Showing papers on "Acoustic interferometer published in 2000"

Pulsed optoacoustic characterization of layered media

Abstract: Thermoelastic waves generated by absorption of short laser pulses are used to characterize the layer structure of materials. The method is based on the analysis of the distribution of absorbed laser energy from temporal profiles of recorded acoustic signals. Particularly in view of noninvasive medical applications, optoacoustic front surface transducers are investigated in this study, where irradiation of the surface and detection of the acoustic wave take place on the same side of the sample. Front surface detection of optoacoustic waves is studied theoretically and experimentally, with special emphasis on acoustic diffraction and the differences between measurements in the acoustic near and far field. In the experiments, samples with stepwise and continuously varying depth profiles of absorption coefficient were irradiated with laser pulses of 6–8 ns duration. For the detection of the acoustic waves either an optical ultrasound sensor or an annular piezoelectric film was used. Generating the optoacousti...

Method and apparatus of spectro-acoustically enhanced ultrasonic detection for diagnostics

Abstract: An apparatus for detecting a discontinuity in a material includes a source of electromagnetic radiation (110) has a wavelength and an intensity sufficient to induce an enhancement in contrast between a manifestation of an acoustic property in the material (10) and of the acoustic property in the discontinuity (20), as compared to when the material is not irradiated by the electromagnetic radiation. An acoustic emitter directs acoustic waves to the discontinuity in the material. The acoustic waves have a sensitivity to the acoustic property. An acoustic receiver (120) receives the acoustic waves generated by the acoustic emitter after the acoustic waves have interacted with the material (10) and the discontinuity (20). The acoustic receiver also generates a signal representative of the acoustic waves received by the acoustic receiver. A processor (130), in communication with the acoustic receiver and responsive to the signal generated by the acoustic receiver, is programmed to generate informational output about the discontinuity (134) based on the signal generated by the acoustic receiver.

Influence of circumferential partial coating on the acoustic radiation from a fluid-loaded shell

Abstract: Acoustic compliant coatings are a common approach to mitigate the radiation and scattering of sound from fluid-loaded submerged structures. An acoustic compliant coating is a coating that decouples an acoustic source from the surrounding acoustic medium; that is, it provides an acoustic impedance mismatch (different density and speed of sound product). Such a coating is distinct from an ordinary compliant coating in that it may not be resilient in the sense of low stiffness, but still provides an acoustic impedance mismatch. Ideally, the acoustic coating is applied uniformly over the entire surface of the fluid-loaded structure to minimize the acoustic radiation and scattering. However, in certain instances, because of appendages, it may not be practically possible to completely cover the surface of a fluid-loaded structure to decouple it from the adjacent acoustic medium. Furthermore, there may be some inherent advantages to optimizing the distribution of the coating around areas from which the acoustic radiation appears to be dominant. This would be analogous to the application of damping treatment to a vibrating structure in areas where the vibration levels are highest. In the case of the acoustic radiation the problem is more complex because of the coupling between the acoustic fluid and the structure. In this paper, the influence of a partial coating on the acoustic radiation from a fluid-loaded, cylindrical shell of infinite extent and excited by either a line force or an incident plane acoustic wave is examined. The solution to the response and scattered pressure is developed following the procedure used by the authors in previous work on the scattering from fluid-loaded plates and shells. The coating is assumed to be normally reacting providing a decoupling layer between the acoustic medium and the structure; that is, it does not add mass or stiffness to the base structure. The influence of added mass or stiffness of the coating can be included as an added inhomogeneity and treated separately in the solution.

A new formalism for time-dependent wave scattering from a bounded obstacle

Abstract: A time-dependent three-dimensional acoustic scattering problem is considered. An incoming wave packet is scattered by a bounded, simply connected obstacle with locally Lipschitz boundary. The obstacle is assumed to have a constant boundary acoustic impedance. The limit cases of acoustically soft and acoustically hard obstacles are considered. The scattered acoustic field is the solution of an exterior problem for the wave equation. A new numerical method to compute the scattered acoustic field is proposed. This numerical method obtains the time-dependent scattered field as a superposition of time-harmonic acoustic waves and computes the time-harmonic acoustic waves by a new “operator expansion method.” That is, the time-harmonic acoustic waves are solutions of an exterior boundary value problem for the Helmholtz equation. The method used to compute the time-harmonic waves improves on the method proposed by Misici, Pacelli, and Zirilli [J. Acoust. Soc. Am. 103, 106–113 (1998)] and is based on a “perturbative series” of the type of the one proposed in the operator expansion method by Milder [J. Acoust. Soc. Am. 89, 529–541 (1991)]. Computationally, the method is highly parallelizable with respect to time and space variables. Some numerical experiments on test problems obtained with a parallel implementation of the numerical method proposed are shown and discussed from the numerical and the physical point of view. The website: http://www.econ.unian.it/recchioni/w1 shows four animations relative to the numerical experiments.

