Showing papers on "Acoustic interferometer published in 2011"

Enhanced and reduced transmission of acoustic waves with bubble meta-screens

Abstract: We present a class of sonic meta-screens for manipulating air-borne acoustic waves at ultrasonic or audible frequencies. Our screens consist of periodic arrangements of air bubbles in water or possibly embedded in a soft elastic matrix. They can be used for soundproofing but also for exalting transmission at an air/water interface or even to achieve enhanced absorption.

Acoustic Absorption in Porous Materials

Abstract: An understanding of both the areas of materials science and acoustics is necessary to successfully develop materials for acoustic absorption applications. This paper presents the basic knowledge and approaches for determining the acoustic performance of porous materials in a manner that will help materials researchers new to this area gain the understanding and skills necessary to make meaningful contributions to this field of study. Beginning with the basics and making as few assumptions as possible, this paper reviews relevant topics in the acoustic performance of porous materials, which are often used to make acoustic bulk absorbers, moving from the physics of sound wave interactions with porous materials to measurement techniques for flow resistivity, characteristic impedance, and wavenumber.

Ultrasonic/photoacoustic imaging devices and methods

Abstract: Devices are disclosed for obtaining data of a sample, particularly data capable of being processed to produce an image of a region of the sample. An exemplary device includes a light-beam source, an acoustic-wave source, an optical element, and an acoustic detector. The optical element is transmissive to a light beam produced by the light-beam source and reflective to acoustic waves produced by the acoustic-wave source. The optical element is situated to direct the transmitted light beam and reflected acoustic wave simultaneously along an optical axis to be incident at a situs in or on a sample to cause the sample to produce acoustic echoes from the incident acoustic waves while also producing photoacoustic waves from the incident light beam photoacoustically interacting with the situs. The acoustic detector is placed to receive and detect the acoustic echoes and the photoacoustic waves from the situs. The acoustic detector can comprise one or more hydrophones exploiting the acousto-electric effect.

Sound field separation with a double layer velocity transducer array (L)

Abstract: In near-field acoustic holography sound field separation techniques make it possible to distinguish between sound coming from the two sides of the array. This is useful in cases where the sources are not confined to only one side of the array, e.g., in the presence of additional sources or reflections from the other side. This paper examines a separation technique based on measurement of the particle velocity in two closely spaced parallel planes. The purpose of the technique is to recover the particle velocity radiated by a source in the presence of disturbing sound from the opposite side of the array. The technique has been examined and compared with direct velocity based reconstruction, as well as with a technique based on the measurement of the sound pressure and particle velocity. The double layer velocity method circumvents some of the drawbacks of the pressure-velocity based reconstruction, and it can successfully recover the normal velocity radiated by the source, even in the presence of strong disturbing sound.

Acoustic scattering cancellation via ultrathin pseudo-surface

Abstract: We propose the use of an ultrathin cloak made of an acoustic surface impedance that leads to invisibility for acoustic waves. Unlike current acoustic cloaks that require volumetric metamaterials and a significant shell thickness, the mantle cloak presented here is based on a patterned acoustic metasurface that produces similar effects in a thinner geometry. We show that by covering a cylindrical obstacle by a specific acoustic surface impedance, the total scattering may be significantly reduced in the near- and the far-field, thus suppressing its overall acoustic signature. Potential applications lie in low-detectability, camouflaging, and non-invasive acoustic probing.

Observationally constrained modeling of sound in curved ocean internal waves: examination of deep ducting and surface ducting at short range.

Abstract: A study of 400 Hz sound focusing and ducting effects in a packet of curved nonlinear internal waves in shallow water is presented. Sound propagation roughly along the crests of the waves is simulated with a three-dimensional parabolic equation computational code, and the results are compared to measured propagation along fixed 3 and 6 km source/receiver paths. The measurements were made on the shelf of the South China Sea northeast of Tung-Sha Island. Construction of the time-varying three-dimensional sound-speed fields used in the modeling simulations was guided by environmental data collected concurrently with the acoustic data. Computed three-dimensional propagation results compare well with field observations. The simulations allow identification of time-dependent sound forward scattering and ducting processes within the curved internal gravity waves. Strong acoustic intensity enhancement was observed during passage of high-amplitude nonlinear waves over the source/receiver paths, and is replicated in the model. The waves were typical of the region (35 m vertical displacement). Two types of ducting are found in the model, which occur asynchronously. One type is three-dimensional modal trapping in deep ducts within the wave crests (shallow thermocline zones). The second type is surface ducting within the wave troughs (deep thermocline zones).

