bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantifying the noise environment: effects of the wearer's voice on body-mounted noise dosimeter measurements
Authors: Ryherd Steve , Persson Waye Kerstin , Kleiner Mendel , Ryherd Erica
Published: May 2008

The purpose of this project was to investigate the effects of the wearer's voice as a dominant sound source on body-mounted noise dosimeters in medium-level acoustic environments. Noise dosimeters provide a convenient method of quantifying an occupant's acoustical exposure. In recent years, interest in personal noise exposure has expanded beyond a necessary safety measure used in industrial settings to be used as a means of documenting a person's exposure to sound pressure levels in lower level environments like hospitals and schools. This study quantifies the contribution of the wearer's voice to the dosimeter measurement in sixteen different office conditions. Statistical analysis was used to determine the effects of the following experimental variables on the measured levels: 1) the type of room in which the measurement is taken, 2) the type of background noise present, 3) the level of background noise. Preliminary statistical results suggest significant main effects of the experimental variables with no significant interaction effects. The statistical effect of the subject's hearing level was also considered. The results of this study can improve the interpretation of dosimeter measurements in medium-level environments and may provide further motivation for alternate methods of quantifying sound pressure levels associated with body-mounted measurements.
Evaluation of Speech Privacy Index and Noise Isolation Class rating of medical examination rooms and comparison with predictions
Authors: Pettyjohn Steve
Published: May 2008

The Health Insurance Portability and Accountability Act of 1996 (HIPAA) set speech privacy requirements for medical related information without defining speech privacy for all situations. Areas of special concern for medical organizations are examination rooms because of the need to exchange information between patient and care giver. These rooms are usually constructed in groups with up to three walls common to other examination rooms and a fourth wall next to a corridor. Each adjacency can pose special problems because of construction and position of the equipment in the room. Medical groups are attempting to design and build examination rooms to achieve what they perceive as acceptable levels of privacy while staying within budget and waiting for definitions and requirements. This study provides results of NIC and SPI tests of examination rooms for two medical groups using several different designs. A comparison is given between measured and predicted values based on wall heights and construction details. The wall designs ranged from standard products and construction to employing specialized products, but with only partial height walls. All rooms employed acoustical tile ceilings rather than hard lids. Construction details were found to be the major factor affecting SPI.
Prediction of speech privacy between rooms
Authors: Keränen Jukka S. , Virjonen Petra , Hongisto Valtteri O.
Published: May 2008

The main purpose of sound insulation is usually to provide an appropriate level of speech privacy between rooms. However, the desired privacy is not always reached if, e.g. the background noise level of receiving room has not been considered or rooms are very small. This is often the case in dwellings and office rooms. Thus, sound reduction index does not correlate well with speech privacy. The aim of this study is to present a simple and validated model to predict the speech privacy between two arbitrary rooms when basic room and wall parameters are known. Speech privacy was described using Speech Transmission Index, STI. STI can be determined when the speech effort, room dimensions, early decay times of the rooms and background noise level of the reception room are known. The model was validated in several cases. The model is useful when economic optimization is appreciated. It can lead to major reductions or increments of conventional recommendations for Rw value, especially, when room dimensions are unusual or the rooms have special purposes. The optimization is very easy using a web-based software.
Measuring absorption coefficients of open ceilings in multi-purpose halls
Authors: Kim Yong Hee , Lee Hye Mi , Jeon Jin Yong
Published: May 2008

This paper investigates the acoustical characteristics of open ceilings in multi-purpose halls using a 1:25 scale model. A steel truss, duct system, catwalk and opening were selected for the major components of open ceilings from a field survey of 17 existing halls. Absorption characteristics of the equipped ceilings with the 1:25 scale model were measured in a reverberation chamber according to ISO 354. It was found that different volume and materials of the ceiling spaces cause the composite decay characteristics to be similar to those of coupled room effects. Results showed that the absorption coefficients of an empty ceiling with 50% opening and 6 m of depth are 0.2-0.3 above 500 Hz. Adding steel trusses to the ceiling increases the absorption coefficient by 0.1 at 125-2,000 Hz; ducts and catwalks with steel trusses yield an increase in the absorption coefficient at high frequencies. The average absorption coefficients of the various composite ceiling structures were 0.19 to 0.61.
Historical and chronological evolution of the concert hall acoustics parameters
Authors: Lacatis Radu , Giménez Alicia , Barba Sevillano Arturo , Cerdá Salvador , Romero José , Cibrián Rosa
Published: May 2008