Optical methods for selectively sensing remote vocal sound waves

Abstract: Methods for remotely sensing sound waves in an optically transparent or semitransparent medium through detecting changes in the optical properties of the medium, which are caused by the sound waves. For example, to implement a microphone that can sense sound at a distance from the sound source. The variations in the attenuation or the phase of a beam of light that is received after passing through the sound waves are sensed and converted to an electrical or other signal. For the attenuation method, the wavelength of the beam of light sensed is selected to be one that is highly attenuated by a constituent of the medium, so that the changing instantaneous pressure of the medium due to the sound pressure waves can be detected through the changing light attenuation due to the changing density of the air along the light path. For the phase shift method, the velocity of light, and therefore its phase is changed by the changing density of the air due to the sound waves, and this can be detected through interferometric means.

Acoustic loss mechanisms in leaky SAW resonators on lithium tantalate

Abstract: We discuss acoustic losses in synchronous leaky surface-acoustic wave resonators on rotated Y-cut lithium tantalate substrates. Laser probe measurements and theoretical methods are employed to estimate the radiation of leaky waves into the busbars of the resonator and the excitation of bulk-acoustic waves. We find that the escaping waves lead to a significant increase in the conductance, typically in the vicinity of the resonance and in the stopband, but that they do not explain the experimentally observed deterioration of the electric response at the antiresonance. At frequencies above the stopband the generation of fast shear bulk-acoustic waves is the dominant loss mechanism.

Apparatus for the measurement of liquid level in a tank

Abstract: Measurement device has an ultrasonic sensor (5) for generating ultrasonic waves in the liquid and for receiving reflected waves from the liquid level and an evaluation unit (8) for deriving the level from the transition times of the ultrasonic waves. Measurement reflector (4) is mounted near floor of container (1) at a predefined distance from sensor. Evaluation unit compares the transition times of the ultrasonic waves reflected at liquid leveler and at measurement reflector

Active device for attenuating the intensity of sound

Abstract: An active device for attenuating noise in a defined region using anti-noise waves. Sensors capable of detecting noise waves and the direction of the waves and providing data to a processor for controlling an electro-acoustic source so that the source emits anti-noise waves in a direction counter to the direction of the incoming noise waves.

V(x,t) acoustic microscopy method for leaky surface acoustic waves parameters measurements

Abstract: In this paper, a new method for the measurement of the acoustical parameters of the laterally uniform specimen is considered. Two focused large angular aperture transducers are used in this technique. Foci of the transducers are placed on the specimen surface and received voltage V(x,t) is acquired during the relative transducers translation along the specimen surface. Due to geometry of the ultrasonic system, angular range of the generated and detected waves can be close to (0, /spl pi//2) and the length of the recording distance is unlimited. Velocity and attenuation of the leaky wave measured by this method do not depend on the temperature of the immersion liquid. Also, contrary to V(z) method, angular resolution of the V(x,t) method is better for small incident angles.

Thermally coupled interfacial acoustic waves observed in transient surface-grating measurements

Abstract: We report the observation of interfacial acoustic waves in the gas above opaque condensed media excited by pulsed laser radiation in transient surface–grating experiments. They differ from previously described interfacial waves in the coupling between the media: Stoneley, Scholte and others described elastically coupled interfacial waves, whereas our analysis, based on approximate solutions of the Navier–Stokes equations, shows that thermal coupling is dominant in this case. Our model relates the amplitude and phase velocity of these interfacial waves to the thermal, elastic and optical properties of the adjoining media. The new thermo–acoustic effect may be of use in the study of thermal and elastic properties of gases at frequencies above 1 MHz, where conventional ultrasonic techniques fail.

Experimental considerations on water-couplant temperature for accurate velocity measurements by the LFB ultrasonic material characterization system

Abstract: The line-focus-beam ultrasonic material characterization (LFB-UMC) system can measure the phase velocity of leaky surface acoustic waves (LSAWs) excited on the water-specimen boundary. The temperature distribution in the water-couplant, however, is the source of some measurement errors in the LSAW velocity. A method for obtaining the proper water-couplant temperature and longitudinal velocity has been developed using the measured temperature distribution and the small interference signals between the V(z) curve signals and the carrier leakage signals arising from the RF tone burst pulse generation circuit used in the system. A procedure to obtain the LSAW velocity accurately is established and the system achieves relative accuracy of LSAW velocity better than /spl plusmn/0.002% at a single chosen point and better than /spl plusmn/0.003% in two-dimensional measurements.

