bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection of Shallow Underground Buried Object Using Air Vibration Probe
Authors: Sato Yuji , Okamura Tomohiro , Mizutani Koichi , Wakatsuki Naoto
Published: May 2008

An air vibration probe is a device to measure an acoustic impedance using acoustic delay line oscillation. The frequency is changed when the acoustic impedance is changed. If some objects are varied, the frequency is expected to be changed in the case of the shallow underground detection. The advantage of this device is that it can detect the underground object easily without any contacts or destructions. Two experiments were practiced to study the relation among the frequency, the space between the probe and the ground, and the depth of object. The space was changed with the buried objects in various depths. The frequency became higher when the space became wider. In addition, the frequency was changed more obviously when the space was narrower. The probe scanned the buried objects in the fixed space. The objects were buried in various depths. The frequency became high when the object was buried shallower. In conclusion, the air vibration probe can detect the buried object because the frequency became high when something was buried.
More experimental evidence favouring the hypothesis of significant wall vibration influence on radiated horn sound
Authors: Kausel Wilfried , Mayer Alexander
Published: May 2008

The question whether wall vibrations of wind instruments do or can affect the radiated sound has not been finally answered yet. Instrument makers and musicians make a strong claim that wall thickness, material and conditioning are crucial factors for sound quality and response of wind instruments, while acousticians rather tend to question that claim. Recent experiments on horns are presented favoring the hypothesis that wall vibrations do matter. Although horn sound in general appears to change quite significantly when wall vibrations, particularly those of the bell, are dampened during artificial playing, it becomes more and more evident that more than one single mechanism has to be considered to explain the whole phenomenon. Radiation of the bell as multi-pole will add directivity and strengthen higher harmonics while absorption by the wall will rather weaken them. Dynamic interaction between air column and oscillating bore profile theoretically depends on broken symmetry. Feedback of structural resonances to the oscillating lips can be avoided by decoupling the mouthpiece from the instrument. Experiments and statistical evaluation have been laid out in order to exclude or identify certain mechanisms as well as possible artifacts like changes of mouthpiece position, bore or acoustical environment caused by damping forces.
Observations on bow changes in violin performance
Authors: Demoucron Matthias , Askenfelt Anders , Causse René E.
Published: May 2008

Players of bowed instruments commonly separate notes by changing the direction of the bow motion ("bow changes"). The separation can be made more or less pronounced (detaché - portato - martellato). In contrast, long notes, requiring more than a full bow stroke, are played by making the bow changes as inaudible as possible. Acceptable bow changes require accurate control and coordination of a set of bowing parameters, in particular bow speed, bow force and bow-bridge distance. Long practice is required before optimal control is achieved. Detailed descriptions of basic bowing gestures such as bow changes are of great interest for various fields of violin-related studies, including realistic control of synthesis algorithms. We present recent measurements that provide an accurate description of the evolution of bow speed, acceleration and bow force during bow changes at the tip and the frog, respectively. Using these data for controlling a synthesis algorithm, we will discuss how modifications of the parameters influence the bow-string interaction and resulting string vibrations. The simulations are used to model efficient implementations of bow changes.
Source location prediction of subsonic isothermal jet flows
Authors: Battaner-Moro Juan , Azarpeyvand Mahdi , Self Rod
Published: May 2008

The location of jet noise sources is a far from trivial problem that is of great importance for both understanding the noise production and radiation mechanisms and also for finding new jet noise reduction strategies. This paper presents comparisons of theoretical results with data for a number of jets. The theory used is based on the MGBK method but including a novel time scale based on the rate of energy transfer through the turbulent cascade. This new technique has been shown to give a number of advantages over existing models. The experimental results were obtained using the Polar Correlation Technique and were made at QinetiQ's Jet Noise Facility in the UK as part of the EU FP6 programme CoJeN. The high resolution jet noise images resulted from using a 64 microphone polar arc array set at two reference angles, namely 60 and 90 degrees to the jet axis. Comparisons with experimental data are made for coplanar and short cowl nozzles at different working conditions for predictions from different theoretical models. It is shown that the best agreement is obtained for the prediction methodology using the energy transfer rate timescale
Aeroacoustic research complex for aircraft source noise characterization
Authors: Downing Micah , McKinley Robert , Hall John , Mobley Frank , James Michael
Published: May 2008

