Acoustic surface wave correlators and convolvers

Claim 2

An acoustic surface wave device, suitable for use as a correlator or convolver, comprising: a substrate capable of propagating an acoustic wave across its surface; two pairs of electrode structures disposed upon the surface of the substrate, each pair aligned parallel to the direction of wave propagation, one pair parallel to the other, but not in the same line as the other pair; each of the four electrode structures being connectable to an input electrical signal, which, upon transduction upon the surface of the substrate, causes an acoustic wave to propagate in a path along the surface of the substrAte, both acoustic waves being parallel, the acoustic waves generated by the same pair of electrode structures propagating in the same line, either in the same direction or in opposed directions, and interacting acoustically at some region in the propagating path; each electrode structure comprising: a pair of sets parallel, interdigitated, electrodes, oriented in a direction substantially perpendicular to the direction of surface wave propagation; a pair of bus bars, at opposite ends of, perpendicular to, and connecting, the interdigitated electrodes, one bus bar connecting some of the interdigitated electrodes, the other bus bar connecting the remaining electrodes; the four electrode structures being so coded that the sum of their autocorrelation functions is equal to a delta function; absorber stripes disposed at each end of the substrate, perpendicular to the direction of wave propagation, for absorbing unwanted acoustic reflections; a pair of integrators, disposed upon the substrate at the regions of acoustic interaction, one for each in-line pair of electrode structures; one integrator having as its input the acoustic interaction of the surface wave outputs from two of the in-line electrode structures; the other integrator having as its input the acoustic interaction of the surface wave outputs from the other two inline electrode structures; each integrator spatially integrating an acoustic field produced by the interaction of outputs of the correspond two electrode structures; and a substraction circuit, having as its two inputs the outputs of the pair of integrators, and whose output signal corresponds to the convolution or correlation of the two different inputs signals to the two pairs of electrode structures, a convolution if one input signal is time-reversed with respect to the other, otherwise a correlation.

Claim 3

The surface wave device according to claim 1, wherein each of the integrators is disposed between its associated pair of electrode structures; the subtraction circuit is so connected that it takes the difference of the outputs of the integrators; the surface wave device thereby being a cross convolver.

Claim 4

The surface wave device according to claim 1, wherein the the spacing between adjacent electrodes connected to a common bus bar, of each of the four electrode structures, is uniform.

Claim 5

The surface wave device according to claim 1, wherein the interdigitated electrodes are weighted, so that the algebraic sum of the weightings is zero, or approximately zero.

Claim 6

An acoustic surface wave device, suitable for use as a correlator or convolver, comprising: a susbstrate capable of propagating an acoustic wave across its surface; two pairs of electrode structures disposed upon the surface of the substrate, each pair aligned parallel to the direction of wave propagation, one pair parallel to the other, but not in the same line as the other pair; each of the four electrode structures being connectable to an input electrical signal, which upon tranduction upon the surface of the substrate, causes an acoustic wave to propagate in a path along the surface of the substrate, both acoustic waves being parallel, the acoustic waves generated by the same pair of electrode structures propagating in the same line, and interacting acoustically at some region in the propagating path; each electrode structure comprising: a pair of sets parallel, interdigitated, electrodes, oriented in a direction substantially perpendicualr to the direction of surface wave propagation; a pair of bus bars, at opposite ends of, perpendicular to, and connecting, the interdigitated electrodes, one bus bar connecting some of the interdigitated electrodes, the other bus bar conecting the remaining electrodes; the four electrode structures being so coded that the sum of their autocorrelation functions is equal to a delta function; absorber stripes disposed at each end of the substrate, perpendicular to the direction of wave propagation, for absorbing unwanted acoustic reflections; means for delaying the input signal to one of the tranducers of each in-line pair so that output signals from both transducers of the in-line pair are coincident at some region in the propagating path; a pair of integrators, dipsoed upoon the substrate at the regions of acoustic interaction, one for each in-line pair of electrode structures; one integrator having as its input the acoustic interaction of the surface wave outputs from two of the in-line electrode structures; the other integrator having as its input the acoustic interaction of the surface wave outputs from the other two in-line electrode structures; each of the integrators being disposed to one side of its associated pair of electrode structures; each integrator spatially integrating an acoustic field produced by the interaction of outputs of the corresponding two electrode structures; and a signal summer, disposed upon the substrate, and so connected that it sums its two input signals; the surface wave device thereby being a cross-correlator.

