Showing papers on "Acoustic interferometer published in 2008"

Alignment of particles in microfluidic systems using standing surface acoustic waves

Abstract: We report on the use of standing surface acoustic waves, formed on a single-crystal piezoelectric substrate, to organize micron-scale latex particles into an array comprising a series of lines in an adjacent microfluidic system. The lines of particles are formed parallel to the substrate surface and perpendicular to the surface acoustic wave vector. They extend across the width of the acoustic beam aperture, with a periodicity of one-half the surface acoustic wavelength. The position and spacing of the particle arrays can be altered by adjusting the acoustic wave frequency within the device passband. We discuss the mechanism responsible for the formation of the lines, which could be widely applicable to the alignment of microscopic objects held in suspension.

Microfabricated VHF acoustic crystals and waveguides

Abstract: Microfabricated acoustic crystals have been designed and experimentally verified. The acoustic crystals are realized by including tungsten (W) scatterers in a SiO2 matrix. Wide frequency ranges where acoustic waves are forbidden to exist (acoustic bandgaps, ABG) are formed due to the large acoustic impedance and mass density mismatch between W and SiO2. The acoustic crystal structures are fabricated in a 7-mask process that features integrated aluminum nitride piezoelectric couplers for interrogating the devices. Acoustic crystals in a square lattice have been measured at 67 MHz with greater than 30 dB of acoustic rejection and bandwidths exceeding 25% of the midgap. Single and multimode acoustic waveguides have been realized by defecting the acoustic crystals through removal of a subset of the W scatterers. These waveguides achieve relative transmission of up to 100% for the propagating modes.

An absolute distance interferometer with two external cavity diode lasers

Abstract: An absolute interferometer for length measurements in the range of several metres has been developed. The use of two external cavity diode lasers allows the implementation of a two-step procedure which combines the length measurement with a variable synthetic wavelength and its interpolation with a fixed synthetic wavelength. This synthetic wavelength is obtained at ≈42 µm by a modulation-free stabilization of both lasers to Doppler-reduced rubidium absorption lines. A stable reference interferometer is used as length standard. Different contributions to the total measurement uncertainty are discussed. It is shown that the measurement uncertainty can considerably be reduced by correcting the influence of vibrations on the measurement result and by applying linear regression to the quadrature signals of the absolute interferometer and the reference interferometer. The comparison of the absolute interferometer with a counting interferometer for distances up to 2 m results in a linearity error of 0.4 µm in good agreement with an estimation of the measurement uncertainty.

Acoustic imaging probe incorporating photoacoustic excitation

Abstract: Embodiments of the present invention provide for a photoacoustic imaging probe for use in a photoacoustic imaging system, said probe comprising a cohesive composite acoustic lens incorporating aspheric geometry and exhibiting low or practically no measurable dispersion of acoustic waves constructed of at least one material with a low acoustic impedance and attenuation and a relatively low acoustic velocity and at least one other material with a low acoustic impedance and attenuation and a relatively high acoustic velocity is immersed in preferably a low acoustic velocity and low acoustic impedance fluid. The lens may be designed as a single cohesive composite telecentric lens, an acoustic zoom lens, or a catadioptric lens. The lens focuses acoustic waves on an acoustic imager which detects the image. The lens may be considered to be essentially monochromatic.

Origin of Rayleigh scattering and anomaly of elastic properties in vitreous and molten GeO2

Abstract: Vitreous (v) and molten (m) GeO 2 were studied by Rayleigh and Mandel’shtam–Brillouin scattering spectroscopy and high-temperature acoustics. Original measurement apparatus and procedure were used that included Bayseian deconvolution of light scattering spectra of vGeO 2 and a specially designed high-temperature (up to 1500 °C) acoustic interferometer to measure temperature and frequency dependence of ultrasonic (US) velocity and attenuation in mGeO 2 . Landau–Placzek ratios for vGeO 2 were found optically (from the light scattering spectrum) and acoustically (through the Schroeder’s formalism). Dispersion of optical and other physical parameters of vGeO 2 found by many authors is explained by the existence of small amount of GeO in the samples. It means that properties of vGeO 2 are under the influence of redox synthesis conditions controlling the GeO 2 ↔ GeO and coordination [GeO 4 ] ↔ [GeO 6 ] equilibrium in vGeO 2 . Measurements of temperature dependencies of longitudinal ultrasonic velocities in mGeO 2 and in the PbO–GeO 2 glass melts as a function of PbO concentration shows existence of ‘water-like anomaly’ in mGeO 2 and in liquid germanates with the rich content of GeO 2 where equilibrium sound velocity increases with the temperature.

