Patent GB-1331424-A (GB)
Title: Apparatus for producing an image of an object
IPC: H04N5/30
Filed: 1970-11-06
Abstract: 1331424 Correlation devices EMI Ltd 6 Nov 1970 [6 Aug 1969] 39290/69 Heading G1U [Also in Divisions G4 and H4] An image of an object is produced by sensing the amplitude distribution over an aperture of waves derived from the object, phase-weighting sensed amplitude values according to the respective sensing positions within the aperture, thereby effectively converting the distribution for spherical waves from the object into the distribution which would be sensed for plane waves, generating from the phase-weighted waves magnitudes each proportional to the amplitude of a wave from a single respective point of the object, and displaying image points each with a brightness corresponding to a respective one of the generated magnitudes. These magnitudes may be generated by Fourier transformation or, in the embodiment to be described, by correlation with reference phase functions. In the Fig.4 system for effectively determining the amplitude distribution of ultrasonic waves over 25 x 25 array of hydrophones 1001-1625 at two instants in quadrature (i.e. separated by one quarter of the wave period), gates 3001-3625 are opened in the order 3001, 3001, 3002, 3002 etc, by clock pulse pairs from timer 10 to pass pairs of quadrature amplitude samples to A-to-D converter 13. The time gap between the two resulting digital words W, W1 of each pair is closed up by gating the words one directly and the other through delay unit 15 to the parallel inputs of gates 101-125. The words are then entered into a circulating storage system of twenty-five delay lines or shift-registers 201-225, each line or register having a capacity to hold all the words from one hydrophone row of the array. The phase-weighting is applied to the words W, W<SP>1</SP> in the Fig.5 system, which forms the quadrature values U, U<SP>1</SP> given by U = W cos # + W<SP>1</SP> sin #, U<SP>1</SP> = W<SP>1</SP> cos # - W sin #, where # is a parabolic function of the position, within the array, of the respective hydrophone associated with a word pair W, W<SP>1</SP>. Delay 23 enables the two words of a pair to be brought into time coincidence. W is gated to analogue or digital multipliers 28, 29 and W<SP>1</SP> is gated to multipliers 30, 31. Functions cos # and sin # generated at 32 are fed respectively to multipliers 28, 30 and 29, 31. U is derived from summing the outputs of multipliers 28, 31 and U<SP>1</SP> from the difference of the outputs of multipliers 29, 30. In the Fig. 6 system the intensity value of a single image point to be displayed is found by computing the integral S, over the whole aperture, of the function U cos #-U<SP>1</SP> sin #, and the integral S1, over the whole aperture, of the function U<SP>1</SP> cos # + U sin #, where # is a phase function dependent on both the position of the image point and the position of a hydrophone within the aperture. It is shown that the required intensity is proportional, without ambiguity, to S<SP>2</SP> +S1<SP>2</SP>. The integration is repeated to determine the intensities for other image points. Multipliers 42-45 receive the inputs U, U<SP>1</SP> on lines 40, 41 and the inputs cos #, sin # on lines 47, 48. Units 54, 59 generate values of the co-ordinates respectively of image points and hydrophone position. The multiplier outputs are combined by adder 50 and subtractor 49, whose outputs are integrated at 51, 52. The integrator outputs are squared and added at 53 and the resulting signal intensity modulates the beam of a cathode ray tube display (e.g. of the storage type) whose deflection is controlled by co-ordinate generator 54.