Effects Of Acoustic Coupling Research Articles

Noise reduction through periodic serial side branches containing two defects

Noise pollution is a challenging issue requiring the development of acoustic systems that can reduce noise. Besides the environmental impacts of noise pollution, it can cause serious health problems. This work originally discusses noise reduction using a new configuration of side branches grafted in series with different terminations. The combination of two serial resonators shows acoustic coupling effects. This effect is used to increase localized modes of two serial defective resonators located in the middle of the structure. The transmission of acoustic waves can be controlled by the dimensions of the introduced defects as well as their boundary conditions. We also show that defects can totally filter the transmission of the pass-bands. The proposed structure can then play the role of an acoustical filter.

Sound power from coupled structures using elementary radiators

Sound power measurements are of interest in numerous applications, and several methods are available for obtaining the sound power of a system. A recent method that has been developed, referred to as the Vibration-Based Sound Power (VBSP) method, utilizes vibration measurements obtained from a Scanning Laser Doppler Vibrometer (SLDV). The VBSP method has previously been used to obtain the sound power radiated from flat plates, cylindrical shells and curved plates. This paper will present further developments to extend VBSP measurements to multiple coupled structures and investigate the acoustic coupling effects that may exist. Two coplanar flat plates separated by a distance d were modeled using the boundary element method. The sound power was determined within the boundary element software and the structural velocities were also exported and processed using the VBSP method. Computational and experimental results will be shown to demonstrate abilities and limitations for the VBSP method to accurately determine the radiated sound power for coupled structures. [Funding for this work was provided by the National Science Foundation (NSF).]

Photoacoustic tomography of fingerprint and underlying vasculature for improved biometric identification

Capitalizing on the photoacoustic effect, we developed a new fingerprint sensing system that can reveal both fingerprints and underlying vascular structures at a high spatial resolution. Our system is built on a 15 MHz linear transducer array, a research ultrasound system, and a 532-nm pulsed laser. A 3D image was obtained by scanning the linear array over the fingertip. The acquired fingerprint images strongly agreed with the images acquired from ultrasound. Additional experiments were also conducted to investigate the effect of acoustic coupling. We discovered that high-quality fingerprint and vessel images can be acquired from both wet and dry fingers using our photoacoustic system. The reduced subdermal features in dry coupling can be enhanced through post-processing. Compared to existing fingerprint scanners, the photoacoustic approach provides a higher quality 3D image of the fingerprint, as well as unique subdermal vasculature structures, making the system almost impossible to counterfeit.

All-optical dynamic analysis of the photothermal and photoacoustic response of a microcantilever by laser Doppler vibrometry

Light absorption induced thermoelastic and photoacoustic excitation, combined with laser Doppler vibrometry, was utilized to analyze the dynamic mechanical behavior of a microcantilever. The measured frequency response, modal shapes, and acoustic coupling effects were interpreted in the framework of a simple Bernouilli-Euler model and quantitative 3D finite element method (FEM) analysis. Three opto-mechanical generation mechanisms, each initiated by modulated optical absorption and heating, were identified both by an analytical and finite element model. In decreasing order of importance, optically induced cantilever bending is found to be caused by: (i) differences in photoacoustically induced pressure oscillations in the air adjacent to the illuminated and dark side of the cantilever, resulting from heat transfer from the illuminated cantilever to the nearby air, acting as a volume velocity piston, and (ii) thermoelastic stresses accompanying temperature and thermal expansion gradients in the cantilever, (iii) photoacoustically induced pressure oscillations in the air adjacent to the illuminated cantilever holder and frame.

Analysis of Structure–Acoustic Coupling Characteristics Between Adjacent Flexible Panels and Enclosed Cavity

Abstract This article studies the structure–acoustic coupling mechanism between two adjacent flexible panels and an enclosed cavity by analytical and mathematical methods based on modal expansion methods and impedance mobility techniques. The results show that the coupling relations among subsystem modes of the coupled system have selectivity characteristics. The coupling strength depends on the normalized mode–shape coupling coefficients. The coupling relationship between two flexible panels is established through the enclosed cavity. The structural–acoustic coupling effect mainly affects the low-order modes of the coupled system, especially the first-order modes of the panels and cavity. When one panel is weakly coupled with the cavity, the two flexible panels are decoupled. The vibration of the panel only depends on its structural characteristics and external excitation, and the panel radiates sound into the cavity. The vibration of another panel depends not only on its structural characteristics but also on its coupling effect with the cavity.

