bluuebunny/crossref_metadata_2025 huggingface dataset:
Noise in an Emergency treatment ward
Authors: Beristain Sergio
Published: May 2008

It is beign assessed the noise inside a typical social service Hospital in Mexico City, several sources and relevant areas have been identified and evaluated. This paper presents a detailed description of the Adults Urgency Room, where all the emergency cases are received and attended arround the clock. In this section of the hospital, forty to sixty patients are attended at the same time in a large open plan room, separated only by curtains, with only a few private rooms for doctors in order to attend incoming patients, trying to solve each case immediatelly, allow him/her entrance into the main room for full emergency treatment, or find a bed inside the hospital for a longer treatment. Noise sourcees are all over the place, and noise variablity is large.
Vibration reduction of thermal break balcony connections
Authors: Schneider Martin , Fischer Heinz-Martin
Published: May 2008

In energy efficient buildings concrete balconies have to be thermally insulated from the concrete floor to reduce heat loss and to increase surface temperature. This thermal break is obtained by polystyrene in combination with high-strength concrete thrust-force bearings and an arrangement of stainless steel straight and bent bars to act as tension and shear reinforcement. The acoustic performance of such thermal break units was investigated under laboratory conditions. Therefore the vibration level difference at different junctions between balcony and the thermal isolated concrete floor as well as the normalized impact sound pressure level of the floor when the balcony is excited with the standard tapping machine are measured. The influence of the number of tension and shear steel bars and the type of thermal insulating material was studied on typical sized balconies connected to small test floors. The vibration isolation at low frequencies was determined using modal testing.
Development of thermoacoustic floating floors for use between parking and dwellings
Authors: Guigou-Carter Catherine , Chene Jean-Baptiste
Published: May 2008

The French thermal regulation (RT2005) is favoring thermal floating floor between spaces such as parking or stores, and dwelling units. However, these solutions do not fulfill the French acoustic regulation with regards to airborne noise. This paper discusses the development of solutions allowing fulfilling both the thermal and the acoustic regulation. To achieve this goal, a mixed approach combining measurements and numerical predictions is used. Furthermore, the laboratory characterization of such floating systems usually involves a concrete base floor 140 mm in thickness (following the NF EN 140-8 standard) and a floating concrete layer 40 mm in thickness. However, in situ the concrete base floor as well as the floating concrete layer can be thicker. Therefore, some laboratory measurements are performed on a thermal floating floor system combining a 200 mm thick concrete base floor, a thermal insulation layer (polystyrene or polyurethane based foam for example) and a 60 mm thick floating concrete layer. The prediction method shows that this type of thermal floating systems is not acceptable with respect to the acoustic regulation. The behaviour of such multilayered systems is investigated using a wave approach based prediction tool in order to develop solutions allowing fulfilling the acoustic regulation.
Comparisons of predicted and measured values of speech, noise, reverberation and early reflections in optimized classrooms
Authors: San Souci Sooch , Guerra Line , Campbell Richard
Published: May 2008

12 newly renovated classrooms have been studied to determine the accuracy of prediction software used to guide architects, acousticians and interior designers. Several variations in renovation techniques based on traditional precepts were compared. After the renovations were complete, measurements and recordings were made of speech, noise, and reverberation when the rooms were both occupied and nonoccupied by students. A systematic map of the results was compiled, which when presented on a seat by seat basis, defined values of merit for the presumed optimizations and were compared to the predicted values. The two principle indices chosen as targets were increases in total speech level and decreases in total noise level (including late reverberation). When referred to these targets, several novel strategies proved to offer higher value/cost ratios while a few traditional strategies proved to be deficient and in some cases detrimental to at least one of the principle indices. Emerging from this study is what appears to be evidence for two points: (1) that some common acoustic criteria are inadequate for classrooms and (2) there are several strategies that might offer significant advantages over some of the traditional guidelines for acoustic treatments for learning spaces.
The primary noise sources associated with turbulent Coanda wall jets
Authors: Lubert Caroline
Published: May 2008

A wide variety of aeronautical and aerospace applications utilize the Coanda effect. However, due to the enhanced turbulence levels observed with devices using this effect, turbulent mixing noise is a primary noise source. For supersonic jets close to Coanda surfaces, shock-associated noise (both broadband and screech tones) is also a significant source of sound. A theory has been developed to predict the turbulent mixing noise emitted by unit-volume of jet-type shear-layer turbulence close to a rigid plane, and extended to a plane two-dimensional wall-jet. However, most flows of practical interest are three-dimensional and, in the case of the Coanda jets, exhibit significant curvature. This paper extends the previous models for turbulent mixing noise to predict the aeroacoustic characteristics of a three-dimensional turbulent flow over a Coanda surface. Details of experimental observations of the shock-cell structure associated with supersonic Coanda wall jets, and a method of modeling the corresponding shock-associated noise, is also discussed.
Community response to military shooting noise immissions
Authors: Brink Mark , Wunderli Jean Marc , Boegli Hans
Published: May 2008

