Acoustic interferometer

About: Acoustic interferometer is a research topic. Over the lifetime, 1493 publications have been published within this topic receiving 19355 citations.

Generation and detection of acoustic waves in metals by means of electromagnetic radiation

Abstract: A macroscopic theory is presented to explain the electromagnetic generation of acoustic waves in a metal in the presence of a steady magnetic field, and to account for the effect of these acoustic waves on the surface impedance. The theory is valid for the limiting case where the skin depth is much smaller than the wavelength of sound. In particular, the size and shape of the surface impedance singularities at frequencies corresponding to the formation of standing acoustic waves in a metal plate are calculated. Absolute measurements of the surface resistance and reactance of gallium single crystals are reported which are in quantitative agreement with the predictions of the theory.

Laser Generation of Convergent Acoustic Waves and Applications to Materials Evaluation

Abstract: A converging-wave technique for laser generation and detection of focused acoustic waves is described together with a number of applications to the nondestructive testing and characterization of industrial materials. An annular-shaped wave is produced by irradiating the inspected material with a laser beam focused through a suitable combination of spherical and conical lenses. The ultrasonic pulse reaches a relatively high amplitude in the center of convergence, where it is probed by a noncontact interferometric optical sensor. Applications to the ultrasonic characterization of ceramic materials, coating thickness evaluation, detection of delaminations in layered materials as well as crack inspection are described.

The Fabry-Perot Interferometer at Millimetre Wavelengths

Abstract: The design and operation of an interferometer of the Fabry-Perot type at wavelengths around 8 mm is discussed. The reflectors have been made using multiple quarter wavelength sheets of dielectric, and extremely sharp fringes have been obtained giving selectivity or Q factors exceeding 60 000. The effects of diffraction on the interferometer are discussed and wavelength measurements made at various positions. The frequency of the millimetre wave source has been stabilized to a high degree and the wavelength measurements at wider reflector spacings shown to agree with a substandard cavity wavemeter within the accuracy attempted of a few parts in 105. Errors in the measured wavelengths at other positions of the interferometer do not exceed a few parts in 104, the measured values being greater than the true value. Measurements of dielectric constants and dielectric loss have been made using the interferometer, and results are in agreement with values obtained by other methods. Since the interferometer is the free space analogue of the cavity wavemeter it is particularly suitable for measurements on materials of low loss tangent at millimetre wavelengths. Finally, the use of the interferometer for length measurements is mentioned, and also its possible use for the accurate determination of the velocity of electromagnetic waves.

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.