Showing papers on "Acoustic interferometer published in 1998"

Spectral properties of classical waves in high-contrast periodic media

Abstract: We introduce and investigate the band gap structure of the frequency spectrum for classical electromagnetic and acoustic waves in a high-contrast, two-component periodic medium. The asymptotics with respect to the high-contrast is considered. The limit medium is described in terms of appropriate self-adjoint operators and the convergence to the limit is proven. These limit operators give an idea of the spectral structure and suggest new numerical approaches as well. The results are obtained in arbitrary dimension and for rather general geometry of the medium. In particular, two-dimensional (2D) photonic band gap structures and their acoustic analogues are covered.

Microfluidic motion generation with acoustic waves

Abstract: This paper presents a novel approach for producing microfluidic motion by loosely focused acoustic waves (generated by piezoelectric zinc oxide thin film). Results show that the acoustic waves generated by radio frequency (r.f.) sources with frequencies corresponding to the thickness-mode resonances of the piezoelectric film are very effective in moving liquid around when the waves are loosely focused. The device operates without any significant temperature increase in the liquid, and will be very attractive for mixing or transporting temperature-sensitive fluids.

Ultrasonic surface waves above rectangular-groove gratings

Abstract: A modal model, initially developed to modelize diffraction of electromagnetic waves by rectangular-groove gratings, is used to describe ultrasonic surface waves above the same structures in air. A simple analytical formulation which provides results comparable to the modal method is presented. Measurements performed on ultrasonic surface waves are compared to predictions obtained with the simplified formulation and the modal model.

Acoustic Localization in Bubbly Liquid Media

Abstract: Acoustic wave propagation in liquid media containing many air-filled bubbles is ab initio considered. A self-consistent method is used to derive a set of coupled equations describing rigorously the multiple scattering of waves in such media. The wave transmission and backscattering are then solved exactly. The numerical results indicate localization of acoustic waves in a range of frequency.

Device for generating acoustic shock waves, especially for medical applications

Abstract: A device for generating acoustic shock waves, comprising at least two electrodes which form a spark discharge gap G in a fluid volume and a reflector for the acoustic shock waves generated during the spark discharge made of an electrically conductive material, and wherein the power to one of the electrodes is supplied by way of the reflector.

Experiments with a new acoustic particle velocity sensor in an impedance tube

Abstract: The development of a new acoustic sensor makes it possible to measure acoustic particle velocity instead of sound pressure. The new sensor, called the Microflown, can be used in the frequency range of 0 to approximately 20 kHz. As one of the first applications, the new sensors are applied in an impedance tube to determine the impedance of an aluminium sample at the end of the tube. The sample has an orifice which accounts for the sound absorption. Comparing the results with theory and measurements with microphones leads to an excellent agreement. The characteristics of the Microflowns, like the simplicity and the small dimensions, make it a very attractive alternative to the microphones. Furthermore, the sensitivity to the direction of the acoustic waves and the matching of the phase and sensitivity of two sensors can be used in other research fields in acoustics as well.

Shape measurements of mirror surfaces with a lateral-shearing interferometer during machine running

Abstract: A common path lateral-shearing interferometer with a minimum number of optical components has been developed. Because the interferometer is little affected by mechanical vibrations and air turbulence, it can be mounted on an ultraprecision lathe and can be used to measure the shapes of workpieces. A plane parallel glass plate is used to shear the wavefront under test in the interferometer. To analyze the interference fringes obtained by the interferometer precisely, a fringe-scanning method using a slight tilt of the glass plate is used. Zone plates that are computer-generated holograms are used to measure spherical and aspherical surfaces with the interferometer. A spherical and a parabolic concave mirror were measured with the interferometer. The spherical mirror was also measured by a Fizeau interferometer to compare the error with that measured by the lateral-shearing interferometer. The experimental results agreed well with those measured by the lateral-shearing interferometer.

Surface waves above thin porous layers saturated by air at ultrasonic frequencies

Abstract: Experimental evidence of surface waves above thin porous layers of thickness varying from 18 to 6 mm of plastic foams having a porosity close to one is presented Phase velocity measurements at 40 kHz indicate the presence of waves propagating slower than homogeneous plane waves The pole of the reflection coefficient related to these waves is detected by near-field holography at 20 kHz The different experimental results are compared with predictions obtained by replacing the air inside the layers by an equivalent fluid, and using methods developed in the context of electromagnetism to localize the poles of the reflection coefficient

Non-contact measurements of ultrasonic waves on paper webs using a photorefractive interferometer

Abstract: An apparatus and method for non-contact measurement of ultrasonic waves on moving paper webs employs a photorefractive interferometer. The photorefractive interferometer employs an optical head in which the incident beam and reflected beam are coaxial, thus enabling detection of both in-plane and out-of-plane waves with a single apparatus. The incident beam and reference beams are focused into a line enabling greater power to be used without damaging the paper.