The assessment of the impact of any kind of noise exposure on the population is a fundamental step in the process of noise abatement. Data about the exposure-response relationship for annoyance due to noise emissions from military shooting grounds are rather scarce at the time. In order to establish new legal exposure limit values for shooting noise from heavy and light weapons, we conducted an extensive telephone interview survey in several - mostly rural - municipalities affected by military shooting noise in Switzerland. The exposure assessment for each respondent was calculated based on the source models of a range of weapons and ammunitions of the Swiss army. Preliminary results suggest that although the responses of the population to noise from military weapons are rather dispersed, data should be sufficiently consistent to establish an exposure-response relationship which can help in defining a binding exposure limit value.
Roof-top urban wind turbines in London
Authors: Dance Stephen , Liviani Linda
Published: May 2008

With the Mayor of London's office decision to allow planning permission only if 10% of the building's energy consumption is from renewable sources, wind turbines are starting to be erected on rooftops of residential blocks. A Proven 6 kW, 6m horizontal axis turbine was positioned on an 11 story 1960s concrete construction block of flats in the summer of 2007. Noise and vibration measurements were taken on the roof-top and in the nearest flat. In addition, energy performance was monitored, wind speed and direction recorded and weather noted. Results confirm that central London is a 24 h city and, given the right conditions, the turbine generators meaningful amounts of electricity.
Remarks on a blast sound propagation model for noise management purposes at military training areas
Authors: Hirsch Karl
Published: May 2008

Germany will introduce a daily shooting noise management at its military training areas. Roughly speaking, this management adopts the basic ideas of ISO 17201-5 but uses in addition a rating scheme that allows 18 exceedance days per year (5%). For management purposes, the underlying sound prediction scheme must support two decision (1) Whether or not, the noise load of the daily planned occupancy is within certain noise limits. (2) Whether or not, the daily changing occupancy is close to a low noise minimum for the requested training options. The propagation model must consider particular weather conditions and the terrain shielding to enable the operator to optimise the occupancy with respect to these important conditions on a daily basis. The prediction must be fast enough to run several alternatives within minutes. Therefore, the prediction could not base on a sophisticated physical propagation model but must be done along a reasonable technical scheme. This paper discusses a ray tracing approach that is expected to substitute the currently in-use formula based on fitted empirical parameters. This model will at least provide one parameter to describe the sound refraction (radius of curvature) and a rule on how to estimate up wind propagation.
Simulation of highway traffic noise with utilization of equivalent sound level of pass-by vehicle
Authors: Pamanikabud Pichai , Tansatcha Marupong
Published: May 2008

This paper presents study and building of a highway traffic noise simulation model by utilizing equivalent sound level over 20 s of passing-by vehicular noise in the analysis of nine types of vehicular basic noise. The basic noise of each vehicle type is applied into the formulation of the main highway traffic noise simulation model. The coefficient of propagation and ground effect for this model is also estimated and applied to the highway traffic noise model. This highway traffic noise model is then tested for its goodness-of-fit to field observations. The testing result shows that this model provides an effective prediction for highway noise in Thailand.
Detection and localization capability of the European infrasound network
Authors: Ceranna Lars , Le Pichon Alexis , Vergoz Julien , Evers Laslo
Published: May 2008

The infrasound network of the International Monitoring Network (IMS) for the compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT) is currently not fully established. However, it has demonstrated its capability for detecting and locating infrasonic sources like meteorites, as well as volcanic eruptions on a global scale. Such ground-truth events are rare; therefore regions providing a dense network of infrasound stations have to be considered to test and to calibrate detection and location procedures. In central Europe, several years of continuous infrasound waveform data are available for nine stations in Sweden, the Netherlands, France, and Germany, whereas only one of them is part of the IMS. This exquisite setting with an average interstation distance below 500 km allows the analysis of natural and artificial infrasonic activity in Europe. The results of the association of multiple arrays demonstrate the need of continuous infrasound monitoring on a regional scale to advance the development of automatic location procedures. Beside the seasonal variation of the network's detection capability, which is dominated by the prevailing stratospheric winds, dominant source regions showing repeating events will be discussed in detail considering the next recording stations.
Continuous infrasound monitoring for atmospheric studies
Authors: Le Pichon Alexis , Brachet Nicolas , Ceranna Lars
Published: May 2008

