signal going directly through capacitance between transducers and signals reected from the edge of piezoelectric substrate have been presented. Results of theoretical analysis have been compared with experimental examinations.