Patent GB-1221623-A (GB)
Title: Continuously variable electroacoustic delay device
IPC: H03H9/38
Filed: 1969-10-13
Abstract: 1,221,623. Acoustic delay lines. SANDERS ASSOCIATES Inc. 13 Oct., 1969 [14 Oct., 1968], No. 50202/69. Heading H3U. A delay line which may be continuously variable comprises, Fig. 1, a conventional electron gun 10 having a cathode 16, grid 18 and anode 20. A D.C. power supply 22 is connected between 16, 20 and the input signal source 24 to be delayed is connected between 16, 18 so that the beam 26 of charged particles is amplitude modulated by the signal source. An electrostatic beam deflection system 12 has lateral deflection plates 32, 34 connected to a power supply 38 and longitudinal deflection plates 28, 30 connected to a power supply 36 for directing the beam on to an electroacoustic transducer 15 constituting the delay element. At the spot 52 where the beam 26 strikes the transducer 15 an electrical charge is built up and produces an electric field. Under the influence of the field the transducer 15 undergoes acoustic resonance resulting in an acoustic wave travelling away from the spot 52 in both directions along the longitudinal axis of the transducer, this wave being accompanied by an electric charge generated by the wave on the transducer surface. The electric charge is removed by leads 54, 56 connected to terminal strips 42, 44 and constitutes two delayed output signals. The two delays depend on the distances between the spot 52 and the respective strips 42, 44 and these may be varied by changing the voltage of supply 36 to move the spot along the transducer 15. The entire apparatus is housed within an evacuated glass enevlope 50. In a modification (not shown) an ion source replaces the electron gun 10 and the envelope 50 is gas-filled. The transducer 15 may be piezoelectric, pyroelectric, thermoelastic, piezomagnetic, magnetoelastic, thermomagnetic, electrostatic or ferroelectric. Examples of suitable materials are: quartz cadmium sulphide, lead zirconate, barium titanate, sodium potassium niobate, yttriumiron-garnet. A recirculating delay line may be formed by feeding an output signal back to the source 24 as indicated by the broken line 43. In a modification (Fig. 2, not shown) the transducer 15 has a thin layer of high secondary emission material provided on the face on which the spot 52 impinges so as to intensify the signal. Suitable materials for the layer are potassium chloride, barium fluoride, magnesium oxide, aluminium oxide. The transducer 15 may be in the form of a spiral (Fig. 3, not shown) to produce a long delay. In another modification (Fig. 4, not shown) the input signal source 24 is connected across the lateral deflection plates 32, 34 and a D.C. source is connected between the cathode 16 and grid 18. In this modification the spot 52 is laterally deflected off the transducer 15 except when there is an input signal at the source 24. In another embodiment (Fig. 5, not shown) three transducers are arranged side-by-side and the spot 52 impinges on each one. The three transducers are formed of different electroacoustic materials whereby different delay times are obtained for the output signals from the respective transducers. In another modification (Fig. 6, not shown) two separate signal input sources 24 are provided together with respective deflection systems 12. The two beams 26 of charged particles are caused to impinge on the transducer 15 at the same spot whereby the two inputs are mixed. In a final embodiment, Fig. 7, employing a magnetic deflection system 108 the beam 26 is moved through a distance X to a position 26a whereby the electric charge associated with the acoustic wave when it arrives at the spot on the transducer 15, corresponding to beam 26a, causes repulsion of the beam back along path 26b. The return beam 26b is incident upon a series of particle multiplying dynodes 102a . . . 102e and then upon a particle detector anode 104, the delayed output signal being taken from leads 106.