Infrasound data processing on a routine-basis provides a powerful tool to quantify relationships between infrasonic observables and atmospheric specification problems. In particular, studies of continuous sources of infrasonic waves provide further evidence that long-range propagation primarily depends on the seasonal variability of the prevailing zonal winds. It confirms that most of the detected infrasound energy propagates in the stratospheric waveguide. The observed detection capability of the IMS network is compared to the predicted one using near-real time atmospheric updates. Moreover, on regional scales, signals from volcanic activities open up new fields for investigations into inverse problems for atmospheric remote sensing in a range of altitude where routine ground based or satellite measurements are rare. With the increasing number of IMS and experimental arrays deployed around the globe, a valuable contribution can be anticipated in the understanding of the dynamics of the upper atmosphere. In return, such studies will help to optimize the siting of infrasound arrays with respect to both the number and configuration in order to monitor infrasonic sources of interest.
Gravity and rumble of distant sources
Authors: Delorme Philippe , Menexiadis Geraldine
Published: May 2008

The subject of this paper is the comprehension of this physical phenomenon: Let an atmospheric source emiting an impulsive signal (such as thunder, explosion...). The received signal at short distance is itself impulsive but at long distance one can hear a rumble which can last up to one minute. If one models the propagation of the sound by the traditional equation of the waves, as the Green function is a distribution whose support is the sphere of radius CT (C: speed of sound, T: the travel time), the received signal (calculated by convolution) should last only the duration of emission. If one uses ray tracings to take into account the heterogeneity of the medium, one obtains the same conclusion (only the time of arrival is modified) in contradiction with the experimental results such as those obtained for example during the First World War to detect the position of the enemy batteries. A similar phenomenon can be observed in the study of the propagation of a sonic boom (although less obvious because the support of the two-dimensional Green function is not a circle). We thus propose a critic of the physical models, and our conclusion lays on the need for taking into account gravity.
Misty picture: A unique experiment for the interpretation of the infrasound propagation from large explosive sources
Authors: Gainville Olaf , Blanc-Benon Philippe , Blanc Elisabeth , Roche Roger , Millet Christophe , Le Piver Francoise , Despres Bruno , Piserchia Pierre-Franck
Published: May 2008

In the framework of the Comprehensive Nuclear-Test-Ban Treaty, the International Monitoring System develops a 60 micro-barometric stations network. These stations, which records infrasound, detect various powerful natural and artificial sources like long range explosions, oceanic swell, and volcano eruptions. For data analysis, the CEA, in collaboration with the LMFA, develops specific methods based on measurements, data processing and numerical simulation. The Misty Picture experiment is a high explosive event (4685 Tons of ANFO) realized in 1987 in New Mexico (US). Infrasounds were recorded by 22 sensors until a distance of 1000 km in a quiet background noise condition. Multireflected tropospheric, stratospheric and thermospheric phases are detected. Signals recorded near the source (1 km away) and observed in the geometrical shadow zone (between 150 km and 250 km from the point source) are of particular interest. This reference experiment very well documented is used to improve our understanding of the atmospheric propagation of infrasound as well as to evaluate our models. Using various methods such as ray tracing, parabolic equation and finite differences, we investigate effects of the wind, atmospheric absorption, nonlinearity, refraction, (2D and 3D) and scattering by small atmospheric scales on observed phase kinds, their travel time and their waveform.
Localized nonlinearity time reversal imaging with chaotic cavities
Authors: Bou Matar Olivier , Li Yifeng , Preobrazhensky Vladimir L. , Pernod Philippe
Published: May 2008

Recent results have shown that nonlinear elastic wave spectroscopy (NEWS) and time reversal (TR) techniques can be combined to localize defects. NEWS techniques can be used either as a post-treatment of TR used as a tool for generating strong localized stress (TR-NEWS), or as a pretreatment, of TR used as a tool for defect identification (NEWS-TR). The TR process can be implemented with a programmable multielements ultrasonic system. But recently, it has been demonstrated that a single PZT ceramic glued on the sample can also be used as a TR mirror. In this case the quality of the retrofocusing process, and so the microdamage localization, depends on the sample geometry. In this study, numerical and laboratory studies, performed in order to determine and enhance the possibility to localize microdamage based on a combination of a time reversal technique using an emitter with a chaotic shape and nonlinear elastic wave response, will be presented. The benefit of using such emitters is clearly found in breaking the symmetry of the problem, leading to an unambiguous retrofocusing. Moreover, chirp-coded excitation, instead of short pulses, is studied in order to transmit more energy on the defect without increasing the peak intensity of the excitation.
Landmine detection using nonlinear vibrations excited by time reversal techniques
Authors: Libbey Brad , Sutin Alexander , Sarvazyan Armen
Published: May 2008

