Patent GB-1316906-A (GB)
Title: Holographic system for forming images of both stationary and moving objects
IPC: G01S17/87
Filed: 1971-04-19
Abstract: 1316906 Acoustic and microwave holography BENDIX CORP 19 April 1971 [6 March 1970] 22858/71 Heading H4D In a method of acoustic or microwave holography capable of providing representations of moving targets in which the targets to be represented are irradiated with coherent oscillatory radiation derived from a master oscillator 35 and emitted from a transmitter 28, reflected waves are received by a two-dimensional array 16 of transducers 18 and the electrical output signals from each transducer are passed through respective individual channels to corresponding locations in a display apparatus 22 to form a holographic representation of the scene (as shown the channels from each individual column of transducers are formed into respective groups 24), the received electric signals in each channel are heterodyned with short bursts of oscillation derived from the oscillator 35, the lengths of the bursts being such that no significant phase change (i.e. no change greater than # radious) occurs during the period of a burst in any heterodyne signal corresponding to a moving target whose velocity is less than a predetermined limiting value, a signal corresponding to the integrated value of the heterodyne signal is stored and the stored signals are passed in turn to the display apparatus to which synchronized scanning waveforms are also applied so that the integrated signals are reproduced on the display apparatus in positions having a one-to-one correspondence with the transducers corresponding thereto. The holographic pattern is formed on a surface in the display device which may comprise a birefringent layer as disclosed in Specification 1,316,905 and illumination of this surface by light from a laser results in the production of an image visible to an observer. Excitation of either manually-operated switch 34 (to initiate operation of the apparatus) or of electrically operated switch 32 causes monostable circuits 30, 40 to transfer for respective adjustable periods to the unstable state. The pulse output from circuit 30 is applied to AND- gate 36 together with the output from oscillator 35 to cause a burst of radiation of predetermined length to be emitted from transmitter 28, the length of the burst determining the depth of the scene rendered visible to an observer by the display apparatus 22. The trailing edge of the pulse output from circuit 40 triggers monostable circuit 42 to deliver a short pulse which effectively determines the period during which reflected radiation received by the array 16 is inspected; thus the length of the pulse from circuit 40 determines the range of the scene of predetermined depth rendered visible to an observer. The short pulse from circuit 42 is applied to AND-gate 44 together with the output from oscillator 35 and the output therefrom to a mixing-gate circuit in each channel of the groups 24 of channels to produce in each channel the result of multiplicatively mixing the output of oscillator 35 with the received output from the corresponding transducer 18 over the period of time during which the monostable circuit 42 is in its unstable state. These signals are applied to respective integrators and store each in its own channel. The trailing edge of the pulse from circuit 42 triggers bi-stable circuit 52 to open gate 56 to permit the passage of timing oscillations from oscillator 58 to a converter circuit 60 which applies read-pulses simultaneously to each of the groups of channels 24 and in sequence to the channels of each group whereby in each group X-gates are opened in turn to allow the stored integrated signal to pass to respective Y-gates 68. Initially the first Y-gate is open so that all the stored signals corresponding to the first column of the array 18 are passed to the display apparatus 22. The production of a read-pulse on the final output line of converter 60 results in the application of a pulse to converter 66 which operates to open the second Y-gate and close the first whereupon the signals stored in the second group of channels are sampled in turn and passed to the display apparatus. This continues until the signals stored in all the channels have been transferred to the display apparatus whereupon pulses from the converter 60 and 66 are applied simultaneously to AND- gate 71 which delivers an output on line 72 to discharge all the signals stored in the channels, an output on line 54 to reset the bi-stable circuit 52 and an output on line 76 to re-excite the switch 32 and initiate a subsequent cycle of operation. The X-read and Y-read pulses from converters 60, 66 are applied to respective converters 64, 70 which produce respective X-scan and Y-scan voltages in correspondence thereto. These are applied to the display apparatus 22 so that each element of the holographic pattern is produced at its correct position on the receiving surface in the display device.