Passive radar apparatus

Abstract: PROBLEM TO BE SOLVED: To solve such problems that, in a conventional radar apparatus, the position of an own station is searched by radio waves in a monostatic radar apparatus whose transmission-reception is performed by the same antenna and that direct waves and reflected waves must be received respectively by separate antennas in order to receive faint reflected waves from a target in the case of a bistatic radar apparatus using radio waves whose transmission factor is unclear. SOLUTION: The direction of the direct waves and that of the reflected waves are estimated by using an ultraresolution algorithm such as MUSIC or the like for a received signal. After that, the direct waves and the reflected waves are separated and extracted from the received signal. Even when transmitted waves are used as the direct waves and even when the direct waves and the reflected waves are received by the same antenna, the distance and the direction of the target can be found, and the position of the own station can not be searched.

Clamping-on ultrasonic flow rate measuring method and multipath ultrasonic flow rate measuring method as well as clamping-on ultrasonic flowmeter and multipath ultrasonic flowmeter

Abstract: PROBLEM TO BE SOLVED: To provide a technique by which a flow rate can be measured with good efficiency even in a single path when the flow rate inside a pipe is measured, to provide a technique by which the flow rate can be measured without increasing the number of paths which are changed into a multipath and to provide a technique by which ultrasonic waves propagated along the wall of the pipe are detected or canceled without improving the pipe itself. SOLUTION: As compared with the acoustic velocity of ultrasonic waves from a transmitting sensor which is provided with a piezoelectric element used to generate the ultrasonic waves and which can be attached to the pipe, the acoustic velocity of ultrasonic waves which are transmitted in a material for the pipe is made small. The ultrasonic waves are detected in a position decided by Snell's law. When the ultrasonic waves are totally reflected, plate waves are used. The wall thickness of the pipe is set in a limited thickness. The ultrasonic waves which excite the plate waves along the wall of the pipe are passed through an average flow velocity path, and the flow rate is measured.

Bulk Acoustic and Surface Acoustic Waves

Abstract: This chapter describes the excitation, detection and propagation of acoustic waves, including SAWs in various propagation media. Although I have tried to explain their physics as simple as possible, the content may seem difficult for readers who have dealt with SAW devices as an electronic element. But readers should not skip this chapter because it provides the technical background for the discussions given in the following sections.

Generation and Radiation of Acoustic Waves from a 2-D Shear Layer

Abstract: A parallel numerical simulation of the radiation of sound from an acoustic source inside a 2-D jet is presented in this paper. This basic benchmark problem is used as a test case for scattering problems that are presently being solved by using the Impedance Mismatch Method (IMM). In this technique, a solid body in the domain is represented by setting the acoustic impedance of each medium, encountered by a wave, to a different value. This impedance discrepancy results in reflected and scattered waves with appropriate amplitudes. The great advantage of the use of this method is that no modifications to a simple Cartesian grid need to be made for complicated geometry bodies. Thus, high order finite difference schemes may be applied simply to all parts of the domain. In the IMM, the total perturbation field is split into incident and scattered fields. The incident pressure is assumed to be known and the equivalent sources for the scattered field are associated with the presence of the scattering body (through the impedance mismatch) and the propagation of the incident field through a non-uniform flow. An earlier version of the technique could only handle uniform flow in the vicinity of the source and at the outflow boundary. Scattering problems in non-uniform mean flow are of great practical importance (for example, scattering from a high lift device in a non-uniform mean flow or the effects of a fuselage boundary layer). The solution to this benchmark problem, which has an acoustic wave propagating through a non-uniform mean flow, serves as a test case for the extensions of the IMM technique.

Detection of laser excited surface acoustic waves by infrared radiation

Abstract: Remote detection of ultrasonic waves is shown experimentally by measuring the infrared (IR) radiation accompanying the adiabatic propagation of surface waves. The Rayleigh waves were excited by a pulsed Nd:yttrium–aluminum–garnet laser on the surface of a steel sample at temperatures up to 700 °C. The observed time-of-flight data of the Rayleigh waves correspond to values obtained by optical interferometry and the measured signal-to-noise ratio of ≈0.1 agrees with the estimated value using an IR detector with a sensitivity of D*=1.7×109 mm √Hz/W. Further improvements of IR detection may lead to a viable tool for laser ultrasonics.

Device for evaluating, with acoustic waves, the temperature of a room

Abstract: The temperature measuring device has a device (4) for generation and detection of sound waves, with determination of the propagation time for the sound waves over a defined path (X) in the room (2), used for calculation of the room temperature (U). The defined path may be determined via a proximity method. An Independent claim for a method for measuring a room temperature using sound waves is also included.