Time reversal focuses seismic waves and excites nonlinear surface vibrations that are large in the presence of a landmine. These soil vibrations provide an accurate localization cue when contrasted with measurements made without a mine. Traditionally nonlinear effects were investigated by measuring the interaction of harmonic waves and nonlinear resonance frequency shifts. These methods provide high signal to noise ratios, but required tuning of excitation frequencies resulting in test times unsuitable for field applications. Time reversal is capable of providing broad band excitation at amplitudes large enough to drive the nonlinear mechanisms at measurable levels while reducing the overall measurement time. Spatial and temporal focusing data will be presented for three different time reversal systems compromising speakers and vibrators for seismic excitation and a Doppler laser vibrometer and geophones for signal recording. The high amplitude signals generated by these systems adequately drive the nonlinear responses. Special processing techniques, phase inversion and varied amplitude, have been developed to extract the nonlinear responses from the broadband response by cancelling the linear part. The remaining nonlinear response shows greater mine/no mine contrast than the linear data. Practical implementations of the developed methods will be discussed.
Time reversal use in detection of buried cracks
Authors: Le Bas Pierre-Yves , Anderson Brian E. , Griffa Michele , Ulrich Tj , Johnson Paul A.
Published: May 2008

Time reversal has the potential to become a powerful tool in nondestructive evaluation. Coupled with nonlinear properties of cracks in a technique known as time reverse nonlinear elastic wave spectroscopy (TRNEWS), it provides the means to detect defects in complex structures. This experimental study explores the capabilities of TR to focus energy inside a 3D medium in order to activate nonlinear features or defects. Special attention is given to buried cracks. The current challenge is introducing sufficient energy in order to excite the buried feature and produce nonlinear scattering. We will provide an overview of the problem.
Improving signal analysis for nonlinear time reversed acoustics: simulation results
Authors: Scalerandi Marco , Gliozzi Antonio S.
Published: May 2008

Nonlinear time reversed acoustics have attracted attention as a tool to localize and identify nonlinear defects in solids [1-4]. The procedure is based on extracting the features due to the nonlinear scatterers from the signals received at the transducer array and back-propagate only the resulting portion of the signals. The usual approach is to filter the received signals to keep only contributions due to higher order harmonics or sidebands. As a result, the signals are very small in amplitude and can be not detectable if transducers are located far from the scatterers. It is evident the need for novel signal processing tools to increase the signal-to-noise ratio of the nonlinear contributions. We have recently proposed a scaling subtraction method [5], which is applied here to nonlinear time reversal virtual experiments, showing the improvements in the signal-to-noise ratio, with resulting better imaging of the nonlinear scatterer. Results will be presented for two approaches to nonlinear time reversal. [1] A. S. Gliozzi et al., J. Acoust. Soc. Am. 120, 2506-2517 (2006). [2] T. J. Ulrich et al., J. Acoust. Soc. Am. 119, 1514-18 (2006). [3] T. J. Ulrich et al., Phys. Rev. Lett. 98, 10430 (2007). [4] T. Goursolle et al., J. Acoust. Soc. Am. 122, 3220 (2007). [5] M. Scalerandi et al., submitted to Appl. Phys. Lett. (2008).
3D numerical study for defect detection with nonlinear elastic wave spectroscopy and time reversal techniques
Authors: Goursolle Thomas , Callé Samuel , Dos Santos Serge , Bou Matar Olivier
Published: May 2008

Nonlinear elastic wave spectroscopy (NEWS) techniques have been developed to study the anomalously high level of “nonclassical” nonlinearity of cracked materials. Within AERONEWS project (http://www.kuleuven-kortrijk.be/aeronews), more recent innovative nondestructive NEWS techniques have been proposed to detect microinhomogeneities like cracks. It has been notably shown that NEWS and time reversal (TR) techniques can be combined to precisely localize cracks with a high sensitivity. NEWS techniques can be used either as a post-treatment of TR used as a tool for strong localized stress generation (TR-NEWS), or as a pre-treatment of TR used as a tool for defect (nonlinear source) identification (NEWS-TR). A 3D multiscale pseudo-spectral time domain (PSTD) code has been developed to simulate nonlinear acoustic propagation in heterogeneous nonlinear hysteretic solids. The hysteretic nonlinearity is introduced owing to a PM space model, based on a multiscale approach, extended in 3D owning to Kelvin notations. Using this algorithm, the influence of various parameters such as the defect position or the filtering method is particularly described for NEWS-TR and TR-NEWS methods. Finally, the sensitivity and feasibility of both methods are discussed.
Varied amplitude method in time reversal acoustic land mine
Authors: Fillinger Laurent , Sutin Alexander , Libbey Brad , Sarvazyan Armen
Published: May 2008

