Showing papers on "Acoustic interferometer published in 2013"

Unidirectional transmission of acoustic waves based on asymmetric excitation of Lamb waves

Abstract: In this paper, an easily fabricated acoustic system has been demonstrated to gain unidirectional transmission with good performance. The unidirectional acoustic transmission originates from the asymmetric excitation of zero-order anti-symmetric Lamb modes. The results show that the single-sided patterned ridges on the steel plate enhance the scattering of the incident waves from the structured side and improve the coupling of the Lamb modes in the plate with them, which leads to high transmission ratio and great transmission difference value of acoustic waves along the opposite directions. All the experimental results show good agreement with the numerical simulations. The proposed acoustic system has potential applications in underwater acoustic and medical ultrasonic devices.

Evaluation of a separation method for source identification in small spaces.

Abstract: This paper investigates the efficiency of a field separation method for the identification of sound sources in small and non-anechoic spaces. When performing measurements in such environments, the acquired data contain information from the direct field radiated by the source of interest and reflections from walls. To get rid of the unwanted contributions and assess the field radiated by the source of interest, a field separation method is used. Acoustic data (pressure or velocity) are then measured on a hemispheric array whose base is laying on the surface of interest. Then, by using spherical harmonic expansions, contributions from outgoing and incoming waves can be separated if the impedance of the tested surface is high enough. Depending on the probe type, different implementations of the separation method are numerically compared. In addition, the influence of the walls' reflection coefficient is studied. Finally, measurements are performed using an array made-up of 36 p-p probes. Results obtained in a car trunk mock-up with controlled sources are first presented before reporting results measured in a real car running on a roller bench.

Multi-Component Acoustic Characterization of Porous Media

Abstract: The characterization of porous materials (e.g., sandstone) is very important for geotechnical and reservoir engineers. For this purpose, often use is made of acoustic waves that are sent through the medium. The desired material parameters can then be estimated from the measured signals. However, often only the velocity or the attenuation of the acoustic waves is employed, and much information that is carried by the waves remains untouched. Therefore, in this thesis we investigate the feasibility of the characterization of porous media using information contained in full acoustic waveforms as observed in different components (e.g., particle motion and fluid pressure). We subsequently address the mathematical description of pseudo interface waves, their experimental detection and the estimation of medium parameters. In the latter part, we show that it is possible to obtain unique and stable estimates of the permeability and porosity of a porous medium by simultaneously exploiting either different waveform attributes of a pseudo interface wave, or the reflection coefficients of different body waves.

Panel acoustic contribution analysis.

Abstract: Formulations are derived to analyze the relative panel acoustic contributions of a vibrating structure. The essence of this analysis is to correlate the acoustic power flow from each panel to the radiated acoustic pressure at any field point. The acoustic power is obtained by integrating the normal component of the surface acoustic intensity, which is the product of the surface acoustic pressure and normal surface velocity reconstructed by using the Helmholtz equation least squares based nearfield acoustical holography, over each panel. The significance of this methodology is that it enables one to analyze and rank relative acoustic contributions of individual panels of a complex vibrating structure to acoustic radiation anywhere in the field based on a single set of the acoustic pressures measured in the near field. Moreover, this approach is valid for both interior and exterior regions. Examples of using this method to analyze and rank the relative acoustic contributions of a scaled vehicle cabin are demonstrated.

The anisotropy of elastic waves in a tellurium crystal

Abstract: For acoustic waves propagating in an acoustooptic tellurium crystal, the dependence of their polarization on the propagation direction with respect to the crystal axes is discussed. The characteristic features of waves propagating in the crystal are considered; these features manifest themselves in an excess of the phase velocity of shear acoustic modes over the velocity of longitudinal modes. The change in the wave type from quasi-longitudinal to quasi-transverse as a result of the variation in the propagation direction of ultrasound is investigated. It is shown that such a behavior of bulk acoustic waves is caused by the specific relation between the elastic moduli, which differs from the corresponding relations observed in other acoustooptic materials.

Multi Reflection of Lamb Wave Emission in an Acoustic Waveguide Sensor

Abstract: Recently, an acoustic waveguide sensor based on multiple mode conversion of surface acoustic waves at the solid—liquid interfaces has been introduced for the concentration measurement of binary and ternary mixtures, liquid level sensing, investigation of spatial inhomogenities or bubble detection. In this contribution the sound wave propagation within this acoustic waveguide sensor is visualized by Schlieren imaging for continuous and burst operation the first time. In the acoustic waveguide the antisymmetrical zero order Lamb wave mode is excited by a single phase transducer of 1 MHz on thin glass plates of 1 mm thickness. By contact to the investigated liquid Lamb waves propagating on the first plate emit pressure waves into the adjacent liquid, which excites Lamb waves on the second plate, what again causes pressure waves traveling inside the liquid back to the first plate and so on. The Schlieren images prove this multi reflection within the acoustic waveguide, which confirms former considerations and calculations based on the receiver signal. With this knowledge the sensor concepts with the acoustic waveguide sensor can be interpreted in a better manner.