The present paper examines the historical evolution of the concert halls acoustic parameters, in the international field. From the beginnings of twentieth century, the acoustic parameters have had a continuous evolution, covering more and more aspects of the concert hall acoustics qualification. Since the bibliography about these is fragmented, we performed in this article, a global and updated presentation on the chronology and the evolution of the studied parameters. Considering the great variety of the same, we presents the appearance of each parameter, located in decades, who has proposed them and, where is possible, indicates articles or publications where they have been presented for the first time. Thus, the historical presentation of the majority of the acoustic parameters of concert halls, it optimizes and can be useful for future research as a central platform in a bibliographical study. The presentation of the same is also grouped according to quality criteria.
Sound absorption control at low frequencies in the new symphonic concert Hall of VillaPrado Valladolid
Authors: Chavez Thielemann Victoria
Published: May 2008

In large concert halls for symphonic orchestras the sound absorption control at low frequencies is a compromise between acoustics and architecture. In general the architectural approach is imposed over acoustical wills. In this way the acoustician must adapt his work to the architectural choice of finishing materials. Commonly is the case of the wood material's choice (usage of thin wood panels in medium density), whose architectural expression is related to orchestra instruments and to the visual warmth. Today the acoustical trend is to obtain in concert halls the appropriate acoustical "warmth". As convention, this acoustical quality in a concert hall is related to the bass sound spotlessness, and an appropriate strength of the bass tones arriving to the audience. In this context we will present the solutions and constructive compromises realised in the auditorium of Villa Prado in the way to obtain the desired warmness. This concert hall has a "shoe box" shape, an audience capacity of 1720 seats and it was made completely - walls, ceiling - in wood panels (architect: R. Bofiil, acoustician: XuAcoustique, inaugurated in April 2007, Spain).
Acoustical design of multichannel audio listening environments
Authors: Gulsrud Timothy
Published: May 2008

The acoustical design of spaces for surround sound music production raises issues concerning room size and shape, loudspeaker placement, and placement of sound-absorbing and sound-diffusing finishes that require different solutions than for 2-channel stereo listening environments. Design and construction of a new room for multichannel audio, rather than renovating a room originally conceived for a 2-channel stereo loudspeaker system, presents an opportunity to address the issues from first principles. This paper presents a case study of the design, construction, and commissioning of a new audio control room for multichannel classical music recording, and discusses unique solutions to the critical issues for these listening environments. The use of a computer model as a design tool and in situ measurements in the completed room are also discussed.
Towards a classification of the "sonic character" of the architectural space
Authors: Rodriguez-Manzo Fausto E.
Published: May 2008

Today it is well-known that an architectural space can be compared with a musical instrument. One of the main characteristics of a musical instrument is its timbre, which makes unique the sound produced by it. We can understand this timbre as the sound quality of the instrument that is produced due to the specific physical characteristics of the instrument. In an architectural space these concepts of timbre and sound quality could be applied through the concept of "sonic character" of the space. The "sonic character" of the architectural space is the sound personality of the space due to the specific physical or architectural characteristics of it. Understanding this concept in architecture could be of great importance to architectural design purposes since this could be the way by which sound can be embodied in an integral way of designing architectural spaces. This paper presents a proposal for the classification of the "sonic character" of the architectural space as an important step of a research towards a better understanding of the need of taking into account the sound as an essential component of the architectural space. The presentation includes also some architectural space examples to improve the understanding of this important concept.
A passive array technique for cavitation mapping during HIFU treatment
Authors: Gyöngy Miklós , Arora Manish , Noble Alison , Coussios Constantin C.
Published: May 2008

During exposure of tissue to HIFU, cavitation has been shown to enhance the rate of heat deposition in tissue and could provide an effective means of treatment monitoring. However, cavitation activity occurring pre-focally or growing unstable around the focal region is known to impede safe and effective treatment delivery. A combined computational and experimental approach is being applied to develop a passive array-based technique for mapping cavitation activity in real-time, using a novel cross-correlation algorithm to combine single-channel information received by an imaging array co-axial to the HIFU transducer. The cavitation maps produced in this manner were validated using two single-element 15-MHz focused PCDs during continuous-wave insonation of a polyacrylamide-based tissue mimicking material by 1.1 MHz HIFU. Initial experiments have shown bubble cloud movement towards the HIFU transducer, in agreement with previously reported observations. Future work will involve applications of advanced imaging techniques to achieve a high spatiotemporal resolution, which is essential because of the unstable nature of cavitation activity and the requirement that treatment be well localized.
Improvement of speech intelligibility by audio hearing systems
Authors: Seidler Hannes
Published: May 2008

All hearing aids and cochlea implants have algorithm to improve the speech intelligibility. The idea is to share human speech and noise to find different ratings. The result should be easier to understand by impaired people. On the market there are big efforts to recognize speech and to separate it from noise. In this field we can notice a remarkable progress in the last years. But the reverberant sound in rooms or noise from same direction like the signal need a lot of work to suppress them effective. The simplest way seems to be to gets the original speech signal direct from the source and to processes it individual in hearing devices. Induction loop systems as well as wireless infrared or radio frequency systems are used in churches, cinemas, theatres and conference rooms. But the available systems are very different in costs and benefit for management and clients. If these systems are used there is a considerable improvement of speech intelligibility. The presentation will show the level of most used external audio hearing systems, their possibilities to improve the signal to noise ratio, the speech transmission index (STI) and the benefit for hearing aid or cochlear implant users.
Vortex sound of the flute and its interpretation
Authors: Bamberger Andreas
Published: May 2008