Aircraft noise has been traditionally measured with either a few ground-based microphones or a linear ground-plane array of microphones. These techniques capture one-dimensional and/or two-dimensional characteristics of aircraft flight noise. The US Air Force Research Laboratory has started the construction of a 3-dimensional measurement facility at White Sands Missile Range in New Mexico. This facility, the Aeroacoustic Research Complex (ARC), will allow aircraft to fly through the array, collecting fully 3D acoustic data. ARC is initially being developed in two phases The first phase includes two 91.4 m tall towers separated by 244 m and will focus on noise from rotary wing and UAV aircraft. The second phase will add two 366 m tall towers separated by 610 m and will focus on large and high performance fixed wing aircraft. This facility will allow more accurate characterization of in-flight noise directivity by providing synchronized 3-dimensional magnitude & spectral acoustical signatures from 50+ microphones. ARC responds to a critical need for validation of existing predictive acoustic models. Such models are used for aircraft design, survivability, nonlinear acoustic propagation research and assessing noise exposure to residents living adjacent to airfields.
Sonic booms, spectral analysis, and diffraction by buildings
Authors: Sparrow Victor W.
Published: May 2008

An analysis has been performed upon conventional and low-amplitude N-wave sonic boom data taken by NASA outside two houses in June 2006 and July 2007. The buildings were one-floor residences which were carefully instrumented with strategically-placed, multiple microphones. The incident sonic booms had a substantial variation in rise times, most likely due to atmospheric effects. Previous work using the June 2006 data [Sparrow, Klos, and Buehrle, J. Acoust. Soc. Am. 122 (5, Pt. 2) 3084] revealed maximum pressure loads near the ground and wall facing the incident boom. A new spectral analysis of the individual booms now confirms that the diffraction of sound over the house tops is substantially affected by the spectral content of each boom. These results indicate that the pressure loading of homes due to conventional or low-amplitude sonic boom will be affected by both the spectral content of each boom's rise phase and each house's exterior geometry. [Work supported by NASA.]
Experimental investigation of sound from flow over a rough surface
Authors: Goody Michael , Anderson Jason , Stewart Devin , Blake William
Published: May 2008

Measurements of radiated noise and unsteady surface pressures have been carried out in order to better understand the mechanism for sound production from flow over a rough surface. In order to investigate scaling relationships, the flow speed, roughness height, geometry and element distribution were varied systematically. When considered in total, previous investigations do not present a consistent picture of the scaling behavior of roughness noise, or the underlying physical mechanism. They have reported roughness noise levels that scale on flow velocity, roughness height, and fetch area and have indicated that the sound production may be dipole or quadrupole in nature. Prevailing analytical models assume that both dipole and quadrupole sources are present. The scaling of roughness noise for large roughness height has not been investigated previously and is part of the current study. A recent developed scattering model (dipole) developed by Glegg et al is interrogated using detailed measurements of the roughness element height distribution, turbulent boundary layer properties, and array-based radiated sound levels.
Validation of a hybrid method of aeroacoustic noise computation applied to internal flows
Authors: Piellard Mélanie , Bailly Christophe
Published: May 2008

A hybrid method of aeroacoustic noise computation based on Lighthill's acoustic analogy is first validated, and then applied to investigate the noise radiated by a low Mach number flow through a diaphragm in a duct. The simulation method is a two-step hybrid approach relying on Lighthill's acoustic analogy, assuming the decoupling of noise generation and propagation. The first step consists in an incompressible Large Eddy Simulation of the turbulent flow field, during which the Lighthill's source term is recorded. In the second step, a variational formulation of Lighthill's Acoustic Analogy using a finite element discretization is solved in the Fourier space. The validation of this method is briefly presented: a general validation is performed on the case of two corotating vortices in a medium at rest; the exit of turbulent structures from the computational domain is accounted for by a spatial filtering; and a study of spatial interpolation from the CFD mesh to the acoustic mesh shows an acceptable level of error. This method is applied to a three-dimensional diaphragm with low Mach number flow, showing good agreement with both experimental results and Direct Noise Computation performed by Gloerfelt & Lafon (Computers & Fluids, 2007).
Active Perturbation on Vortex-Induced Acoustic Resonance
Authors: Cheng Li , Zhou Y , Zhang Ming Ming
Published: May 2008

Flow-induced acoustic resonance results from strong interactions between unsteady separated flows and the acoustic modes of a cavity. This work explores the feasibility of using piezoelectric-actuator-based perturbation technique in the control of vortex-induced noise through systematic experimental studies. A thick rectangular plate was used as the vortex generator and placed upstream of a cavity. Curved piezo-ceramic actuators were embedded in a slot on the top side of the plate to provide a perturbation to the flow. Uncontrolled flow-acoustic interaction was first examined to provide a baseline for comparison. Results show that noises induced by flow separation from the thick rectangular plate and the wall ahead of the cavity have very different critical flow velocities so that their effects can be well separated. Open-loop control tests indicate that vortex-induced acoustic resonance can be successfully controlled using the proposed technique. Analyses suggest that the convection of votices separated from the leading edge along the plate surface was accelerated by the surface perturbation, which interacted vigorously with the formation of the dominant trailing edge vortex, thus weakening the vortex strength in the wake of the plate. This weakened vortex strength substantially alters the flow-acoustic interaction, resulting in a significant impairment of vortex-induced acoustic resonance. (Supported by Research Grants Council of HKSAR. PolyU 5132/07E)
A finite element method for time harmonic acoustics in arbitrary flows
Authors: Bonnet- Ben Dhia Anne-Sophie , Mercier Jean-Francois , Millot Florence , Pernet Sebastien
Published: May 2008