Claim 7

An acoustic surface wave device, suitable for use as a correlator or convolver, comprising: a susbstrate capable of propagating an acoustic wave across its surface; two pairs of electrode structures disposed upon the surface of the substrate, each pair aligned parallel to the direction of wave propagation, one pair parallel to the other, but not in the same line as the other pair; each of the four electrode structures being connectable to an input electrical signal, which upon tranduction upon the surface of the substrate, causes an acoustic wave to propagate in a path along the surface of the substrate, both acoustic waves being parallel, the acoustic waves generated by the same pair of electrode structures propagating in the same line, and interacting acoustically at some region in the propagating path; each electrode structure comprising: a pair of sets parallel, interdigitated, electrodes, oriented in a direction substantially perpendicualr to the direction of surface wave propagation; a pair of bus bars, at opposite ends of, perpendicular to, and connecting, the interdigitated electrodes, one bus bar connecting some of the interdigitated electrodes, the other bus bar conecting the remaining electrodes; the four electrode structures being so coded that the sum of their autocorrelation functions is equal to a delta function; absorber stripes disposed at each end of the substrate, perpendicular to the direction of wave propagation, for absorbing unwanted acoustic reflections; means for delaying the input signal to one of the tranducers of each in-line pair so that output signals from both transducers of the in-line pair are coincident at some region in the propagating path; a pair of integrators, dipsoed upoon the substrate at the regions of acoustic interaction, one for each in-line pair of electrode structures; one integrator having as its input the acoustic interaction of the surface wave outputs from two of the in-line electrode structures; the other integrator having as its input the acoustic interaction of the surface wave outputs from the other two in-line electrode structures; each of the integrators being disposed to one side of its associated pair of electrode structures; each integrator spatially integrating an acoustic field produced by the interaction of outputs of the corresponding two electrode structures; and a signal summer, disposed upon the substrate, and so connected that it sums its two input signals; the surface wave device thereby being a cross-correlator.

Claim 8

The surface wave device according to claim 5, further comprising: a third, field-delineating, electrode structure disposed upon the substrate, interposed between an interleaving the pair of sets of parallel electrodes.

Claim 9

The surface wave device according to claim 6, wherein one pair of electrode structures is coded according to the members of a Golay complementary pair; and the other pair of electrode structures is coded according to the same members of the Golay complemntary pair, with one member of one of the pairs having its coding the negative of the coding of the corresponding member of the other pair of electrode structures.

Claim 10

The surface wave device according to claim 6, further comprising: 2N more pairs of parallel, coded, electrode structures, where N is one or more, each additional two pair being similar to the first-named two pairs, the electrode pairs being disposed upon the surface of the substrate, the coding of all 2N + 2 pairs of electrode structures being such that the sum of the autocorrelation functions of all of the codings is equal to a multiple of a delta function; 2N more integrators, one for each additional parallel pair of electrode structures, disposed upon the substrate in the path of its associated pair of electrode structures; N more signal summers, one for each associated two pairs of electrode structures, each of whose two inputs are the outputs from the associated pair of integrators; and an output summer, whose inputs are the outputs of the N+1 signal summers.

Claim 11

The surface wave device according to claim 8; the electrode structures are coded according to the members of a set of generalized complementary sequences, (cu), (dk), such that

Claim 12

The surface wave device according to claim 9, wherein the set of generalized complementary sequences is a set of Golay complementary sequences.