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An analytical model is presented that describes the acoustical impedance of cylindrical tubes and concentrically connected systems of such tubes valid up to the ultrasonic application. This allows the evaluation of microsized geometries encountered in acoustical microdevices, such as housing enclosures and sound port Helmholtz resonators. Each tube is treated as an acoustic transmission line (TL). Connected tubes are described using a coupling impedance, which accounts for viscous and inertial effects due to duct size changes. The acoustic TL model is directly derived from Navier-Stokes and energy equation, including frequency dependent boundary layer effects of the viscous and thermal dissipation. The results for various evaluated enclosure and resonator geometries are in good agreement with finite element method (FEM) simulation in both audio and ultrasonic frequency range and are compared to dedicated lumped element models referenced in literature. The presented model provides benefits in three ways: it is faster than FEM simulation and allows an implementation into analytical models and circuit simulation tools. Finally, it allows geometries with characteristic dimensions close to and above the wavelength to be treated with high precision in contrast to lumped element models.

We report experiments on high-amplitude sound wave propagation in an acoustic metamaterial composed of an air-filled waveguide periodically side-loaded by holes. In addition to the linear viscothermal and radiation losses, high amplitude sound waves at the locations of the side holes introduce nonlinear losses. The latter result in an amplitude-dependent reflection, transmission, and absorption, which we experimentally characterize. First, we evidence that nonlinear losses change the nature of the device from a reflective to an absorbing one, showing the possibility to use the system as a nonlinear absorber. Second, we study the second-harmonic generation and its beating phenomenon both experimentally and analytically. We find that when considering the propagation of both the fundamental and the second harmonic, nonlinear losses cannot be neglected. Our results reveal the role of nonlinear losses in the proposed device and also provide a quite accurate analytical model to capture the effect of such losses.

Discrete singular convolution (DSC) algorithm is an accurate dynamic analysis method for single structures. However, vibration analysis of connected structures via the DSC method is limited to step beams and plates. This paper extends the applicability of the DSC method in handling acoustic transmission lines composed of several duct elements with different diameter ratios. Connections of elements are handled by setting up continuity equations at geometric discontinuities. Conformity of DSC equations at these connections is carried out using Taylor series expansion. In this study, natural frequencies, mode shapes and power transmission coefficients of acoustic transmission lines are performed to test the proposed DSC implementation. Power transmission coefficients are obtained through the two-load method using the data provided by the DSC approach. The results are compared with finite element method and analytical solutions (if applicable), and the analytical transfer matrix method is also used for validating the power transmission coefficients. This paper shows that the DSC method is accurate and reliable, and so applicable for acoustic transmission line analysis.

Narrow bandwidth and complex structure are the main shortcomings of the existing asymmetric acoustic transmission devices. In this letter, a simple broadband asymmetric acoustic transmission device is proposed by using an acoustic prism filled with xenon gas. The sound pressure field distributions, the transmission spectra, and the prism angle effect are numerically investigated by using finite element method. The proposed device can always realize asymmetric acoustic transmission for the wave frequency larger than 480 Hz because the wave paths are not influenced by the wave frequencies. The asymmetric acoustic transmission is attributed to normal refraction and total reflection occur at different interfaces. Besides, relatively high transmission efficiency is realized due to the similar impedance between the acoustic prism and background. And the transmitted wave direction can be controlled freely by changing the prism angle. Our design provides a simple method to obtain broadband asymmetric acoustic transmission device and has potentials in many applications, such as noise control and medical ultrasound.

We theoretically investigate the nonlinear effects of acoustic wave propagation and dispersion in a cylindrical pipe with periodically arranged Helmholtz resonators. By using the classical perturbation method in nonlinear acoustics and considering a nonlinear response up to the third-order at the fundamental frequency, the expressions of the nonlinear impedance Z NHR of the Helmholtz resonator and effective nonlinear bulk modulus B neff of the composite structure are derived. In order to confirm the nonlinear properties of the acoustic metamaterial, the transmission spectra have been studied by means of the acoustic transmission line method. Moreover, we calculate the effective acoustic impedance and dispersion relation of the system using the acoustic impedance theory and Bloch theory, respectively. It is found that with the increment of the incident acoustic pressure level, owing to the nonlinearity of the Helmholtz resonators, the resonant frequency ω 0 shifts toward the lower frequency side and the forbidden bandgap of the transmission spectrum is shown to be broadened. The perturbation method employed in this paper extends the general analytical framework for a nonlinear acoustic metamaterial.