The reduction of noise in aeronautics motivates an intensive research in aeroacoustics. In particular, there is a need for efficient tools to simulate acoustic propagation in a mean flow. We are interested here by solving the linearized problem in the frequency domain, by a finite element method able to take into account general geometries and flows. To our knowledge, only the potential case has been completely handled. Recently, a new approach has been developed and validated in the case of a parallel shear flow: it relies on a regularized formulation of Galbrun's equation, well-suited for a discretization by Lagrange finite elements, combined with Perfectly Matched Layers. A drawback of the method comes from the additional term of regularization, which requires the evaluation of an oscillating integral, coupling all degrees of freedom located on the same streamline. This difficulty can be avoided by replacing this non-local term by its Low-Mach approximation We show here how to extend this Low-Mach approach to the case of a non parallel flow. Numerical experiments are done. In the case of a potential mean flow, a good agreement with the exact approach is observed, even for quite large Mach numbers.
Henning E. von Gierke and human biodynamics
Authors: Brammer Anthony J.
Published: May 2008

In addition to his well-known involvement in protecting humans from exposure to excessive noise, Dr. Henning E. von Gierke was deeply involved in protecting humans from exposure to excessive mechanical shocks, impacts and vibration. From exploring the limits of survivability during the landing phase of space and aircraft capsules to the more everyday issues of occupational exposure to vibration, he provided scientific insight into problems and leadership in developing solutions. While most of Henning's contributions are buried in past literature, the spirit of his efforts lives on in a review chapter published in Harris' Shock and Vibration Handbook that I have had the privilege to co-author with him through two editions, now extending back more than a decade. The challenge of encompassing the original content of his contribution while introducing the results of more recent research has, so far, yielded a composition that he has endorsed. Henning's involvement and interests in human biodynamics will be illustrated by examples taken from this work.
Henning von Gierke, leader, consensus builder, mentor, and friend
Authors: Suter Alice H.
Published: May 2008

Over his long and illustrious career, Henning von Gierke has had an enormous effect on public policy in noise and vibration, not only because he was active in the field for more than half a century, but because of his intense dedication, his persistence, and his unique, almost legendary ability to build consensus. EPA's Office of Noise Abatement and Control could not possibly have produced its Criteria and Levels documents in response to the timeframe imposed by Congress without Henning's leadership. Those of us who were lucky enough to be mentored by him were able to accomplish more than we ever could have without his guidance. In addition to his invaluable assistance in my doctoral program, I knew him as ASA's Standards Director, then President of ASA, chairman of interagency task forces, chairman of several standards committees, and participant in numerous international activities. He was always willing to share the burden of work and to encourage the rest of us to forge ahead in an effort to make the world a quieter and healthier place.
Noise source mapping for trucks, part 1: development and design
Authors: Plotkin Kenneth J. , Gurovich Yuriy , Blake William , Donavan Paul
Published: May 2008

Mapping and quantifying noise sources on trucks under actual operating conditions on the road are important for traffic noise modeling and mitigation. The purpose of this study is to develop a practical truck noise source localization technique using acoustic beam-forming. An experimental 70+ microphone elliptical array was designed and fabricated for truck testing. Beam-forming software was developed and implemented using a computerized data acquisition system. Proof-of-concept tests were performed at low-speed and high-speed truck testing facilities for a representative sample of trucks with widely different characteristics to validate the measurement system performance. The measurement system design parameters were verified experimentally, and certain improvements to the system were recommended for future implementation based on the field experience. The developed beam-forming measurement system provided adequate noise mapping and localization for various noise sources on trucks, stationary and moving with the speed up to 50 mph. The results of the proof-of-concept testing presented in an accompanying paper (Part 2) confirm that the developed microphone array, data acquisition system and beam-forming software performed generally as expected and required no major adjustments. This ongoing project is funded by the National Cooperative Highway Research Program of the Transportation Research Board of the National Academies, USA.
Perceptive temporal features of train passbys
Authors: Terroir Jonathan , Lavandier Catherine
Published: May 2008