Study by means of liquid side acoustic barrier of the influence of leaky Rayleigh waves on bounded beam reflection

Abstract: The Schoch effect in ultrasonics, when sound is incident at the Rayleigh angle on a liquid-solid interface, consists of a forward beam displacement of the reflected beam, usually accompanied by a null strip in between the specular portion and the nonspecular reflected beam portion. It is a widely accepted idea that the effect is caused by reflected sound in combination with a sound field emitted by leaky Rayleigh waves. The current work presents an experimental technique to separate and investigate both fields separately by applying an acoustic barrier. The experiments are based on acousto-optic Schlieren photography.

Diffraction of dust acoustic waves by a circular cylinder

Abstract: The diffraction of dust acoustic (DA) waves around a long dielectric rod is observed using video imaging methods. The DA waves are spontaneously excited in a dusty plasma produced in a direct current glow discharge plasma. The rod acquires a negative charge that produces a coaxial dust void around it. The diameter of the void is the effective size of the “obstacle” encountered by the waves. The wavelength of the DA waves is approximately the size of the void. The observations are considered in relation to the classical problem of the diffraction of sound waves from a circular cylinder, a problem first analyzed by Lord Rayleigh [Theory of Sound, 2nd ed. (MacMillan, London, 1896)].

Wavelength-scanning white-light interferometry with a 3×3 coupler-based interferometer

Abstract: A novel white-light interferometry capable of retrieving the absolute optical path difference is presented, in which a 3×3 coupler-based interferometer is employed. The measured phase change is in agreement with that obtained by Fourier transform white-light interferometry. The linear property is also experimentally demonstrated.

Gas velocity sensor

Abstract: This invention relates to a gas velocity sensor such as an air velocity sensor for use on an aircraft such that the velocity of the aircraft can be determined. There is provided a gas velocity sensor comprising an electromagnetic radiation source operable to illuminate a gas; a photodetector operable to detect electromagnetic radiation scattered from the gas; an optical path linking the gas to the photodetector; an interferometer positioned on the optical path, the interferometer having an input for receiving electromagnetic radiation scattered by the gas and an output for producing an interference pattern when the interferometer is illuminated; and a spatial filter positioned on the optical path on the output side of the interferometer, the spatial filter having regions that are relatively transparent and relatively opaque that form a structure corresponding to an interference pattern produced by the interferometer.

A comparison of two methods for measuring the sound absorption coefficient using impedance tubes

Abstract: The goal of this paper is to compare the two methods for measuring the sound absorption coefficient, the method that uses the standing wave ratio and the transfer function method, on several different materials. For this purpose, an impedance tube for the transfer-function method was designed and constructed. Measurements were made on mineral wool and foam of different thickness. At the end, measurement results for sound absorption coefficient for each material are shown and compared for two tubes.

Acoustic waves in transversely excited atmospheric CO2 laser discharges: effect on performance and reduction techniques

Abstract: Results are presented on the influence of acoustic waves on the performance of high-repetition-rate TEA CO2 lasers. It is shown that acoustic waves generated inside the laser cavity lead to nonuniform dis- charges, resulting in a deterioration of the laser beam quality, decreased output energy, and an increase in pulse-to-pulse energy variation. The effect of the gas mix on the acoustic behavior is investigated, and ex- perimental results on laser performance across a range of gas mixtures are presented. Methods to reduce the effects of acoustic waves are pre- sented together with experimental results. The influence of acoustic damping measures on laser gain are demonstrated, showing a signifi- cant improvement in gain and output power at high pulse repetition rates. © 2008 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.2968227

A rayleigh wave technique to measure the acoustic nonlinearity parameter of materials

Abstract: Nonlinear ultrasonic techniques have shown great potential for evaluating accumulated damage early in the fatigue life, and ultimately for predicting remaining lifetime of a structural component. The acoustic nonlinearity parameter, a direct measure of the accumulated fatigue damage, is determined from the second harmonic amplitude in finite amplitude sinusoidal ultrasonic waves transmitted through the material. An absolute determination of the acoustic nonlinear parameter is notoriously difficult for several reasons. In this paper, a new experimental technique based on Rayleigh surface waves is presented for determining the absolute acoustic nonlinearity parameter of a relatively thin material specimen. Rayleigh waves are efficiently generated in a specimen by exciting at its edge, and the surface normal velocity of the propagating Rayleigh waves is measured with a laser interferometer system. The high efficiency of the excitation method allows us to drive the transmitting piezoelectric transducer as low as 60 Vpp, and thus to avoid the inherent harmonic distortion from the transducer. The absolute acoustic nonlinearity parameter is then determined from the measured magnitudes of the fundamental and second harmonic surface normal velocities. This technique is applied to determining the acoustic nonlinearity parameters of aluminum alloys 2024 and 6061; the results are compared with those available in the literature. The present technique is especially well‐suited for relatively thin components, and much simpler and efficient than the traditional longitudinal wave technique.