Boundary element method to analyze acoustic scattering from a coupled swimbladder-fish body configuration

A model for computing acoustic scattering by swimbladdered fish is presented. The effect of acoustic coupling between the fish tissue and the swimbladder is included. The swimbladder is considered a gas-filled object whereas the fish tissue is assumed to behave as a homogeneous fluid. Mathematically, this corresponds to considering the problem of two penetrable scatterers immersed in a homogeneous medium, one of which is wholly embedded in the other. The model is formulated in the frame of boundary integral equations whose solution is achieved using the Boundary Element Method (BEM) for a planar triangle mesh. The numerical implementation is verified against benchmark solutions reported in the literature. The model is then applied to a specimen of Argentine hake (Merluccius hubbsi), whose morphometry was determined by CT scanning of a frozen sample, for evaluating its forward and backscattering responses. From the acoustic scattering viewpoint, the swimbladder is considered as a gas-filled object while the flesh constituting the fish body acts like a weak scatterer. The numerical results suggest the swimbladder and the fish body responses, when fully coupled, can lead to substantial differences with respect to the simplified models normally in use in the area of aquatic ecosystem research.

On the role of acoustic reflections from duct boundaries in fan flutter

The role that acoustic reflections from duct boundaries play in aeroengine fan flutter is theoretically investigated. To make a systematic parametric study attainable, a three-dimensional semi-analytical approach is employed. Based on the transfer element method combined with a boundary integral equation method, this approach effectively captures the acoustic coupling effect of an annular rotor undergoing incipient oscillation and a finite-length non-rigid duct in subsonic flow. For a given vibration mode, the disturbances generated both inside and outside the duct are determined by a simultaneous solution. The flutter likelihood is subsequently evaluated through the energy method. Results reveal that near the flutter boundary, the aeroelastic impact of duct boundary reflections becomes evident and critical when propagating (cut-on or weakly damped) acoustic modes exist in the flow duct. Under such condition the aerodynamic interaction between both duct openings strongly affects the sound field distribution, thus contributing to the notable installation effect on aeroelastic stability. Moreover, the flutter-driven acoustic field is also susceptible to the sound reflection effect of the partially lined duct wall. It is found that the variation of the blade aerodynamic damping with the liner impedance is markedly different when the duct end reflections come into play. Under appropriate conditions the mutual effect of the lined wall and the duct openings significantly strengthens their acoustic couplings with the ducted fan, where a reasonable estimate of aeroelastic stability can only be provided with an adequate consideration of the realistic acoustic boundary conditions for the entire duct.

An experimental study on the role and function of the diaphragm in modern acoustic stethoscopes

Vibrations of a diaphragm of an acoustic stethoscope in contact with a body of an auscultated patient are the source of the sound transmitted to the ears of a physician performing examination. Mechanical properties of a diaphragm can thus significantly affect the parameters of the transmitted bioacoustic signals. However, the exact relation remains mostly unclear, as the underlying phenomena involve complex effects of acoustic coupling between the diaphragm and the body of a patient. The present study introduces a detailed methodology for determining vibroacoustic behavior of a diaphragm of a stethoscope during a heart auscultation. A laser Doppler vibrometer is used to measure the velocity of vibrations at various points on the surface of a diaphragm during the examination. Synchronized recordings of electrocardiography signals are used for segmentation. Representative data sets are selected and analyzed for various kinds of diaphragms. The results show significant differences in vibration velocity levels and their distribution across the surfaces of the considered structures, but no significant filtering effects.

An experimental study on the role and function of the diaphragm in modern acoustic stethoscopes

Vibrations of a diaphragm of an acoustic stethoscope in contact with the body of an auscultated patient are the source of the sound transmitted to the ears of a physician performing examination. Mechanical properties of a diaphragm are supposed to significantly affect the parameters of the transmitted bioacoustic signals. However, the exact relation remains mostly unclear, as the underlying phenomena involve complex effects of acoustic coupling between the diaphragm and the body of a patient. The present study introduces a detailed methodology for determining vibroacoustic behavior of a diaphragm of a stethoscope during an auscultation examination. A laser Doppler vibrometer is used to measure the velocity of various points on the surface of a diaphragm during heart auscultation. Synchronized recordings of electrocardiography signals are used for segmentation. Representative data sets are selected and analyzed for various kinds of diaphragms. The results show significant differences in vibration velocity levels and their distribution across the surfaces of the considered structures. In this regard, it is also shown that the currently available solutions can be significantly improved by using structures better matched to the acoustic impedance of a body.

Reduced aerodynamic drag concepts for acoustic liners

The objective of this paper is to describe the development of reduced aerodynamic drag concepts for acoustic liners in turbofan engine nacelles. Conventional acoustic liners help aircraft to achieve U.S. governmental noise regulations, however they are responsible for a measurable increase in the total aerodynamic drag of the aircraft. As regulations on commercial aircraft noise become more strict, additional surfaces may be covered with acoustic liner, heightening the need for the understanding and reduction of aerodynamic drag caused by liners. A linear force balance has been designed at the Mach 0.6 Wind Tunnel at the University of Notre Dame to evaluate the aerodynamic and acoustic characteristics of both conventional and 3D-printed liner samples. Through multi-parameter characterization, reduced drag concepts for future liners have been created. This paper will discuss the experimental work done to develop these reduced drag concepts, outline the future work to be done, and discuss the potential acoustic coupling effect on aerodynamic drag.