This work deals with characterization of temporal features linked to train passages which may act upon annoyance. Two varying parameters in the recordings have been selected: distance from the railway (7.5 meters, 50 and 100 meters) and train category (four types of French trains). A first series of psychoacoustic tests are carried out in order to mainly extract temporal aspects which could be important for sound perception. To avoid the level saliency, a preliminary equalization has been made on LA5. The selection of perceptive factors is carried out through a multidimensional analysis (INDSCAL). Dissimilarity tests highlight several dimensions: train category, slope of the level increase linked to train arrival and passage length. In addition to the dissimilarity between two stimuli estimation, subjects have to choose the one they prefer and explain their answers. The verbalization task helps illustrate multidimensional analysis axis. A second series of tests, designed with recordings varying on two independent parameters (the level and the slope of the temporal evolution) makes it possible to compare perceptive variations on temporal effects to loudness.
Managing Risk by Utilising an Integrated Approach to Quality Assurance During Strategic Noise Mapping
Authors: Shilton Simon J. , Štimac Alan , Trow James , Archer Nathan , Hii Jiu Ta Vincent , Jones Nigel
Published: May 2008

With the proclamation of the Directive on Environmental Noise (2002/49), the process of noise mapping and action planning has begun around Europe. As the development of strategic noise maps is arguably a new experience for many end-users, the first round of noise mapping could potentially lead to uncertainties within many aspects of the process. Noise maps represent a baseline for the implementation of noise management systems and any systematic errors within the noise maps could reduce the effective implementation of the whole management system. The extensive range of data inputs required in strategic noise mapping are usually obtained from different data sources or base datasets and as such, cataloguing with the use of metadata is key. The implementation of a quality assurance system is imperative to maintain consistency between technicians and within multi-disciplinary teams. It is also essential to ensure the control of processes and the ability to review inputs, intermediaries and deliverables. A similar approach may also be applied to calculation and post processing of noise levels. This paper presents collective experience of the implementation of quality assurance procedures used in several EU countries during the successful completion of projects within the first round of mapping.
A methodology for mapping neighbourhood impacts
Authors: Klaeboe Ronny , Engelien Erik , Steinnes Margrete
Published: May 2008

A methodology for the spatial analysis of environmental impacts in urban areas and social gradients is presented. The methodology is computational intensive and requires access to geographically located data at the dwelling level. Neighbourhood information is harvested to provide contextual information, and a spatial smoothing technique used to provide powerful visualisations of residential and neighbourhood impacts. By focussing on impacts rather than exposures, the construction of accumulative non-monetarised and monetarised indicators of impacts such as disability adjusted life years (DALY) and health costs is facilitated. Since the residential dwelling location is, or can be made, the focal point for social, dwelling, environment, neighbourhood, and transportation related indicators, a rich network of information in a uniform format is available for construction of novel indicators. By focussing on neighbourhoods rather than individual dwellings, privacy is enhanced while maintaining useful level of detail for involving the public and politicians in local planning. By combining information on social status and environmental exposures, questions on whether transportation related impacts are distributed fairly and whether social inequity is increased or decreases as a result of a particular measure can be addressed. The methodology is not applicable to rural areas and low probability events.
Environmental Noise Directive - results of noise mapping in Germany
Authors: Hintzsche Matthias
Published: May 2008

The Environmental Noise Directive intends the development of a concept to avoid, prevent or reduce on a prioritised basis the harmful effects, including annoyance, due to exposure to environmental noise and to inform the public on environmental noise and its effects. In a first step noise maps were made for all agglomerations and for all major roads, major railways and major airports. This noise maps are the basics for noise action plans. These plans have the target to prevent and to reduce environmental noise where necessary to preserve environmental noise quality where it is good. The results of the first round for noise mapping in Germany will be presented.
The national noise map of the Netherlands A trend in exposure since 1990
Authors: Van Haaren Rik
Published: May 2008

Noise maps according to the environmental noise directive have been provided by several actors in the Netherlands. The results of the noise maps show the significance of each of the source types, as well as the distribution within and outside agglomerations. In the Netherlands 2.7 million people are exposed to noise levels above 55 dB(A). In some cases up to 4000 people are exposed to level higher than 75 dB(A). In the night period 2.3 million people are exposed to noise levels higher than 50 dB(A). Road noise is the dominant source for annoyance and sleep disturbance. Within agglomerations road noise is responsible for 88% of the highly annoyed population. Major roads, outside agglomerations, contribute less than 10% to the total annoyance due to road traffic. Railways are a second source in producing annoyance and sleep disturbance. 57% of the high annoyance due to railways is produced outside agglomerations. The results of the noise maps for road traffic noise have been compared with results for a selection of cities in 1990. The results show that the total number of exposed people has increased. However, the exposition to the higher bands has decreased.
Sound radiation of the end of cylindrical duct application on industrial stacks
Authors: Simoneau Thierry
Published: May 2008