The flute as an example of flue instruments is investigated for its properties of the jet-labium interaction at 1kHz. The jet and the externally excited acoustic flow in the embouchure especially near the labium is recorded with endoscopic Particle-Image-Velocimetry. Extracting the vorticity the data allows us to calculate the vortex sound according to M. How (1975) . The far field acoustic power of the flute is measured as well and compared with the vortex sound power, which matches in sign and magnitude up to a factor 2 for different sound levels. The non-trivial interpretation of the sound production is based on the near cancellation of the two vortex layers of the jet along its path except near the labium. In order to gain insight of the interplay of the different ingredients of the vortex sound power the coriolis force, the acoustic field and their phase relation are determined. Scaling of laws for these quantities as a function of the jet velocity/pressure of the standing wave are deduced and compared with the acoustic power dependence. A comparison with recently available numerical simulations (ISMA 2007) is discussed.
Ride quality and noise in high speed elevators
Authors: Pierucci Mauro , Frederick Michael
Published: May 2008

Ride quality in an elevator is the latest "hot topic" in elevator design and construction. In skyscrapers being built in Asia, Dubai and the US, the new elevators travel close to and beyond 10m/s. The rides to the highest floors will last well over one minute. From a comfort point of view, it is important that the ride be as smooth and quiet as possible. There are many factors that influence the vibration of the elevator and the concomitant noise. In this paper we will examine the sudden forces that the elevator experiences as it passes each floor. The side forces on the elevator are caused by the asymmetric flow field about the elevator cab. The pressure and streamline flow field was evaluated by using the CFD code FLUENT. Comparison between the numerical and the measured results are given and the pressure disturbances caused by the passage of the elevator and its appendages are discussed together with some solutions to alleviate the pressure disturbances.
Acoustic and aerodynamic dissipations induced by a sound wave-impacted Helmholtz resonator
Authors: Roche Jean-Michel , Leylekian Laurent , Vuillot François
Published: May 2008

The purpose of the work introduced herein is to study the dissipation of the acoustic energy carried by sound waves, by a Helmholtz resonator. Two-dimensional direct numerical simulations (DNS) are performed with the CEDRE code, a Navier-Stokes equations solver developed by Onera, for a resonator with a 0.8 × 0.8 mm square opening. The incident sound pressure level (SPL) varies between 100 dB and 150 dB: it is checked that when the SPL is low, the acoustic energy is dissipated in the resonator opening by viscous wall friction, whereas when the SPL is high, the acoustic energy is converted in kinetic energy carried by micro-vortices induced at the opening mouths. However, when the SPL takes intermediate values, both mechanisms coexist. Thus, for each case, we aim at splitting the aeraoacoustic field into respective acoustic and aerodynamic contributions, and at evaluating the ratio between these two distinct mechanisms in order to quantify their relative weight on the global dissipation. Our results are compared with those obtained by Tam et al. for the same geometry. A three-dimensional study for a Helmholtz resonator with a cubic opening is eventually considered.
The multiple side-branch system as a model for a corrugated pipe
Authors: Tonon Devis , Belfroid Stefan , Willems Jan F. , Hirschberg Avraham
Published: May 2008

Corrugated pipes are used as flexible risers in offshore natural gas production and for vacuum cleaners. Such pipes can display whistling. As theoretical models are available to predict the aero-acoustical behaviour of closed side branches [1], we consider a row of equally spaced closed side branches along a pipe, as a model for a corrugated pipe. We consider side branches with a diameter D and depth L equal to the main pipe diameter, placed at a distance of three diameters from each other. For systems of 11 or 12 side branches the lowest resonance modes are reasonably well predicted by assuming n(λ/2) standing wave modes with an effective speed of sound ceff[2]. Whistling is observed for the n=2 and n=3 modes with a pressure fluctuation amplitude p'/(ρ0c0U0)=O(2×10-2) similar to that observed for sharp edges corrugations in a corrugated pipe (with ρ0 the fluid density, c0 the speed of sound and U0 the main flow velocity). The Strouhal number of these oscillations is SrD=(f⋅D)/U0≃0,70. This is higher than typical values observed for corrugated tubes [3]. References: [1] J.C. Bruggeman et al., J. Sound and Vibration 1991 150(4) 371-393. [2] J.W. Elliot, in "Lecture Notes on the Mathematics of Acoustics" M.C.M. Wrigth, Imperial College Press, London (2005). [3] S. Belfroid et al., ASME paper PVP2007-26503.
Overview of Railway Noise Control in Europe
Authors: Oertli Jakob
Published: May 2008

