Showing papers on "Acoustic interferometer published in 2015"

Collective excitation interferometry with a toroidal Bose-Einstein condensate

Abstract: The precision of most compact inertial sensing schemes using trapped- and guided-atom interferometers has been limited by uncontrolled phase errors caused by trapping potentials and interactions. Here we propose an acoustic interferometer that uses sound waves in a toroidal Bose-Einstein condensate to measure rotation, and we demonstrate experimentally several key aspects of this type of interferometer. We use spatially patterned light beams to excite counterpropagating sound waves within the condensate and use in situ absorption imaging to characterize their evolution. We present an analysis technique by which we extract separately the oscillation frequencies of the standing-wave acoustic modes, the frequency splitting caused by static imperfections in the trapping potential, and the characteristic precession of the standing-wave pattern due to rotation. Supported by analytic and numerical calculations, we interpret the noise in our measurements, which is dominated by atom shot noise, in terms of rotation noise. While the noise of our acoustic interferometric sensor, at the level of $\ensuremath{\sim}\text{rad}\phantom{\rule{0.16em}{0ex}}{\text{s}}^{\ensuremath{-}1}/\sqrt{\text{Hz}}$, is high owing to rapid acoustic damping and the small radius of the trap, the proof-of-concept device does operate at the high densities and small volumes of trapped Bose-Einstein condensed gases.

Manipulation of transmitted wave front using ultrathin planar acoustic metasurfaces

Abstract: Nowadays, the acoustic devices are developing toward miniaturization. However, conventional materials can hardly satisfy the requirements because of their large size and complex manufacturing process. The introduction of acoustic metasurfaces has broken these restrictions, as they are able to manipulate sound waves at will by utilizing ultrathin planar metamaterials. Here, a simple acoustic metasurface is designed and characterized, whose microstructure is constructed with a cavity filled with air and two elastic membranes on the ends of cavity. By appropriately optimizing the configurations of microstructures, the steering of transmitted wave trajectory is demonstrated, and some extraordinary phenomena are realized at 3.5 kHz, such as planar acoustic axicon, acoustic lens, the conversion from spherical waves to plane waves, and the transformation from propagating waves to surface waves.

Stationary waves in tubes and the speed of sound

Abstract: The opportunity to plot oscillograms and frequency spectra with smartphones creates many options for experiments in acoustics, including several that have been described in this column.1–3 The activities presented in this paper are intended to complement these applications, and include an approach to determine sound velocity in air by using standard drain pipes4 and an outline of an investigation of the temperature dependency of the speed of sound.

Characterization and representation of mechanical waves generated in piezo-electric augmented beams

Abstract: Mechanical waves are induced in solids due to the system's coupling with an external excitation. Depending upon the nature of the resulting displacement and phase difference between the vibrating particles at a particular frequency, the mechanical waves can be classified as standing waves, traveling waves or a combination of the two. This study focuses on the identification of these different forms of mechanical waves and discusses methods that can be suitably used for their classification. The Hilbert and Fourier methods of classification were validated using experimental results and then compared against each other. The experimental and theoretical analysis of mechanical waves was conducted on a beam with free-free boundary conditions excited by piezoelectric elements.

Directional excitation of the designer surface acoustic waves

Abstract: We propose an efficient design route to realize directional excitation of the structure-induced surface waves for airborne sound. The whole system consists of a periodically corrugated rigid plate combining with a pair of asymmetric narrow slits. The directional excitation of the mimicked surface waves stems from the destructive interference between the evanescent waves emitted from the double slits. The directionality can be switched conveniently by tuning the external frequency. The theoretical prediction is validated well by simulations and experiments. Promising applications can be anticipated such as in designing compact devices for airborne sound.

Waves in strong centrifugal fields: dissipationless gas

Abstract: Linear waves are investigated in a rotating gas under the condition of strong centrifugal acceleration of the order 106g realized in gas centrifuges for separation of uranium isotopes. Sound waves split into three families of the waves under these conditions. Dispersion equations are obtained. The characteristics of the waves strongly differ from the conventional sound waves on polarization, velocity of propagation and distribution of energy of the waves in space for two families having frequencies above and below the frequency of the conventional sound waves. The energy of these waves is localized in rarefied region of the gas. The waves of the third family were not specified before. They propagate exactly along the rotational axis with the conventional sound velocity. These waves are polarized only along the rotational axis. Radial and azimuthal motions are not excited. Energy of the waves is concentrated near the wall of the rotor where the density of the gas is largest.