In order to determine the sound field emitted by the top end of an industrial stack, a study of the acoustical radiation of unbaffled semi-infinite cylindrical duct ends was conducted. Firstly, the main publications on the subject were studied. A calculation model of the radiation directivity of the end of a chimney, based on H. Levine and J. Schwinger's results for the fundamental mode and on the Geometrical Theory of Diffraction for the modes of superior order, was established. In order to validate the model, measurements on scaled model were made in an anechoic chamber. Tallying between theoretical and experimental results is very good, especially at low frequencies, where the number of radiating modes is low. Moreover, measurements on a real size industrial site have been made. They also show satisfying tallying between the theory and experimentation.
Measuring low-frequency noise indoors
Authors: Pedersen Steffen , Mo/ller Henrik , Persson Waye Kerstin
Published: May 2008

At low frequencies, the sound pressure level may vary 20-30 dB in a room due to standing waves. For assessment of annoyance, mainly areas with the highest occurring levels are relevant, since persons present in such areas are not helped by the existence of lower levels in other areas. The level that is exceeded in 10% of the volume of a room L10 is proposed as a rational and objective target for a measurement method. In Sweden and Denmark rules exist for measuring low-frequency noise indoors. The performance of these procedures was investigated in three rooms. The results from the Swedish method were close to the L10 target, but, due to a doubtful use of C-weighting in the scanning, it may give too low results in case of complex sounds. The Danish method was found to have a high risk of giving results substantially below the target, unless complainants can precisely appoint measurement positions, where the sound is loudest/most annoying - which they often cannot. An alternative method using measurements in four three-dimensional corners of the room is proposed. This easy and straightforward method seems to give reliable results close to the proposed target.
Characterization of an acoustic ceramic liner in a subsonic flow by mean of Laser Doppler Velocimetry
Authors: Pethieu Romain
Published: May 2008

As aircraft traffic constantly increases, serious efforts are made to reduce engine noise. Among them, the design of high performance absorbing materials (liners) placed on the nacelle's internal walls is an exciting challenge. Optimizing these media requires to know the mechanisms of acoustical propagation near them in the conditions encountered in jet engines: high speed hot shear flows. Particular interest is being granted to the influence of the grazing flow in contact with the liners. This is due to its known effects on the liners characteristics: efficiency of absorption and frequency resonance. This influence is remarkable for those configurations based on perforated plates. Therefore, a testing method based on non-intrusive measurements has been developed at ONERA. This technique consists in measuring acoustic velocities by laser Doppler velocimetry to determine acoustic quantities under grazing turbulent high-speed flow, thanks to an Eulerian-Lagrangian description of the perturbations. Experimental activity is performed on a honeycomb material, via the achievement of acoustical pressure and intensity fields, for different Mach numbers. Moreover, these measurements bring into evidence a coupling between acoustical modes and hydrodynamic modes (from Kelvin-Helmholtz instability) which modify the material acoustical behaviour.
Influence of boundary slip on the acoustical properties of microfibrous absorbents
Authors: Umnova Olga , Tsiklauri David , Venegas Rodolfo
Published: May 2008

In the past decades a variety of new highly porous materials with unusually small pores have been manufactured. In aerogels, for instance, pores can be less than 20 nm in diameter. The conventional models have to be modified when applied to describe acoustical properties of those materials. The non-slip condition on a pore surface is no longer valid and needs to be replaced by the Knudsen boundary condition. In attempt to provide an insight into the behaviour of microfibrous materials, an analytical model has been developed, which accounts for the boundary slip in a medium consisting of rigid parallel fibres assuming different directions of sound propagation with respect to fibres. It has been shown that the presence of the boundary slip leads to a significant change in model predictions. For instance, in a material with fibre radius 80 nm and 95% porosity the sound speed decreases and attenuation increases by more than 20% compared to the values obtained assuming no boundary slip. The effect is stronger for smaller size fibres, lower porosity values and for sound propagating parallel to fibres. Numerical computations have been performed to simulate oscillatory flow around the cylindrical fibres assuming Knudsen boundary conditions and the results have been compared with the analytical model predictions
Periodically non-homogeneous acoustic beams and their application in acousto-optics
Authors: Balakshy Vladimir I. , Linde Bogumil B.
Published: May 2008

Light diffraction by ultrasonic waves is of great interest in the view of both fundamental physics and diverse applications. Acousto-optic devices are used for modulation of optical wave parameters, for optical information processing in real time, etc. In the given research, basic attention has been focused on the analysis of characteristics of anisotropic acousto-optic cells in which acoustic waves are excited by means of a phased array of transducers. Current technology makes it possible to create easily such transducers with antiphase excitation of adjacent elements of the array. The directional diagram of this composite transducer consists of several lobes whose spatial orientation varies with frequency. This peculiarity results in changing the Bragg condition. In the case of the anisotropic acousto-optic diffraction, every branch of the Bragg angle frequency dependence is split into several curves. This opens up new possibilities for optimization of acousto-optic devices. In this work, we have analyzed amplitude, frequency and angular characteristics of the phased transducer cells depending on crystal cut and transducer parameters. In particular, it has been shown that, in spite of a noticeable phase mismatch between interacting waves, the diffraction efficiency can approach 100%.
Differential properties of acousto-optical tunable filters in phase-modulation mode
Authors: Pozhar Vitold , Pustovoit Vladislav , Beryoza Sergey
Published: May 2008