European and national legislation, increasing freight traffic, political pressure and many more factors contribute to make noise an issue of increasing importance for the railways. This paper provides an overview of railway noise abatement efforts throughout Europe. Different countries in Europe have adopted varying noise abatement strategies, ranging from an emphasis on infrastructure based measures to a combination of rolling stock measures with noise barriers. Important in the current European discussion is the development and retrofitting of freight wagons with K- and LL-brake blocks. To support this retrofitting a wide variety of incentives, such as differential track access charges, operational restrictions or direct subsidies are being discussed. The current efforts by the European Commission, the International Union of Railways (UIC), the Community of European Railways (CER) and other international organisation to promote silent railways are presented.
Railway vibration mitigation - An innovative concept
Authors: Le Corre Frederic , Charles Christine , Girardi Marcel
Published: May 2008

These last decades, rail transportation has known an amazing development. Hence, the resulting pollution on people living alongside lines or above underground lines has become a crucial subject of consideration. The disturbance has two origins: the direct noise or vibration from the railway traffic and the noise produced by vibration of the building walls, the so-called re-radiated noise. Noise and vibration excitation is essentially due to wheel and rail roughness at the contact point. From this excitation point, the track acts as a filter of vibrations. Hence, spectrum of emitted vibrations can be controlled with the design of railway track. Providing vibration mitigation with the track is now commonly encountered, especially on urban projects (LRT MRT). This is usually achieved by introducing an adequate resilient layer to provide the required attenuation. Alstom Transport and Sateba are developing a system to mitigate vibrations. This system called AFST is based on the booted sleeper system. After a complete analysis of critical parameters, a special design has been drawn. The resulting antivibratile solution is a high-performance system suiting areas where vibration mitigation and/or attenuation of re-radiated noise are required.
In Situ Characterization and Noise Mapping of Ships Moored in the Port of Venice
Authors: Di Bella Antonino , Tombolato Andrea , Cordeddu Stefano , Zanotto Emanuele , Barbieri Marco
Published: May 2008

The acoustical characterization and the mapping of noise emitted from ships were carried out on behalf of the Venice Port Authorithy in the frame of the European Project NoMEPorts (Noise Management in European Ports). According to the Directive 2002/49/CE (END), different noise sources (like roads, railways, aircraft, industrial sites, ports) have to be considered and mapped separately; so, in the first step, the acoustical characterization of ships is required. Annex IV of the Directive, in particular, establishes that the strategic noise maps for agglomerations shall put a special emphasis on the noise emitted by, inter alia, industrial activities, including ports. Three kinds of ships were investigated, using the Italian technical standards UNI 10855 and UNI 11143: 1. inland navigation ships (along wharves); 2. ferries (along wharves and when maneuvering); 3. cruises (along wharves and when maneuvering). As for the maneuvering, it could be said that a supplementary noise indicator is needed, as the END, Annex I, forsees in the case the average number of noise events in one or more of the day periods is very low (for example, less than one noise event an hour).
Managing Input Data Uncertainty within Strategic Noise Mapping by Utilising Data Schema Specifications
Authors: Shilton Simon J. , Jones Nigel , Trow James
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. Large scale wide area noise modelling requires an extensive range of data inputs. The requirements for these inputs are driven by several factors, including the noise calculation methodologies, noise mapping software system, GIS and the deliverables set out within the Directive and recommended Reporting Mechanism. Utilising a staged approach to project design led to the development of detailed noise mapping data schema specifications prior to the collation of input datasets for the calculation process. The data schema may be used throughout the mapping project as a framework to manage dataset concatenation, data capture or the use of defaults and GPGv2 Toolkits to infill data gaps. They also enable data pre-processing guidelines to be passed to non-acoustic GIS specialists, and help to guide and catalogue data processing steps. This paper presents experience gained whilst developing a number of noise mapping data schema specifications and their implementation within successful projects during the first round of mapping. Railway noise mapping is used as an example of how a data schema may be used to develop solutions to technical problems as well as coordinate data capture.
On railway noise modelling - an approach to the european interim method
Authors: Bento Coelho J. Luis , Alarcão Diogo
Published: May 2008

Railway noise results from a number of sources, with airborne and structure borne transmission mechanisms being responsible for the noise radiation and propagation. The European Directive 2002/49/EC requires the drawing of noise maps for areas near major transport infrastructures. The Portuguese Noise Act of 2007 further requires the drawing of noise maps for all transport infrastructures. This paper reports on our experience on noise mapping of the major Portuguese railway lines. The interim calculation model RMR96/SRMII, recommended in Directive 2002/49/EC, was adopted for the prediction of the railway noise, where a 1/1 octave band noise spectrum curve fitting approach was followed. Details on the implementation, adaptation and validation of the calculation procedure are reported. Emphasis on the required data such as train categories, superstructure, and speed profiles will be given. Examples and results for a number of major railway lines will be presented.
Is DNL appropriate for airport noise zoning
Authors: Slama Jules G. , Mora-Camino Félix A. , Revoredo Teo C.
Published: May 2008

