Acoustic hologram reconstructor using surface acoustic wave devices

Claim 1

A hologram reconstructor, which is part of a system for converting an acoustical hologram developed from a square acoustic image comprising N 2 elements, into a focused optical image, the square having a side of length L, comprising: means for accepting a stream of electrical input data, A cos φ and A sin φ developed from the acoustic image, A being an amplitude and φ being a phase angle, both being a function of Z, the distance from a point acoustic source to the plane of N 2 transducers located in an array perpendicular to Z, one output of this means being the discrete signal U s (nl, ml ), where m=n=0,1,2, . . . , N-1, l = (L/N) = the spacing between the hydrophones, another output of the means being the quantity Z; a memory, connected to and which receives the U s (nl,ml), signal from, said input data means, which stores the N 2 discrete values of the signal U s (nl,ml); means, connected to said memory, for controlling the movement of the stream of electrical input data; a first function generator, whose input is connected to said input data means and said controlling means which generates the signals cos α n 2 and sin α n 2 , the term α including a focusing term for the Z dimension of the planar array, which corrects for near-field phase curvature; a second function generator for generating the two functions sin (π/N) k 2 and cos (π/N) k 2 ; a pair of convolvers, whose inputs are connected to the outputs of said controlling means and said two function generators, which convolve the input signals, said controlling means causing a row-by-row flow of a continuous stream of Fourier coefficients from said two convolvers, which coefficients are written back into said memory, read out column-by-column, and fed back into said convolvers, to be transformed into two-dimensional Fourier transform coefficients; and a squaring and summing circuit, whose input is connected to the output of said controlling means, which accepts the Fourier transformed coefficients from said two convolvers, where they are converted into N 2 intensity signals in a square array of N rows and N columns.