Patent GB-674235-A (GB)
Title: Improvements in or relating to apparatus for examining the interiors of bodies by means of ultrasonic waves
IPC: G01N29/06
Filed: 1949-04-06
Abstract: 674,235. Supersonic inspection devices. BABCOCK & WILCOX, Ltd., and CARSON, H. L. April 6, 1950. [April 6, 1949] No. 9374/49. Class 118 (ii). Relates to methods of locating flaws in an extended body, e.g. a plate, by observing the intensity of supersonic waves. transmitted through the body or reflected from the interior thereof. According to the present invention the waves are transmitted into the body sequentially from a plurality of spaced points on the surface.forming a two-dimensional array and the corresponding transmitted or reflected waves are applied to modulate the intensity of a cathode-ray tube whose beam is scanned in discrete steps in correspondence with the transmission. As shown in Fig. 1, the transmitter transducer comprises a piezo-electric crystal plate 4 with a continuous electrode 5 on the side in contact with the work piece 2, the other electrode comprising a two-dimensional rectangular array of conductive elements 6, Fig. 2 (not shown), the elements being connected to the cathodes of respective thyratrons 9 whose anodes are connected in parallel to electrode 5 and a tuned circuit 10 being connected between the anode and cathode of each thyratron. The thyratrons constitute a ring circuit which is triggered by a pulse generator and so that the thyratrons are fired sequentially thereby exciting the circuits 10 and the corresponding elements of the crystal in the same sequence. The receiver transducer comprises a piezo-electric plate 15 with continuous electrodes 16 and 17 coupled via an amplifier and rectifier 18 to the grid of a cathode-ray tube 19 whose beam is scanned in correspondence with the sequential excitation of the transmitter elements by means of line and frame thyratron counter chains 20 and 21 coupled to the pulse generator 8 via an amplifier 23 and an adjustable mercury delay line 22 provided to compensate for the propagation time through plate 2. The size of the cathoderay spot is adjusted so that adjacent spot areas just touch, Fig. 3 (not shown), the presence of a flaw in the plate 2 being indicated by a reduction in the intensity of one or more spots. Fig. 4 (not shown) illustrates a reflection system in which the transmitting and receiving transducers are adjacently. mounted on wedges of similar material to the plate under test, the duration of the transmitted pulses is short compared with the recurrence period and the receiver. amplifier is normally blocked, being gated on by pulses from the delay means corresponding to delay 22 in Fig. 1. If the delay is adjusted to correspond to the propagation time of pulses reflected from the back surface of the plate, all the spot areas on the cathode ray screen will be illuminated uni- , formly in the absence of flaws and the presence of a flaw will be indicated by a local reduction in illumination.. Alternatively, the delay may be progressively reduced so that illumination of the screen is produced only by flaws located at a depth corresponding to the delay. Good contact between the crystals and work piece may be obtained by a film of transformer oil or tin amalgam.