The coexistence of pressure waves in the operation of quartz-crystal shear-wave sensors

Abstract: It is demonstrated that an AT-cut quartz crystal driven in the thickness-shear-wave mode and typically used as a sensor to monitor the viscoelastic shear-wave properties of a fluid also produce longitudinal pressure waves. Unlike the shear wave, these waves are capable of long-range propagation through the fluid and of reflection at its boundaries, notably at an outer fluid–air interface. They introduce a component into the measured electrical impedance and resonance frequency shift of the crystal, which reflects the setting up of cyclic pressure-wave resonances in the fluid. This has important implications for the practical employment of these crystal as sensors. Under appropriate conditions, as demonstrated for water and n-octane, it is possible to determine the propagating properties of sound waves in a fluid simultaneously with the viscoelastic shear-wave properties. These experiments are supported by an analysis of the appropriate hydrodynamic equations for waves in the crystal–fluid system, which pr...

An experimental model of a acousto-electromagnetic sensor for detecting land mines

Abstract: A hybrid technique is presented in this paper that simultaneously uses both electromagnetic and acoustic waves in a synergistic manner to detect buried land mines. The configuration of the system currently being studied is shown. The system consists of an electromagnetic radar and an acoustic source. An acoustic surface (Rayleigh) wave is induced in the Earth by means of a stationary transducer on the surface. The transducer is placed behind the region being scanned for mines and directs the surface acoustic wave into the region being searched. The surface acoustic wave interacts with the mine and causes both the mine and the surface of the Earth to be displaced. The displacement of the mine is different than the Earth, because the acoustic properties of the mine are quite different than those of the Earth. The displacement of the surface of the Earth when a mine is present is different than when it is not present because of the waves scattered from the mine. The electromagnetic radar is used to detect these displacements and, thus, the mine.

An optical fibre interferometer for remote detection of laser generated ultrasonics

Abstract: A 15 MHz bandwidth active homodyne fibre-optical interferometer for remote detection of laser-induced ultrasonic waves in metallic and non-metallic targets is reported. The fibre interferometer design and associated electronics are described in sufficient detail for it to be easily constructed. The interferometer uses a low-power He-Ne laser and the reflected signal from the natural surface of the target at a distance of 200 mm. Despite its use of an open air path in the sensing arm and an all-fibre design, the interferometer achieved a single-pulse noise equivalent displacement of 0.4 nm and a figure of merit of 0.1 pm .

Acoustic impedance measuring device

Abstract: PROBLEM TO BE SOLVED: To provide a feasible acoustic impedance measuring device that can display acoustic impedance of an object to be measured in a high resolution and a high speed, and as an image. SOLUTION: Trapezoidal wave or rectangular wave of pulse signal is inputted from a pulsar circuit 2 to an ultrasonic transducer 1. Generated ultrasonic wave, after delayed by an acoustic delaying medium, is returned to the ultrasonic transducer 1 to generate a response signal. Parameters are extracted from frequency characteristic of this response signal, and the acoustic impedance is measured using a parameter strongly correlated with the acoustic impedance, and is displayed as an image.

Acoustic transducer with liquid-immersed, pre-stressed piezoelectric actuator in acoustic impedance matched transducer housing

Abstract: A liquid-filled acoustic transducer for finishing an exposed surface of a work medium, such as plastic concrete, transmits acoustic energy generated within an enclosed liquid medium, through a transducer housing member, and into the exterior work medium. Acoustic waves are generated by electrically-actuated liquid-immersed piezoelectric elements housed within the device. The efficiency with which acoustic waves are transmitted from the interior of the device to the adjacent work medium is enhanced by providing an intermediate transducer housing member, disposed between the liquid in which the piezoelectric elements are immersed and the work medium, having acoustic impedances at its two major surfaces matching the respective acoustic impedances of the respective interfacing media and a continuous acoustic impedance gradient between those two surfaces.

