GB941573A - Improvements in flaw detection and like systems using pulsed sonic or ultrasonic waves - Google Patents

Abstract

941,573. Sonic and ultrasonic pulse-echo systems. KELVIN & HUGHES Ltd. Nov. 7, 1960 [Nov. 6, 1959], No. 37750/59. Heading H4D. A flaw detection, underwater echo ranging or like system utilizing pulsed sonic or ultrasonic waves comprises a receiving transducer divided actually or effectively into a plurality of parts in predetermined positions with respect to each other and connected to a receiver through such phase shifting or time delay means as delay signals received by the transducer parts by progressively different amounts and thereby cause the transducer to be focused to receive energy from a predetermined region (the focus), and means responsive to the transmission of pulsed energy from an associated transmitter for varying the delays produced by the phase shifting or time delay means in such a manner as to cause the focus to move away from the transducer through a predetermined range following each pulse transmission, and during such movement to traverse a plurality of points at times at which energy reflected from the points would be received at the receiving transducer. The embodiments relates to an ultrasonic flawdetecting system in which a transmitting transducer 11 is fed by a transmitter 12 driven by a pulse generator 13 generating pulses of predetermined repetition frequency. Receiving transducer portions 14a ... 14e, shown in plan view in Fig. 2 and of the kind described in Specification 820,165, are connected to individual modulators 15, the outputs of which are of frequencies dependent on the instants of reception of echo waves at respective transducer portions; the modulator outputs are fed to different tappings on a frequencydependent delay line 16 which combines the signals after phase-shifting them by predetermined different amounts. It is demonstrated Fig. 3 that, if the instantaneous focus 0 is at a range r normal to the line EG representing a transducer with coplanar concentric rings, the phase delay of the signals at ring F as compared with those at ring B at distance a is substantially equal to (# a<SP>2</SP>/#)/r, where # is the wavelength of the ultrasonic waves. The modulatordelay line combination is such that the phase shifts produced are directly proportional to the frequency f of the signals applied; range r of the focus is then proportional to f<SP>-1</SP>. Modulators 15 vary the frequency of the signals fed therethrough continuously and cyclically through a predetermined range of values under the control of a sweep waveform from generator 17 driven by pulse generator 13. The construction of the delay line and modulators may be as described in the article " Electronic Sector Scanning," Journal of the British Institute of Radio Engineers, Vol. 18, No. 8, August, 1958. The sweep control waveform is so arranged that the focus moves away from transducer 14 following each pulse transmission and arrives at points in its path at times at which pulses reflected at the points would be received by the transducer. The combined signals are applied to the Y-plates of a cathode-ray oscilloscope (C.R.O.) 19, to the X-plates of which is applied the output of time base generator 20 controlled by pulse generator 13. In a modification the receiving transducer sections are connected through individual buffer amplifiers to tappings on each of a plurality of delay lines corresponding to different focal points and the delay line outputs are rapidly scanned by an electronic switch controlled by the generator 17, Fig. 4 (not shown). In a further modification a frequency-swept oscillator is connected to a delay line the tappings on which are each connected to a double-balanced modulator circuit arrangement fed also from a corresponding part of the receiving transducer, and the modulator outputs are fed to an additive mixer, Fig. 5 (not shown). The transmitting transducer may be focused at the most distant range to compensate for the decline of echo signals with increasing range. Common or coaxial transmitting and receiving transducers may be used.