GB1412264A - Continuously variable acoustic surface wave delay lines - Google Patents

Abstract

1412264 Delay lines ETAT FRANCAIS DIRECTION DES RECHERCHES ET MOYENS D'ESSAIS 10 Nov 1972 [10 Nov 1971 31 Oct 1972] 52107/72 Heading H3U A continuously variable ultrasonic surface wave delay line comprises launching transducer 2 mounted on quartz piezoelectric substrate 1, the receiving transducer comprising a grid 3 on the face of the substrate, electrostatically coupled to metal block electrode 4 in the form of a plate of length L less than or equal to the input transducer length, or of polygonal or cylindrical shape for output signal profiling, and movable longitudinally of, and spaced from the grid, to determine the delay time. Electrode 4 may have constant spacing from the grid, Fig. 2 (not shown), or the spacing may decrease as delay time increases, Fig. 3 (not shown) such that the gain is independent of delay time. A base electrode 5 is optionally provided to which one of the electrodes of transducer 2 may be connected, as may the electrode 4. The output signal is taken between electrode 4 and grid 3. If electrode 5 is absent, grid 3 is earthed. The roles of input, resp. output, transducers may be interchanged. Mechanical construction, and input/output couplings, Fig. 4.-A brass box 6, with a lid (not shown) has fixed in its base, by cellulose varnish, the piezoelectric substrate 11. The input transducer, shielded by brass screen 9 and partition 7 is connected to the input terminal 20 via circuit 8 containing a fixed inductance in series with a variable capacitance shunting the transducer input capacitance. Grooves in the box sides support nylon sliding frame 12 to which the movable electrode block 13 is fixed an adjustable distance above the substrate, see Fig. 6 (not shown). Sliding frame 12 supports output amplifier 14, flexible coax. 16, 17 connecting the latter to output terminals 18, 19. Leadscrew and nut 21, 23, control movement of frame 12, the leadscrew being controlled via a milled vernier head (not shown). Pointer (24, Fig. 5) on the nut is viewed through a slot in the lid and moves in front of a scale showing the delay. The electrodes are deposited by A1 photoengraving, using reduction from a drawing. Operating frequency, delay characteristic, passband, input and output impedance, and gain data are disclosed, as are the dimensions and accuracy. The passband may be increased by reducing the number of input transducer teeth. Teeth spacings may differ from those shown.