Determination of phase velocity and attenuation of surface acoustic waves with improved accuracy

Abstract: The phase velocity and the attenuation of surface acoustic waves (SAW) are determined for Rayleigh waves on free and metallized quartz substrates. The measurement setup and the evaluation procedure based on the direct modeling of the phase for the transmitted signal are discussed. The used method is compared to other evaluation techniques. The results for the phase velocity are given and compared to theoretical values determined with a boundary element method (BEM). Parameter values for an improved model are extracted for the phase velocity as well as for the attenuation. The model is applied to the simulation of TCF-resonators and a comparison between experiment and simulation is performed.

Remote control device for controlling electronic devices

Abstract: The present invention is generally directed to a method of remotely controlling electronic devices by using the change in time required for sound waves to travel from an emitter to a detector. The time needed for emitted sound waves to reach a detector depends on the distance from the emitter to the detector. The present invention uses a system which measures the time between emission and detection of two or more successive sound pulses or sound waves. The change in time for sound waves to travel the distance from the emitter (or emitters) to the detector (or detectors) is determined and then used for controlling electronic devices. The sound waves are produced by a sound generator, and the detector is designed specifically for the detection of sound waves. In certain embodiments, ultrasonic sound waves or pulses are produced by the sound generator and are used to control an electronic device such as a computer cursor or vehicle.

Theory of acoustic streaming generated by ultrasonic Lamb waves

Abstract: A theory on acoustic streaming generated by Lamb waves propagating in a thin composite membrane was developed. Using this theory, the mass-transport velocity in water, which is loaded on a 4-μm-thick membrane, due to Lamb waves at 4.7 MHz was calculated. The results are in good agreement with the experimental values measured by Moroney et al. [Appl. Phys. Lett. 59, 774 (1991)].

Direct detection of acoustic waves by laser light diffraction and proposals of the optophone

Abstract: The conventional light diffraction method cannot be applied to the measurement of the acoustic waves with a long wavelength, where the diffracted optical waves propagate in the penetrating optical beam and cannot be measured because of the disturbance by the latter. In this study, the Fraunhofer diffraction method, which was developed as a new means to detect the electromagnetic radiation scattered within the penetrating light beam in the plasma‐nuclear fusion research, is applied to the measurement of acoustic waves. It is experimentally demonstrated that the acoustic wave with a wavelength longer than 8.5 mm can be detected by a visible laser of 5 mW, and the amplitude of the electrical output signal from a photodiode is linearly proportional to the sound pressure and the probe laser power, as predicted by the theory. The frequency property and directivity of the optical sound‐antenna are roughly estimated by the preliminary experiment. Furthermore, the Optophone (the optical microphone) of various type...

X-ray diffraction by standing surface acoustic waves

Abstract: X-ray diffraction by standing surface acoustic waves was investigated under total external reflection conditions. A standing surface acoustic wave was formed on the surface of a YZ-cut of a LiNbO 3 crystal by superposition of two travelling surface acoustic waves. The diffracted X-ray radiation intensity was found to oscillate with twice the frequency of the surface acoustic wave excitation.

Anisotropy of sound velocity for a new PbB4O7 crystal as determined by the laser ultrasonic technique

Abstract: O7 crystal is a new nonlinear optical crystal. For the first time the anisotropy of the velocities of its longitudinal and surface acoustic waves (SAWs) are determined by laser ultrasonic technique. The velocities of surface waves for X-, Y-, and Z-cut crystals are also calculated. The theoretical calculations of slowness curves are in good agreement with experimental results. The SAW slowness curve is elliptical for Y- or Z-cut crystal wafers, and circular for an X-cut wafer.

Variable path cryogenic acoustic interferometer

Abstract: We describe a variable path acoustic interferometer for use at cryogenic temperatures. Movement is enabled without mechanical coupling via two piezoelectric bimorphs wired and mounted in a manner that preserves the parallelism of two ultrasonic transducers that define the acoustic path. A certain degree of in situ alignment can also be accomplished. Path length sweeps from 0 to 180 μm have been made at cryogenic temperatures and preliminary sound velocity measurements in liquid 4He and gaseous 3He near 4 K are presented which agree well with past measurements.

