Showing papers on "Acoustic interferometer published in 2004"

Negative refraction of acoustic waves in two-dimensional phononic crystals

Abstract: Negative refraction of acoustic waves in two-dimensional phononic crystals has been demonstrated through both analysis and exact numerical simulation. The methods to achieve this behavior have been discussed. A microsuperlens for acoustic waves has also been designed. It is shown that refractive devices based on phononic crystals behave in a manner similar to that of optical systems. Therefore, a negative square root of the effective density or negative refraction index for acoustic waves can be introduced to describe this phenomena very well as the case of electromagnetic waves in the photonic crystals.

Component operating with bulk acoustic waves and a method for producing the component

Abstract: A component operating with bulk acoustic waves has a carrier substrate, a thin-film resonator and an acoustic mirror arranged between the resonator and carrier substrate The acoustic mirror is formed by at least one high acoustic impedance layer, which is covered by a low acoustic impedance layer and the uppermost low impedance acoustic layer is planarized to form a flat planar surface on which the thin-film resonator is formed

Use of electromagnetic acoustic transducers in downhole cement evaluation

Abstract: A bond log device comprising a sonde, an acoustic transducer, and an acoustic receiver. The acoustic transducer is comprised of a magnet combined with a coil, where the coil is energizable by an electrical current source. The acoustic transducer can also be comprised of an electromagnetic acoustic device. The acoustic transducer is capable of producing various waveforms, including compressional waves, shear waves, transversely polarized shear waves, Rayleigh waves, Lamb waves, and combinations thereof.

An ultrasonic frequency sweep interferometer for liquids at high temperature: 1. Acoustic model

Abstract: [1] A general acoustic model for a frequency sweep rod-liquid-rod interferometer applicable to high-temperature silicate liquids is presented. The wave propagations in the acoustic model are solved according to the accurate elastic wave equation and the acoustic wave equation. The solutions indicate that when a pulsed wave is sent down a buffer rod, which is partially immersed in a silicate liquid, the return signal consists of a series of plane waves (mirror reflections from the liquid) and two series of interfering pulses (modes A and B), which are propagating disturbances guided by the cylindrical surface of the upper rod. The acoustic model gives mathematical expressions for the time delays between the various interfering pulses and between the mirror reflections, which are predicted to vary according to the material and dimensions of the upper buffer rod and liquid. These predictions are verified by experiments on molybdenum and aluminum rods of varying dimensions in air, water, and silicate liquid. These results demonstrate that mirror reflections from the liquid can be isolated from the interfering pulses in the return signal by appropriate choice of the dimensions and material of the upper rod. This theoretical model provides a critical foundation for construction of an acoustic interferometer that is uniquely able to measure relaxed sound speeds in silicate liquids at high temperature and high pressure by the frequency sweep method. INDEX TERMS: 3994 Mineral Physics: Instruments and techniques; 3919 Mineral Physics: Equations of state; 3939 Mineral Physics: Physical thermodynamics; 3999 Mineral Physics: General or miscellaneous; 5102 Physical Properties of Rocks: Acoustic properties; KEYWORDS: ultrasonic interferometer, sound speed, silicate liquids

Coda wave interferometry

Abstract: An interferometer is an instrument that is sensitive to the interference of two or more waves (optic…

A new method to measure viscosity and intrinsic sound velocity of liquids using impedance tube principles at sonic frequencies

Abstract: The attenuation of the sound energy produced by a liquid contained in a cylindrical tube (wave guide) depends on the liquid’s viscosity, sound frequency, tube wall thickness, and tube material. By measuring the acoustic impedance of plane sound waves in a cylindrical wave guide, one can obtain the liquid’s viscosity. Impedance measurements can also provide sound velocity in the liquid medium as another important physical characteristic. In this study a method using the impedance tube technique is presented. This research details the instrument’s principles of operation along pertinent analytical equations and reports experimental results conducted using viscosity standard liquids. It is shown that the instrument can measure both liquid’s viscosity and intrinsic sound velocity with reasonable precision.