Tailoring the transmission function of acousto-optical tunable filters (AOTF) via acoustic waves control is one of the most challenging tasks, which is promising for optical spectroscopy applications. In our early work it was theoretically predicted and experimentally demonstrated that collinear AOTF with fast periodic phase manipulation exhibits differential properties, in particular capability of detection spectrum derivatives. In the report, the form of the instrument function of such AOTF was measured with use of Ne-lamp linear spectrum. Comparison to theoretically calculated function shows rather good agreement. Also the form of window of equivalent differential filter was determined and proved to be quite similar to AOTF classical window. Advantages of using this differential detection technique are considered. Its applicability to fluorescence spectroscopy is discussed.
Transformation of Acoustic Modes in Case of Arbitrary Reflection in Acousto-Optic Crystals
Authors: Polikarpova Nataliya , Voloshinov Vitaly , Declercq Nico F.
Published: May 2008

The phenomenon of unusual reflection of plane elastic waves is examined in the crystalline compounds of tellurium and mercury. It is predicted and registered in experiments that energy flow of one of the reflected waves may propagate practically in a back direction with respect to an incident energy flow. This phenomenon is observed in the materials with a strong anisotropy of elastic properties. In the case of inclined incidence, the reflection may take place strictly in the back direction with respect to the intrinsic energy flow. Moreover, all incident elastic energy may be reflected in a form of a back elastic wave. The analysis was carried out for all exisiting cases of inclined incidence in the crystals. It was proved that relative intensity of the unusually reflected wave might be close to a unit in a wide variety of incidence and cut angles in the crystals. A comparative analysis of the effect in new anisotropic materials and in the well-known crystals has been carried out. Since the crystals under investigation possess relatively high magnitudes of acousto-optic figure of merit, e.g. paratellurite and calomel, principal results of the research are of significance in development of new generations of acousto-optic devices.
Optimization of KDP-based acousto-optic imaging filters
Authors: Yushkov Konstantin B.
Published: May 2008

Acousto-optic devices can perform spatial and spectral tunable filtration of light with the use of anisotropic Bragg diffraction. In the near UV range of spectrum, KDP single crystals provide the highest acousto-optic figure of merit among uniaxial crystals. The report is devoted to the problem of optimization of the filter parameters in order to maximize angle aperture of the instruments. It was found that the maximum angle aperture of wide angle tunable acousto-optic filters is equal to 3 degrees in air at output of the KDP crystals. This magnitude of the angle aperture is limited by a narrow deflection angle of light in KDP that is due to a relatively low birefringence of the material. The investigation showed that the diffraction efficiency of light depends on the dimensions of the acousto-optic cell, i.e. linear aperture and length of a piezoelectric transducer. A discussion on trade-off between transmission coefficient and the spatial resolution in the filter is presented in the report.
Sound waves in 3D periodic granular materials
Authors: Mouraille Orion , Luding Stefan
Published: May 2008

The sound propagation mechanisms inside dense granular matter, even for periodical structures, are challenging the attempts to describe it because of the discrete nature of the material. Phenomena like dissipation, scattering, and dispersion are hard to predict based on the material state and/or properties and vice-versa. We propose here a simulation method using dynamic discrete elements in order to get more insight in this problem. The small perturbation created on one side of a dense, static regular packing of grains is examined during its propagation and when it arrives at the opposite side. Both longitudinal and shear perturbation are studied and an interesting wave-acceleration is observed [1]. Moreover the rotational degree of freedom permits to observe the role of rotations in the wave propagation. The control of the inter-particle forces like, contact potential, cohesion and friction make possible to observe the effect of these micro-parameters on the macro-behavior (at the wave scale). Long term goal is to predict the large-scale macroscopic material behavior from the microscopic structure and material parameters. [1] O. Mouraille, W A Mulder and S. Luding: Sound wave acceleration in granular materials, J. Stat. Mech. (2006) P07023.
BEM analysis of plane waves scattered from periodic surfaces
Authors: Bansal Mahesh , Ahnert Wolfgang , Feistel Stefan
Published: May 2008

Periodic surfaces like stairs, seats and repetitive designs on walls are very common and integral part of room acoustics. Effective simulation of the sound field inside enclosures requires the investigation of scattering from such periodic surfaces. In this work, we perform BEM analysis to calculate the scattering coefficients of different samples. For comparison purposes we also introduce a simple point-source based model to calculate the scattered wave fronts. Both approaches are implemented in a computational tool called EASE Scatterer. The incident plane waves are considered at various angles and scattered waves computed in both models are then compared with the measured data. It is found that while the point-source model can give reasonable asymptotic results, the BEM model matches with the measurement data significantly better in quantity and quality. Moreover, a study by varying the number of periods for the given sample is also performed.
Diffraction phenomena associated with a composite plate containing an interior periodically corrugated interface
Authors: Herbison Sarah W. , Declercq Nico F.
Published: May 2008

