Theory of complex-coordinate transformation acoustics for non-Hermitian metamaterials

Transformation acoustics(TA)has emerged as a powerful tool for designing several intriguing conceptual devices,which can manipulate acoustic waves in a flexible manner,yet their applications are limited in Hermitian materials.In this work,we propose the theory of complex-coordinate transformation acoustics(CCTA)and verify the effectiveness in realizing acoustic non-Hermitian metamaterials.Especially,we apply this theory for the first time to the design of acoustic parity-time(PT)and antisymmetric parity-time(APT)metamaterials and demonstrate two distinctive examples.First,we use this method to obtain the exceptional points(EPs)of the PT/APT system and observe the spontaneous phase transition of the scattering matrix in the transformation parameter space.Second,by selecting the Jacobian matrix's constitutive parameters,the PT/APT-symmetric system can also be configured to approach the zero and pole of the scattering matrix,behaving as an acoustic coherent perfect absorber and equivalent laser.We envision our proposed CCTAbased paradigm to open the way for exploring the non-Hermitian physics and finding application in the design of acoustic functional devices such as absorbers and amplifiers whose material parameters are hard to realize by using the conventional transformation method.

Panel Acoustic Contribution Analysis in Automotive Acoustics Using Discontinuous Isogeometric Boundary Element Method

In automotive industries,panel acoustic contribution analysis(PACA)is used to investigate the contributions of the body panels to the acoustic pressure at a certain point of interest.Currently,PACA is implementedmostly by either experiment-based methods or traditional numerical methods.However,these schemes are effort-consuming and inefficient in solving engineering problems,thereby restraining the further development of PACA in automotive acoustics.In this work,we propose a PACA scheme using discontinuous isogeometric boundary element method(IGABEM)to build an easily implementable and efficient method to identify the relative acoustic contributions of each automotive body panel.Discontinuous IGABEMis more accurate and converges faster than continuous BEM and IGABEM in the interior sound pressure evaluation of automotive compartments.In this work,a contribution ratio is defined to estimate the relative acoustic contribution of the structure panels;it can be calculated by reusing the coefficient matrix that has already been generated in the sound pressure evaluation process.The utilization of the parallel technique enables the proposed method to be more efficient than conventional methods;it is validated in two numerical examples,including a car passenger compartment subjected to realistic boundary conditions.A sound pressure response experiment based on a steel box is conducted to verify the accuracy of the interior sound pressure calculation using discontinuous IGABEM.This work is expected to promote the practical process of IGABEM for application in automotive acoustic problems.

五十载金禧纪念 一百对限量呈献 Falcon Acoustics LS3/5a Gold Badge Golden Madrone 50周年 金章限量版

对英国“隼”Falcon Acoustics而言,2023是一个非常重要的年份。适逢建厂50载金禧致庆,掌门人Jerry Bloomfield先生早有推出纪念版之意,唯独多年来一直未有觅得能切合金禧纪念主题的木皮。

A Modified Formulation of Singular Boundary Method for Exterior Acoustics

This paper proposes amodified formulation of the singular boundarymethod(SBM)by introducing the combined Helmholtz integral equation formulation(CHIEF)and the self-regularization technique to exterior acoustics.In the SBM,the concept of the origin intensity factor(OIF)is introduced to avoid the singularities of the fundamental solutions.The SBM belongs to the meshless boundary collocation methods.The additional use of the CHIEF scheme and the self-regularization technique in the SBM guarantees the unique solution of the exterior acoustics accurately and efficiently.Consequently,by using the SBM coupled with the CHIEF scheme and the self-regularization technique,the accuracy of the numerical solution can be improved,especially near the corresponding internal characteristic frequencies.Several numerical examples of two-dimensional and threedimensional benchmark examples about exterior acoustics are used to verify the effectiveness and accuracy of the proposed method.The proposed numerical results are compared with the analytical solutions and the solutions obtained by the other numerical methods.

A primary study of the acoustics of Chinese traditional theatrical buildings

The traditional performing arts and theatrical buildings in China can be traced back to a long history and were well developed during Song and Yuan Dynasties, 11th-14th centuries. Pavilion stage, opened on three sides and thrusting into the audience area, was unique and the most popular form in the open-air theatres, the courtyard theatres, and the indoor theatres up to the present day. As the traditional Chinese opera is performed in an abstract way, no stage settings are required and used. Therefore, the pavilion stage including the flat or domed ceiling and the back wall is virtually functioned as a reflective shell, which increases the early reflections and also intensifies the sound in the audience area. Meanwhile, it provides sufficient self-support to the performers. Acoustical parameters including reverberation time RT, early decay time EDT, acoustic ratio C （50）, strength index （loudness） G, and stage support factor ST1 were measured and reported on several traditional theatrical buildings.

