Book review

Just forty years ago,Zwikker and Kosten‘s classical work"Sound AbsorbingMaterials"was published and the theoretical foundation of sound absorbing materi-als was laid.And Mechel‘s monograph"Schallabsorber"is an important develop-ment.The book consists of three volumes.Volume one is outer sound field,thatis,interaction between sound field and sound absorber;volume two is internalsound field,or the structure and application of sound absorber;volume three iscomputer program,a supplementary volume.Volume one is now published.The     

A wideband combined transducer for measuring system in sound tube

A wideband transducer for sound tube system is presented,which combines longitudinal transducer and ClassⅣflextensional transducer to improve the performance at low frequency and broaden the working band.The equivalent circuit is obtained and used to analyze the coupling mechanism between longitudinal transducer and flextensional transducer.A prototype of the transducer is developed after optimizing the electro-acoustic performances by Finite Element Method.The standing wave in the sound tube stimulated by this transducer has been studied and the sound absorbing coefficients of two acoustic materials samples are measured using this sound tube,which shows that the transducer can meet the requirements of acoustic material measurement with the working band ranging from 1.4 kHz to 23 kHz.     

Sound transmission across lightweight all-metallic sandwich panels with corrugated cores

The transmission of sound through all-metallic sandwich panels with corrugated cores is investigated using the space-harmonic method. The sandwich panel is modeled as two parallel panels connected by uniformly distributed translational springs and rotational springs, with the mass of the core sheets taken as lumped mass. Based on the periodicity of the panel structure, a unit cell model is developed to provide the effective translational and rotational stiffness of the core. To check the validity of the model, it is used first to study the sound insulation properties of double-panel structures with air cavity, and the analytical predictions agree well with existing experimental data. The model is then employed to quantify the influence of sound incidence angle and the inclination angle between facesheet and core sheet on sound transmission loss （STL） across sandwich panels with corrugated cores. The results show that the inclination angle has a significant effect on STL and it is possible to avoid STL dips by altering the inclination angle. Moreover, it is found that sandwich panels with corrugated cores are more suitable for the insulation of sound waves having small incidence angles.     

Directional sensitivity of auditory ascending neuron in the bushcricket Gampsocleis gratiosa

Quantitative analyses on phonotactic behavior of the bushcricket havedemonstrated that the bushcricket possesses good capability to determine directionof sound source.The morphological structure,laterality and directional sensitivityof the auditory ascending neuron in the prothoracic ganglion of the bushcrickethave been studied.At its best frequency of 15 kHz,the laterality threshold differ-ence of the neuron is great up to about 16 dB.Its directional sensitivity dependsclosely on stimulus frequency.The higher the stimulus frequency,the greater thedirectional threshold differences.Spike count and latency shift of the ascendingneuron in response to each stimulus depend on the angle of incidence of sound.Therefore,the two parameters can be used as directional cues of sound source bythe ascending neuron.     

Bubble translation driven by pulsation in a double-bubble system

The pulsation and translation of two cavitation bubbles are studied numerically in sound field. The results show that bubbles' pulsation driven by the sound makes them translate. Different pulsations lead to different translations. Two bubbles will be mutually attractive to each other if they pulsate in phase, while they will be repulsive if out of phase. Furthermore,the secondary Bjerknes force for small phase difference is attractive, and it becomes repulsive for other phase differences up to π phase difference due to the nonlinear effect, although the attractive strength between two bubbles is much larger than the repulsive strength. Finally, one bubble pulsation and the other bubble stationary make the bubbles repel each other.     

Sound characteristics of viscoelastic coating containing periodic cavities by the finite element method

The finite element method (FEM) is applied to analyze sound characteristics of the viscoelastic coatings containing doubly periodic cavities immersed in water or adhered to steel plate between water and air. The reflection coefficients and transmission coefficients are obtained for the coatings with spherical, cylindrical or conic cavities in above two conditions. Moreover, the vibration modes of the coatings are analyzed. Numerical results show that the cavities have great impact on the sound characteristics at low frequency.     

Acoustic topological adiabatic passage via a level crossing

Stimulated adiabatic passage has been extensively studied to achieve robust and selective population transfer in quantum systems. Recently, the quantum-classic analogy has been rapidly developing and can be considered responsible for the implementation of the adiabatic transfer of sound energy in cavity chain systems. In this article, we investigate the adiabatic transfer of sound energy between two topological end states in the Su-Schrieffer-Heeger(SSH) cavity chain, which can be considered to be the acoustic analog of the quantum chirped-pulse excitation. The topological adiabatic passage in SSH cavity chain has two categories. When the single-cavity resonance frequencies on the sublattices A and B in the SSH cavity chain do not switch their spectrum positions, the topologically protected adiabatic evolution results in the returning passage of the sound excited in one end cavity. When a level crossing with single-cavity resonance frequencies on the sublattices A and B exhibits switch in the frequency spectrum, acoustic energy is observed to be topologically pumped between the two end cavities of the SSH chain.     

