Showing papers on "Acoustic interferometer published in 1964"

The coupled modes of acoustic waves and drifting carriers in piezoelectric crystals

Abstract: The amplification of acoustic waves in piezoelectric semiconductors is analyzed in terms of the normal modes of the uncoupled system. The characteristics of the growing wave are presented for a range of the crystal parameters in terms of the conduction frequency (σ/e) and the diffusion frequency (v2/D). Boundary conditions are worked out to show that an acoustic wave at the input to the amplifying section will couple into the growing wave without appreciable initial loss. The experimental results with CdS at 500 Mc confirm the general features of the theory and serve to point out two problems which must be overcome. The first is one of eoupling into the acoustic waves from an external source. Present methods are quite inefficient. The second is one of internal oscillations within the crystal which occur when the drift velocity exceeds the velocity of sound. If these problems can be solved, it should be possible to use this gain mechanism well into the microwave region.

Microwave acoustics

Abstract: During the last few years, generation and propagation of acoustic waves have been extended to frequencies high into the gigacycle region. This paper deals with microwave acoustics, with emphasis on effects and techniques utilized at cryogenic temperatures. The extremely short wavelengths require the use of single crystal propagation media, free from defect scattering, supercooled to reduce wave attenuation from phonon interactions. Interactions of acoustic phonons with other phonons, electrons or holes, and spin waves are possible, with interchanges of energy that can produce attenuation or amplification of acoustic waves. The fundamental characteristics of acoustic wave propagation in crystanine media are discussed, with a review of experimental techniques and results. Microwave acoustic waves in solids and transducers suited to generation and detection are discussed, and a basic analysis of plane wave piezoelectric coupling is presented.

Strain Amplitude of Mc/sec Ultrasonic Waves in Solids

Abstract: The strain amplitudes of 10 Mc/sec sound waves in solids were measured under conditions in which standing waves were set up, as well as under pulsed conditions. The methods used were (1) measuring the equivalent electrical resistance of the transducer, (2) measuring the heating produced by absorbing the sound waves, (3) diffraction of light from standing acoustic waves, and (4) the changes in a nuclear magnetic‐resonance‐absorption signal produced by the sound waves. All these methods were in substantial (±20%) agreement with one another. Measurements with different characteristics for the coupling between the transducer and sample showed the importance of this thin film. The highest strain amplitudes were obtained at frequencies slightly higher than the quartz‐transducer resonant frequency. Even higher strains could be obtained with coupling films approximately 14‐wavelength thick.

Mode conversion of ultrasonic waves at flat boundaries

Abstract: The energy partition between reflected and refracted plane ultrasonic waves at water-solid and solid-water boundaries is considered. Some general features are discussed and applications of the results to velocity measurements are pointed out. Results of calculations for a Plexiglas-water boundary show that the curves one obtains are quite dissimilar if one either considers or neglects the shear wave in the Plexiglas.

Broad‐Band Excitation of Microwave Ultrasonic Waves

Abstract: The conventional techniques for generation and detection of microwave acoustic waves employ resonant cavities and are thus unsuited to applications that require a broad bandwidth. Microwave structures, made from coaxial transmission line or from microstrip, that operate in the TEM mode have the advantage of being broad‐bandwidth devices, and the rf electric and magnetic fields in these structures may be used with both piezoelectric and magnetostrictive transducers to generate acoustic waves. The design and performance of microstrip structures are presented. The tranducer loss (defined as the sum of the losses incurred in the generation and detection of acoustic waves) was found to be 116±6 dB at frequencies between 300 and 1000 Mc/sec for a microstrip structure that generates transverse waves along the x axis in quartz. The dimensions of the quartz crystal were N = 0.100, Y = 0.050, and Z = 0.500 in. Measurements on other structures are discussed as well.