Extraordinary acoustic shielding by a monolayer of periodical polymethyl methacrylate cylinders immersed in water

Abstract: We study, both experimentally and numerically, the acoustic transmission through a monolayer of periodical polymethyl methacrylate cylinders immersed in water. Beyond our expectation, nearly-total reflection is observed for the system, consisting of two ingredients with low impedance contrast. Our investigation manifests that this extraordinary acoustic shielding mostly stems from the resonant excitation of the localized Stoneley surface waves in individual cylinders. Such local modes are rooted in the complicated coupling between the longitudinal and transverse waves and are unique in acoustic systems.

Acousto-optic cell based on paratellurite crystal with surface excitation of acoustic waves

Abstract: An acousto-optic cell based on a paratellurite (TeO2) crystal, in which bulk acoustic waves are excited directly from the surface due to an intrinsic piezoelectric effect in the material, has been studied. The bulk shear acoustic waves with a frequency of 50 MHz propagate along the [001] and [110] axes with a polarization along the \(\left[ {\bar 110} \right]\) axis. The ultrasound has been excited by a simple system of two electrodes formed on one face of the crystal. Characteristics of the acousto-optic cell have been determined and the parameters of acoustic waves have been measured at 633 nm by optical beam diffraction on the acoustic diffraction grating.

Acoustic transducer apparatus, systems, and methods

Abstract: In some embodiments, apparatus and systems, as well as method and articles, may operate to launch acoustic waves along a first acoustic path length from an acoustic transducer toward an axis of rotation, to impinge on a first front surface of a target substantially fixed with respect to the axis, and to receive a reflection of the acoustic waves from the first front surface at the acoustic transducer. After rotating the acoustic transducer about the axis along a substantially circular path, additional activities may include launching acoustic waves along a second acoustic path length, different from the first acoustic path length, from the acoustic transducer toward the axis to impinge on a second front surface of the target, and receiving a reflection of the acoustic waves from the second front surface at the acoustic transducer. Additional apparatus, systems, and methods are disclosed.

Measuring arrangement for determining level and/or concentration of e.g. oil in oil tank mounted in motor car, has deflection device whose interface is formed on prism shaped element in which sound waves are propagated and impinged

Abstract: The measuring arrangement has a receiving space for receiving the liquid. A transmitter converts an electrical signal into sound waves and emits sound waves in a predetermined direction. A deflection device (30) has an interface (38) for reflecting and deflecting the sound waves. A receiver receives the sound waves and converts sound waves into electrical signal after passing through a measuring path. The interface is formed on prism shaped element (32) in which the sound waves are propagated and impinged.

Radial layout for acoustic wave touch sensor

Abstract: Surface acoustic waves in a radial pattern are used to detect touch. Different radial transducer arrangements may allow for locating multiple simultaneous touches without ambiguity. Instead of transmitting along a line to be reflected at multiple points, the surface acoustic waves are transmitted radially. The surface acoustic waves are transmitted along different angles in an angular span spread out over at least part of the touch region. Using acoustic waves traveling along intersecting paths, a point location of a touch may be determined by detection, in part, of at least one angle.

Estimating surface acoustic impedance with the inverse method.

Abstract: Sound field parameters are predicted with numerical methods in sound control systems, in acoustic designs of building and in sound field simulations. Those methods define the acoustic properties of surfaces, such as sound absorption coefficients or acoustic impedance, to determine boundary conditions. Several in situ measurement techniques were developed; one of them uses 2 microphones to measure direct and reflected sound over a planar test surface. Another approach is used in the inverse boundary elements method, in which estimating acoustic impedance of a surface is expressed as an inverse boundary problem. The boundary values can be found from multipoint sound pressure measurements in the interior of a room. This method can be applied to arbitrarily-shaped surfaces. This investigation is part of a research programme on using inverse methods in industrial room acoustics.

Three-port interferometer in silicon-on-insulator for wavelength monitoring and displacement measurement

Abstract: The wavelength of a narrow-band optical signal can be accurately tracked by means of an interferometer having a fixed path length difference. For example, a low-cost Fiber Bragg Grating (FBG) interrogation system which tracks the FBG reflection wavelength over time can be based on such an interferometer. Alternatively, an interferometer is operated at fixed wavelength to monitor displacement, as applied in metrology.

Meandering collimated beam of surface acoustic waves on a trigonal crystal ball

Abstract: To fully exploit high-quality piezoelectric crystals in acoustic wave devices, it is necessary to remove limitations not related to the crystal quality. Among them, the “diffraction loss” is most serious. Previously, we have developed the ball surface acoustic wave (SAW) sensor using crystal ball. However, because of the piezoelectric crystal’s strong anisotropy, we could not control the propagation route of SAWs on a ball. Here, we report a discovery that the beam propagates along a meander route, identical at every turn. Consequently, we succeeded in completely removing the diffraction loss. Since it can fully exploit the quality of crystals, it will stimulate progress of crystal technology.