Method and apparatus for acoustical power transfer and communication

Abstract: Systems and methods for transmitting power and information using acoustic energy are provided. The systems have particular application for powering and communication with electronics through drilling and pipe systems. An acoustic fiber having a core region radially surrounded by a cladding region is used to transmit acoustic power and signals between paired transducers. Pairs of acoustic wedges are provided for sending energy and information through a substrate. Each wedge has an angled transducer which can be used to produce angled longitudinal waves which, upon reaching a substrate interface, produce shear waves in the substrate. The shear waves propagate down the substrate and are received by a second acoustic wedge. The shear waves in the substrate transition back to longitudinal waves on reaching the second acoustic wedge, and they are converted back into electrical signals by a second transducer.

Polarization phase shifting cyclic interferometer for surface profilometry of non-birefringent phase samples

Abstract: A rectangular path cyclic interferometer has the unique property that the counter-propagating wavefronts travelling in the interferometer arms are folded with respect to each other in the plane of the interferometer although the two wavefronts finally emerge from the interferometer unfolded. A phase disturbance introduced in one lateral half of the interferometer arm is therefore manifested in complementary lateral halves of the observed interference pattern. This phenomenon is utilized to evaluate the surface profile of a reflecting sample placed on one of the interferometer mirrors. The sample phase is retrieved using polarization phase shifting. Experimental results showing three-dimensional surface morphology of a small scale integrated circuitry directly etched on silicon are presented.

X-ray diffraction study of surface acoustic waves and pseudo-surface acoustic waves propagation in La3Ga5.5Ta0.5O14 crystal

Abstract: X-ray diffraction on the crystal La3Ga5.5Ta0.5O14 modulated by surface acoustic waves (SAW) and pseudo-surface acoustic waves (PSAW) with wavelength of Λ=8 μm was studied using a double axis X-ray diffractometer at the BESSY II synchrotron radiation source. The propagation of SAW and PSAW leads to sinusoidal modulation of the crystal lattice and gives rise to diffraction satellites on the rocking curve, with the intensity and angular divergence between the diffraction satellites depending on the wavelength and amplitude of the crystal lattice acoustic modulation. The analysis of diffraction spectra enables the determination of the amplitude and acoustic wavelengths, and power flow angles of acoustic energy propagation. The investigation of acoustic wave fields showed that PSAW is a flowing back wave which propagates at an angle to the crystal surface.

Sound field analysis for biological acoustic impedance microscope for its precise calibration

Abstract: Acoustic impedance microscopy for biological soft tissues was proposed. A target is placed on a plastic substrate. Ultrasonic beam, which is focused on the target, is transmitted and the reflection is received by the same transducer. The reflection is normalized by using pure water, and interpreted into acoustic impedance. As the beam is focused, oblique incident analysis is required to acquire a precise interpretation. Sound potential is calculated at a particular plane, and decomposed into plane wave components with different wave numbers using Fourier Transform. Both pressure and shear waves are generated and taken into account, when oblique incident impinging the substrate. As a pulsed wave is propagating, pressure and shear waves can be separated in time domain. Reflection signal is calculated for each plane wave component, and the integral through the k-space represents the received signal. As the substrate has higher acoustic impedance than target, the normalized reflection intensity reduces with the increase in acoustic impedance of the target. The experimental plots were acquired by using different contents of saline solutions. They agreed with the calculation results by sound field analysis. Frequency dependence is negligible in the region of 30 - 100 MHz. By scanning the transducer, an acoustic impedance microimage was acquired and calibrated based on the above analysis.

Properties of copper film characterized by scanning acoustic microscope

Abstract: The scanning acoustic microscope is used to detect the properties of film or coating materials. The ultrasonic wave propagates in the materials with thickness h, sound velocity c, acoustic impedance Z2 between medium with acoustic impedance Z1. The echoes from different interfaces overlap and interfere. The interference phenomena are observed in spectrum of echoes. The spectrum has periodic maximums at integral multiples of base frequency f0. When thickness h is known, speed c of the specimen can be calculated by the relation of fn = nc/2h. According to the principle, the properties of copper films such as thickness, acoustic impendence and elastic modulus are detected by scanning acoustic microscopy. The experimental results are accorded with the actual properties of specimens.