The interest in the study and applications of phononic crystals has naturally lead to the investigation of other novel periodic structures. The present work examines the case of a plate constructed of two solid layers of differing elastic properties separated by a periodically corrugated interface. It is shown how the dispersion curves are influenced by the internal corrugated interface and how they evolve as a function of the magnitude of this corrugation. Internal diffraction effects alter the dispersion properties and thus have an important effect on the composite when it is used as an acoustic filter. These effects are also important for the transmission and reflection of sound when the composite is used as a panel or when it is the intention to generate Lamb waves to investigate the composite plate nondestructively.
Multiple scattering of acoustic waves from two transversely isotropic cylinders
Authors: Sodagar Sina , Honarvar Farhang , Sinclair Anthony N.
Published: May 2008

The study of the interaction of acoustic waves with cylindrical structures has numerous applications including the ultrasonic nondestructive testing of materials. The scattered pressure field from a submerged cylinder contains valuable information about its physical properties. Scattering of acoustic waves from single cylindrical components including solid cylinders, shells, and multilayered cylinders has been of interest during the past two decades. These studies include theoretical modeling, numerical calculations, and experimental measurements of the scattered field of these objects. The more complex problem of multiple scattering from a grating of cylindrical components has also been considered during the past few years. These studies usually deal with either rigid or isotropic cylindrical objects. In this paper, the mathematical modeling for the scattering of plane acoustic waves from two adjacent infinite anisotropic solid cylinders will be presented. The type of anisotropy considered is transverse isotropy (hexagonal symmetry). The mathematical model accounts for the effects of the scattered filed of each cylinder on the total resultant pressure field. Numerical calculations are used to verify the validity of the developed mathematical model.
Diffraction influence on the SAW tag characteristics
Authors: Sveshnikov Boris V.
Published: May 2008

The diffraction of acoustic beams may influence notably on the responses of the SAW based RFID systems. In order to prevent such an influence one cannot increase the tag acoustic aperture too much because of ohmic loss in a transponder. On the other hand, usually the tag length should be large enough. There is a very specific and unique feature of the acoustoelectric scattering of SAW beam on the coding sequence of the reflective metal electrodes placed on a piezoelectric substrate. The point is that the SAW itself is formed by two coupled sub-systems, namely: elastic displacements and electric field. Both of them are scattered on every discontinuity because of two kinds of the boundary condition perturbation: electric shorting beneath electrodes and mass-loading effect. A uniform metal electrode scatters differently from each other the "elastic" and "electric" subsystems with non-uniform wave-front caused by diffraction. The closed form expressions are found, allowing us to describe consistently the mentioned phenomena. Their numerical analysis has been added by the analytical one in case of parabolic approximation of the crystal slowness curve. The synthesis algorithm of SAW tags with high capacity is proposed taking into account the diffraction effect in a natural way.
Criterion to select meteorological factors to evaluate uncertainties in sound propagation
Authors: Maijala Panu
Published: May 2008

Most of the environmental factors have some effect on sound propagation outdoors. Many of these factors can be properly implemented to a sound propagation model. However, it is not easy to handle sound scattering due to the turbulence, and at the same time, the turbulence is the most important source of uncertainties. Concurrently with the studies of turbulence models we have developed a concept to get an estimate of the excess attenuation using a state-of-the-art physical model and to evaluate the uncertainties using a statistical model. This statistical model is based on two years continuous measurements using extensive acoustical and meteorological measurement facilities and producing over 100 factors hourly. Many meteorological factors had a strong and significant correlation with the excess attenuation, but between each other too. To avoid instable model due to the collinearity many factors were abandoned. In this paper the criterion and methods to select best explaining factors and to form this statistical model are considered.
Field experiments on the influences of wind speed and direction on outdoor sound propagation over flat ground
Authors: Yokota Takatoshi , Makino Koichi , Yamamoto Kohei , Okada Yasuaki , Yoshihisa Koichi
Published: May 2008

