H. J. Shaw

AMPLIFICATION OF ACOUSTIC SURFACE WAVES WITH ADJACENT SEMICONDUCTOR AND PIEZOELECTRIC CRYSTALS

Strong interaction between the wave on the surface of a piezoelectric crystal and the wave on the drifting carriers in a nearby semiconductor is reported. Amplification can result and two‐port net terminal gain of 7 dB at 108 MHz with a delay of 9 μsec has been observed.

HIGH‐PERFORMANCE LITHIUM NIOBATE ACOUSTIC SURFACE WAVE TRANSDUCERS AND DELAY LINES

Radiation resistance measurements have been made on 20 electrode pair interdigital transducers deposited on poled crystals of lithium niobate, for a variety of cuts and propagation directions, with the objective of determining optimum geometries for the efficient wideband generation of acoustic Rayleigh waves. Using Y cut, Z axis propagating lithium niobate and five‐electrode pair transducers a 100‐MHz delay line has been constructed with an insertion loss of 11.5 dB at a delay of 8.9 μsec, and a −3‐dB bandwidth of 24 MHz.

Continuous Deflection of Laser Beams

An optical beam has been continuously deflected through an angle of 4° by tuning an acoustic wave in a birefringent crystal of sapphire from 1.28 to 1.83 Gc. The method is based on the change in polarization of the deflected light as compared to the incident light. The system should be capable of deflecting an optical beam through 1000 spot diameters.

PULSE COMPRESSION BY BRAGG DIFFRACTION OF LIGHT WITH MICROWAVE SOUND

Pulse compression of a 240‐nsec rf pulse, swept linearly over 75 MHz about 1400 MHz, has been accomplished. The method is dependent on self‐focusing associated with Bragg diffraction of light by chirped shears waves in optically anisotropic sapphire. Realization of time bandwidth products exceeding 1000, with built‐in side lobe suppression, are predicted.

ACOUSTIC SURFACE WAVE COUPLING ACROSS AN AIR GAP

Transfer of acoustic surface waves between two noncontacting surfaces by means of passive, co‐directional piezoelectric coupling is achieved in LiNbO3. Minimum coupling loss is less than 3 dB. When the surfaces are maintained parallel, periodic variation of insertion loss with coupling length is observed. Measurements are in close agreement with predictions using coupled mode theory. A 100‐MHz delay line with a mechanically variable, nondispersive differential delay of 6.1 μsec and a total insertion loss less than 17 dB which utilizes this coupling mechanism is reported.

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.

EFFICIENT MICROWAVE SHEAR‐WAVE GENERATION BY MODE CONVERSION

It is found that efficient conversion from longitudinal acoustic waves to shear waves is possible in YAG by surface conversion at an incline surface, with both the input and output waves traveling along crystal axes. Using this process, existing efficient longitudinal‐wave transducers are applicable to shear‐wave generation. Laser beam probe measurements indicate that the surface conversion loss is of the order of 0.1 dB at 1461 MHz, and that the shear wave column has approximately the expected cross‐sectional shape.

Saturation Effects in Ferrimagnetic Resonance

Saturation curves of susceptibility as a function of rf magnetic field have been measured for a number of samples of polycrystalline yttrium iron garnet of varying linewidth. The curves exhibit a region of susceptibility linear in 1/hrf at high rf powers. The region of the initial decline in susceptibility is linear in hrf2, which is predicted both by a small signal relation derived from Callens ferromagnetic dynamical equation and by a calculation of Schlomann which includes inhomogeneity interactions.A new method of determining the critical field for spinwave build-up is discussed. This method takes account of the fact that the initial decline in susceptibility is not simply due to the Suhl mechanism for saturation in ferrites.

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.