Patent GB-1023549-A (GB)
Title: Apparatus comprising piezo-electric elements and circuits used in conjunction therewith
Inventor: BRADFIELD GEOFFREY
IPC: G10K11/34
Filed: 1962-10-26
Abstract: 1,023,549. Ultrasonic testing devices; pulse and gating circuits. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Jan. 27, 1964 [Oct. 26, 1962], No. 40635/62. Headings H3P, H3T and H4D. Each element or each group of elements of an array of piezo-electric transducers is connected to one end of a balanced winding on a transformer, there being a transformer for each element or group thereof, the other end of the balanced winding is connected to a balancing network, and the balance point of the winding is connected to means for applying an input pulse to the transformers in a predetermined time sequence. In an embodiment transducers 11 to 18 of barium titanate or lead zirconate are connected to corresponding transformers T11 to T18, the balancing networks are capacitors BC11 to BC18, which may be shunted by resistors, and a pulse is supplied to the transformers in sequence by means of a delay line IDL and thyratrons D11 to D18. Each thyratron anode circuit includes a tuned circuit, and a potentiometer in the H.T. feed affords adjustment for equality of amplitude of the wave from each element of the transducer array into piece 19 under test. The delay line sections may be adjustable and ganged. Switching arrangements may be provided to permit a trigger pulse to be injected from either end of the line also to permit alteration of the number of inductance and capacitance sections between tapping points TP. As an alternative to the delay line the bias of each thyratron may be pre-set so that triggering can be effected by a triangular waveform. Thyratrons may be replaced by equivalent PNPN semi-conductor devices. The echoes received by the array elements are fed via the transformers T to tapping points on delay line ODL of which the inductance elements may be ganged to a single control and similarly for the capacitative elements. Switch S permits the output to be taken from either end of line ODL. Alternatively a scheme may be employed wherein signals are changed in frequency before being applied to the tappings of a delay line the delay of which varies with frequency (J. Brit. I.R.E., 1959, 19, p. 681 et seq.). The embodiment may be utilized for varying the direction of the ultrasonic inspection investigation, e.g. transmission being arranged to give two alternative directions and the reception, five directions. The transducer array may be a single crystal grooved as in Specification 703,508, if the object surface is plane. By varying the delay across the array a plane wave front is focused, a curved wave front rendered plane, or a focused wave front defocused. By varying the bias on the corresponding thyratron automatic compensation for displacement of an array element by a local irregularity in the surface of the test object can be afforded. Side-lobes in the ultrasonic beam may be reduced by grading the excitation across the array by means of potentiometers P11 . . . P18. The invention may be applied to a matrix or mosaic of transducers so as to deflect the beam in two orthogonal directions, the receiving and transmitting systems affording beam deflections in orthogonal planes, Fig. 2 (not shown). The transducers may be provided with damping backings as described in Specification 772,083; and they may be constructed to be operable over a range of frequencies as described in Specification 841,512.