Effect of randomly varying impedance on the interference of the direct and ground-reflected waves.

Abstract: A randomly varying ground impedance is introduced into the solution for the sound field produced by a point source in a homogeneous atmosphere above a flat ground. The results show that in general the ground with a random impedance cannot be represented by an effective, non-random impedance. The behavior of the solution is studied with a relaxation model for the impedance in which porosity and the static flow resistivity are random variables. Mean values and standard deviations are adopted from measurements of two types of ground surfaces. For both surfaces, the mean intensity of the sound field above a random-impedance ground deviates only slightly from the intensity above a non-random impedance. The normalized standard deviation of intensity fluctuations can, however, be greater than one, thus indicating that for a particular realization of the random impedance, the sound intensity might significantly deviate from the intensity for a non-random impedance.

A new definition for acoustic dose

Abstract: This paper discusses a recent proposal for definitions of acoustic dose and acoustic dose-rate. Acoustic dose is defined as the energy deposited by absorption of an acoustic wave per unit mass of the medium supporting the wave. Its time-derivative, acoustic dose-rate, Qm, in W kg−1 is central to the prediction of both rate of temperature rise and radiation force. These quantities have spatial and temporal dependency, depending on the local field parameters (acoustic pressure, particle velocity, intensity) and local material properties (absorption coefficient, αa, and mass density, ρ0). Spatial and/or temporal averaging can be applied where appropriate. For plane-wave monochromatic conditions in a homogeneous medium, Qm=2αaI/ρ0, (I is the time-averaged intensity), a simple expression which may also incorporate frequency dependencies of energy deposition. Acoustic dose and acoustic does-rate are exact analogues for Specific Absorption and Specific Absorption Rate (SAR), quantities central to radiofrequency (RF) and microwave dosimetry. Acoustic dosimetry in the presence of tissue/gas interfaces remains a considerable challenge.

Laser acoustic method for the inspection of flaws in metals and the metallized coatings of dielectrics

Abstract: The propagation of acoustic waves in an aluminum specimen without flaws and in specimens with artificial flaws is considered. A method for the combined diagnostics of metal surfaces of materials using the developed experimental system was suggested on the basis of the performed analysis of the time travel and reflection diagrams of ultrasonic waves.

Floquet-bloch waves in bound one-dimensional photonic crystals

Abstract: Floquet-Bloch waves in a bound one-dimensional photonic crystal are considered. It is shown that a single Floquet-Bloch wave can be excited in a one-dimensional photonic crystal located between two homogeneous media. An exact solution of the wave equation corresponding to this case is represented in the form of a set of heterogeneous waves. For the case of incidence of the plane wave from a homogeneous medium on a bounded one-dimensional photonic crystal, the functions for the reflection and transmission coefficients are obtained based on the exact solution of the wave equation. It is shown that the transmission function for the one-dimensional photonic crystal has a form similar to that for the traditional Fabri-Perot interferometer and is determined by the interference of the Floquet-Bloch waves excited in the crystal. The evolution of the amplitude profile of the decaying Floquet-Bloch waves and the reflection spectrum of the bounded one-dimensional photonic crystal are considered in the first-order forbidden band.

Material anisotropy unveiled by random scattering of surface acoustic waves

Abstract: We consider launching a monochromatic surface acoustic wave packet on a large set of random scatterers The interference of the multiple scattered waves creates a random pattern of ripples on the crystal surface that is recorded by optical interferometry The Fourier transform of the amplitude and phase data of the measured wave field unveils the complete slowness curve, ie, the wave-vector as a function of the propagation angle A simple acoustic speckle model is proposed to explain this observation

Brillouin scattering measurements of the temperature dependence of sound velocity and acoustic absorption in simple alcohols

Abstract: A scanning Fabry–Perot interferometer was used to measure Brillouin spectra of methanol, isopropanol and a 95% ethanol–water mixture for temperatures ranging between 285 K and 320 K. The Brillouin frequency shifts and linewidths were used to calculate the velocities and absorption coefficients of hypersonic acoustic waves in these liquids. The temperature dependence of sound speed and acoustic attenuation was determined. For all three materials, both sound velocity and absorption coefficient decreased with temperature.

