Showing papers on "Acoustic interferometer published in 1965"

End-fire array of virtual sound sources arising from the interaction of sound waves

Abstract: Westervelt and Bellin and Beyer have studied the scattering of intermodulation frequency sound waves arising from the nonlinear interaction of two collimated and coincident plane waves of sound of different frequencies. This work is extended to account for the finite aperture formed by the cross-section of the column; experimental results are compared with those obtained theoretically and with Bellin and Beyer's results.

Group velocity and power flow relations for surface waves in plane-stratified anisotropic media

Abstract: Two aspects of power flow associated with electromagnetic waves in plane-stratified, dispersive, anisotropic media that are also lossless and linear are considered. One aspect is the relation between group velocity and the velocity of energy transport of surface waves in such media. It is shown that the group velocity of surface waves is equal to the ratio of the real part of the complex Poynting vector, integrated over the coordinate of stratification, to the corresponding integral of the stored energy density. The second aspect is the relation between the dyadic surface impedance representing either a slab of plane-stratified medium above a perfectly conducting plane or a semi-infinite region, the latter for the case of evanescent fields, and the power flow in the respective structures. The significance of the surface impedance and power relations for surface waves is discussed.

The laser as a light source for the Mach-Zehnder interferometer

Abstract: A gas laser was used as a light source for a Mach-Zehnder interferometer. The operation of this system is compared with the familiar arrangement employing a mercury vapour lamp. High contrast fringes are demonstrated and it is further shown that the interferometer adjustments may be simplified when a laser is used.

End-fire array of virtual acoustic sources produced by the interaction of cylindrically spreading acoustic waves

Abstract: An experimental study of the interaction between cylindrically spreading acoustic waves in water is described, and experimental results are given. The experimental results are compared with theoretical work separately published by one of the authors.

Interaction of charge carriers with acoustic waves in single-valley and multi-valley semiconductors

Abstract: The interaction of two streams of change carriers with acoustic waves by means of the deformation potential is investigated. The mathematical description is in the form of double perturbation (streams perturbed by the acoustic waves, and acoustic waves perturbed by the streams) yielding a dispersion relationship which shows clearly the presence of mutual coupling between stream a, stream b and the lattice. A few special cases of the dispersion equation are investigated and it is shown that for certain acoustic waves in multi-valley semiconductors the two streams may be replaced by one stream void of space charge. A formula for the gain obtainable in the latter case is derived and it is shown that in the limit of ωτ→∞ the equations agree formally with those of Pierce(13) derived for travelling wave tubes. A consequences of this analogy is that the electron velocity for maximum gain agrees with the sound velocity. Experiments for observing the effect in n-type Germanium are proposed.

Excitation of acoustic waves in plasmas

Abstract: This paper repo rt s early re s ults in an experime nt al s tudy to d ete rmine the e ffects of perturbing weak lyi(lnized gaseous plasmas with acoustic waves e m a natin g from tran sdu cers tl, a t ope rate in Ihe audio and ultraso ni c freque ncy ranges . Compact louds pe ake rs incorporated int o cylindri c al plas ma discha rge tubes provid e the source of acous ti c s igna ls. Modulation of elec tromag neti c wav f'S by th e aco us ti ca ll y-disturbed p las ma is meas ure d in a unique rec ta ngular cavity whose output is de tec ted and fed to a wave a na lyzer. Res ult a nt wave-a na lyze r responses indi cate that the co lli sion fre qu e ncy is modula te d in addi tion 10 th e plas ma frequ e ncy, and s ugges t that the varia tions in bot h arc proporlional to the magnitu de of louds peaker diaphragm de flec tion , as pre di c te d by simple acolls ti c theory. Knowin g that two forms of modulation occu r s im ult a neous ly, a ca libration sc he me was deve loped to se pa ra te the var iation tJ.J;, in the p lasma freque ncy from the tot a l res ponse . Meas ure ments to dat f' ind icate that tJ.N, /N,.= C1N/N (whe re N, and N are elec tron and ne utra l-molecul e dens ities, respect ive ly) for s li ghtl yionize d gases whi c h are s ubjec le d to low-frequency press ure variation in th e order of 10-5 mm Hg, a nd th a t s uc h variation s produce pl as mafreq ue ncy perturbalions of 0 140 kc/s a t plas ma frequ enc ies up to 800 Mc/s_

Excitation and detection of acoustic waves in plasmas

Abstract: : This report contains initial results of an experimental study of acoustic disturbances in weakly ionized gaseous plasmas which exist in the positive column of dc discharges. One phase of the research concerns itself with the effects of externally perturbing such a medium with acoustic waves emanating from transducers that operate in the audio and ultrasonic frequency ranges. The balance of the effort is devoted to the observation of sound waves generated by natural and uncontrolled low-frequency oscillations which commonly occur in laboratory discharges. Compact transducers incorporated into cylindrical discharge tubes provide the source of acoustic signals and serve as microphones in detecting sound waves. Modulation of electromagnetic waves by the intentionally disturbed plasma was measured in a novel rectangular cavity whose output was detected and fed to a wave analyzer. Resultant wave-analyzer responses indicate that the electron collision frequency was modulated in addition to the electron plasma frequency, and that the variations in both were proportional to the magnitude of loudspeakerdiaphragm deflection, as predicted by simple acoustic theory.

Generation of Acoustic Waves in Cadmium Sulfide

Abstract: The possibility of generating high‐frequency acoustic waves by illuminating the negative end of a cadmium sulfide rod with light of periodically varying intensity exists. The strains produced and the acoustic gain present under different conditions of drift current and resistivity are calculated for three decades of frequency.