Sound speed profile inversion using a horizontal line array in shallow water

It is better to use a simple configuration to enhance the applicability of ocean environment inversion in shallow water.A matched-field inversion method based on a horizontal line array(HLA)is used to retrieve the variation of sound speed profile.The performance of the inversion method is verified in the South China Sea in June,2010.An HLA laid at bottom was used to receive signals from a bottom-mounted transducer.Inverted mean sound speed profiles from 9-hour long acoustic signals are in good agreement with measurements from two temperature chains at the sites of the source and receiver.The results show that an HLA can be used to monitor the variability of shallow-water sound speed profile.     

AN ELECTROPHYSIOLOGICAL STUDY ON HEARING OF THE CICADA CRYPTOTYMPANA ATRATA FABRICIUS(HOMOPTERA:CICADIDAE)

The characteristics in response to sound and directional sensitivity of the auditory primary neurons andinterneurons of the cicada Cryptotympna atrata were studied with neurophysiological techniques.Theseneurons are tuned to a similar characteristic frequency,which is in correspondence with the dominantfrequency of calling song of the cicada.They are able to code sound intensity within the dynamic range of 4OdB above thresholds with an increment of about two spikes per 10 dB.The auditory neurons possess gooddirectiond sensitivity with the threshold difference of 10—12 dB at the best frequency between contra-andipsilateral stimulations.     

Modeling of Nonlinear Propagation in Multi-layer Biological Tissues for Strong Focused Ultrasound

A theoretical model of the nonlinear propagation in multi-layered tissues for strong focused ultrasound is proposed. In this model, the spheroidal beam equation （SBE） is utilized to describe the nonlinear sound propagation in each layer tissue, and generalized oblique incidence theory is used to deal with the sound transmission between two layer tissues. Computer simulation is performed on a fat-muscle-liver tissue model under the irradiation of a 1 MHz focused transducer with a large aperture angle of 35°. The results demonstrate that the tissue layer would change the amplitude of sound pressure at the focal region and cause the increase of side petals.     

Patch nearfield acoustic holography combined with sound field separation technique applied to a non-free field

The conventional nearfield acoustic holography(NAH) is usually based on the assumption of free-field conditions, and it also requires that the measurement aperture should be larger than the actual source. This paper is to focus on the problem that neither of the above-mentioned requirements can be met, and to examine the feasibility of reconstructing the sound field radiated by partial source, based on double-layer pressure measurements made in a non-free field by using patch NAH combined with sound field separation technique. And also, the sensitivity of the reconstructed result to the measurement error is analyzed in detail. Two experiments involving two speakers in an exterior space and one speaker inside a car cabin are presented. The experimental results demonstrate that the patch NAH based on single-layer pressure measurement cannot obtain a satisfied result due to the influences of disturbing sources and reflections, while the patch NAH based on double-layer pressure measurements can successfully remove these influences and reconstruct the patch sound field effectively.     

Recovery of the free field in noisy environment by using the spherical wave superposition method

To remove the scattering effect of the disturbing sound on the target source when implementing nearfield acoustic holography in a non-free field, a free field recovery technique based on the spherical wave superposition method is proposed. In the method, the sound field separation technique based on the spherical wave superposition method is first used to separate the incoming and outgoing fields, and a further step for separating the radiated and scattered fields is performed by utilizing the surface admittance of the target source as the boundary condition. The technique makes it possible to correctly identify noise sources in a non-free sound field. The basic principle of the technique is described firstly, a method for choosing the optimal number of spherical wave expansion terms is given, and two numerical simulations are used to demonstrate the validity of this technique. It is shown that, for the lower frequency, the scattering effect can be neglected, and the radiated field of the target source can be obtained by the sound field separation technique, however, as the increasing of the frequency, the scattering effect cannot be neglected, and the free field recovery technique has to be used to obtain the radiated field of the target source.     

Impedance theory of sound scattering: General relations

The problem of sound scattering by an elastic body of arbitrary geometry in an acoustic medium is solved by the impedance method. It is shown that, for a complete solution, three impedance matrices are necessary: one of them characterizes the scatterer and the other two, the medium. The scattering matrices and other characteristics of the solution are expressed through the incident field and these three impedance matrices. The necessary general relations are presented, and the most important particular cases are considered. Three new representations of the diffraction field are proposed in the form of a sum of two components obtained as solutions to two simpler boundary-value problems. Original Russian Text ￠ Yu.I. Bobrovnitskiĭ, 2006, published in Akusticheskiĭ Zhurnal, 2006, Vol. 52, No. 5, pp. 601–606.     

A numerical study of sound field radiated by the flow around a circular cylinder

The Von-Karman vortex street flow behind a circular cylinder issuccessfully solved at R_e=100 for incompressible N-S equations in theform of stream function and vorticity.The method adopted here involvesADI-BGE schemes,a recent treatment of body boundary conditions anda new acceptable perturbation model.The solutions of the flow fieldobtained here are better than previous numerical ones and agree with theexperimental data closer.Therefore,it can be used to study sound fieldnumerically.The Curle equation is directly and numerically solved to ana-lyze the distribution of sound sources and the characteristics of their radi-ated sound field at R_e=100 and to compare with the solution fromthe theory of vortex sound.It is shown that this method is successful.     