Acoustic methods of land mine detection are being developed for nonmetal mines where conventional electromagnetic methods fail. One such method, based on time reversal acoustic principles, is the hhase-inversion method; which detects quadratic and even ordered harmonic nonlinearities in the surface vibration above a mine. While this has shown higher sensitivity than linear methods it cannot detect all nonlinear components. These components can be detected by the Varied Amplitude method that is based on wide band excitation of surface vibration using the principles of time reversal acoustics. The nonlinear effects are measured for surface vibrations with different amplitudes and the normalized received signals can then be subtracted to reveal all the nonlinear components. We conducted a set of experiments using a box with six loudspeaker and an array of spatially distributed geophones to measure the linear and nonlinear components for various types of mines in different soils. Information about nonlinear components' spatial distribution allows one to observe greater mine/no mine contrast than with linear and other nonlinear techniques. [Work was supported by the U.S. Army RDECOM CERDEC Night Vision and Electronic Sensors Directorate.]
Discussion on the validity domain of SEA
Authors: Le Bot Alain , Cotoni Vincent
Published: May 2008

This paper is concerned with the validity domain of SEA which is defined in terms of four criteria. The mode count N and the modal overlap M must be high, the normalized attenuation factor m and the coupling strength gamma must be small. The application of the dimensional analysis on the governing equations of plates gives the space of dimensionless parameters in which the validity domain of SEA must be delimited. This domain is discussed on the basis of the geometric properties of the surfaces delimiting it. The diagrams of validity of SEA are introduced and proposed as a tool for a practical use of SEA.
Experimental study of lamb mode conversions at the junction of two joined plates
Authors: Belhoussine Drissi Taoufiq , Morvan Bruno , Pareige Pascal
Published: May 2008

In this study we are interested in a welded junction of two plates. Plates have the same thickness and are joined along their edges. Some previous theoretical studies have shown that guided Lamb waves are suitable for the characterisation of the interface between two plates [C. Scandrett and N. Vasudevan & M.V Predoi and M. Rousseau]. In a first time a junction perpendicular to the plates is experimentally investigated. Aluminum, copper and steel plates are used. Incident S0 Lamb wave is excited by a contact piezocomposite transducer and the surface displacements of the plate are detected by use of a laser vibrometer on both side of the junction. Converted waves are observed. From the measured normal surface displacements, reflection and transmission energy coefficients of the incident S0 wave through the junction are calculated. These coefficients are in a good agreement with the theoretically predicted ones. In a second time, the studied junction is not perpendicular to the plate. Experimental results are presented and compare to numerical ones obtained with the Comsol® Finite Element code.
Conversion of a Scholte - Stoneley wave at the extremity of a fluid loaded plate: comparison between finite element method, radiation mode theory and experiments
Authors: Lamkanfi Ebrahim , Declercq Nico F. , Van Paepegem Wim , Degrieck Joris
Published: May 2008

The radiation theory has proved to produce results in agreement with experiments when the conversion is investigated of a Scholte - Stoneley wave at the extremity of a fluid loaded plate. The drawback of the radiation mode theory is that it is not universally applicable and is also very cumbersome. The advantage is that it is an exact method. There is a trend in acoustics to develop finite element models to describe the interaction of sound waves with materials. This investigation compares a newly developed finite element model to simulate the considered effect. Results are compared with the exact results obtained by the radiation mode theory [J. Acoust. Soc. Am. 101(3), 1347-1357, 1997] and experimental observations [J. Acoust. Soc. Am. 95(1), 13-20, 1994]. The study shows correspondence between the finite element analysis and earlier obtained experimental and theoretical results as a function of a relationship between mesh properties and the evanescence (rather than the wave length) of the considered Stoneley waves.
Nonlinear phase conjugate ultrasonic waves in moving media
Authors: Preobrazhensky Vladimir L. , Pernod Philippe , Pyl'Nov Yuri , Smagin Nikolay
Published: May 2008

The basic principle of acoustic wave phase conjugation provides compensation of phase incursions during back propagation of the phase conjugate waves (PCW) towards the source of the primary emission. This feature of PCW results from time reversal invariance of acoustic field in a stationary medium. In moving media or in the presence of flows the time reversal invariance is broken resulting in essential modification of PCW properties. The incident wave spatial distribution is not reproduced completely by the phase conjugate wave and the phase incursions are not compensated any more. In the present paper the general theory of PCW propagation in moving nonlinear media is developed. The theory is applied for description of PCW acoustic rays and calculation of noncompensated phase shift of PCW on the source of the primary probing wave. The treatment of the phase shift of the PCW is developed as a new method of diagnostics and imaging of flow velocity distributions in liquid. The method is approved experimentally on examples of laminar and vortex flows and immersed fluid jet in water. Improvement of quality of the images of flows using nonlinear modes of propagation and interaction of phase conjugate waves is demonstrated.
Functionally graded plates studied by laser ultrasonic technique
Authors: Pan Yongdong , Wang Qian , Zhong Zheng , Rossignol Clément , Audoin Bertrand
Published: May 2008

