Leland P. Solie

SAW/BAW Bragg cell

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 kB be the projection of the BAW wave vector on the surface, and let kS be the wave vector of the SAW. Then, if kG is defined to be the wave vector of the grid, i.e., kG =2π/d, where d is the periodicity of the reflecting strips at the frequency under consideration, the phase match condition is kG =kB -kS. A reflector designed to satisfy this condition will reflect the SAW into a BAW at any desired angle (as specified by kB). 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.

Three wave surface acoustic wave (SAW) signal processor

A surface acoustic wave processor capable of performing convolution, correlation, time expansion/compression, and time reversal utilizes the nonlinear interaction between two input surface waves to generate a third surface wave. Phase matching for the third surface wave to perform an integration function is provided by a fan multistrip coupler (FMSC) which appropriately alters the velocity of an electric field pattern transferred from one track of the FMSC to a second track thereof.

Coded wireless temperature sensors with design specified sensitivity

ASR&D has developed a patented surface acoustic wave (SAW) temperature sensor with individual sensor identification codes and design-controlled temperature sensitivity. Temperature sensitivities demonstrated during this work range from −165ppm/°C to +680 ppm/°C, all on YZ lithium niobate, a piezoelectric substrate with an inherent temperature sensitivity of magnitude 94ppm/°C. A set of 32 individually identifiable coded SAW temperature sensor devices were developed. Wireless measurements confirmed the ability to selectively detect any single sensor out of the combined response of multiple sensors. The wireless electronic reader system currently being developed at ASR&D is a single-channel reader that can be manually adjusted to select any one sensor out of a group of up to 32 sensors simultaneously operating in the field of view (FOV) of the reader. This system avoids code collision problems typical of prior coded SAW wireless sensor systems, and can be extended to read 32 or more sensors operating in the FOV of one reader, at ranges of up to 100 feet, with sampling times of 1–10 msec.