The use of the DNL metric in airport noise zoning is based in the works of Schultz, that were later improved by Fidell. The basic idea is to use the percentage of highly annoyed people as a parameter to organize the area around airports. In urban zoning it is recommended to use the equivalent sound level LAEQ, which uses different criteria to day and night periods to define the land use. With regards to airport noise one may use LAD and LAN metrics which are the equivalent sound levels determined for day and night period, respectively. In this case, the maximum levels chosen to the establishment of the zoning are based on the land use. It is possible, through a simple equation, to determine the DNL level associated to a LAD, LAN pair. The inverse problem, however, has not a unique solution, once this relation depends on the number of daily and night flights of the airport. Thus, the use of DNL in airport noise zoning may lead to completely different results for different airports. Exemples are presented and discussed for two main brazilian airports: Recife and Congonhas.
Cost-effectiveness of railway noise measures in practice
Authors: Roovers Chiel
Published: May 2008

The Dutch noise nuisance law enforces railinframanager ProRail to take noise measures when railway transport is growing, new lines are built or changes are made to the existing lines. Also, measures are taken by the Dutch government at existing "hotspots". At the moment the toolbox of measures includes noise barriers, sleeper renewal, raildampers, acoustic grinding and façade insulation. The life-cycle costs of these measures have been derived from recent projects. This paper focuses on the evaluation of the cost-effectiveness of these measures in typical situations where the choice of the application of noise mitigation measures was made recently. In what circumstances is it considered to be appropriate to take measures, and how much money will be available? Are source measures like raildampers more cost-effective compared to noise barriers? The introduction of a track-access-charge system which differentiates on the noise emission of trains concludes this paper.
Structure borne sound source data of building service equipments for EN 12354 part 5 - Round Robin measurements
Authors: Simmons Christian
Published: May 2008

At the conference, results will be presented of a round robin test where sound pressure levels and vibration data have been measured in 7 sites using two laundry machines and one heating compressor as sources. The vibrations are determined as transversal vibration levels of the concrete slabs (with the structural loss factors) according to a draft standard prEN 15657-1, as well as relative levels compared to the standardized tapping machine (ISO 140-8). The purpose is to study whether these data may be applied to predict structure borne sound in nearby spaces, according to the draft standard prEN 12354 parts 5 and 2, with a reasonable accuracy as compared to the measured sound pressure levels. The variations in space and time will be monitored carefully to observe any modal coincidence and whether the time and spatial average is the best descriptor of these types of source.
Ground vibration requirements in vehicle projects
Authors: Färm Janne , Leth Siv , Rüst Philipp
Published: May 2008

The climate is right for trains and the environmental targets regarding noise and vibration have to be met to enhance the competitiveness of rail over other forms of transport. Ground vibration is one part that needs to be further addressed. Customer requirements on ground vibration are often included in vehicle contracts even if the vehicle is only one part of the system determining the ground vibration at the receiver point. For the design of new lines there is a need for a better optimization of overall generation of noise and vibration where both the infrastructure and vehicle parameters are included. An overview of the diversity of ground vibration requirements in different vehicle projects is given and the relation to a number of vehicle and track parameters. The potential conflict between ground vibration reduction and increased airborne noise generation is analyzed for particular examples. The background analysis clearly points out the need for a standardization regarding both setting and evaluation of requirements. There is also a need for developing one commonly used, widely accepted, validated prediction tool for ground vibration. It should facilitate engineering level decision making and allow assessment of mitigation measures.
Observations and models of dynamic earthquake triggering
Authors: Gomberg Joan , Johnson Paul A.
Published: May 2008

Seismologists have long accepted the idea that step-function perturbations to the deformation field acting on a fault can change its likelihood of, or 'trigger', failure as fault slip. We review the observations that have lead to the very recent recognition that transient perturbations (e.g., associated with seismic waves) also affect failure probabilities, and more broadly, observations of the spatial and temporal variations in both triggering deformations and triggered responses. Many of these cannot be explained by conventional models of earthquake nucleation, requiring consideration of ideas developed in other disciplines, such as those describing and explaining nonlinear dynamic elasticity from rock-mechanics. In addition to the scientific challenges, these observations and models significantly impact earthquake forecasts and hazard assessments. We focus on observations of natural earthquakes and from the rock-mechanics laboratory, and some of the explanatory models that we and others have proposed. While many of these observations and models are just being vetted now, even newer ones related to slow aseismic fault slip and non-volcanic tremor (seismic radiation that scales very differently from that from earthquakes) may lead to substantive modifications and advances. We conclude with a few tantalizing examples as a prelude to a companion presentation.
Strongly nonlinear behavior of granular chains and granular composites
Authors: Nesterenko Vitali F. , Herbold Eric B. , Benson David J. , Kim Jeonghoon , Daraio Chiara
Published: May 2008