Optical measurement of transient ultrasonic shock waves

Abstract: In order to measure acoustic shock waves generating pressures of some tens of MPa in water, an ideal sensor has to be calibrated, wideband and sufficiently robust to support acoustic cavitation. We measure high intensity ultrasonic displacements and shock waves in water, using the phase modulation of an optical beam reflected by a thin immersed membrane materializing moving particles. With either an analog or a digital demodulation process, a 1-/spl mu/m ultrasonic transient displacement (corresponding to a 22-MPa acoustic pressure in water) has been measured with a standard heterodyne interferometer. Results are in good agreement with those given by a hydrophone designed to measure high pressure waves. This sensitive optical method provides absolute measurements with a 50- /spl mu/m lateral resolution, in a large bandwidth (from 20 kHz to 50 MHz). If the low cost membrane used in the experimental set-up is damaged by the acoustic cavitation, it can be easily replaced. We compare three phase detection techniques that require no calibration. The maximum measurable displacement is limited by the frequency bandwidth of the instrument. Since the photodetector cuts frequencies higher than 120 MHz, the interferometer is able to measure a 22-MPa peak acoustic pressure in water. This performance can be improved by increasing the frequency shift of the probe beam, to obtain a wider bandwidth. For measuring acoustic pressures up to 45 MPa, we have built an interferometer operating at a 140-MHz carrier frequency.

Guiding and filtering acoustic waves in a two-dimensional phononic crystal

Abstract: An experimental and theoretical study of the guiding, bending and filtering of acoustic waves in an ultrasonic crystal is reported. The crystal consists of a 2D periodical array of steel rods immersed in water, for which a complete acoustic band gap is found experimentally. Waveguides for acoustic waves are created by removing one row of rods and the possibility of including sharp bends, owing to the strong spatial confinement within the full band gap, is demonstrated. Stubs can be further added by removing rods from the side-walls of the waveguide. Depending on the stub geometry, definite wavelengths are reflected from the stubs creating a 1D bandgap within the waveguide transmission spectrum, the bandwidth of which can be controlled by arranging a proper sequence of stubs.

Plate and gap acoustic waves for highly sensitive gas and liquid sensors

Abstract: Properties of acoustic waves in thin plates and of gap waves are investigated theoretically and search of optimal orientations in piezoelectric plates is performed for highly sensitive gas and liquid sensor(s) designs.

Investigations of High Pressure Acoustic Waves in Resonators with Seal-Like Features

Abstract: 1) Standing waves with maximum pressures of 188 kPa have been produced in resonators containing ambient pressure air; 2) Addition of structures inside the resonator shifts the fundamental frequency and decreases the amplitude of the generated pressure waves; 3) Addition of holes to the resonator does reduce the magnitude of the acoustic waves produced, but their addition does not prohibit the generation of large magnitude non-linear standing waves; 4) The feasibility of reducing leakage using non-linear acoustics has been confirmed.

Speed of Sound in Binary Mixtures of Pentafluoroethane and 1,1-Difluoroethane from 243.15 K to 333.15 K and Pressures up to 30 MPa

Abstract: The speed of sound in the liquid phase for binary mixtures of pentafluoroethane (CHF2CF3) and 1,1-difluoroethane (CHF2CH3) was measured along six isotherms from (243 to 333) K and at pressures from near the saturation line up to about 30 MPa. The measurements were carried out by a sing-around technique operated at a frequency of 2 MHz employing the fixed-path acoustic interferometer. The combined uncertainty is estimated to be within ±0.2% in the high-density region. The speed of sound in the saturated liquid was estimated by an extrapolation of data obtained for the compressed liquid to the vapor pressure. The results for (1 − x)CHF2CF3 + xCHF2CH3 measured for mole fractions x = 0.3806, 0.6445, and 0.8447 were correlated by the polynomial equation as functions of temperature and pressure. The variations in the speed of sound with the composition at various temperatures and pressures are discussed for the system investigated as well as for (1 − x)CHF2CH3 + xCF3CH2F and (1 − x)CHF2CH3 + xCF3CH3 reported el...

Application of Fiber Velocity Interferometer System for Any Reflector in High Pressure Physics

Abstract: On the basis of traditional velocity interferometer,a fiber velocity interferometer system for any reflector(FVISAR) with wide spectrum laser is illustrated.The important properties of the FVISAR are ideal space interference and convenient delay-time setup.Preliminary tests of FVISAR (using) Hopkinson Bar system shows that the FVISAR works well for low velocity measurement.