In a functionally graded plate, the composition and structure change continuously along the thickness direction, resulting in corresponding changes of the acoustic impedance of the material. The study of the wave propagation in such a plate is important for both the nondestructive evaluation of properties of functionally gradient materials and engineering. In this work, the experimental system of laser ultrasonic measurement is introduced, and a theoretical model is proposed to predict the transient displacement field generated by laser in a functionally graded plate (FGP). After the laser line source is assumed as an idea transient force, and the FGP is considered as an inhomogeneous plate along its thickness direction, the transient displacement field is numerically solved by the Peano expansion method. Laser ultrasonic measurement was carried on several FGPs, and the direct arrivals of longitudinal and shear waves were observed in the experimental displacement field. The agreement between experimental and calculated theoretical waveforms provides a promise for both experimental and theoretical methods.
Influence of polymeric nanocomposite film on acoustic waves in piezoelectrics
Authors: Kuznetsova Iren E. , Zaitsev Boris D. , Kuznetsova Anastasia S.
Published: May 2008

At present the attention of researchers is attracted by investigation of multilayer acoustical waveguides with using of well known as well as novel materials. Also in present time there exist a lot of papers devoted to novel nanocomposite polymeric materials. But the influence of such materials on parameters of acoustic waves in piezoelectrics did not study. In this connection the paper is devoted to theoretical investigation of acoustic waves in structure “piezoelectric - polymeric nanocomposite film.” The analysis was carried out by the example of polymeric nanocomposite film with various contents of Fe and CdS nanoparticles and lithium niobate plate or substrate. As a result of conducted calculation the velocity and attenuation per wavelength have been found for acoustic waves propagating in aforementioned structure. The conducted analysis has showed that for certain value of nanocomposite film thickness d the attenuation of investigated waves has the resonant behavior. The obtained results allow choose such values of d for which the acoustic wave does not practically attenuate in the presence of the film. This opens, for example, the prospects of development of undisturbed substrates of nanocomposite materials for thin piezoelectric plates. This work is supported by RFBR 06-08-01011, RNP.2.1.1.8014 (Russia), contract 2007-3-1.3-07-15-036 (Russia).
Low frequency airplane noise measurement
Authors: Di Xiao , Hetzer Claus , Wagstaff Ronald A. , Mir Ali M.
Published: May 2008

Low frequency airplane noise during takeoff and landing periods is a serious environment hazard. Also, the low frequencies originating from the airplanes could potentially be an easy target for detection. Since there is very little attenuation at the low frequencies, the low frequency sound can propagate to relatively long distances. Several field experiments were conducted to identify the low frequency signal and noise content from many different airplanes. What is different in our experiment from most other noise experiments is that we will identify the very low frequency content of the airplane noise spectrum, from 200 Hz down to the infrasound range, 0.02 Hz. During the experiments, two infrasound microphone systems were used: Chaparral 50, which has a bandwidth from 0.02 to 50 Hz, and Chaparral 2.5, which has a bandwidth from 0.1 to 200 Hz. In addition to the infrasound systems, a recording system with B&K microphones was also used. The data were collected before, during, and after landing and takeoff periods. The low frequency signal and noise content during each of those periods will be analyzed and reported on.
Correlating electromagnetical and infrasonic signals from thunderstorms
Authors: Assink Jelle , Evers Laeslo G. , Holleman Iwan
Published: May 2008

During thunderstorm activity, electromagnetical and infrasonic signals are emitted due to the process of lightning and thunder. It is shown that correlating infrasound detections with results from a electromagnetical lightning detection network is successful up to distances of 50 km from the infrasound array. Infrasound recordings clearly show blast wave characteristics, relatable to CG discharges, with a dominant frequency between 1-5 Hz. Amplitude measurements can partly be explained by the beam pattern of a line source. The ability to measure thunderstorm activity with infrasound arrays has both positive and negative implications for infrasound verification purposes.
Coherency of infrasound studied with a large aperture infrasound array in the Netherlands
Authors: Mentink Johan , Evers Laeslo G.
Published: May 2008

A large aperture infrasound array (LAIA) is being constructed in the Netherlands as geophysical part of an astronomical low frequency array, i.e., the LOFAR project. This array extends the detection capabilities of infrasound up to the mHz range, including acoustic-gravity and gravity waves as well. Owing to its large aperture (80 km) and number of interstation distances, this 30 element microbarometer array is ideally suited to study the coherency of infrasound as function of frequency under various atmospheric conditions. Based on conventional and modern correlation techniques, the ultimate aim is to experimentally determine and quantify infrasound propagation characteristics. As a result, we gain understanding in the physical mechanisms responsible for decoherence, which in turn will be used to develop infrasound as a passive atmospheric probe. Knowledge on the coherency length as function of the state of the atmosphere also has direct implications for the design of optimal infrasound arrays. This study will outline the characteristics of LAIA and present the first results of the coherency studies.
Modeling real porous tube infrasonic arrays
Authors: Marston Timothy , Gabrielson Thomas
Published: May 2008

