Showing papers on "Acoustic interferometer published in 1973"

III Interaction of Light and Acoustic Surface Waves

Abstract: Publisher Summary This chapter describes the interaction of light and acoustic surface waves. It discusses two major areas in the interaction of light and acoustic surface waves. One is the light diffraction by acoustic surface waves and the other is the interactions of optical guided waves and acoustic surface waves. The study of light diffraction by acoustic surface waves results in a convenient optical probing technique to study the propagation characteristics of acoustic surface waves that are needed for the design and utilization of acoustic surface wave devices. The interest in the interaction of light and acoustic surface waves began after the recent advance of acoustic surface technology. In designing acoustic surface wave devices, it is necessary to have a detailed knowledge of the propagation characteristics of these waves on any isotropic or anisotropic substrate. Optical probing of acoustic surface waves based on the light diffraction by acoustic surface waves has become a convenient tool in studying and utilizing these waves.

An Experimental Investigation of Subharmonic Generation in an Acoustic Interferometer

Abstract: In our previous study [J. Acoust. Soc. Amer. 49, 119(A) (1971)], we showed that the nonlinear properties of the medium can induce coupling among the modes in a multiresonant system and the theory is able to predict the threshold and the steady‐state response of subharmonic components. Such a mechanism is further illustrated by observing the subharmonic generation phenomenon in an acoustic interferometer. The experimental investigation was conducted with a 1.5‐mHz driving signal and used filtered and degassed water as the medium. Data concerned with the actual modes of the interferometer, the loss factor associated with the subharmonic modes, and the threshold of subharmonic generation, with length of the interferometer and the driving frequency varying, are consistent with the analytic results provided that cavitation is carefully avoided. [The work was carried out at Harvard University and supported by the Office of Naval Research.]

Measured and calculated transmission losses of sound waves through a helium layer

Abstract: An experiment was performed to measure the transmission losses of sound waves traversing an impedance layer. The sound emanated from a point source and the impedance layer was created by a low-speed helium jet. The transmission losses measured were of the order of 12 db for frequencies of the source between 4 and 12 kHz. These losses are greater than those predicted from analysis when the observer angle is less than about 35 deg, but less than those predicted for larger observer angles. The experimental results indicate that appreciable noise reductions can be realized for an observer shielded by an impedance layer, irrespective of his position relative to the source of sound.

Acoustic waves along oilfilled streamer cables

Abstract: There are different types of acoustic noise induced in streamer cables. One type consists of pulsed waves preferentially generated by vertical motions of the towing ship or of the tail buoy. The pulsed waves travel along the streamer with low attenuation and a velocity about 15% less than the velocity of water. Frequencies observed lie between 5 and 15 Hz. These pulsed waves are well known and for the last few years acoustic isolator sections have been used to reduce their generation. But under bad weather conditions and especially in cold water these waves become stronger. Recent investigations demonstrated that the pulsed waves are able to produce a high noise level even in new streamers with acceleration cancelling hydrophones. We point out that the material of the hoses has a dominant effect on the amplitude picked up by the hydrophones. Acoustic theory is applied to understand the phenomenon of these waves.

Low frequency parametric acousto-optical imaging method and apparatus

Abstract: An object situated in an acoustic medium, such as water or soil, characterized by relatively high acoustic absorption is optically imaged by a novel acousto-optical imaging technique. Relatively low frequency acoustic waves which are subject to relatively low attenuation by the ambient medium are transmitted through the medium to the object and emanate from the object as distorted acoustic waves containing information defining an image of the object. These distorted acoustic waves are received by an acousto-optical coupling medium which is excited by relatively high frequency and large amplitude acoustic waves. The distorted low frequency acoustic waves and high frequency waves undergo non-linear interaction to produce in the coupling medium resultant acoustic wave sets having frequencies equal to the sum and difference, respectively, of the low and high frequencies and each containing essentially the same image information as the distorted waves. A monochromatic light beam is projected through the coupling medium to impinge the wave fronts of one resultant wave set, preferably the sim wave set, at an oblique angle which causes Bragg diffraction of the light waves by the acoustic waves, such that the light waves emerging from the coupling medium form an optical image of the object.

Acousto-optical underwater imaging system

Abstract: An underwater acousto-optical imaging system for receiving water-borne acoustic waves representing an image of an object in the water and converting the image information to a corresponding optical image of the object. The acoustic waves are focused by an acoustic lens into a Bragg coupling medium wherein a monochromatic light beam is Bragg diffracted by the acoustic waves to produce a modulated light side band defining the optical image. A television camera converts this optical image to electrical signals for viewing of the image at a remote video monitoring station. The imaging system may be driven in a scanning motion for operation in a search made and may include an acoustic source for generating acoustic probing waves which reflect from objects in the water back to and are converted to optical images by the imaging system.

Experiments in Molecular Physics with an Acoustic Interferometer

Abstract: An acoustic interferometer provides an inexpensive means for making precise studies of the kinetics of gas molecules. Two experiments are described: (1) Measurement of the vibrational relaxation time of gas molecules and (2) determination of intermolecular (van der Waals) forces in molecules.

Generation of acoustic waves in piezo-electric devices

Abstract: In this paper the in tegra l equat ion formulation of scat ter ing or diffraction problems associated w i t h wave mot ions in a piezo-electric solid is investigated. Star t ing from t h e basic equat ions a power ba lance and a reciprocity relation are derived. In the power balance the mechanical and the electric power flow density occur . The reciprocity relation serves as a s ta r t ing point for the integral equa t ion formulation of diffraction problems. In the reciprocity relation, two possible bu t different field s i tuat ions occur, In one of them the field quan t i t i e s are chosen to be t he ac tua l ones, in t he other t he field quanti t ies are chosen to be t he auxil iary ones t h a t are generated by either an electric p o i n t charge or a mechanical point force. In this way, Helmholtz type of in tegra l representa t ions for the electric potent ia l and the mechanical d isplacement are obta ined. For t he technically impor tan t configuration of a piezo-electric component excited by a finite number of electrodes, t he homogeneous, linear relations between t h e potent ia ls on t he electrodes and the currents fed into these are represented th rough the impedance ma t r ix . I t is shown t h a t t he elements of this impedance mat r ix can be obta ined from certain integral equations, A method for ob ta in ing the auxil iary fields used in the integral representat ions for the electric potent ia l and the mechanical displacement is outlined in an append ix . Nomenclature Latin symbols Ci,};p,Q stiffness tensor a t cons tant electric field Di electric flux densi ty El electric field vector etj-p piezo-electric tensor

Resonant interaction of standing acoustic waves with a spin system

Abstract: A theory is developed of the reaction of a spin system to a resonant action of an acoustic field and an electromagnetic field. It is shown that it is important to allow for the coherent properties of the acoustic field that excites the spin system both for the calculation of the line profile of direct acoustic absorption and for the line profile of saturation of paramagnetic resonance by sound. By studying the influence of the acoustic field on the profile of the absorption line of rf power it becomes possible to determine the magnitude and sign of the spin-phonon interaction constant.