X-cut quartz crystal impedance meter for liquid characterization

Abstract: A new procedure to determine the compressional acoustic impedance of liquids within ±0.05% resolution and ±0.25% accuracy is presented. This method is based on the measurement of the bandwidth of a piezoelectric transducer, vibrating in thickness-expansion mode and having a high quality factor (e.g., air-backed X-cut quartz crystal), in direct contact with the sample. In combination with other ultrasonic techniques (pulse-echo or through-transmission), it is possible to simultaneously obtain the main ultrasonic parameters (characteristic acoustic impedance, speed of sound and attenuation coefficient), and deduce important physicochemical properties of liquids, such as density and adiabatic compressibility. Experimental results for selected liquids and solutions are shown.

Propagation of plate acoustic waves in contact with fluid medium

Abstract: PROPAGATION OF PLATE ACOUSTIC WAVES IN CONTACT WITH FLUID MEDIUM Nagaraj Ghatadi Suraji Marquette University, 2011 The characteristics of acoustic waves propagating in thin piezoelectric plates in the presence of a fluid medium contacting one or both of the plate surfaces are investigated. If the velocity of plate wave in the substrate is greater than velocity of bulk wave in the fluid, then a plate acoustic wave (PAW) traveling in the substrate will radiate a bulk acoustic wave (BAW) in the fluid. It is found that, under proper conditions, efficient conversion of energy from plate acoustic waves to bulk acoustic waves and vice versa can be obtained. For example, using the fundamental anti symmetric plate wave mode (A0 mode) propagating in a lithium niobate substrate and water as the fluid, total mode conversion loss (PAW to BAW and back from BAW to PAW) of less than 3 dB has been obtained. This mode conversion principle can be used to realize miniature, high efficiency transducers for use in ultrasonic flow meters. Similar type of transducer based on conversion of energy from surface acoustic wave (SAW) to bulk acoustic wave (BAW) has been developed previously. The use of plate waves has several advantages. Since the energy of plate waves is present on both plate surfaces, the inter digital transducer (IDT) can be on the surface opposite from that which is in contact with the fluid. This protects the IDT from possible damage due to the fluid and also simplifies the job of making electrical connections to the IDT. Another advantage is that one has wider choice of substrate materials with plate waves than is the case with SAWs. Preliminary calculations indicate that the mode conversion principle can also be used to generate and detect ultrasonic waves in air. This has potential applications for realizing transducers for use in non-contact ultrasonic’s. The design of an ASIC (Application Specific Integrated Circuit) chip containing an amplifier and frequency counter for use with ultrasonic transducers is also presented in this thesis.

The non-rigid surface acoustic concave mirror model and sound field analysis

Abstract: The focused acoustic field of impedance surface acoustic concave reflector was studied by theoretical calculation. The influence of the different material parameters of reflector covering layers to the focused intensity and the beam partner were analyzed. The results showed that the main influencing factors to the focused acoustic field characteristics are the real part of admittance when the real part increase, the reflector focus ability reduced largely. But it is less influenced to the width of main lobe, and the side-lobe is decreased.

An ultrasonic model for revealing electronic package’s inner structure using acoustic impedance

Abstract: The reflected ultrasonic echo’s amplitude is relative to the sample material’s acoustic impedance change. So the distribution of acoustic impedance is correlated with the inner structure. In this paper, an ultrasonic model is suggested to reveal electronic package’s inner structure using acoustic impedance. The model first reconstructs the impedance profile of layered medium through an incidence point, then gets other position’s impedance by moving the transducer regularly. Finally, the inner structure of the package can be revealed by the 3D image formed with the impedance matrix.

Acoustic suppression systems and related methods

Abstract: An acoustic suppression system for absorbing and/or scattering acoustic energy comprising a plurality of acoustic targets in a containment is described, the acoustic targets configured to have resonance frequencies allowing the targets to be excited by incoming acoustic waves, the resonance frequencies being adjustable to suppress acoustic energy in a set frequency range. Methods for fabricating and implementing the acoustic suppression system are also provided.

Gas Leakage in Buried Gas Pipe Based on Wavelet Analysis for Vibro-Coustic Signal in a Long Duct

Abstract: Gas leakage is often caused by the mechanical impact forces of construction equipment. In a long duct with large diameter, acoustic waves caused by the impact force are transferred to a far distance through the medium inside the duct. This wave is very complex since it includes an acoustic wave and solid wave. In general, the solid wave is attenuated faster than the acoustic wave in a buried duct because it is damped out by the soil covering the duct. The acoustic wave is propagated to the far distance with direct and reflective waves on the wall. The directive wave is non-dispersive and the reflected waves are dispersive due to the cavity modes of the duct. The typical correlation method has used both dispersive and non-dispersive waves to estimate the arrival time delay. Thus this method induces a degree of error for leak detection. In this article, time-frequency method is developed to classify the wave speed of direct waves (non-dispersive waves) and the reflective waves (dispersive waves), respective...