UNDERWATER ACOUSTICS AND CAVITATING FLOW OF WATER ENTRY

The fluid mechanics of water entry is studied through investigating the underwater acoustics and the supercavitation.Underwater acoustic signals in water entry are extensively measured at about 30 different positions by using a PVDF needle hydrophone.From the measurements we obtain (1)the primary shock wave caused by the impact of the blunt body on free surface;(2)the vapor pressure inside the cavity;(3)the secondary shock wave caused by pulling away of the cavity from free surface;and so on.The supercavitation induced by the blunt body is observed by using a digital high-speed video camera as well as the single shot photography.The periodic and 3 dimensional motion of the supercavitation is revealed.The experiment is carried out at room temperature.

On a general theory for compressing process and aeroacoustics:linear analysis

Of the three mutually coupled fundamental processes （shearing, compressing, and thermal） in a general fluid motion, only the general formulation for the compress- ing process and a subprocess of it, the subject of aeroacous- tics, as well as their physical coupling with shearing and thermal processes, have so far not reached a consensus. This situation has caused difficulties for various in-depth complex multiprocess flow diagnosis, optimal configuration design, and flow/noise control. As the first step toward the desired formulation in fully nonlinear regime, this paper employs the operator factorization method to revisit the analytic linear theories of the fundamental processes and their decomposi- tion, especially the further splitting of compressing process into acoustic and entropy modes, developed in 1940s-1980s. The flow treated here is small disturbances of a compressible, viscous, and heat-conducting polytropic gas in an unbounded domain with arbitrary source of mass, external body force, and heat addition. Previous results are thereby revised and extended to a complete and unified theory. The theory pro- vides a necessary basis and valuable guidance for developing corresponding nonlinear theory by clarifying certain basic issues, such as the proper choice of characteristic variables of compressing process and the feature of their governing equations.

Magnetic microbubble:A biomedical platform co-constructed from magnetics and acoustics

Generation of magnetic micrbubbles and their basic magnetic and acoustic mechanism are reviewed. The ultrasound （US） and magnetic resonance （MR） dual imaging, the controlled therapeutic delivery, as well as theranostic multifunctions are all introduced based on recent research results. Some on-going research is also discussed.

Acoustics Based Monitoring and Diagnostics for the Progressive Deterioration of Helical Gearboxes

Gearbox condition monitoring(CM)plays a significant role in ensuring the operational reliability and efficiency of a wide range of critical industrial systems such as wind turbines and helicopters.Accurate and timely diagnosis of gear faults will improve the maintenance of gearboxes operating under sub-optimal conditions,avoid excessive energy consumption and prevent avoidable damages to systems.This study focuses on developing CM for a multi-stage helical gearbox using airborne sound.Based on signal phase alignments,Modulation Signal Bispectrum(MSB)analysis allows random noise and interrupting events in sound signals to be suppressed greatly and obtains nonlinear modulation features in association with gear dynamics.MSB coherence is evaluated for selecting the reliable bi-spectral peaks for indication of gear deterioration.A run-to-failure test of two industrial gearboxes was tested under various loading conditions.Two omnidirectional microphones were fixed near the gearboxes to sense acoustic information during operation.It has been shown that compared against vibration based CM,acoustics can perceive the responses of vibration in a larger areas and contains more comprehensive and stable information related to gear dynamics variation due to wear.Also,the MSB magnitude peaks at the first three harmonic components of gear mesh and rotation components are demonstrated to be sufficient in characterizing the gradual deterioration of gear transmission.Consequently,the combining of MSB peaks with baseline normalization yields more accurate monitoring trends and diagnostics,allowing the gradual deterioration process and gear wear location to be represented more consistently.

ACOUSTIC PROPAGATION IN SHEARED MEAN FLOW USING COMPUTATIONAL AEROACOUSTICS

Acoustic propagation problems in the sheared mean flow are numerically investigated using different acoustic propagation equations , including linearized Euler equations ( LEE ) and acoustic perturbation equations ( APE ) .The resulted acoustic pressure is compared for the cases of uniform mean flow and sheared mean flow using both APE and LEE.Numerical results show that interactions between acoustics and mean flow should be properly considered to better understand noise propagation problems , and the suitable option of the different acoustic equations is indicated by the present comparisons.Moreover , the ability of APE to predict acoustic propagation is validated.APE can replace LEE when the 3-D flow-induced noise problem is solved , thus computational cost can decrease.