Time-resolved detection of propagating Lamb waves in thin silicon membranes with frequencies up to 197 GHz

Abstract: Guided acoustic waves are generated in nanopatterned silicon membranes with aluminum gratings by optical excitation with a femtosecond laser. The spatial modulation of the photoacoustic excitation leads to Lamb waves with wavelengths determined by the grating period. The excited Lamb waves are optically detected for different grating periods and at distances up to several μm between pump and probe spot. The measured frequencies are compared to the theoretical dispersion relation for Lamb waves in thin silicon membranes. Compared to surface acoustic waves in bulk silicon twice higher frequencies for Lamb waves (197 GHz with a 100 nm grating) are generated in a membrane at equal grating periods.

Transformation of acoustic modes in acousto-optical devices

Abstract: The results from studying previously unknown cases of the reflection of bulk acoustic waves in an acousto-optical paratellurite crystal with arbitrary incidence of an elastic wave on a free interface between the crystal and vacuum are presented. The incidence of waves at different angles in the XOY plane of the material is analyzed. New cases of the reflection of acoustic waves are considered and the efficiency of the transformation of energy from an incident elastic wave into the energy of reflected waves are investigated.

A combined non‐contact acoustic thermometer and infrared hygrometer for atmospheric measurements

Abstract: Temperature and humidity measurements in the upper atmosphere are of critical importance for understanding the climate of the Earth. However such measurements are difficult for several reasons. Firstly, measurements are typically made on a rising sonde which carries moisture upwards with it, compromising measurements in the dry stratospheric environment. Secondly, the difference in the time-constants of thermometers and hygrometers on a rising sonde leads to difficulties in determining the extent of saturation of the air - a critical variable for understanding cloud formation. Finally the effects of insolation and the poor thermal contact with the air compound the other measurement problems. To address these issues we have designed a new combined temperature and humidity sensor which makes rapid measurements in approximately 10 litres of air of without requiring thermal contact. The temperature measurements are made using an acoustic interferometer which is servo-controlled at around 15 kHz to keep a fixed number of wavelengths in the measurement volume. The volume being measured is that between a parabolic dish 20 cm in diameter and an acoustic mirror 50 cm away. These elements are held together in a carbon-fibre open frame. Humidity measurements are made using a Tuneable Diode Laser Absorption Spectrometer (TDLAS) which interrogates the same volume of air through holes in the mirror and parabola. Here we report tests on the device at NPL at a pressure of 1 atmosphere, and from simulated ascents through the atmosphere at the MARS Simulation facility at the University of Aarhus, Denmark.

Modulation of the intensity of reflected x-rays and control of its parameters in the presence of volume acoustic waves

Abstract: X-ray diffraction from the reflecting atomic planes \((10\bar 11)\) of a quartz single crystal with the AT-cut in the geometry of Laue in the presence of volume acoustic waves was experimentally studied. Some problems are discussed to obtain the spatial modulation of intensity of reflected beam and to control its parameters in the presence of acoustic waves.

Theoretical and experimental study on the acoustic wave energy after the nonlinear interaction of acoustic waves in aqueous media

Abstract: Based on the Burgers equation and Manley-Rowe equation, the derivation about nonlinear interaction of the acoustic waves has been done in this paper. After nonlinear interaction among the low-frequency weak waves and the pump wave, the analytical solutions of acoustic waves’ amplitude in the field are deduced. The relationship between normalized energy of high-frequency and the change of acoustic energy before and after the nonlinear interaction of the acoustic waves is analyzed. The experimental results about the changes of the acoustic energy are presented. The study shows that new frequencies are generated and the energies of the low-frequency are modulated in a long term by the pump waves, which leads the energies of the low-frequency acoustic waves to change in the pulse trend in the process of the nonlinear interaction of the acoustic waves. The increase and decrease of the energies of the low-frequency are observed under certain typical conditions, which lays a foundation for practical engineering applications.

Methods and apparatuses to attenuate acoustic waves

Abstract: Apparatuses and methods to attenuate acoustic waves are provided. The method may include shifting the phases of a plurality of portions of the acoustic waves and merging the portions of the acoustic waves after phase shifting. Because, for example, the phases of the acoustic waves may be out-of-sync when being merged, the acoustic waves may be attenuated. A muffler incorporating the method of attenuating acoustic waves can include a plurality of acoustic paths, each of which may have different acoustic impedance and/or length. The acoustic paths may help the acoustic waves have out-of-sync phases after the acoustic waves passing through the acoustic paths, resulting in acoustic wave attenuation.