Ultrasonic and hypersonic phononic crystals

Abstract: We report on the experimental and theoretical investigation two kinds of acoustic waves in two dimensional phononic crystal: bulk acoustic waves and surface acoustic waves. For bulk acoustic waves, the work focuses on the experimental observation of full acoustic band gaps in a two-dimensional lattice of steel cylinders immersed in water as well as deaf bands that cause strong attenuation in the transmission for honeycomb and triangular lattices. For surface acoustic waves, complete acoustic band gaps found experimentally in a two-dimensional square-lattice piezoelectric phononic crystal etched in lithium niobate will be presented. Propagation in the phononic crystal is studied by direct generation and detection of surface waves using interdigital transducers. The complete band gap extends from 203 to 226 MHz, in good agreement with theoretical predictions. Near the upper edge of the complete band gap, it is observed that radiation to the bulk of the substrate dominates. This observation is explained by introducing the concept of sound line.

Parametric sound fields by phase-cancellation excitation of primary waves

Abstract: By radiating bifrequency primary waves from two ultrasonic emitters with changing the phases of the primary waves, we can obtain the sound fields that are different from the usual in‐phase excitation. Especially, for the excitation of out‐phase by 180 degrees the difference frequency wave has the directivity of almost uniformity near the acoustic axis. Additionally, the sound pressure levels of the harmonic components of the difference frequency and the primary waves as well are suppressed by 10 dB and more.

Measurement of residual stress of magnetic substance by surface acoustic waves

Abstract: In magnetic substances under oscillating stress due to the application of acoustic waves (such as ultrasonic waves), an oscillating anisotropic field may be generated by the inverse effect of magnetostriction. If this magnetic field oscillation can be detected, the stress state inside the magnetic substance can be determined. Based upon this principle, we have set up an apparatus for stress measurements, applied it to Ni plates with different residual stresses, and have obtained output signals corresponding to different stresses. This measuring technique makes it possible to know the stress state in structures before the formation of cracks, and hence offers a very promising nondestructive testing device.

Method of determining acoustic transit times for material having high acoustic attenuation properties

Abstract: A method for determining time a single transit of an acoustic wave through a test material using a calibration material having known acoustic velocity characteristics and an acoustic pitch-catch system with a signal recorder for recording a received signal as a function of time. The system includes a first configuration for transmission of acoustic shear waves and a second configuration for transmission of acoustic longitudinal waves. In the first configuration, a first acoustic zero is determined when the acoustic shear waves are applied to the calibration material. In its second configuration, a second acoustic zero is determined when the acoustic longitudinal waves are applied to the calibration material. Each configuration is coupled to a test material with the respective first and second acoustic zeroes identified on the recorder. The signal recorder determines a single transit time for the acoustic waves through the test material.

Liquid measuring device and automatic analyzer

Abstract: A liquid measuring device and an automatic analyzer which employs a resonance phenomenon of sound waves to detect an amount of a liquid reserved in a vessel with an opening are provided. The liquid measuring device includes a sound source that emits sound waves toward the opening, a control device that controls a frequency of the sound waves emitted by the sound source, a wave receiver that measures a resonance generated as the sound waves emitted by the sound source causes an air column in the vessel to resonate, a detector that detects a resonance frequency of the resonance measured by the wave receiver, and a liquid-amount determination unit that determines, based on the detected resonance frequency, an amount of the liquid reserved in the vessel.

Adaptive interferometric array-receivers for detecting surface acoustic waves

Abstract: Laser ultrasonic detectors are configured as point- and line-array receivers using wave mixing in photorefractive BSO crystals. The arrays are formed by passing a collimated laser beam through a phase or a transmission mask. The array receivers can be used with narrowband surface acoustic waves to improve the sensitivity of laser ultrasonic systems.

Quantitative visualization of ultrasonic acoustic waves by means of digital laser speckle-technologies

Abstract: An original version of digital laser speckle photography has been used for visualization and quantitative diagnosis of acoustic waves in liquids in the megahertz frequency range. Standing acoustic waves were generated in tanks of special configuration which permitted obtaining analytical dependences of refraction angles of the probe laser radiation on the wave intensity. These refraction angles were determined experimentally by the change in contrast of the speckle fields arising in the scattered probe radiation and recorded by means of high-resolution digital CCD matrices. Quantitative diagnosis of the pressure and velocity fields in acoustic waves was carried out by measuring the deformation of the laser intensity correlation functions in recorded speckle fields.

