Elastic wave generator and amplifier

摘要

1,002,280. Electromechanical delay lines and amplifiers. RAYTHEON CO. March 27, 1962 [Sept. 1, 1961], No. 11766/62. Heading H3U. A delay line for use in the kilo-megacycle range makes use of a body of microwave gyromagnetic material in which are produced resonant magnetic spin modes of oscillation, these being coupled to longitudinal or shear-mode elastic waves in the body. As shown (Fig. 1), a microwave field h is excited in a rectangular cavity 15 coupled to an input waveguide by an iris 14. Situated opposite the iris is a disc 16 of yttrium iron garnet subject to a biasing field H produced by an electromagnet 29. The so-called " spin-modes " utilized in the invention are associated with the non-linear saturation effects obtained during ferromagnetic resonance and are to be distinguished from the uniform spin precession mode. The wave member (or inverse wavelength) of such modes is given by Dk2 sp = He - H, where D is a constant, k sp is the wave member and He is a limiting value of H for the spin modes and corresponds to the value of biasing field necessary for ferromagnetic resonance. The frequency of the spin mode generated depends upon the frequency of the microwave field and, under the conditions shown, is one half of the latter. It is stated in the Specification that coupling takes place between the spin waves and elastic waves in the body when the frequency and wave member of the two waves are substantially equal. Since the wave member of the spin wave depends upon the biasing field, this may be adjusted until coupling takes place and a magneto elastic waves are generated. The waves are substantially independent of the dimensions of the body 16. They give rise to shear or longitudinal mechanical waves in a quartz rod 19 which extends into a re-entrant cavity 22 where microwave oscillations are generated piezoelectrically. The quartz rod (which acts as a delay line) is supported in a tube 21 of PTFE which also surrounds the YIG disc 16. The disc and the rod are welded together with indium. In a modification described as an amplifier, two quartz rods respectively providing input and output mechanical-wave transducers are used. Both are coupled to a YIG disc situated in a microwave cavity. It is stated that, in all cases, the apparatus may be cooled by a liquid gas in order to reduce attenuation.