United States of America As Represented by the Secretary of the Air Force

James C Sethares

Daniel J Burns

Harold M Frost

Gerald G Sweet

Nondestructive testing and analyzing of surface acoustic wave (SAW) interdigital transducers is accomplished by observing electro-optic changes in a layer of liquid crystals produced by the effects of electric fields resulting from an electrical potential applied to the transducer. A display cell comprising a liquid crystal layer covered with a gold coated glass coverplate is fabricated on the surface of the SAW substrate under test. The assembled display cell is positioned for viewing under a microscope equipped for vertical illumination by a light source and a beam splitter. Polarizers are positioned in the illumination and viewing paths. An electrical potential is applied to the SAW device transducers and in some instances to the coverplate gold coat. Electro-optic effects produced in the liquid crystal by the electric field effects of the applied electrical potential are viewed through the microscope and are analyzed and interpreted.

Method for testing and analyzing surface acoustic wave interdigital

Extremely sensitive velocity and position measurements are achieved with a surface acoustic wave (SAW) resonator device. A surface acoustic standing wave field is established on a movable SAW propagation surface by means of induced SAW pulses traveling on the propagation surface and their reflection from a SAW reflecting mechanism. Movement of the propagation surface causes periodic variations in the standing wave field amplitude. The frequency of the standing wave field amplitude variation is directly related to the SAW propagation surface velocity and its phase (i.e., total number of standing wave field amplitude variations from a reference point) indicates the SAW propagation surface position or how far it has moved from the reference point. One implementation comprises a rotatable aluminum cylinder on the surface of which SAWs are launched and detected by proximate but non-contacting transmitting and receiving electromagnetic transducers (EMTs). The reflecting mechanism used to initiate the standing wave results from the proximity of the EMTs and the coupling effect of the EMT magnetic fields. Frequency and phase information is extracted from the receiving transducer output by visually (CRT) or electronically counting standing wave amplitude variation cycles. Other implementation includes translatory planar SAW propagating surfaces and various transducer configurations and arrangements.

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Burlington, MA, United States of America

James C Sethares