Measured values of acoustic resistance in porous hoses have been implemented into a previously developed porous tube model for infrasonic arrays [J. Acoust. Soc. Am. 122, 2960 (2007)]. Garden soaker hoses are commonly used in porous infrasonic arrays, and a simple method for the measurement the acoustic resistance of a segment of soaker hose will be presented. This experimentally determined resistance value can be implemented into the porous tube model for an improved array response prediction. It is anticipated that this analysis will give rise to improved phase and magnitude predictions for this type of array. Applications include design optimization of porous tube arrays, and infrasonic propagation through porous ducts. [Research funded by the Applied Research Laboratory Educational and Foundational Fund.]
Finite difference time domain synthesis of infrasound propagation through an absorbing atmosphere
Authors: Degroot-Hedlin Catherine D.
Published: May 2008

Equations applicable to finite difference time domain (FDTD) computation of infrasound propagation through an absorbing atmosphere are derived and examined in this paper. It is shown that over altitudes up to 160 km, and at frequencies relevant to global infrasound propagation, i.e., 0.02-5 Hz, the acoustic absorption in dB/m varies approximately as the square of the propagation frequency plus a small constant term. A second-order differential equation is presented for an atmosphere modeled as a compressible Newtonian fluid with low shear viscosity, acted on by a small external damping force. It is shown that the solution to this equation represents pressure fluctuations with the observed form for infrasound propagation, i.e., sound is attenuated as (β+γ f2). Increased dispersion is predicted at altitudes over 100 km. The equation is separated into two partial differential equations that are first order in time for FDTD implementation. A numerical analysis of errors inherent to this FDTD method shows that the attenuation term imposes additional stability constraints on the FDTD algorithm. Comparison of FDTD results for models with and without attenuation shows that the predicted transmission losses for the attenuating media agree with those computed from the synthesized waveforms.
Guided modes modeling in multilayered composites plates
Authors: Ben Amor Morched
Published: May 2008

Due to the periodicity of the composite structure the Floquet wave approach seems well suited for medium characterization. The pass and stop band domains for [0/45/90/-45] cross ply composites have been plotted. Dispersive guided wave propagation through a lossy composite laminates immersed in water have been investigated. Our interest is focused on a guided mode in the frequency range from 1.6 MHz to 5 MHz. This mode has been pointed out by both reflection coefficient and energy vector analysis in term of incident angle. In this paper it is investigated how by fine-tuning the frequency and the incident angle, internal displacement and stress field vary in the multilayer. When the frequecy is increased the mode changes from a plate mode to a surface mode. The description includes real Floquet wave numbers as well as complex wave numbers.
Influence of the calorimetric system setup on the output acoustic power measurement results
Authors: Petosic Antonio , Ivančević Bojan , Svilar Dragoljub
Published: May 2008

The problem of measuring an output acoustic power using calorimetric method has been considered in different regimes of transmitter working. The transmitter has been driven at different excitation electrical power levels and the influence of sonotrode tip position in the different calorimetric systems on the measurement results is considered. Two calorimetric systems with different volumes of loading liquid (water) and different geometries (having influence on thermodynamical losses) have been used in the experiments. The exponential experimental temperature-time curves have been fitted with theoretical and time constants, losses, output acoustic power and electroacoustic efficiency factor have been found assuming that all ultrasound energy is absorbed in the system. The pressure field in the box is complicated and radiation impedance (radiated power) depends on the position in the complex ultrasound field where the point source is located. In the nonlinear regime of working strong cavitation activity occur with oscillating bubles in the front of vibrating tips and the radiated power is decreased because the tip is only partially radiating due to radiation impedance variations. The electroacustic efficiency factor has been compared with equivalent circuit approach where parameters of transmitter have been found for unloaded and loaded transmitter.
Spectral properties of the surface SH waves in a vertically periodic half-space
Authors: Golkin Stanislav V. , Poncelet Olivier , Shuvalov Alexander
Published: May 2008

We consider shear horizontal (SH) waves propagating under a free surface of semi-infinite medium with vertically periodical continuous or discrete variation of material properties. This case is marked by certain special features. It is known that the dispersion spectrum embracing 'physical' and “non-physical” (in the sense of radiation condition) surface SH waves precisely coincides with another spectrum, which describes the SH waves in a single period with traction-free edges and which is relatively straightforward to calculate [1]. Of a particular interest for possible applications is that the distribution of those spectral bands, where the surface SH waves are “physical” and hence do exist, depends essentially on the profile of variation of material properties across the unit cell. In the present paper, we analyze the link between the periodic-inhomogeneity profile and the existence of surface SH waves in the frequency-wave number domain, and we show how this feature manifests itself in the time-space response. [1] A. L. Shuvalov, O. Poncelet, and A. N. Podlipenets, “On the guided and surface shear horizontal waves in monoclinic transversely periodic layers and halfspaces with arbitrary variation of material properties across the unit cell,” Stud. Geophys. Geod. 50 381-398 (2006)
SH surface wave in multicracked solids
Authors: Poncelet Olivier , Golkin Stanislav V. , Aristegui Christophe , Caleap Mihai , Shuvalov Alexander
Published: May 2008

