Patent GB-926850-A (GB)
IPC: G01S1/72
Abstract: 926,850. Locating sounds. G. M. VOGLIS, H. F. WILLIS, and J. BUCKINGHAM. May 9, 1957 [April 10, 1956], No. 10959/56. Class 40 (7). Apparatus for directional reception of sound propagated in a fluid and for periodic uniform and continuous deflection of the direction of maximum sensitivity of reception at a selected scanning frequency comprises a transducer immersed in the fluid and subdivided into elements, means for coherently modulating the outputs of each element and for processing their resultants so as to introduce between the outputs of any element and its adjacent element to one particular side effective and coherent phase shifts linearly varying with time but always the same for all adjacent pairs of elements at every instant of the modulation cycle, means for adding the processed modulation products to produce a single carrier modulated electrical signal of carrier frequency smaller, larger, or equal to the acoustic frequency and of carrier amplitude proportional to the magnitude of the sound appropriate to the deflection of the direction of maximum sensitivity at any instant, and means of determining (as by display on an oscillograph) from the phase of the scanning cycle at the instant of maximum carrier amplitude response, the direction or bearing of a transmitting or reflecting source of the received sound relative to the normal to the transducer face. In all the systems shown in the Figures, the transducer consists of N elements numbered from - n to +n (the centre element O would be omitted if N were even), and the output from each element is amplified in a pro-amplifier P.A. In Fig. 1, the output from each element, except the centre one, is split before being modulated and one part is phase shifted by #/2; the outputs of the modulators are fed to a common adder unit, and thence through a band-pass filter and amplifier to the display. In another system, Fig. 2 (not shown), the phase shifters P.S. and their associated modulators are omitted; the outputs of the modulators on the left of the axis are fed through an adder unit and a low-pass filter to a common adder where they are added to the outputs of the modulators to the right of the axis, which have been fed through a high-pass filter, and to the output of the centre element. The whole is then passed through a band-pass filter to the display. In Fig. 13 the half outputs of corresponding pairs of elements on either side of the centre are combined to form the sums and differences which are modulated and combined in two groups. The two groups are fed through units P.E.1 and P.E.2, which impart a relative phase change of # to the upper side bands of the group of signals on the left of the centre, and thence to the display. In a modification, Fig. 4 (not shown), the difference signals are modulated by sin #rwst instead of cos #rwst, the units P.E.1 and P.E.2 are omitted, and the outputs of the two groups are fed to a #/2 broad band phase shifter and adder. In a further modification, Fig. 3 (not shown), the difference signals are subjected to a #/2 phase shift before being modulated by sin #rwst, and all the signals are then fed to a common adder. Scanning at a frequency other than the sound frequency may be achieved by modulating the output of each transducer with cos wt, where w is any frequency, and then subjecting the modulated outputs to any of the processes described in Figs. 1-4 and 13, or by substituting modulating frequencies of cos (#+#rws)t or cos wt cos #rwst for cos #rwst. Figs. 7-9 (not shown). Modulation may be applied at two or more stages. In a two-stage system the transducer is divided into g 1  subtransducers of n 1  elements each, and each subtransducer is scanned at a frequency fs by any of the methods described above; since all the subtransducers have the same number of elements the modulating voltages are identical for all subtransducers. The output of each subtransducer is passed through a band-pass filter, and the outputs are then scanned at a frequency n 1 fs as though they were the outputs of a fictitious g 1  element transducer. With this two-stage system the scanning may be changed from scanning the whole sector to scanning 1/nth of the sector by arranging the modulating voltages to the first stage modulator so that each first stage subtransducer output is proportional to the vector sum of all the n 1  voltages induced in the elements; this may be done by substituting a direct current for modulating voltages of the type cos rwst and short circuiting the modulation terminals of all remaining modulators.