Modeling of acoustic resonators and resonator arrays for use in passive noise control

Acoustic resonators, such as the Helmholtz and quarter-wave resonator, can be used to attenuate unwanted noise in a space. Classic formulations can be used to approximate resonator performance for a given resonator configuration, but may lack sufficient accuracy for some applications. This research aims to improve the analytical characterization of resonators to provide better correlation to experimental results. Using higher order approximations and proper end corrections, more accuracy can be obtained in calculating the impedance and resonance frequency of a single resonator, which will then carry over into the overall configuration of the model. The impedance of a system of resonators in parallel is also considered, where the effects of acoustic coupling can be observed. Resonators with complex, non-ideal geometries are explored for applications where space is limited.

Numerical study of acoustic coupling in spinning detonation propagating in a circular tube

Spinning detonations propagating in a circular tube were numerically investigated with a two-step reaction model by Korobeinikov et al. The time evolutions of the simulation results were utilized to reveal the propagation behavior of single-headed spinning detonation. Three distinct propagation modes, steady, unstable, and pulsating modes, are observed in a circular tube. The track angles on a wall were numerically reproduced with various initial pressures and diameters, and the simulated track angles of steady and unstable modes showed good agreement with those of the previous reports. In the case of steady mode, transverse detonation always couples with an acoustic wave at the contact surface of burned and unburned gas and maintains stable rotation without changing the detonation front structure. The detonation velocity maintains almost a CJ value. We analyze the effect of acoustic coupling in the radial direction using the acoustic theory and the extent of Mach leg. Acoustic theory states that in the radial direction transverse wave and Mach leg can rotate in the circumferential direction when Mach number of unburned gas behind the incident shock wave in the transverse detonation attached coordinate is larger than 1.841. Unstable mode shows periodical change in the shock front structure and repeats decoupling and coupling with transverse detonation and acoustic wave. Spinning detonation maintains its propagation with periodic generation of sub-transverse detonation (new reaction front at transverse wave). Corresponding to its cycle, whisker is periodically generated, and complex Mach interaction periodically appears at shock front. Its velocity history shows the fluctuation whose behavior agrees well with that of rapid fluctuation mode by Lee et al. In the case of pulsating mode, as acoustic coupling between transverse detonation and acoustic wave is not satisfied, shock structure of spinning detonation is disturbed, which causes failure of spinning detonation.

Effect of acoustic coupling on power-law flame acceleration in spherical confinement

A model describing acoustically-generated parametric instability in a spherical chamber is developed for quasi-one-dimensional, low-Mach number flames. We demonstrate how sound waves generated by a centrally-ignited, outwardly-propagating accelerating flamefront can be incorporated into an existing theory of self-similar flame acceleration in free space [V. Akkerman, C. K. Law, and V. Bychkov, “Self-similar accelerative propagation of expanding wrinkled flames and explosion triggering,” Phys. Rev. E 83, 026305 (2011)]10.1103/PhysRevE.83.026305. Being reflected from the chamber wall, flame-generated acoustics interact with the flamefront and the attendant hydrodynamic flamefront cellular instability. This in turn affects the subsequent flame morphology and propagation speed. It is shown that the acoustics modify the power-law flame acceleration, concomitantly facilitating or inhibiting the transition to detonation in confinement, which allows reconciliation of a discrepancy in experimental measurements of different groups.

Acoustic mode coupling resulting from an internal solitary wave approaching a shelf break in South China Sea

An internal solitary wave (ISW) encountering the shelf break, making the waveguide is compressed, can cause different joint coupling effect for acoustic modes. In this paper, the extended criterion for adiabatic invariance is developed by parameterizing the joint mode coupling effect of an ISW encountering the shelf break and is used for sensitivity studies considering various internal wave amplitudes and slope angles of shelf break, to examine the acoustic coupling effect resulting from both bathymetry and ISW. The modeling results are accurately predicted by the extended criterion of adiabatic invariance and compared to experimental observations from ASIAEX and NLIWI of the effect of acoustic waveguide being compressed by the shelf break and ISW. Results demonstrate that the coupling of acoustic energy to higher modes as the waveguide is compressed when the ISW encounters the shelf break. And as amplitude of the ISW and the incline of the sloping bottom increase, coupling strength for both adjacent- and non-adjacent modes is enhanced. [This research is sponsored by national science council.]

