Patent GB-1372657-A (GB)
Title: Echo-sounder
IPC: G01S7/62
Filed: 1973-04-30
Abstract: 1372657 Echo-sounding COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT-ALCATEL 30 April 1973 [28 April 1972] 20521/73 Heading H4D In apparatus for providing a visual representation of an object, a transmitter irradiates the. object, an array of detectors receives reflected radiation and provides signals representing a complex function of the co-ordinates of the detectors, this function undergoes Fourier transformation into a function which provides a representation of the object. A trigger 14 (manual or automatic) causes transmitter 4 to radiate ultrasonic energy which is reflected from object 2 to an array 6 of crystal detectors D 1 - D 1600 . The detectors are arranged at certain intersections of rows and columns in the array according to a pseudo-random manner. This ensures the optimum performance to number of detectors ratio. Each detector output is amplified, mixed with the local oscillator 8 output and fed to a sampling device 10, divided into two identical sections G 1 -G 16  and E 1 -E 16 . The array 6 is divided into sixteen sectors containing 100 detectors centred on the centre P 0  and each section E n  or G n  corresponds to one sector. In each half of the sampling device, each sector section has a switch C n  (or Q n ) which has one hundred inputs and a single output, a digital encoder K n  (or L n ) and an addresser T n  (or U n ) with one input and one hundred outputs. A clock H (or J) controls the switching of the switch and addresser such that the output of the detector D n  is digitally encoded and fed through to a corresponding part V n  (or W n ) of the memory in the fast Fourier transform device TF. The delay between switching from one detector to the next is made proportional to the square of the detector distance from the array centre P 0  and inversely proportional to the object range. This allows the spherical nature of the incident wave to be allowed for. The pulse from trigger 14 is also supplied to control 16 which produces at terminal 18 a pulse delayed by the transit time to the object 2. This pulse starts the operation of clock H and after a delay 22 equal to one quater of a wavelength of the frequency of the mixer outputs, starts clock J. Since each detector output is fed to both halves of sampler 10, the corresponding parts V n , W n  of the Fourier transformer TF contain samples separated by the quarter wavelength, which form a complex signal, W n  being the real part and V n  the imaginary part. Control 16 further provides a signal at terminal 24 indicating the delay produced at terminal 18 which is set by knob 20. This signal is used to regulate the equal frequencies of clocks H, J so as to perform the sampling in a short time compared to the transit time. The content of the memory in the Fourier transformer TF repesents a complex signal which is a function of the detector co-ordinates. After the Fourier transform is completed, the outputs of the transformer are passed to device CM which provides an output representing the modulus of the complex signal. These output signals are supplied to display 12 which shows a two-dimensional representation of the object 2.