Strongly nonlinear behavior of granular phononic crystals composed of stainless steel cylinders and PTFE spheres is considered experimentally and numerically. The tenability of phononic band gap in this two-mass prestressed chain was investigated. The results show that the phononic band gap exists within audible frequency regime (20–20,000 Hz) and can be tuned by changing the value of prestress. Influence of the weak and strong nonlinearity on the propagation of signals with frequencies inside band gap was investigated. The mechanical properties of reactive materials (e.g., high density mixtures of polytetraflouroethylene (PTFE), aluminum (Al) and tungsten (W) powders) where unconsolidated granular packing of metal particles plays significant role in the dynamic behavior was investigated. It was found that dynamic strength can be tailored by changing the morphology of the particles and porosity. Cold isostatically pressed PTFE-Al-W powder composites with fine metallic particles and a higher porosity exhibited higher ultimate compressive strength than less porous composites having equivalent mass ratios with coarse W particles. Based on the numerical analysis it was concluded that a mesoscale force chains between the fine metallic particles are responsible for this unusual phenomenon. This work was supported by the NSF DCMS03013220 and by MURI ONR N00014-07-1-0740.
Mechanisms of acoustic absorption in weakly wet granular media
Authors: Brunet Thomas , Jia Xiaoping , Mills Pierre
Published: May 2008

Multiply scattered elastic waves provide a sensitive probe for studying the viscoelastic properties of a granular medium at the length scale of grains. Based on a diffusion model, we can infer the structural and viscoelastic properties of the material from the fitting parameters such as the diffusion constant D and quality factor Q. In this work, we characterize quantitatively the acoustic dissipation occurring at the grain contacts by measuring the Q factor in different granular samples. We focus a particular attention on the effects of on the internal loss by adding a small amount of liquid in the granular medium (̃0.05%). Using the Hertz-Mindlin contact theory we have identified two different mechanisms of acoustic absorption: frictional and viscous dissipations.
Acoustic wave propagation in granular systems
Authors: Somfai Ellak , Roux Jean-Noel , Snoeijer Jacco H. , Van Hecke Martin , Van Saarloos Wim
Published: May 2008

We present numerical simulations of acoustic wave propagation in granular systems consisting of particles interacting with the three-dimensional Hertz-Mindlin force law. The response to a short mechanical excitation on one side of the system is found to be a propagating coherent wavefront followed by random oscillations made of multiply scattered waves. We find that the coherent wavefront is insensitive to details of the packing: force chains do not play an important role in determining this wavefront. The coherent wave has a well defined velocity, which is roughly compatible with the predictions of macroscopic elasticity, and its amplitude and width depend as a power law on distance. As there is at present no theory for the broadening and decay of the coherent wave, we numerically and analytically study pulse-propagation in a one-dimensional chain of identical elastic balls. The results for the broadening and decay exponents of this system differ significantly from those of the disordered packings. We briefly discuss the eigenmodes of the system and effects of damping are investigated as well.
Scattering of ultrasonic waves in randomly layered materials
Authors: Pakula Michal , Cieszko Mieczyslaw , Kubik Jozef
Published: May 2008

The goal of the paper is the proposal of a new macroscopic description of scattering of elastic waves at internal inhomogeneities of the material. Within the studies the microscopic inhomogeneity of the medium is modeled as the alternately arranged two kinds of elastic layers of random thicknesses and different mechanical properties. Calculations of the acoustical characteristics of such medium (reflection and transmission coefficients) are performed in two stages: (i) first the problem of interaction of plane harmonic wave with the half space of the randomly layered medium for the case of normal wave incidence is analyzed; (ii) then the interaction of the harmonic wave with the slice composed of randomly layered structure is considered. Such approach allowed to derive analytical relations for the phase velocity of wave propagation and attenuation as the explicit functions of frequency, stochastic structural parameters of the medium and material properties of layers. The obtained formulas are helpful for interpretation of experimental ultrasonic data and may serve for identification of the characteristic size of material inhomogeneity based on the measured wave parameters like frequency dependent phase velocity, attenuation as well as backscattering coefficient.
Design of III-Nitride multi-layer structures for optical and surface acoustic wave interaction
Authors: Dupont Samuel , Kastelik Jean-Claude , Zhang Victor Y. , Causa Federica , Meng Qingbin , Sarma Jayanta
Published: May 2008