Influence of non-homogeneous uniaxial pressure on the propagation of bulk acoustic waves in crystals

Abstract: The development of the theory of propagation of small amplitude bulk acoustic waves in crystals under uniaxial mechanical pressure has been made by taking into account the condition of non-homogeneous deformation of crystal sample. It has been shown that the path of bulk acoustic waves will be a function of the non-homogeneous deformation. As an example, calculations for some crystal directions of cubic crystal Bi/sub 12/GeO/sub 20/ (23 point symmetry) have been made.

Measuring Scanning Acoustic Microscope with a Harmonic Sounding Signal

Abstract: A concept of a scanning acoustic microscope with a harmonic sounding signal for measuring the parameters of local homogeneous regions of flat samples is proposed. The distinctive feature of the device is the utilization of the Doppler effect that occurs in the sounding wave reflected from the sample surface when the sample is uniformly moved relative to the focusing ultrasonic transducer of the microscope. It is theoretically demonstrated that the spectrum of the received signal is determined by the product of the reflection coefficient and the transfer function of the transducer. The errors of the measurement technique are considered, and the sources of signal distortions are analyzed. High sensitivity of the measurement results to the errors of the scanning system is demonstrated. The developed measuring microscope is described, in which an acoustic interferometer is used to provide the necessary precision of the scanning coordinate measurement. The microscope transfer function is measured for the frequency of the sounding signal 65 MHz, and the values of density and bulk wave velocities are determined for a homogeneous sample by the measured phase of the reflection coefficient using the technique of nonlinear estimation of parameters. With fused quartz used as an example, it is shown that the measurement error is 7.2% for density and 2.3 and 0.7% for the velocities of longitudinal and transverse waves, respectively. In addition, the velocity of a leaky surface wave (SAW) is determined by two methods. One method is based on measuring the position of the inflexion point for the experimental phase of the reflection coefficient, and the other is based on calculating the SAW velocity corresponding to the measured values of density and bulk wave velocities. The errors of these methods are found to be equal to 0.42 and 0.17%, respectively.

Cleaning objects using sound waves involves displacing maxima and minima of oscillations to homogenize sound intensity in time and space within medium exposed to sound waves

Abstract: The method involves cleaning objects in fields of standing sound waves, preferably ultrasonic waves, whereby the objects to be cleaned are placed in a medium to be subjected to the sound waves. The maxima and minima of the oscillations are displaced in order to homogenize the sound intensity in time and space within the medium exposed to the sound waves. Independent claims are also included for the following: an arrangement for implementing the method.

2000 /EEE/EIA hternational Frequency Control Symposium and Exhibition INFLUENCE OF NON-HOMOGENEOUS UNIAXIAL PRESSURE ON THE PROPAGATION OF BULK ACOUSTIC WAVES IN CRYSTALS

Abstract: The development of the theory of propagation small amplitude bulk acoustic waves in crystals under the uniaxial mechanical pressure has made by taking into account the condition of non-homogeneous deformation of crystal sample. It has been shown that the path of bulk acoustic waves will be function of a kind non-homogeneous deformation. As an example the calculation for some crystal directions of cubic crystal Bi12GeOzo (23 point symmetry) has made.

Restrictions and possibilities for the SAW velocity measurement utilizing the two-beams optical interferometer

Abstract: The precise quantitative study of two optical beam diffraction by SAW corresponding the real experimental situations in crystals has been done. Acoustical anisotropy, light diffraction, and interference are taking into account. It helps to find restrictions and possibilities for the SAW velocity measurement utilizing the two-beam optical interferometer. The new measurement algorithm and scheme for the SAW velocity studding that increases the methods possibilities are described.

On the interaction of finite-amplitude saw-tooth sound waves with an axisymmetric supersonic jet

Abstract: The results of an experimental investigation of the interaction of finite-amplitude saw-tooth sound waves (with a sound pressure level of 170 dB) with an axisymmetric supersonic air jet are presented. It is shown that the passage of sound waves through the jet is accompanied by sound refraction on averaged-flow nonuniformities, interaction between the sound and shock waves, and diffraction.

Acoustic scattering of metallic springs in elastic medium

Abstract: In applications such as ultrasonic immersion testing, damping of flow noise in pipes and ducts and coating of acoustic control surfaces, it is very useful to reduce the reflection of acoustic waves from surfaces. Significant echo reduction can be achieved by addition of an anechoic coating. According to some general design guidelines for a single layer of homogenous coating, a single layer of 15 dB coating must be at least one wavelength thick. For absorbing acoustic waves of low frequencies, inhomogeneities such as metallic fillers, cavities and irregular metallic helices can be introduced into the lossy matrix to substantially enhance the acoustic absorption by acoustic scattering. In this presentation, the acoustic scattering of a single metallic spring embedded in an infinite elastic medium has been investigated using a boundary element formulation. The cross sections of the scattered longitudinal and shear waves have been calculated for various spring sizes, orientations and wave numbers. It will be ...