Hybridization of backward acoustic waves in piezoelectric plates

Abstract: The phenomenon of hybridization of the backward acoustic waves propagating in a piezoelectric crystal plate has been studied. In an electrically free plate (in particular, of potassium niobate) with a crystal orientation for which a sagittal plane is the symmetry plane, the dispersion curves of backward acoustic waves exhibit points of intersection and hybridization is absent. However, for a small change in the direction of wave propagation, the dispersion curves exhibit “repulsion” and the waves become coupled. The degree of hybridization is quantitatively evaluated in terms of the hybridization coefficient, which is defined as the ratio of the total mutual energy density and the total energy density of the interacting waves. It is demonstrated that the extent of repulsion of the dispersion curves for the interacting waves is determined by the dependence of the hybridization coefficient on the product of the plate thickness and the wave frequency.

Reflection and refraction of acoustic waves at the boundary between the ferromagnetic Heusler alloy and liquid

Abstract: Reflection and refraction of quasi-longitudinal and quasi-transverse acoustic waves at a flat interface between a liquid and a ferromagnetic crystal of the Heusler alloy Ni2 + x + y Mn1 − x Ga1 − y (in the region of its premartensitic and martensitic phase transitions) is considered. The directions of propagation and polarization and the amplitude of reflected quasi-longitudinal and quasi-transverse and of transmitted longitudinal waves in the (110) plane of the crystal are determined. In a wide region of phase transformations of this alloy, the possibility is shown of using temperature to efficiently control the angles of reflection and refraction of wave modes and the coefficients of their conversion due to a colossal acoustic anisotropy of the crystal. Beginning from a certain critical angle of the quasi-transverse wave, the quasi-longitudinal wave arising upon reflection acquires the nature of the accompanying surface vibration and at a large proximity to phase transition can be emitted into the bulk of the crystal. On the basis of the available experimental data for Ni2MnGa crystals, numerical estimations of the above acoustic effects have been carried out.

A source of waves simulating acoustic-emission signals

Abstract: A source of acoustic waves simulating acoustic-emission signals, a technique for calculating the force acting for a short time on the surface of a tested object, and formulas for calculating the displacement amplitudes for bulk longitudinal and transverse waves excited by this source are proposed. The possibility of calculating the amplitude of the normal component of antisymmetric mode a0 of Lamb waves is considered. It is shown that it is desirable to use such a source in acoustic-emission testing of trunk and industrial pipelines of the fuel and energy industry.

Finite amplitude acoustic waves in liquid 3He and 4He

Abstract: Equation of state of Helium is given and its solutions are discussed in order to study acoustic waves in liquid Helium 3 and Helium 4.(AIP)

The Loss Mechanism in a Composite Acoustic Microwave Resonator Based on a Sapphire Single Crystal

Abstract: Acoustic loss in a composite longitudinal-wave resonator structure operating in the microwave band are studied. The resonator structure contains a rather thick sapphire plate coated with a piezoelectric film with electrodes. It is shown that, in a wide frequency band, attenuation is determined by interaction with acoustic phonons. The role of diffraction loss is discussed. Scattering of acoustic waves by asperities of reflecting surfaces is considered, and the contribution of scattered acoustic waves to the total loss is estimated.

Influence of strong acoustic anisotropy on reflection of bulk acoustic waves in crystals

Abstract: Propagation and reflection of plane elastic waves in the acousto-optic crystals tellurium dioxide and calomel as well as in the ferroelectric material barium titanate is examined in the paper. The reflection of the waves from a free and flat boundary separating the crystal and the vacuum is investigated in the (001) planes of TeO2, Hg2Cl2 and BaTiO3 in the case of glancing acoustic incidence on the boundary. The analysis shows that as much as two elastic waves may be reflected from the crystal surface. Energy flow of one of the reflected waves in paratellurite and calomel propagates in a quasi-back direction with respect to the incident energy flow so that both energy flows are separated by an angle as narrow as a few degrees. It is found that a relative intensity of the unusually reflected wave in the acousto-optic crystals may be close to a unit in a wide variety of crystal cuts. Possible applications of the examined phenomena in acousto-optic devices are discussed in the presentation.

Diffraction and Nonlinear Effects in the Generation of Higher Harmonics in High‐Intensity Acoustic Beams

Abstract: The results of experimental studies of the effect of initial aperture of intense acoustic beams at a frequency of 3 MHz on the frequency and spatio‐temporal parameters of nonlinear acoustic waves propagated in pure degassed water are presented. The experiments were carried out in weakly diverging acoustic waves generated by piston‐like piezo‐ceramic radiators. A wideband miniature calibrated MHA9 receiver by Force Technology, capable of correctly analyzing over 20 harmonics of the received acoustic signal, was used in the experiments. The influence of initial aperture of the beam is studied on the spatial distributions of higher‐harmonic amplitudes in nonlinear waves formed at moderate values of the Reynolds number Re. The received‐signal profiles as functions of the reception point in the acoustic beam are analyzed for various relationships between the nonlinear and diffraction effects.