Showing papers on "Acoustic interferometer published in 1990"

Fluid motion produced by ultrasonic Lamb waves

Abstract: Fluid motion induced by traveling flexural waves in 4- mu m-thick membranes was observed using 2.5- mu m-diameter polystyrene spheres in water to make their fluid motion visible. Visual observation of the spheres indicates that their velocity is in the direction of wave propagation and is proportional to the square of the acoustic amplitude. The maximum speed is 130 mu m/s for an RF drive voltage of 7.1 V/sub rms/ at 3.5 MHz; the wavelength is 100 mu m. Sphere motion has been observed in regions without acoustic waves, suggesting fluid recirculation. Standing Lamb waves, which can be seen visually with a phase-contrast microscope, are found to trap particles, including bacteria located in a drop of water in contact with the membrane. A first-order model of Lamb-wave micropumping is based on acoustic streaming theory. Possible applications include temperature redistribution in ICs and miniature chemical processing systems. >

A michelson twin interferometer for precise measurements of the refractive index of gases between 100 K and 1300 K

Abstract: A Michelson twin interferometer is described, which is used for precise measurements of the refractive index n of gases in the visible wavelength range and temperatures between 100 K and 1300 K. The evacuated twin interferometer (length 2.4 m, diameter 90 mm) consists of two adjacent identical Michelson interferometers A and B, using the same beam splitter and mirrors. Interferometer A serves as the proper measuring interferometer with the gas sample cell in measuring beam 1 and the identical, but evacuated, reference cell in its reference beam 2. Interferometer B is used only for controlling the geometrical changes of the interferometer equipment during the refractive index measurements performed with interferometer A. Both the gas sample cell and the reference cell are made from quartz glass and thermostated. The construction of this very stable twin interferometer as well as the devices for gas pressure and temperature measurements are described in detail.

Analysis of acoustic properties of multi-layered structures by means of effective acoustic impedance matrix

Abstract: The effective acoustic impedance matrix (Z(k)) is proposed, and its applications are discussed. After defining (Z(k)), it is shown that (Z(k)) for any kind of multilayered structure can be determined successively from the bottom substrate to the top layer. The use of (Z(k)) obviates some problems often occurring in the numerical calculation of multilayered structures. Using three typical examples, it is shown how (Z(k)) can be conveniently applied to characterize acoustic wave excitation and propagation in certain complicated layered structures as well as in semi-infinite substrates. >

K/sup +/ detection using shear horizontal acoustic modes

Abstract: An acoustic delay line sensor for the detection of potassium ion concentration in water has been implemented and tested. The device uses the propagation of shear horizontal (SH) waves in a piezoelectric plate (Love waves) in order to minimize acoustic energy loss in the liquid. One of the plate surfaces is covered with a polyvinyl-chloride-valinomycin membrane, a well-known ligand for the detection of potassium ions. The devices has shown a fairly good linearity of the response in the analyzed pK/sup +/ range of K/sup +/ concentration between 1.49 and 4. The operation is reversible and the response is highly reproducible. Measurements have demonstrated a high selectivity of the device with respect to exposure to Na/sup +/ solutions. >

Acoustic holographic array measurement device and related material

Abstract: An acoustic device and related method for measuring the shape of an object. The device includes a plurality of transmitters for transmitting acoustic waves at an object to be measured and a plurality receivers for receiving the acoustic waves reflected by the object. A phase detector measures phase data of the reflected acoustic waves, the phase data being processed to calculate a value representing a shape of the object as a function of the phase data. This value is then compared with known reference value to accurately identify the shape of the object.

Electromagnetically induced acoustic well logging

Abstract: An electromagnetic source or sources in a sonde in a well bore is caused to emit electromagnetic forces into the well casing. The electromagnetic forces cause displacement of the casing, inducing acoustic waves. The acoustic waves may be either P-waves or S-waves, depending on the type of electromagnetic source used. The response of earth formations to the acoustic waves, once detected, is used to detect fractures in the formations.

Effect of piezoelectricity on the excitation and radiation of acoustic waves in rotated Y‐cut quartz

Abstract: Recently we reported a far field theory of transverse acoustic waves radiated from an interdigital transducer deposited on a singly rotated quartz crystal. This was done by an approximation called the local decoupling approach, allowing us to consider electrical effects as forcing fields for the mechanical motion. The present analysis demonstrates that this approximation is not valid in predicting the complete spectrum of acoustic waves. It is shown that near the cutoff frequency the bulk wave may be converted into a surface wave of Bleustein–Gulyaev type in the free surface case, and that a surface metallization reinforces the strength of this conversion. Velocity of surface waves are determined by means of the effective permittivity function and correct radiation diagrams are plotted in the far field.

Arctic acoustics ultrasonic modeling studies

Abstract: : A unique collection of laboratory ultrasonic modeling results are presented revealing and characterizing hidden pulsed seismoacoustic wave phenomena from 3-D range dependent liquid/solid boundaries. The research succeeded in isolating and identifying low-frequency (10-500 Hz) transmission loss mechanisms and provided physical insight into Arctic acoustic problems generally beyond the state-of-the-art of theoretical and numerical analysis. The ultrasonic modeling studies dealt with controversial issues and existing discrepancies on seismo-acoustic waves at water/ice interface, sea-ice thickness determination, low-frequency transmission loss, and bottom leaky Rayleigh waves. The areas investigated include leaky Rayleigh waves at water/ice interface, leaky flexural waves in floating ice plates, effects of dry/wet cracks in sea- ice on plate waves and near-grazing acoustic waves, edge waves in floating plates, low-frequency backscatter from ice keel-width resonances, conversion of underwater acoustic waves into plate waves by keels, nondispersive flexural wave along apex of small-angle solid wedge, Scholte and leaky Rayleigh waves along apex of immersed 90 ice wedge, backscatter from trailing edge of floes, floating plate resonances associated with near-grazing underwater acoustic waves, acoustic coupling between adjacent floes, and multiple bottom leaky Rayleigh wave components in water layer over solid bottom.

