D. K. Winslow

VACUUM DEPOSITION OF AlN ACOUSTIC TRANSDUCERS

Thin‐film microwave acoustic transducers of piezoelectric aluminum nitride (AlN) have been vacuum deposited by two methods. Aluminum nitride was deposited on metallic film substrates at 300°–1200°C by evaporating aluminum in the presence of either nitrogen gas dissociated in an ac discharge or in the presence of ammonia gas. Longitudinal ultrasonic waves were generated in a sapphire rod with a one‐way‐tuned conversion loss of 10 dB at 1700 MHz.

ZINC‐OXIDE FILM MICROWAVE ACOUSTIC TRANSDUCERS

Thin‐film zinc‐oxide microwave acoustic transducers have been formed successfully by vacuum deposition techniques upon a cooled substrate (−50°C) by evaporation of zinc with an oxygen beam. The films are hexagonal preferentially oriented with c axis normal to the substrate. A device consisting of a ZnO film (1.9 μ) deposited on a metallic film on a sapphire delay line had a one‐way conversion loss of 6 dB at 1.6 GHz with a large bandwidth indicating that zinc‐oxide thin films deposited by this method make good ultrasonic transducers at frequencies above 1 GHz.

Measurement of Microwave Acoustic Attenuation in Sapphire and Rutile using Nickel‐Film Transducers

Initial investigations on the room‐temperature acoustic attenuation in sapphire and rutile at S band, which were reported earlier, showed the attenuation in both of these materials to be relatively low. These measurements have now been extended to other frequencies, and curves of attenuation are shown for rutile shear waves and sapphire longitudinal waves covering the frequency range from L band to X band, and for sapphire shear waves from L band to S band. The attenuation has a nearly linear variation with frequency at the lower frequencies, and increases monotonically as frequency increases. This behavior may be attributable to Rayleigh scattering from submicron scattering centers within the crystals. Nickel‐film magnetostrictive transducers, coupled to dielectric resonators, were used to generate the acoustic waves in the samples under study, and the acoustic attenuation was determined from echo measurements. Conversion efficiencies and certain other observed properties of nickel‐film transducers over ...

ACOUSTIC QUARTER‐WAVE PLATES AT MICROWAVE FREQUENCIES

The use of birefringent acoustic media in microwave—shear‐wave polarization transformers is described. Restrictions on the properties of the acoustic medium are discussed as well as the limitations imposed by the use of imperfect bonds between the transformer section and a delay medium. The principles are illustrated by application to a double‐ended variable delay line.

Pumping Effects Contributing to the Excitation of Phonon Instabilities in Ferromagnetic Insulators

A survey is made of mechanisms contributing to the excitation of phonon instabilities in ferromagnetic insulators. The distinction between the morphic and intrinsic dependence of elastic stiffness on the direction of magnetization is discussed, and conclusions are drawn about the relative importance of morphic and intrinsic pumping effects. Transverse and parallel magnetoelastic pumping effects are described, and a theory of transverse magnetoelastic pumping is developed for both cubic and uniaxial crystals. An estimate of the transverse magnetoelastic pump threshold for Zn2Y is given.

CONTROL OF ACOUSTIC SURFACE WAVES WITH PHOTOCONDUCTIVE CdS FILM

Optical patterns imaged on photoconductive CdS films have been used to generate, detect, attenuate, and reflect acoustic surface waves on a 100‐MHz LiNbO3 delay line. Optically induced acoustic attenuation on the order of 1 dB/wavelength has been measured. A 180° reflection coefficient of approximately −7 dB has been observed from an optical grating, and 90° (right angle) reflect on has also been observed with a different optical grating. A transducer using an optical pattern (rather than evaporated interdigital electrodes) has been constructed with a one‐way conversion efficiency of −20 dB.

Traveling-Wave Frequency Doubling in Ferrites

A perturbation analysis has been made of frequency doubling in a ferrite-loaded rectangular waveguide. These calculations give quantitative predictions for second-harmonic power output as a function of various parameters. The values and ranges chosen for these various parameters are the same as used in experiments which were performed to check the theory. Good correlation has been obtained between experimental results and second-order perturbation theory.

Parametric Excitation of Acoustic Wave Instabilities in Ferromagnets

Experimental measurements of saturation effects in single‐crystal Zn2Y, with the easy plane lying in the plane of the disk, have been observed experimentally at 1.3 G/sec—below the bottom of the spin‐wave manifold. Thresholds observed are comparable with theoretical predictions based upon the assumption of the magnetoelastic pumping effect as the dominant mechanism. In these experiments the order of the first resonant spin‐wave instability permitted has been varied from the second to the fifth by adjusting the position of the spin‐wave manifold relative to the pump frequency.

Current Distribution in Modulated Magnetically Focused Electron Beams

Detailed measurements have been made of the dc and rf current distribution in a modulated, magnetically focused electron beam having normalized parameters in the range of values appropriate for practical medium‐power and high‐power klystrons. The ratio of the total rf current to the total dc current in the beam as a function of drift distance was determined experimentally under Brillouin‐flow conditions for selected values of α (the ratio of the rf voltage at the input gap to the dc beam voltage). These experimental values are compared with the results predicted theoretically. Similar experimental results are presented for higher focusing fields. Detailed radial distributions of the dc and rf current were experimentally determined by using an iris (a plate with a small hole) to allow only a small portion of the beam to be selected at any radial position. These measurements were made at various values of α and drift distance. The results for small values of α show, as predicted by theoretical consideration...