The absorption intensity of the acoustic waves in the ocean

Abstract: В статье исследуется влияние пузырьков газа на поглощение звуковой волны в жидкости. В отличие от ранее опубликованных работ, используется модель баротропной пузырьковой жидкости с учетом капиллярного эффекта. Описываются основные закономерности распространения и затухания звука в морской воде. Дается физическая интерпретация этих закономерностей. В работе исследуются два типа решения: первое – синусоидальное по координате и затухающее экспоненциально во времени возмущение, второе – синусоидальное по времени колебание, затухающее экспоненциально по длине возмущения, являющееся волновым аналогом вынужденных колебаний. Показано, что коэффициент поглощения, согласно классической теории затухания, возрастает с увеличением вязкости жидкой фазы. Результаты численных расчетов показали, что затухание звука в газожидкостной среде усугубляется тем, что поглощение наиболее сильно происходит именно на резонансной частоте. In this article we investigate the influence of gas bubbles on the absorption of sound wave in the liquid. In contrast to published studies using barotropic model bubbly liquid with the capillary effects. Describes the basic laws of propagation and damping of sound in seawater. Physical interpretation of these laws are given.We study two types of solutions. The first decision – sinusoidal coordinate and decay exponentially in time perturbation. A second solution – sinusoidal oscillation time, decaying exponentially with the length of the disturbance is a wave analogue of forced oscillations. It is shown that the absorption coefficient according to the classical theory of damping increases with the viscosity of the liquid phase. The numerical results showed that the damping of sound in the gas-liquid medium is compounded by the fact that the absorption occurs is most strongly at the resonance frequency.

Acoustically driven microfluidic devices based on hexagonal phononic crystal structures

Abstract: This paper demonstrates a hexagonal phononic crystal structure based microfluidic device, which is actuated by surface acoustic waves, for centrifugation of micro particles in microliter droplet. In this work, the phononic structure interacts with the acoustic waves, providing reflection, scattering and diffraction, causes asymmetry on the propagation path. Thus, at the interface of the silicon and liquid, the acoustic waves could only be refracted into part of the droplet, and results in acoustic streaming in the droplet. Then, by recirculation, angular momentum will be induced within the sample drop and efficient centrifugation of micro particles could be performed. Advantages of this technique include fast manipulation speed, simple electrode structures, and wide actuating frequency range.

Non-destructive acoustic metrology for void detection

Abstract: Advanced interconnect technologies such as Through Silicon Vias (TSVs) have become an integral part of 3-D integration. Methods and systems and provided for laser-based acoustic techniques in which a short laser pulse generates broadband acoustic waves that propagate in the TSV structure. An optical interferometer detects the surface displacement caused by the acoustic waves reflecting within the structure as well as other acoustic waves traveling near the surface that has information about the structure dimensions and irregularities, such as voids. Features of voids, such as their location, are also identified based on the characteristics of the acoustic wave as it propagates through the via. Measurements typically take few seconds per site and can be easily adopted for in-line process monitoring.

Beam forming and steering of helical guided waves in pipe-like and plate-like structures

Abstract: A method of inspecting a pipe for flaws includes emitting ultrasonic waves, controlling the emission of the ultrasonic waves, receiving reflections of the ultrasonic waves, and determining at least one characteristic of one or more flaws. The ultrasonic waves are emitted in a helical pattern through the pipe from an array of ultrasonic transducer elements. The emission of the ultrasonic waves from the array is controlled such that the ultrasonic waves are emitted at a plurality of helical angles within a range of helical angles. The reflections of the ultrasonic waves are caused by impingement of the ultrasonic waves on the one or more flaws. The at least one characteristic of the one or more flaws is determined based on the received reflections of the ultrasonic waves.

Acoustic transmission enhancement through a soft interlayer with a reactance boundary

Abstract: Research has shown that acoustic transmission enhancement (ATE) can occur in stiff materials with high acoustic impedance that include a soft interlayer with low acoustic impedance inserted between them without any opening (i.e., without any links between the two stiff materials). Previously, ATE was induced either by coupling acoustic surface waves or Love waves with the Fabry–Perot resonant modes inside the apertures or by the locally resonant modes of the structure. However, in this article ATE is achieved using wave-vector redistribution induced by a reactance boundary. An optimal boundary was designed to adjust the wave vector in the propagation direction, decreasing reflection caused by impedance differences. The role of boundary conditions on ATE was also clarified.

