A new analysis of oblique-incidence reflective array gratings is presented. Gratings with a constant spatial period and with a linear spatial chirp are considered. lutions are derived for the grating waves that incorporate a1 1 orders of ,nul ti ple reflections and power depletion within the gratings. are obtained using coupling-of-modes theory. solutions shed new light on the operation of such grating devices. In particular they permit a more detailed and exact analysis of the reflective-array compressor (RAC) than was previously possible with complex numerical computer analyses. The implications of the new analysis for RAC design are examined in detail and distortions of the device response, caused by previously ignored effects, are elucidated. For the first time exact soThe solutions These

A Closed-Form Analysis of Reflective-Array Gratings

While the interdigital transducer is the most important periodic structure for Rayleigh waves, it labours under limitations. To perform its function it must consist of continuous metal strips connected together in a certain configuration. Periodic reflective array structures suffer no such limitations. A rich variety of structures can be conceived and many have been investigated. Examples of periodic arrays are shown in Fig. 1 which may consist of dielectric or metal films or of grooves.

Rayleigh Waves and Reflective Periodic Structures

The authors report the design and fabrication of a surface acoustic wave (SAW) device with improved power transfer due to modification of its delay path. Typically, SAW delay-line devices suffer from relatively high insertion loss (IL) (∼10–30 dB). Our approach is to incorporate an array of microcavities, having square cross-sectional area (λ/2 × λ/2) and filled with tantalum, within the delay path to maximize acoustic confinement to the surface and reduce IL. To determine the effectiveness of the cavities without expending too many resources and to explain trends found in actual devices, a finite element model of a SAW device with tantalum filled cavities having various depths was utilized. For each depth simulated, IL was decreased compared to a standard SAW device. Microcavities 2.5 μm deep filled with tantalum showed the best performance (ΔIL = 17.93 dB). To validate simulated results, the authors fabricated a SAW device on ST 90°-X quartz with microcavities etched into its delay path using deep react...

Design and fabrication of a SAW device with Ta filled microcavities inserted into its delay path for improved power transfer

Considerations relating to the design of surface-acoustic-wave (SAW) reflective array pulse compressors (RACS), including the effect of array width on power reflected, the transmitted beam profile and the effect of randomized arrays, are discussed. Only a first-order analysis is used. Potential misunderstandings of these issues that could arise from the existing literature are clarified. >

L. Solymar

Papers

Reflection of Surface Acoustic Waves from Arrays of Strips