Resonant absorption of p-modes by sunspots

Abstract: Explanations for the observed p-mode absorption in sunspots are examined. It is demonstrated that any dissipative process like radiative, viscous, or resistive dissipation leads to the resonant absorption of acoustic waves incident on the sunspot tube, and that the resultant heating rate can be shown to be consistent with the observed absorption of the p-mode power impinging on an isolated inhomogeneously structured sunspot.

Measurements of SAW velocity by using divergent-beam ultrasound transducers

Abstract: A SAW (surface acoustic wave) velocity measurement system that uses a pair of divergent-beam ultrasound transducers positioned in parallel with a specimen in a liquid is presented. Of the divergent wave emitted by the transmitter, a specific angular-spectrum component that is incident on a specimen at the Rayleigh critical angle excites a leaky SAW on the specimen surface. Of various angular-spectrum components of the reflected wave, the receiver selectively detects the specularly reflected wave and the reradiation of the leaky SAW. These two components take the same path when the specimen is brought to a specific position. Since the two components are in opposite phase at the position, their interaction causes a so-called null zone in the reflected beam and a corresponding intensity minimum is detected by the receiver. >

Interaction of acoustic waves generated by coupled plate

Abstract: When two substructures are coupled, the acoustic field generated by the motion of each of the substructures will interact with the motion of the other substructure. This would be the case of a structure enclosing an acoustic cavity. A technique to model the interaction of the generated sound fields from the two components of a coupled structure, and the influence of this interaction on the vibration of the structural components is presented. Using a mobility power flow approach, each element of the substructure is treated independently both when developing the structural response and when determining the acoustic field generated by this component. The presence of the other substructural components is introduced by assuming these components to be rigid baffles. The excitation of one of the substructures is assumed to be by an incident acoustic wave which is dependent of the motion of the substructure. The sound field generated by the motion of the substructure is included in the solution of the response.

Theoretical study of the anisotropic diffraction of light waves by acoustic waves in lithium niobate crystals

Abstract: The anisotropic diffraction of light by high frequency longitudinal ultrasonic waves in the tangential phase matching configuration may present some definite advantages over the same interaction using transverse acoustic waves. A systematic search for favorable crystal cuts in lithium niobate was worked out. The main results of this study are reported here; they enable the choice of the best configuration for a given operating center frequency.

Finite amplitude acoustic waves in liquid 3He and 4He

Abstract: Finite-amplitude acoustic waves have been propagated in liquid3He and4He. The acoustic cell has been operated at 83, 250, and 420 MHz and down to 17 mK. Our measurements of the anharmonic effects are in agreement with theoretical predictions and with previous experimental work that investigated a restricted temperature range.

On sound absorption in two-phase systems

Abstract: The scattering of an external acoustic wave in a two-phase system is considered. For such a system respective coefficients of attenuation of the energy of acoustic waves have been computed. It is predicted that in such substances a high absorption of sound and an increase of absorption cross-section in a certain range of pressures in the liquid phase is possible. The problem of the scattering of sound in a structure similar to paper, comprising a chaotic succession of fibers and free volumes, has also been examined. It is shown that the porosity is a major characteristic of such substance.

Interferometric investigation of laser-supported absorption waves

Abstract: Interferometry of laser-supported absorption waves and the resulting gas dynamic disturbances are studied. It is possible to show the propagation of shock, geometri cal shapes of the waves and vaporization of target material.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Acoustical imaging of vibrating structures using the extended angular spectrum method

Abstract: A field expansion technique for analyzing the surface velocity patterns of vibrating structures is presented. The technique is based on the angular spectrum method of field analysis. In this approach, acoustic wave propagation between parallel planes is modeled by applying the two-dimensional discrete Fourier transform to a cross section of an acoustic pressure field. The transform decomposes the cross section into plane-wave components, each of which is multiplied by an appropriate phase factor taking into account the propagation distance and the characteristics of the propagation media. The resulting propagated spatial spectrum is then inversely transformed to yield a cross-sectional reconstruction of the field. The technique developed is applicable to both monochromatic and wideband pulsed fields. An experimental system was built to determine the vibrational patterns of complex acoustic radiators. Sources examined included those with circular planar, circular focused, and rectangular phase-steered geometries. The results demonstrate the ability of the extended angular spectrum method to reconstruct accurately the surface velocity distributions of complex vibrating structures. >

Novel types of guided SAW reflectors for micro-resonators

Abstract: Surface acoustic waves (SAWs) for micrograting reflectors are characterized Based on the perturbation theory, eight different types of structures on an acoustic waveguide are analyzed Results of simulations of all eight types of corrugation structures are evaluated in order to find the least leaky waveguide, the most efficient reflector (with minimum necessary perturbations), and the optimal mode shape for improved performances General design curves are presented in order to illustrate the behavior of the incident and reflected waves under a variety of structural conditions Analytic expressions for the calculations of the mode amplitude and mode shape, and for general acoustic corrugations are derived Simulation results are presented >