Anomalous sound propagation due to the horizontal variation of seabed acoustic properties

Sound speed profile and the bottom acoustic property are two of the most important factors, which influence the sound propagation in shallow water. The activities of the internal waves make the temperature of the sea-water varying with the time and space, and then affect the sound propagation in the sea. In 1991 Zhou and his colleagues postu-lated that unusually high transmission losses (TL) over a limited frequency range found in annual measurements taken in the Yellow Sea was due to the in…     

The parametric source method for measuring characteristics of underwater acoustic materials in a pressure vessel

A truncated broadband parametric array with a primary frequency of 500 kHz and difference frequency range of 1 kHz to 30 kHz was designed as a sound source of the underwater acoustic material measurement system.By analyzing the theoretical calculation and actual measurement results in array directivity of the truncated broadband parametric source at typical frequencies,we observed that the curves of the two results were basically consistent,which proved that the calculation model was correct.Application of bell-shaped short-duration pulse to achieve broadband measurement for characteristics of underwater acoustic materials was beneficial to reduce the effects of diffraction from the panel edges.The measurement system was established for measuring the sound pressure reflection coefficients,sound pressure transmission coefficients and absorption coefficients of the large panel sample in the pressure vessel.The size of this tank is φ4 m×12 m,the maximum hydrostatic pressure is 4.5 MPa,and the corresponding measuring frequency range is from 1 kHz to 30 kHz.The measured curves had a good agreement with theoretical curves,which verified that the parametric source measurement method was feasible.Then,the sound absorption properties of the rubber plate sample were measured under different hydrostatic pressures.The studying results could show that the parametric source measurement method had the potential application in the limited space water,such as the pressure vessel.     

Sound field separation technique with double holographic planes and its applications in acoustic holography

Sound field separation technique with double holographic planes is proposed, which overcomes the limitation on applications of near-field acoustic holography (NAH) and broadband acoustic holography from intensity measurement (BAHIM). The limitation is that sound field on one side of holographic plane must be free, that is to say, all the sound sources must be confined to the other side; but it is not easy to achieve for industrial measurements. The technique builds the sound field separation formula in wave number domain according to the wave field extrapolation theorem, and the sound pressure caused by sources on one side of holographic plane can be obtained as expected by taking two-dimensional Fourier transform of the formula. The derivation of the principle verifies the technique theoretically. The numerical simulations demonstrate its feasibility and effectiveness.     

SHAPE AND ACOUSTICAL CHARACTERISTICS OF ANCIENT BELLS

In addition to the Great Bell of the Yongle period,there are more than thirty ancient bells at the Templeof Great Bell in the west outskrit of Beijing.Most of the them were cast in the Ming Dynasty and Qing Dynasty.Only a few were cast in the Song and Yuan Dynasties.The heights of the bells from 79cm to 210cm andthe corresponding weights from 114kg to 3108kg.The largest and the samllest opening radius are 84cm and31.5cm respectively. In this paper the dynamic spectra of bell sound,beat frequencies and sound decay characteristics havebeen studied,The relationshps between fundamental frequeney and bell shape are discussed.For bells withsimilar shape,fundamental frequency is approximately proportional to T_0/R_0~2,where R_0 is the openingradius of bell and T_0 is the thickness of bell rim.The subjective appraisal of the sound quality of bell sound ispresented.     

A study on the multi-freedom broadband impedance model for time-domain simulations

The purpose of this paper is to construct a general broadband impedance model, which is suited for predicting acoustic propagation problems in time domain.A multi-freedom broadband impedance model for sound propagation over impedance surfaces is proposed and the corresponding time domain impedance boundary condition is presented.Basing on the extended Helmholtz resonator,the multi-freedom impedance model is constructed through combing with a sum of rational functions in the form of general complex-conjugate pole-residue pairs and it is proved that the impedance model is well posed.The impedance boundary condition can be implemented into a computational aeroacoustics solver by a recursive convolution technique, which results in a fast and computationally efficient algorithm.The two dimensional and three dimensional benchmark problems are selected to validate the accuracy of the proposed impedance model and time domain simulations.The numerical results are in good agreement with the reference solutions.It is demonstrated that the proposed impedance model can be used to describe the broadband characteristics of acoustic liners,and the corresponding time domain impedance boundary condition is viable and accurate for the prediction of sound propagation over broadband impedance surfaces.     

A NEW FINITE DIFFERENCE METHOD FOR COMPUTING SOUND FIELD IN LINED DUCTS

This paper presents a new finite difference method to calculate problems of sound propagation in linedducts.The MacCormack time-split explicit scheme has been used to solve the basic equations for determiningthe acoustic pressure and velocity.The problems of sound propagation in 3-D rectangular ducts have beensolved successfully by use of this scheme with the making of an approach to the acoustic boundary conditions.The finite difference schemes for full grid points and the stability condition of the method are also given in thepaper.This new method needs less storage and is more stable.Moreover,it is easier to program and debug,and,especially,is suitable for computing 3-D sound field.