Modelling the bandwidth behaviour of fibre Bragg gratings excited by low-frequency acoustic waves

Abstract: A model is presented to explain the dynamically induced bandwidth increase of fibre Bragg grating spectra, when those are excited by acoustic waves at low frequencies. The approach considers the existence of both flexural and longitudinal waves propagating simultaneously in the fibre.

Exotic absorption peaks of acoustic waves in one-dimensional layered phononic crystal

Abstract: In this article, we demonstrate the existence of exotic absorption peaks when acoustic wave propagates through a one-dimensional layered phononic crystal (PC) at frequencies within the band gap into a material of large acoustic impedance mismatch. By analyzing the displacement field distribution, it indicates that the absorption peaks are due to the excitation of the resonant interface states at boundary between the last layer of the PC and emergent material. The number of period and the thickness of last layer of the PC play the decisive role in determining the magnitude and frequency of absorption peaks. And the absorptivity can be nearly unity with a reasonable design of the structure. Specifically, these absorption peaks would almost disappear when the incident direction of acoustic waves is reversed. This property can be employed to design an acoustic wave unidirectional absorption device.

Theoretical study of different attenuation measurement by acoustic microscopy

Abstract: Many works are devoted to study the attenuation of surface waves in media, particularly, leaky surface acoustic waves (LSAW). In this work, a big part of the study is based on the intensity of the output signal, i.e., acoustic signature, V(z). The latter is obtained by the use of quantitative mode of acoustic microscopy in order to measure the velocity and the attenuation of those excited waves at the limit between the specimen and the coupling liquid. Our aim is to compare the attenuation values of the LSAW propagation in porous silicon obtained with three different methods. The first is obtained by resolving Viktorov equation. The second method is the spectral analysis acoustical signature V(z) curves. The third method uses the dark field. The obtained results are in a good agreement with those experiments.

Acoustic diodes and methods of using same

Abstract: Acoustic diodes, devices incorporating such diodes and methods of using such devices are disclosed. An acoustic diode may include a periodic acoustic grating and a uniform plate. The periodic acoustic grating may include a plurality of gratings. The uniform plate may foe separated from the periodic acoustic grating by a resonant cavity. The acoustic diode may be configured to have a first transmission efficiency for acoustic waves incident on the periodic acoustic grating that is greater than a second transmission efficiency for acoustic waves incident on the uniform plate. The acoustic waves may have a wavelength within a range of wavelengths. Devices incorporating the acoustic diode may include medical imaging devices, such as ultrasound devices, and noise reduction devices.

Phase-shifting interferometer for monitoring flat and spherical optical components

Abstract: This paper discusses an automatic interferometer that makes it possible to measure the surface profile of flat and spherical (with a large radius of curvature) optical items. The interferometer’s field of view is as much as 30 mm in diameter. The vertical configuration of the main optical elements of the interferometer allowed it to be made compact and insensitive to vibrations. The surface profile is automatically measured by means of a nine-step phase-shift method. The results of experimental testing of the interferometer and its technical characteristics are presented.

Compressional acoustic waves in structure “Piezocylinder - viscoelastic layer - liquid”

Abstract: In this paper the characteristics (phase velocity and attenuation coefficient) of compressional acoustic waves propagated in piezoelectric cylinder covered by viscoelastic polymeric layer and immersed into viscous fluid are investigated. It is well known that propagation of such waves can be accompanied by radiation of bulk acoustic wave into liquid contacting with the waveguide. This happens in the case if the phase velocity of the wave in the corresponding structure exceeds the speed of sound in the liquid. Due to this, the attenuation of corresponding waves caused by two reasons: it is the viscosity of the liquid and radiation losses. Our calculations allow us to estimate the contribution of each of these mechanisms into the overall attenuation.

Very near field of a dipole source above the impedance plane

Abstract: A theoretical background for a new technique intended for in-situ measuring of sound absorption is presented. The measurement technique is a refinement of the classical method using reflection over the impedance plane. Refinement is based on the directivity pattern of dipole source in a very near field. Theoretical analysis of acoustical setup is based on the Rayleigh integral, which is used for calculations of sound propagation from complex sources. Analytical results with numerical simulations based on FEM analysis are compared in this preliminary study. Influence of flow resistivity on the sound pressure around a dipole source positioned over the impedance plane is investigated. Theoretical results provide an excellent starting point for the design platform of the new sensor for sound absorption.