GB1219530A - Improvements in ultrasonic delay lines and methods of and apparatus for manufacturing the same - Google Patents

Abstract

1,219,530. Electromechanical delay lines. THOMSON-CSF. 17 Nov., 1969 [20 Nov., 1968], No. 56232/69. Heading H3U. A method of manufacturing a plurality of strip delay lines comprises the steps of: forming a stack of strips of a material through which ultrasonic waves may be propagated; grinding surfaces of the stack to form input and surfaces on the strips; securing plated pieces of piezoelectric material to the ground surfaces of the stack; and separating the delay lines from each other by forming slots in the said pieces at positions situated between the strips. One embodiment of an individual delay line, Figs. 1a 1b, comprises a steel-nickel alloy strip 1 having a thickness less than one half of the wavelength of the signal to be propagated, the ends of the strip having piezo-electric bars 2 soldered thereto, the length h of the bars being less than the width I of the strip. The bars 2, polarized to operate in the shear mode, are plated with an electrode along the long edge in contact with the end of the strip and also along the opposite outward facing edge, leads 12, 13 making connection with the electrodes. The long edges of the strip 1 have absorptive tapes 3 applied thereto. In another embodiment, Fig. 2, the strip 8 has a dihedral edge supporting transducers 9 and the opposite edge 11 acts as a reflector, the other edges of the strip having absorptive tapes 10. In the manufacturing method, Fig. 4, a plurality of steel strips 21 separated by spacers 22 are temporarily clamped together to form a stack and those faces of the stack to which the piezo-electric plates 26 are to be soldered, are trimmed by grinding. Fig. 4 shows a single plate 26 having metallized opposite faces 25, 27, the face 27 being secured by a solder joint 28 to a ground face of the stack. The face 25 has an electrical connection in the form of a foil 24 and another foil 23 is soldered to the strips 21. The individual delay lines are produced by a frame saw having cutter wires 29 which saw into the spaces formed by the spacers 22. In a modification (Fig. 5, not shown), the cutter wires 29 are replaced by diamond cutter disc. The steel strips are dimensioned to have a delay time slightly less than the desired value, the final value being achieved by mechanically deforming the strips over a localized area by a hammering operation (Fig. 6, not shown), by a rolling operation (Fig. 7, not shown) or by a stretching operation (Fig. 8, not shown). The delay line strip 59 may be subsequently bent into the shapes shown in Figs. 9, 10.