We focus on the dispersion spectra of surface coherent waves in damaged semi-infinite elastic solids. The damage region is located within the surface layer containing depth-depending concentration of parallel closed cracks. The dispersion equation is similar to that for the Love waves in a coated substrate, except that the layer's effective elastic properties, being deduced from multiple scattering theory, are frequency-dependent and complex. For healthy elastic solids, the grazing SH wave is nondispersive. The dispersion under study is induced by the presence of cracks. The effect of both the magnitude of crack-concentration and its profile into the depth is investigated. The reliability of the semianalytical predictions is also discussed through a comparison with the numerical results obtained by using a finite-difference code.
Modelization of acoustic waves radiation from sources of complex geometry aperture
Authors: Serhane Rafik , Boutkedjirt Tarek
Published: May 2008

The Rayleigh integral giving the impulse response for the acoustic velocity potential cannot always be determined analytically for all types of transducer apertures. The shape of the transducer surface and the spatial distribution of the excitation on its surface can complicate the calculation. This makes using numeric methods indispensable. One of these methods consists in discritizing the aperture surface in polygonal shape elements. Our work makes use of both methods of Jensen and Faure [IEEE UFFC 39-2(1992)262, Acta Acustica 2(1994)257]. In the former, the transducer surface is subdivided in triangles. The latter one uses additional virtual triangles one side of which is that of the physical element and its summit is the field point projection on the plane containing the considered physical element. Additionally, a rotation of the virtual triangle around the field point projection is performed. In this work, the orientations of those virtual triangles are considered according to Jensen method and their contributions to the impulse response are calculated according to the two situations described by Faure. The combination of the two methods is, then, generalized to the case of nonplanar complex surfaces such as concave phased arrays.
Unified and stable scattering matrix formalism for acoustic waves in piezoelectric stacks
Authors: Zhang Victor Y. , Laude Vincent
Published: May 2008

This paper presents a unified and full scattering matrix (s-matrix) formalism. A stable recursive algorithm is derived for computation of the total s-matrix of a multilayered stack in terms of the interface s-matrix, both referring to the eigen-modes amplitudes. The derivation is direct and succinct, the derived expressions of the s-matrix are terse and concise, and the recursion is efficient and convenient for implementation. By combining the s-matrix formalism and the surface impedance matrix of the external media, various terminations of the stack can be easily handled. Numerical examples are given to show its numerical superiority over other currently used matrix formalisms: including unconditional stability throughout large and small thicknesses and pole-free feature.
Coherent elastic wave propagation through nonuniform spatial distributions of cracks
Authors: Aristegui Christophe , Caleap Mihai , Poncelet Olivier , Golkin Stanislav V. , Shuvalov Alexander
Published: May 2008

Models for multiple scattering of elastic waves usually concern uniform distributions of scatterers. The aim of this work is to predict the propagation of SH coherent waves through nonuniform distribution of parallel closed cracks. The spatial variation of the distribution properties is taken into account via replacing heterogeneous media by stacks of effective homogeneous layers. Propagation in each layer is then governed by the effective acoustic impedance and the effective wave number, derived in the framework of Waterman and Truell approach. On this basis, the reflection and transmission coefficients of the nonuniform distributions are calculated by using the transfer matrix method. We focus especially on distributions of crack size and concentration. Impact of the distribution profiles is also investigated. The semianalytical predictions are compared with numerical results obtained by using a finite-difference code.
Scattering of seismic waves by a fracture zone containing randomly distributed frictional cracks
Authors: Caleap Mihai , Aristegui Christophe
Published: May 2008

An investigation is conducted how the geometrical properties of a crack distribution in a fault fracture zone and the frictional characteristics of the crack surface are reflected in the attenuation and dispersion of incident seismic waves. All cracks are assumed to be either aligned or randomly oriented. The crack width is assumed to obey a power law distribution, according to seismological knowledge. The crack surface is assumed to be stress-free, or to undergo viscous friction. To deal with cracks under high confining pressure, the latter case will be more realistic than the stress-free crack, due to the existence of fluid in the earth's crust and the viscoelastic response of contacting solid material to seismic waves under high confining pressure. When the crack distribution is statistically homogeneous, the calculated dispersion and attenuation exhibit that the variance of crack size affects in different way the coherent wave. The analysis on the effect of the friction shows that the crack scattering decreases as the viscosity increases, which is expected since for high viscosity, the crack faces remain almost welded to each other. The results obtained in this work will be applicable to the state close to the occurrence time in large earthquakes.