Importance

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Abstract

An acoustic signal is launched as a surface acoustic wave (SAW) by a hyperbolically tapered transducer and then reflected into a bulk acoustic wave (BAW) by a tapered reflector. At each frequency the tapered reflector must satisfy the phase match conditions between the SAW and BAW as defined by their wave vectors. Let k.sub.B be the projection of the BAW wave vector on the surface, and let k.sub.S be the wave vector of the SAW. Then, if k.sub.G is defined to be the wave vector of the grid, i.e., k.sub.G =2.pi./d, where d is the periodicity of the reflecting strips at the frequency under consideration, the phase match condition is k.sub.G =k.sub.B -k.sub.S. A reflector designed to satisfy this condition will reflect the SAW into a BAW at any desired angle (as specified by k.sub.B). The laser beam is then Bragg scattered by the BAW in the usual manner. The advantage of this scheme is that the tapered transducer separates the acoustic signals spatially so no intermodulation products are formed. Furthermore, the tapered transducers are able to handle higher power levels than other transducers so high acoustic signals can, in fact, be used. An additional improvement in Bragg scattering efficiency can be achieved by curving the reflective array in such a way as to direct the BAW so that the Bragg angle for optimum scattering efficiency is exactly met for all frequencies. This insures that the device can be used over a broad bandwidth without a fall off in the Bragg scattering efficiency.

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First Claim