Holographic Storage of Acoustic Surface Waves with Schottky Diode Arrays.
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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Silicon Schottky-diodes have been used to store images of surface acoustic waves propagating on lithium niobate. These images were subsequently employed to provide programmable matched filter or coherent integration fuctions. This technique could also be used to holographically store a large number of acoustic beams to provide a storage capacity as large as 100,000 bits of information. The basic storage element is a Schottky diode with an overlay of polysilicon. Many such diodes are arrayed on centers which are less than an acoustic wavelength apart. When the acoustic signal is in position beneath the diode array, the diodes are forward-biased for several nsec, which causes charge to flow to the diode contact in response to the piezoelectric field of the surface wave. These charges diffuse into the polysilicon in several microseconds, after which a succeeding signal can be overlayed in the array. These charges, which are an image of the acoustic signal are retained in the polysilicon for as long as 100 ms. The stored image is proportional to the acoustic signal in every respect, including the amplitude, phase and wavefront details. This procedure could be repeated for many acoustic beams, and a subsequent signal along a given stored beam causes an electrical signal to appear across the silicon-lithium noibate composite which is proportional to the cross-correlation of the signal with all stored images. This gives rise to the desired output signal, plus undesirable cross-talk signals. Also the desired signal is relatively weak, and its signal-to-noise ratio needs to be increased with a coded interrogating signal and a matched filter. Author
- Line, Surface and Bulk Acoustic Wave Devices