Optimization of SPL and THD Performance of Microspeakers Considering Coupling Effects

Mobile phones have become more versatile as a result of advances in mobile communication technology. The latest mobile phones are able to provide dazzling multimedia entertainment with portability. A microspeaker has become a generic electromechanical part of mobile phones that enables multimedia features. Therefore, the performance of the microspeaker must be improved in line with the increasing demand for high-quality sound produced by the phone. Sound pressure level (SPL) and total harmonic distortion (THD) are the two most common evaluation criteria that are used to quantify the performance of the microspeaker. Therefore, it is necessary to implement an analysis procedure that predicts and quantifies the SPL and THD characteristics. This manuscript suggests a multiphysics analysis procedure that comprehensively considers electromagnetic, mechanical, and acoustic coupling effects. The experimental results confirm the validity of the proposed analysis procedure.

Lower atmospheric anomalies following the 2008 Wenchuan Earthquake observed by GPS measurements

The Mw=8.0 Wenchuan Earthquake occurred on May 12, 2008 at the Longmen Shan fault, the western Sichuan Basin, China, killing more than ten thousand people in several cities and causing large economic losses. Global Positioning System (GPS) observations have provided unique insights on this event, including co-seismic ionospheric disturbances, co-/post-seismic crustal deformations and fault slip distributions. However, the processes and the driving mechanisms are still not clear, particularly possible seismo-lower atmospheric–ionospheric coupling behaviors. In this paper, the lower atmospheric (tropospheric) variations are investigated using the total zenith tropospheric delay (ZTD) from GPS measurements around this event. It has the first found co-seismic tropospheric anomalies during the mainshock with an increase and then a decrease, mainly in the zenith hydrostatic delay component (ZHD), while it is also supported by the same pattern of surface-observed atmospheric pressure changes at co-located GPS site that are driven by the ground-coupled air waves from ground vertical motion of seismic waves propagation. Therefore, the co-seismic tropospheric disturbances (CTD) indicate again the acoustic coupling effect of the atmosphere and the solid-Earth with air wave propagation from the ground to the top atmosphere.

A double-panel active segmented partition module using decoupled analog feedback controllers: Numerical model

Low-frequency sound transmission has long plagued the sound isolation performance of lightweight partitions. Over the past 2 decades, researchers have investigated actively controlled structures to prevent sound transmission from a source space into a receiving space. An approach using active segmented partitions (ASPs) seeks to improve low-frequency sound isolation capabilities. An ASP is a partition which has been mechanically and acoustically segmented into a number of small individually controlled modules. This paper provides a theoretical and numerical development of a single ASP module configuration, wherein each panel of the double-panel structure is independently actuated and controlled by an analog feedback controller. A numerical model is developed to estimate frequency response functions for the purpose of controller design, to understand the effects of acoustic coupling between the panels, to predict the transmission loss of the module in both passive and active states, and to demonstrate that the proposed ASP module will produce bidirectional sound isolation.

Spectral Characteristics and Localization of Modes in Acoustically Coupled Enclosures

In this paper spectral characteristics and a mode localization in acoustically coupled enclosures were studied numerically. In a theoretical model a low-frequency limit was considered where eigenmodes are weakly damped, thus they were approximated by normal acoustic modes for rigid room walls. The effect of acoustic coupling on the mode frequency, the integrated density of states (IDOS) and the existence surface of modes were investigated for several coupling areas. Numerical results indicate that a decrease in coupling area causes a decrease of IDOS and results in a stronger localization of modes.

Measurement of wave velocities and attenuation using an ultrasonic test system

The use of ultrasonic testing to determine pulse velocities and small-strain elastic constants for rocks has been standardized in American Society for Testing and Materials (ASTM) standard D2845-95. However, the use of ultrasonic testing to determine pulse velocities and small-strain elastic constants of soils is less common, as soils have higher damping characteristics which result in measurement difficulty. The signal transmitted through soil is weak and very noisy. As a result, the signal must be properly processed to provide a reliable estimate of the wave travel time. In this paper, an ultrasonic test system consisting of compression and shear wave transducers, a pulser, and a data-acquisition system is evaluated for measurement of both compression and shear wave velocities. Among the specimens tested were fully saturated and unsaturated soil specimens. The effects of acoustic coupling and signal processing on the transmitted pulse were investigated. The strain levels associated with the determination of the wave velocities were also measured. Furthermore, a method for determining attenuation characteristics for soil specimens from the frequency spectra is suggested.Key words: laboratory, compression wave, shear wave, velocity, attenuation, ultrasonic.

Radiation of sound by two concentric free-flooded cylindrical shells excited by a point force

Radiated acoustic pressure fields are obtained when two concentric free-flooded cylindrical shells of finite lengths are excited by a time-harmonic point force. Integral equations are formulated for the two elastic thin shells with simply supported boundary conditions at both ends. Near and far-field acoustic pressures are calculated and effects of acoustic coupling between two shells are discussed.