Standing Waves and Acoustic Heating (or Cooling) in Resonators Filled with Chemically Reacting Gas

Abstract: Standing waves and acoustic heating in a one-dimensional resonator filled with a chemically reacting gas, is a subject of investigation. The chemical reaction of $A \rightarrow B$ type, which takes place in a gas, may be reversible or not. Governing equations for the sound and entropy mode which is generated in the field of sound are derived by use of a special mathematical method. Under some conditions, sound waves propagating in opposite directions do not interact. The character of nonlinear dynamics of the sound and relative acoustic heating or cooling depends on reversibility of a chemical reaction. Some examples of acoustic heating in a resonator are illustrated and discussed.

Influence of liquid on properties of backward acoustic waves in piezoelectric plates

Abstract: In the paper the characteristics of shear-horizontal direct and backward acoustic waves of the higher orders propagating in XY potassium niobate plates in band including the cutoff frequencies have been theoretically investigated. It also has been theoretically investigated the influence of nonviscous and nonconductive liquid on their properties. It has been found that the presence of liquid are reduced the velocity of waves under study. The range of the backward wave existence is increased with increasing of the wave order number.

Study of Laser-Array-Source-Generated Narrow-Band Acoustic Waves Interacting with Surface-Breaking Cracks Using Finite Element Method

Abstract: Based on the classical theory of laser ultrasound generation in the thermoelastic regime, the generation of ultrasound by the irradiation of a laser array source is simulated by the finite element method. The interaction of ultrasound with a surface-breaking crack is studied. By changing the space distribution of a simultaneously triggered laser array source, narrow-band acoustic waves can be obtained. The characteristics of the narrow-band acoustic waves in the frequency domain are analyzed. By comparing with the spectrum of wide-band reflected acoustic waves generated by a single laser source, the mechanism of the interaction of a surface-breaking crack on the reflected narrow-band acoustic waves is studied. According to the variation of a reflected narrow-band acoustic wave spectrum on cracks with different depths, the influence of the crack-depth variation on different components of the narrow-band acoustic waves is obtained. Results suggest that the narrow-band acoustic waves could also be sensitive to the variation of the crack depth so that it can provide an alternative option for crack-depth gaging using all-optical methods.

Cancellation of acoustic waves in scattering media

Abstract: We find scattering cancellation in diffusive transport of acoustics waves propagating through strongly scattering media and for ballistic sound in the long wavelength limit.

Experimental and numerical investigations of resonant acoustic waves in near-critical carbon dioxide

Abstract: Flow and transport induced by resonant acoustic waves in a near-critical fluid filled cylindrical enclosure is investigated both experimentally and numerically. Supercritical carbon dioxide (near the critical or the pseudo-critical states) in a confined resonator is subjected to acoustic field created by an electro-mechanical acoustic transducer and the induced pressure waves are measured by a fast response pressure field microphone. The frequency of the acoustic transducer is chosen such that the lowest acoustic mode propagates along the enclosure. For numerical simulations, a real-fluid computational fluid dynamics model representing the thermo-physical and transport properties of the supercritical fluid is considered. The simulated acoustic field in the resonator is compared with measurements. The formation of acoustic streaming structures in the highly compressible medium is revealed by time-averaging the numerical solutions over a given period. Due to diverging thermo-physical properties of supercritical fluid near the critical point, large scale oscillations are generated even for small sound field intensity. The strength of the acoustic wave field is found to be in direct relation with the thermodynamic state of the fluid. The effects of near-critical property variations and the operating pressure on the formation process of the streaming structures are also investigated. Irregular streaming patterns with significantly higher streaming velocities are observed for near-pseudo-critical states at operating pressures close to the critical pressure. However, these structures quickly re-orient to the typical Rayleigh streaming patterns with the increase operating pressure.

Acoustic Radiation, Sound Waves and Fields

Abstract: The present chapter presents definitions of the main acoustic notions and quantities along with the regularities and characteristics of the sound fields. Special instruments for measuring noise parameters of the studied objects are described. The features critical in measuring HF noise are stated. Information is presented on the methods of acoustic intensimetry and holography that are widely applicable in studying noise in friction systems.

Acoustic wave transducer construction and method for accomplishing mechanical waves

Abstract: An object of the invention is an acoustic wave transducer construction for accomplishing mechanical waves to an object. The construction comprises at least one source (100) for receiving electrical current and for producing mechanical waves on the basis of the received current and receiving means (108, 110, 111) for detecting said mechanical waves. The source (100) comprises material having impedance characteristics close to the impedance characteristics of the object, and the construction further comprises an attenuation material (104) for directing the produced mechanical waves to the object.