Patent GB-1159309-A (GB)
Title: Improvements in or relating to Ultrasonic Delay Devices
Inventor: LEWIS MEIRION FRANCIS
IPC: H03H9/125
Filed: 1967-05-05
Abstract: 1,159,309. Delay device. GENERAL ELECTRIC & ENGLISH ELECTRIC COMPANIES Ltd. May 6, 1968 [May 5, 1967], No.20943/67. Heading G1A. [Also in Division H3] A delay device includes a single crystal in which the ultrasonic signal is delayed, this crystal being of cubic structure and of a non- metal having parameters such that the quantity 1À8 Î 10<SP>10</SP> K/(d#<SP>5</SP>V<SP>5</SP>/ 3 ) is less than unity, where (K) is its thermal conductivity in ergs per second per centimetre per degree Kelvin, (d) is its density in grams per cubic centimetre, # is its Debye temperature in degrees Kelvin, and (V) is its average volume per atom in cubic Angstrom units. Suitable materials for the crystal are magnesium aluminate spinel, zinc aluminate spinel, yttrium iron garnet, magnesium oxide and diamond. The device is intended for delaying very high frequency signals in the range 1 to 30 Gc/s. In the embodiment shown in Figs. 1, 2 a cylindrical single crystal 1 of magnesium aluminate spinel is cut so that its geometrical axis extends either in a <100> or in a <110> direction and has plane parallel end-faces 2, 3 on which are deposited thin-film magnetostrictive nickel transducers 4, 5. The crystal ends extend into cavity resonators 7, 9 having flexible adjustable cover plates 24, 25 for tuning. Passages 15, 18 communicate, respectively, with input and output waveguides 14, 17. A horseshoe magnet 23 sets up a field of the order of 5000 Oersteds in the direction of the geometrical axis of the crystal 1. In operation, assuming an input A of 9 Gc/s, the 9 Gc/s fluctuations of the magnetic-field vector of the net electromagnetic-field energy in cavity 7 interact with the transducer 4 and induce ultrasonic waves in the crystal 1, these waves being received by the transducer 5 which produces a 9 Gc/s output signal B delayed by about 1À5 x 10<SP>-6</SP> secs. In a modification Fig.3 (not shown) the two cavity resonators 7, 9 are arranged back-to-back and the crystal extends through apertures in the rear walls of the cavities. In another modification Figs. 4, 5 (not shown) there is only a single cavity resonator and this is connected by a single passage to the input and output waveguides. Only that end of the crystal which extends into the cavity is provided with a transducer which serves for both input and output, the other end of the crystal acting as a reflector. Instead of nickel, thinfilm magnetostrictive tranducers of iron or cobalt may be employed; alternatively, Piezoelectric transducers comprising one or more films of cadmium sulphide may be used. As a further alternative, spin-wave transducers of yttrium iron garnet may be used. In other modifications (not shown), the waveguides are replaced by coaxial cables; also, the crystal 1 may have the shape of a cuboid to form a folded-path delay line. In another modification (not shown) the output transducer 5 is omitted and instead a laser introduces into the crystal 1 a beam of coherent light of frequency F. The ultrasonic signal of frequency g acts as a optical diffraction grating and provides output light of frequencies F and FŒg). The light of one of the frequencies (FŒg) is supplied to an optical mixer together with light of frequency F from the laser so as to generate an output electromagnetic signal of frequency g which is fed into the waveguide. The delay time may be varied by altering the position at which the laser beam is incident upon the crystal.