The influences of wind on outdoor sound propagation are investigated both by field experiments and numerical simulations. At first, measurements of sound propagation at a distance of 160 m were carried out under various wind speed and direction. The relationship between vector wind speed and the variation of sound pressure level has been examined not only for the up/down wind conditions but also for the cross wind conditions. Secondly, the short term sound fluctuations were investigated by the use of a high energy impulsive sound generator and a loud speaker as sound sources. Sound propagation up to 300 m was examined with frequency range from 16 Hz to 4 kHz octave band. Finally, the sound speed profiles in the measurement field were estimated by two methods; one was based on the time interval during the sound propagation from the source to the receivers, the other was based on the wind speed at height of 0.6 m, 1.2 m, 2.4 m and 4.8m, and the temperature. By using those sound speed profiles, the excess attenuation was calculated by the PE method. The measured and the calculated values have been compared and the methods to estimate the influences due to wind condition have been discussed.
A model based monitoring system for aircraft noise
Authors: Van Den Berg Frank , Eisses Arno R. , Van Beek Pieter J.
Published: May 2008

A new approach for an airport noise monitoring system is presented that comprises not only a number of measuring stations, but also a dedicated sound propagation model and an aircraft noise emission model. This approach enables estimation of noise levels in the whole area around the airport and not only at the location of the measuring stations. An additional advantage is that the locations of the measuring stations can be chosen more freely. Traditionally the measuring stations must be located near residential areas where the influence of other noise sources (such as cars or wind) cannot be eliminated. Better locations can be found that yield more reliable data and therefore more reliable noise levels. To update the sound propagation model frequently, the measuring stations not only measure noise levels, but also other parameters, like temperature and wind profile. The sound emission of the aircraft is derived from a directional aircraft noise emission model. A tool was developed to visualize the power of combining data and models in this model-based monitoring system. The use of models opens possibilities for interesting applications such as i) short term noise forecasts, ii) scenario studies with various aircraft distributions and iii) enforcement of noise limits.
The variability of acoustical turbulence in the atmospheric boundary layer
Authors: Cheinet Sylvain
Published: May 2008

Outside sound propagation is affected by small-scale turbulence in the atmospheric boundary layer through refractive processes. These effects modulate the performance of acoustical sensors, and are at the basis of the atmospheric remote sensing by sodar. Previous studies have documented the impact of a mean turbulence profile or a statistical distribution of turbulence. In this study, we use a high-resolution atmospheric model called LES to reveal the spatial and temporal variability of the small-scale turbulence. First, we introduce some standard results on the role of various eddy sizes on acoustical propagation. Second, we discuss the methodology to derive the acoustical refractive index fluctuations from LES data. Third, we analyze the LES prediction in the case of a fair-weather boundary layer, emphasizing the impact of large-scale convective organization. Finally, we discuss some challenges in attempting to predict the acoustical turbulence from present-day weather forecasts.
Horizontal wave number spectra of atmospheric acoustic fields in range-dependent environments
Authors: Gilbert Kenneth E , Di Xiao , Parakkal Santosh
Published: May 2008

The parabolic equation (PE) is a powerful method for computing sound propagation in range-dependent environments. However, the PE gives only the total field, with no information on the horizontal wave number spectrum of the acoustic field. In many situations, e.g., for propagation over irregular terrain, the horizontal wave number spectrum is valuable for analyzing the modal content of the acoustic field. For example, one might want to know the strength of the surface wave component at different ranges. A spectral decomposition method developed by Gilbert and Evans for ocean acoustics is applied here to atmospheric propagation over irregular terrain. This paper shows that for a PE field p(z) at range r, the horizontal wave number spectrum φ(κ,z) can be obtained directly and efficiently by solving a one-dimensional elliptic equation that uses the field p(z) as a source term. The derivation of the spectral decomposition equation is given along with a numerical method for solving it. Examples are presented and discussed for propagation over irregular terrain. [Research supported by the U. S. Army TACOM-ARDEC at Picatinny Arsenal, New Jersey]
On the optical generation and detection of high frequency ultrasounds: thermal and non-thermal processes
Authors: Ruello Pascal , Babilotte Philippe , Zhang Shuo , Mounier Denis , Breteau Jean-Marc , Edely Mathieu , Laffez Patrick , Bulou Alain , Perrin Bernard , Gusev Vitali
Published: May 2008

We report on the results of the generation and detection by femtosecond laser pulses of the acoustic waves at frequencies of tens to hundreds GHz in semiconductors and in oxides compounds exhibiting phase transition. We focus first on the generation mechanisms involved to achieve opto-acoustic transformations. Particular attention will be paid to the cases where classical thermal effects (thermoelastic coupling) drive the mechanism of generation of acoustic phonons and those where non-thermal effects become significant and sometimes dominant sources of acoustic phonons field. In the latter cases, we will especially focus on the phonons generation based on photo-induced modifications of microscopic internal electric fields (potential deformation) and also on the use of photoexcited carriers dynamics (carriers recombination) as a tuning parameter of the photo-generated ultrasounds spectrum. Secondly, we give the examples demonstrating that the choice of optical frequency for ultrasound detection influences not only the amplitude of the detected signal but provides an opportunity to detect separately high or low frequencies in the spectrum of ultrasounds. This study was supported by CPER and ANR project No. BLAN06-3-136284.