SAW sensor for liquid chromatography using 2-port resonator

Abstract: The propagation characteristics of surface acoustic waves (SAW) along a solid surface vary considerably depending on the ambient environment. Therefore, SAW devices are used as sensors in a variety of fields. In particular, surface acoustic waves propagating in the shear horizontal (SH) mode only possess components for which particle displacements are parallel to the surface, which means that, even in a liquid, they propagate without loss of energy. Sensors that utilize such waves are thus suitable for sensing the characteristics of liquids. A flow-type liquid sensor using a 2-port SH-SAW resonator was constructed and used to measure properties, such as electrical characteristics, density and viscosity, of various liquids. Results of measurements using this liquid flow sensing system on a variety of liquids are presented. Finally, this sensing system is demonstrated to be an effective sensor in liquid chromatography, due to its small size, enabling measurement on a very small amount of liquid, and its highly stable operation.

A novel technique for enhancing the signal to noise of laser-based ultrasonic systems

Abstract: Conventional laser ultrasonic systems use pulsed laser sources to generate broadband acoustic waves. The theoretical signal to noise ratio (SNR) of these systems, in the shot noise limit, is inversely proportional to the square root of the bandwidth of the detection system. Previous researchers have shown that improvements in the SNR can be made by generating narrowband acoustic signals using temporally and/or spatially modulated laser pulses, and reducing the detection bandwidth accordingly. The paper describes the generation of high frequency acoustic waves using an amplitude modulated continuous wave (CW) laser. The acoustic signals are detected using a path stabilized Michelson interferometer coupled to an RF lock-in amplifier. This allows for control of the detection bandwidth, which can be reduced by several orders of magnitude below typical broadband laser ultrasonic systems. Experimental results are given showing CW generated acoustic waves in various material systems. The magnitude and phase of the acoustic signals in the frequency domain are detected by the interferometer/lock-in amplifier system, and these data are in turn processed to synthesize the time domain response. The use of narrowband generation/detection combined with subsequent time domain reconstruction allows for a large increase in SNR without losing the ability to distinguish individual acoustic arrivals or modes in the time domain.

Acousto-optic intensity modulation on glass-integrated optic

Abstract: An elastic beam of waves in the Megahertz range, generated using a PZT ceramic, crosses one arm of an integrated Mac-Zehnder interferometer realised by ion-exchange in a glass substrate. Elastic waves modify locally the refractive index of glass. A laser beam of 0.83 μm wavelength is injected into the interferometer. For a sine excitation voltage of 7 volts of the piezoelectric transducer, the variation of the optical intensity measured at the interferometer output is greater than 20% of the intensity observed without elastic waves. Refractive index variation of 9.4×10 -7 were obtained. The optical intensity observed at the output of the interferometer varies at the frequency of the piezoelectric crystal excitation. A model taking into account the elastic and the optical effects is proposed. This model allows the optimisation of the piezoelectric transducer in order to obtain the maximum of elastic strain at the position of the optical waveguides. The theoretical results obtained with the model are in accordance with the experimental results.

Experimentally study of a sharp bending wave-guide constructed in a sonic-crystal slab of an array of short aluminum rods in air

Abstract: We have made a sonic-crystal slab (SCS) of a square-array of 16/spl times/12 short Al rods between a pair of parallel Al plates in air, as an alternative of a 2D sonic crystal. The observed full band-gap was between 15.1-18.8 kHz below -20dB, although the lower and higher boundaries were not sharp enough as 2D sonic crystals. An acoustic wave-guide was constructed in the SCS with a sharp bend. We have measured the intensities of the sound waves traveled along the wave-guide and the leaky waves which propagated straight, without turning the bend. Especially at the center of the full band-gap of the SCS, about 17 kHz, the sound waves were well guided and the ratio of the guided waves to the leaky waves was 22 dB. We have reported here the first experimentally measured characteristics of a pair of acoustic coupled waveguides constructed in an SCS. The coupling between the sound waves travelling along the waveguides was almost uniform inside of the full band-gap of the SCS. They functioned as a 3/spl sim/4 dB unidirectional acoustic coupler.