Research efforts into Surface Acoustic Waves (SAW) devices built on III-Nitrides has recently significantly intensified because of the increasing availability of good-quality epitaxial material. Owing to their strong piezoelectricity and high acoustic velocity, high-Al-content materials are of particular interest in high-speed applications (GHz electronics). For optoelectronics applications III-Nitrides cover a wide range of wavelengths from ultra-violet (AlN) to blue (GaN) to infra-red (InN); thus providing great flexibility in the choice of operating wavelength. III-Nitrides, therefore, become particularly attractive for the development of acousto-optic modulators where the SAW is used to create a controllable (moving) optical grating, causing the diffraction of the Optical Guided Wave (OGW). The interaction is governed by the momentum and energy conservation and importantly by the field overlap of the two waves. We present here design guidelines and modelling results for the development of III-Nitride-based multi-layer structures to support both OGW and SAW. The purpose of this study is to attempt to optimise the device efficiency compared to single GaN-layer structures typically used in the literature where only the SAW characteristics are optimised.
Acoustic wave scattering from infinite cylinders made from functionally graded materials
Authors: Jamali Jalil , Honarvar Farhang , Naei Mohammad Hasan
Published: May 2008

Functionally graded materials (FGM's) are superheat-resistive materials which show attractive properties in many applications including furnace liners. FGM's consist of two distinct materials, for example a ceramic and a metal alloy. These two materials are mixed such that the composition of each material changes continuously along a specific direction resulting in a continuous change of microstructure along that direction. The change in microstructure induces chemical, material, and microstructural gradients, and makes functionally graded materials different in behavior from homogeneous materials and traditional composites. In this paper, the scattering of an incident plane acoustic wave from an infinite solid cylinder made from functionally graded materials is studied. Expressions are derived for the far-field scattered pressure generated by illumination of the infinite FGM cylinder by an infinite plane acoustic wave. The propagation direction of the incident wave can make an arbitrary angle with the normal to the cylinder axis. The mathematical equations are derived and numerical results for cylinders made from specific functionally graded materials are presented at different incidence angles.
Sound diffraction in periodic surfaces in ancient architectural structures
Authors: Cruz Calleja Jorge Antonio
Published: May 2008

In this work is analyzed the sound diffraction in architectural structures caused by periodic surfaces. Is studied the sound interaction with architectural structures using different types of sources, materials and sizes. The apparently scattering effect of the staircases in ancient constructions (like the staircase of the Kukulcan pyramid in Chichen Itza), that allows the speech communication to large distances and the spatial filter effect using the glide repetition pitch theory are also analyzed (Is the Chirp echo of the ancient prehispanic pyramids an intentional effect?). Computational models of the phenomenon and real measurements were used to establish the phenomena physics principles.
Advances in acoustics of liquid crystals
Authors: Kapustina Olga
Published: May 2008

Advances in the fundamental problem of the orientation transition in liquid crystals produced by acoustical action are considered. The theoretical models to describe a variety of liquid crystals orientation transitions in acoustic fields for the homeotropically and planar oriented layers which were developed in the framework of the Leslie-Ericksen hydrodynamics and the new methodology based on the ideas of non-equilibrium thermodynamics and nonlinear hydrodynamics are discussed and are substantiated experimentally. The orientation phenomena in liquid crystals were classified and the physical factors defining a kind of transition (threshold or non-threshold type) and a choice of approach correct to describe adequately the experimental data on a new molecular arrangement induced by acoustical action were established. Among them a macrostructure type of liquid crystals layer, a layer thickness-viscous wavelength in liquid crystal ratio, an angle between the medium optical axe (the liquid crystal director) and the line of acoustical wave propagation, a sound intensity, a type of acoustical boundary conditions at the layer edges. The modern ideas on the distortion peculiarities of liquid crystals above a certain threshold of the structure instability under non-stationary dynamic action on the liquid crystal layer of sound-induced oscillating flows for a wide frequency band were considered.
SH-wave propagation and localization anomalies in semi-infinite 1D magnetic phononic crystal
Authors: Laptyeva Tetyana V. , Tarasenko Sergey V. , Tarasenko Olga S. , Yurchenko Vladimir M.
Published: May 2008

At the present, the composite magnetic materials with a superstructure (magnetic photonic crystals) are actively investigated in view of conditions of electromagnetic wave transmission. Some of these materials are acoustically continuous media and, then, can be considered as magnetic phononic crystals (MPC). However, the dynamic acoustic peculiarities of such structures have been disregarded. Theoretical investigation of SH-wave propagation in the gyrotropic and nongyrotropic semi-infinite one dimensional magnetic phononic crystals (1D MPC) is presented here. We have taken into account magnetoelastic interaction and the commensurability a wavelength and 1D MPC period. The transfer matrix method allowed us to determine the specific features of volume SH-wave localization and propagation near the rigid interface of 1D MPC and nonmagnetic medium. In particular, the necessary conditions of existence and dispersion relations for three types of shear surface acoustic waves localized near the external surface of 1D MPC have been found. This type of elastic excitation are exists also for a case when elastic properties of MPC components are identical. The conditions of reflectionless transmission of volume SH-waves through a finite 1D MPC have been determined.
Zone center phonons in thalium fluoroborate
Authors: Gupta Hem Chandra , Singh Jaya
Published: May 2008