A story in duct acoustics

1 Introduction The science of sound in ducts can be traced back to the time when the sound wave equation was first derived.Many important ideas,concepts,and methods for acoustics were first developed for sound fields in ducts.Anyone with a little training in acoustics must be aware of normal specific acoustical impedance,the standing wave ratio,transmission line theory,and the cut-on frequencies of high-order wave-guide modes.In fact,duct acoustics has been so extensively taught

《Room Acoustics》

CRC Press,Talor&Francis Group,ISBN:978-1-4822-6043-4(Hardback),2017,6th Ed.This book represents a classical text in room acoustics-its original edition having been first pubfished in 1973.The author was a chair professor at the Institute of Technical Acoustics,the Technical University in Aachenl Germany since 1972 until his retirement in 1995.The author of the book intends to introduce

Magnetostriction and Acoustics Properties of Tb_(1-x)Dy_x (Fe_(1-y)Mn_y)_(1.95) Alloys and Their Application to Sonar Transducers

The magnetostriction and acoustics properties of Tb1-x xDyx (Fe1-yMny) 1.95 alloys and their application to sonar transducers were studied. The following results were obtained from experiments. When the applied magnetic field intensity is ≥ 800 kA·m-1, the magnetostrictive coefficients are (1300- 1800)× 10-6. The electromechanical coupling factors are 0.84-0.93, the sound velocities 2168-2856 m·s-1 and the Young's modulus (5.06- 7.26) ×10 N·m-2. A sonar transducer made of the alloy rod, which has a total length of 300 mm and a total weight of 2 kg, is characterized by 2.4 kHz specified resonant frequency, 1 kHz frequency band, 173 kB current response and 45% electroacoustic efficiency.

Finite Element Method Computations of the Acoustics of the Human Head Based on the Projection Based Interpolation Data

In this paper we present the Projection Based Interpolation (PBI) technique for construction of continuous approximation of MRI scan data of the human head. We utilize the result of the PBI algorithm to perform three dimensional (3D) Finite Element Method (FEM) simulations of the acoustics of the human head. The computational problem is a multi-physics problem modeled as acoustics coupled with linear elasticity. The computational grid contains tetrahedral finite elements with the number of equations and polynomial orders of approximation varying locally on finite element edges, faces, and interiors. We utilize our own out-of-core parallel direct solver for the solution of this multi-physics problem. The solver minimizes the memory usage by dumping out all local systems from all nodes of the entire elimination tree during the elimination phase.

Acoustic Multi Emission Lens via Transformation Acoustics

Based on transformation acoustic methodology, we propose an algorithm for designing acoustic non-resonant lens antenna, which is competent to generate multiple directive beams that are pointing at the desired direction.Unattainable with previous works, the present approach is capable of adjusting the directivity of each radiated beam individually, which is of the utmost importance in several acoustic applications such as in sonar systems. A linear transformation function is intentionally used for eliminating the inhomogeneity of the obtained materials and to pave the way towards more general acoustic patterns. Several numerical simulations are performed to show the capability of the proposed method in manipulating the acoustic waves. To authenticate the concept,a structure that can generate four beams with different directivities is realized with non-resonant meta-fluid bi-layered structure through effective medium theory.

Evaluating Room Acoustics for Speech Intelligibility

Room acoustics play an important role in the intelligibility of speech. The main aspect of acoustics that is usually studied is the duration of the reverberation decay, since a long decay causes a blurring of phonemes. However, other parameters of the acoustics such as the strength of the reverberation can actually improve intelligibility. These factors do not receive the same attention. In many common practical situations such as classrooms and residential rooms, it would be of value to quantitatively study the acoustics to optimize the room’s function, but this is not done routinely due to the expected expense or difficulty involved. This research explores inexpensive first-principle methods to quantitatively measure three key parameters of a room’s acoustics: the reverberation decay time RT60, the reverberant intensity IR, and the room’s total absorption A. The required equipment includes two laptops installed with certain free softwares. Generation of the required noise signal and level detection are carried out using the REW software, and long-duration recordings are carried out using the Audacity software. The procedures are simple enough to be performed without specialized training and do not require specialized equipment, only commonly available household resources. This research also sheds light on the fact that not all reverberation is bad and that strong but short-duration reverberation can enhance communication. This information can be expected to benefit schools and other venues where speech intelligibility is vital.

Solid Acoustics 755 Professional 十二面音箱

本来这款扬声器是属于Hi-Fi类，不大适合放在“硬派时尚”这个栏目，但是它长得太酷了，让我们忍不住要将它推到你面前，755 Prolessional共有12个平面，每个平面上都有一个尺寸为10厘米的扬声器，

Boston Acoustics的p400墙挂式音箱

平板电视机挂在墙上天经地义，音箱就不一定了。如果将左／右主音箱和中置音箱及漂亮雅致的等离子电视机硬堆在一起，其结果肯定很不协调。对此，Boston Acoustics公司特意将这前方三只音箱装在一个箱体里，设计出p400墙挂式音箱，可以放在平板电视机的上方或下方。p400宽40英寸，正好与42英寸的等离子电视机理想匹配。p400音箱的网罩有黑色和银色两种外饰供用户选择。

neat acoustics motive SX3

品牌简介英国neat Accoustics成立于1989年,至今有30多年历史。创始人Bob Surgeoner先生,是一位自学成才的音乐家,在成立neat Accoustics之前,除演出外,他没有任何正式工作。后来,他发现自已能够通过销售音响赚钱,于是他决定开发自己的音箱产品,从而成立了neat Accoustics。音乐家参与音箱设计,到底行不行?其实答案就在neat Accoustics成立至今的30多年历史中。