Endfire beampattern processing for acoustic interferometer

Abstract: Arrangement for determination of an acoustic reflection coefficient of a sample by an acoustic interferometer, the interferometer including a tube, a sample holder, a transmitter, at least one receiver and signal processing means, the sample holder and the transmitter located inside the tube. In this arrangement the receiver is arranged to measure at a plurality of intermediate positions between transmitter and sample holder, an acoustic signal including a direct signal from the transmitter and a reflected signal from the sample; and the signal processing means are arranged: -to record the acoustic signal as a function of the intermediate position, -to separate the direct signal and the reflected signal from the measured signals at each intermediate position by endfire beampattem processing, and -to determine the acoustic reflection coefficient from an amplitude ratio of the separated reflected signal over the separated direct signal.

Acoustic Waves in Bulk Blasts in Opencasts

Abstract: This paper reports results from experimental studies of acoustic waves with amplitudes of 1–100 Pa from bulk blasts in opencasts. The wave shape, amplitude, duration, and pulse, and their dependences on the mass of the explosive at epicentral distances of 1–10 km are obtained. It is shown that the vibration amplitudes excited by acoustic waves acting on the frontage of multi‐storey buildings are several times larger than those produced by seismic waves.

Investigation of local rayleigh wave velocity dispersion due to surface residual stress

Abstract: Residual stress induced in materials by surface modification techniques creates a stress gradient very near the top surface. The modified layer can lead to dispersion of Rayleigh surface wave (RSW) velocity. An analysis of the dispersion of RSW is expected to provide a means for nondestructive evaluation of the stress gradient. Small changes in RSW velocity has been measured using an acoustic interferometer based on a three‐element focused transducer. Dispersion results on Ti‐6Al‐4V material of RSW velocity and dispersion in shot‐peened samples are presented.

Radiation-acoustic method for diagnostics of metals and alloys

Abstract: The acoustic emission, which occurs at the interaction of x-ray with metals and alloys is considered. In this work it is shown that during an annihilation of interstitial atoms with generically bound vacancies, thermal spikes take place, which lead to the generation of acoustic waves.

Relation for the amplitudes of acoustic waves excited by thin elastic plates

Abstract: Relations between the amplitudes of acoustic waves excited by a thin elastic plate under the effect of external forces and the amplitudes of waves scattered by this plate are obtained. Two cases are considered: when the plate separates acoustic media filling two half-spaces and when it separates acoustic media filling an acoustic waveguide. The energy conservation law is used to derive the identities that determine the relations between the amplitudes of acoustic waves radiated by a thin elastic plate under the action of forces.

Scattering of acoustic waves from inhomogeneities of the velocity field of a moving medium

Abstract: It is demonstrated that acoustic waves propagating in a moving liquid can be scattered on inhomogeneities of the velocity field of the medium, and a theory of such scattering is developed. The obtained estimates show the possibility of acoustic diagnostics of the velocity field inhomogeneities in moving media.

Acoustic channels and lenses in a medium with inhomogeneous velocity field

Abstract: A homogeneous moving medium can feature waveguide propagation of acoustic oscillations, provided that the velocity of medium is inhomogeneous. A waveguide of a finite length is equivalent to a lens. The waveguides and lenses are nonreciprocal, whereby their characteristics are significantly different for the acoustic waves propagating in opposite directions. Estimates are obtained and the possible applications are discussed.

Two-dimensional FEM analysis of pressure wave generation mechanisms in TSM liquid sensors

Abstract: Due to benefits like high sensitivity, small size, and cost-effective fabrication, acoustic wave sensors have gained considerable importance. For sensing tasks in liquid media, thickness-shear mode (TSM) resonators are commonly utilized devices, as they ideally do not lead to an unwanted excitation of pressure waves in the liquid. However, due to the finite lateral extension of the resonator, spurious pressure waves are radiated into the adjacent liquid. These pressure waves are largely undamped, which can lead to disturbing interference effects if they are reflected by objects in the vicinity of the sensor. To gain insight into the associated phenomena, we recently performed a 3D finite element (FE) analysis where different excitation mechanisms were identified. However, due to the numerical complexity, these phenomena cannot be accurately studied in a 3D FE-analysis. In this paper we present a more extensive 2D model, which allows us to investigate these effects in depth.