The study of phonons in thalium fluoroborate is very important in order to understand the phenomenon of phase transition in perchlorates and fluoroborates.Few studies of structural phase transition have been made of perchlorates and fluoroborates with a higher thalium ion, but their zone center phonons have not been investigated thoroughly. In order to understand the above, the Raman and the infrared frequencies of thalium fluoroborate have been investigated for the first time theoretically in its orthorhombic phase of space group Pnma. A short range force constant model (SRFCM) as well as rigid ion model (RIM) with stretching and bending force constants has been applied to obtain the zone center Raman and infrared phonons. The calculated values of Raman and infrared phonons are in very good agreement with the available observed values. The effect of these calculated interatomic force constants on the phase transition of thalium fluoroborate is discussed.
Shannon Entropy as a Characterization Tool in Acoustics
Authors: Sanchis-Alepuz Helios , Sanchez-Dehesa José
Published: May 2008

Shannon entropy [1] was introduced as a measure of the uncertainty associated with a random variable and initially it was used to quantify the information contained in a binary message. In this work, a definition of Shannon's information entropy is introduced in acoustics, defined in terms of the displacement field, as a measure of the localization of resonant modes. As an example, it is applied to study the avoided crossing appearing in the resonant Zener-like phenomenon in ultrasonic superlattices made of two different fluidlike metamaterials. It is shown that acoustic Shannon entropy gives a correct physical insight of the localization effects taking place and manifest the informational exchange of the involved acoustic states in the narrow region of parameters where the avoided crossing occurs. Results for ultrasonic structures consisting of alternating layers of polymethyl-methacrylate (Plexiglas) and water cavities, in which the acoustic Zener effect were recently demonstrated [2], are also reported. It is concluded that Shannon entropy is a useful tool to characterize localization effects in acoustical systems. [1] C.E. Shannon, Bell Sys. Tech. J. 27, 623 (1948). [2] H. Sanchis-Alepuz, Yu.A. Kosevich, and J. Sanchez-Dehesa, Phys. Rev. Lett. 98 134301 (2007).
Shock waves in nanomechanical resonators
Authors: Blick Robert H. , Beil Florian W. , Wixforth Achim , Wegscheider Werner , Schuh Dieter , Bichler Max
Published: May 2008

The dream of every surfer is an extremely steep wave propagating at the highest speed possible. The best waves for this are would be shock waves, but are very hard to surf. In the nanoscopic world the same is true: the surfers in this case are electrons riding through nanomechanical devices on acoustic waves. Naturally, this has a broad range of applications in sensor technology and for communication electronics for which the combination of an electronic and a mechanical degree of freedom is essential. But this is also of interest for fundamental aspects of nano-electromechanical systems (NEMS), when it comes to quantum limited displacement detection and the control of phonon number states. Here, we study the formation of shock waves in a NEMS resonator with an embedded two-dimensional electron gas using surface acoustic waves. The mechanical displacement of the nano-resonator is read out via the induced acoustoelectric current. Applying acoustical standing waves we are able to determine the anomalous acoustocurrent. This current is only found in the regime of shock wave formation. We ontain very good agreement with model calculations.
Order/disorder transition for ultrasonic propagation in 2D scatterer arrays
Authors: Bretagne Alice , Tourin Arnaud , Fink Mathias
Published: May 2008

Recently, intriguing phenomena in quantum mechanics, such as the Aharonov-Bohm effect [P. Roux et al., Phys. Rev. Lett. 79, 3170 (1997)], weak localization in disordered media [A. Tourin et al., Phys. Rev. Lett. 79, 3637 (1997)] and maybe one of the most striking, tunnelling [S. Yang et al., Phys. Rev. Lett. 88, 104301 (2002)], have been revisited using acoustic waves. The advantages of using ultrasound for such studies lie in the macroscopic character of samples and the possibility of directly measuring the phase of the wavefield. Here we explore propagation of MHz-ultrasound in a medium which is either ordered or disordered in the two transverse dimensions (x,y) but invariant in the propagation direction (z). An equivalent scheme has been recently used in optics to demonstrate transverse localization of light [T. Schwartz et al., Nature 446, 52 (2007)]. Our samples are made of a parallel arrangement of cylindrical scatterers (0.8mm in diameter) embedded in a PVA matrix. In the ordered case, the probe beam undergoes ballistic transport. In the disordered case transport becomes diffusive and as the sample length increases the wave tends to be laterally confined.