Method and apparatus for measuring sound velocity in liquid

Abstract: A method and apparatus for measuring sound velocity in a liquid, said method comprising the transmitting of a sound pulse or a group of sound pulses to the liquid to be measured and the measuring of the transit time of the sound pulse or the group of sound pulses in the liquid to be measured To improve the accuracy of measurement, the sound pulse or the group of sound pulses is simultaneously transmitted with one and the same transmitter both to the liquid to be measured and to the reference material in which sound velocity is previously known The sound pulse or the group of sound pulses arriving from the liquid to be measured and from the reference material is received and the time interval is measured with one and the same measuring means

Phase velocity measurement of in-plane polarized surface acoustic waves with high spatial resolution

Abstract: In this paper we present a new method that allows the measurement of the phase velocity of in-plane polarized SAWs with high spatial resolution. The capabilities of the scanning acoustic force microscope had to be extended by the analysis of torsional cantilever motion. A nonlinear coupling mechanism between in-plane oscillations and this movement could be found, that allows an mechanical mixing of in-plane SAWs. Phase velocity measurements of Love waves on the system Au/SiO/sub 2//ST-quartz are presented. A good agreement with theoretical predictions for the velocities could be found.

Cavitation and capillary wave from a parametric decay scheme

Abstract: Acoustic cavitation in liquids and capillary waves which cause ultrasonic atomization are considered to be related to the 1/2 subharmonic of ultrasonic surface waves via parametric decay instability. The cavitation bubble oscillation mode is an asymmetric surface bubble oscillation that does not easily emit ultrasonic waves into water and accumulates acoustic energy from longitudinal waves. The capillary waves accumulate acoustic energy in a surface of liquid, enough to be used not only for atomization but also the separation of water‐ethanol solution. These were confirmed by experiments using ultrasonic longitudinal waves in water.

Two light beams diffraction by a surface acoustic wave in an anisotropic solid

Abstract: The results of a theoretical investigation of simultaneous two light beams diffraction by a surface acoustic wave (SAW) in crystals are considered. They form the theoretical basis of descriptive work of a new acoustooptic method of SAW velocity measurement based on a two optical beams interferometer. The influence of elastic anisotropy of a solid on the diffraction and interference of light beams and accuracy of measurement of phase and group SAW velocities in anisotropic mediums are considered. It is shown how to realize direct measurement of a SAW steering beam angle. The obtained results considerably increase possibilities of the given method for measurement of the basic characteristics of acoustic waves in crystals.

Determination of the acoustic nonlinearity parameter B/A using a phase locked ultrasonic interferometer

Abstract: The acoustic nonlinearity parameter B/A is an important parameter for characterizing acoustic propagation in fluids. Recent developments in the fields of shock waves and biomedical ultrasonics have necessitated an accurate method for measuring this quantity. This paper presents a new technique based on an ultrasonic interferometer that allows accurate measurements of the change in sound speed within a liquid cavity. The system makes use of a novel continuous wave phase locking principle, which has the effect of nullifying many of the nonlinearities inherent in the acoustic interferometer. The phase lock circuitry automatically adjusts the frequency so as to keep an exact integer number of waves in the cavity regardless of changes in sound speed. Using this principle, B/A is determined by relating a small change in ambient pressure (less than 2 bar) to a change in frequency under isentropic conditions. B/A values are calculated using this experimental setup for several liquids including two slow sound‐spee...

Method of detecting gas cavities in liquids, e.g. motor oil in IC engine

Abstract: The method involves subjecting the liquid to sound waves which pass from a sound generator to a sound receiver, which may be both integrated into an acoustic system (5). The signals detected by the sound receiver are processed to detect gas. The associated arrangement contains a sound generator and receiver and a flow channel (1) in which the liquid flows. The generator and a receiver are arranged so that the flow channel is subjected to the sound waves passing between them. The acoustic system may be at one end of the channel and a mirror (6) may be at the other end of the channel.

Method and device for producing shock waves for technical and specially medico-technical applications

Abstract: Intensive pressure waves can be used as shock waves for medico-technical applications, specially for lithotripsy and/or pain therapy. To this end, sound waves with high energy density are produced by pressure pulsations. According to the invention, the pressure waves are produced by briefly heating a conductive electrolyte, wherein an electrical impulse is used for direct and substantially loss-free conversion of electrical energy in order to heat the electrolyte. A pertaining device to carry out said method is characterized by an arrangement of two electrodes (1, 2, 7, 8, 21, 22) which contain one electrolyte (3) and are controlled by an output pulse generator (5), wherein the sound waves are decoupled by suitable means into a sound propagating medium (4).