A compact model of an airborne capacitive acoustic MEMS transducer is generalized to perform predictive full-system simulations in the audible and ultrasonic regime. The model helps to assess and understand the interaction of the device with the surrounding air for frequencies up to 100 kHz while considering acoustic high-frequency effects and sound wave propagation. We successfully simulate transducers with varying design parameters operating under different working scenarios. The predictive power of the model and its potential for full-system design and optimization are highlighted by the very good agreement between simulations and experimental results.

The local resonant band gap and the negative bulk modulus of the acoustic metamaterial with Helmholtz resonators are strongly affected by the temperature of water. In this paper, the acoustic transmission line method (ATLM) is introduced to investigate the influences of the temperature of water on the local resonant band gap and the negative bulk modulus of the acoustic metamaterial. Results show that the relative variations of the local resonant band gap and the negative effective bulk modulus suffering from the change of the temperature of water are approximately equivalent and are up to about 11%. The reason is that the local resonant frequency is proportional to the sound speed of fluid which is strongly effects by the temperature of water. By achieving the unambiguous relationships between these unusual properties of the acoustic metamaterial and the temperature of water, we find that the temperature-controlled acoustic metamaterial with the active band gap and the active negative bulk modulus can be realized in theory. This idea opens a new avenue for the design of the tunable acoustic metamaterial that can modulate the acoustic wave propagation.

Accurate modeling of acoustic propagation in the ocean waveguide is important to SONAR-performance prediction. Particularly in shallow waters, a crucial contribution to the total transmission loss is the bottom refection loss, which can be estimated passively by beamforming the natural surface-noise acoustic field recorded by a vertical line array of hydrophones. However, the performance in this task of arrays below 2 m of length is problematic for frequencies below 10 kHz It is shown in this paper that, when the data are free of interference from sources other than wind and wave surface noise, data from a shorter array can be used to approximate the coherence function of a longer array. This improves the angular resolution of the estimated bottom loss, often making use of data at frequencies above the array design frequency. Application to simulated and experimental data shows that the technique, rigorously justified for a halfspace bottom, is effective also on more complex bottom types. Dispensing with active sources, small autonomous underwater vehicles equipped with short arrays can be envisioned as compact, efficient seabed-characterization systems. The proposed technique is shown to improve significantly the reflection-loss estimate of an array that would be a candidate for such application.

It has been revealed in experiments that, based on the thermal influence of gases on the surface acoustic wave propagating in a hot acoustic transmission line, it is possible to efficiently detection hydrogen without using gas-sensible coatings. It order to increase the sensitivity, the acoustic transmission line of the sensor is made of a piezoelectric crystal of В12SiO20 with large temperature coefficient of delay and the total phase shift and delay of the wave between radiating and receiving transducers are increased owing to propagation of this wave through two cylindrical roundings. When concentrations are in a range of 0.1–3.2%, the acoustothermic response to hydrogen by an order of magnitude exceeds responses to O2, CH4, NO, and water vapor of the same concentrations. Owing to the absence of a gas-sensible coating, the long-term stability of detection is high and is less than ±2% during six months.

We study dark solitons, namely density dips with a phase jump across the density minimum, in a one-dimensional, weakly lossy nonlinear acoustic metamaterial, composed of a waveguide featuring a periodic array of side holes. Relying on the electroacoustic analogy and the transmission line approach, we derive a lattice model which, in the continuum approximation, leads to a nonlinear, dispersive and dissipative wave equation. The latter, using the method of multiple scales, is reduced to a defocusing nonlinear Schr&ouml, dinger equation, which leads to dark soliton solutions. The dissipative dynamics of these structures is studied via soliton perturbation theory. We investigate the role&mdash, and interplay between&mdash, nonlinearity, dispersion and dissipation on the soliton formation and dynamics. Our analytical predictions are corroborated by direct numerical simulations.

The acoustic isolator is positioned between the bit and the transmitting transducer, it can attenuate a variety of front end of the drill noise signal to avoid the acoustic noise signal propagation along the drill collar, affecting the acoustic signal transmission and used to weaken the influence of downlink acoustic signal with the uplink channel produced by the transducer. This paper improved the characteristic analysis of tapered acoustic transmission model, designed of the size and structure of the acoustic isolator which has the transmission frequency channel of in 700~800Hz and 1200~1300Hz interval.

Flow fields could be of great interest in the study of sound propagation in aeroengines. For ducts with rigid boundaries, the fluid-resonant category may contribute significantly to unwanted noise. An understanding of the multi-modal propagation of acoustic waves in ducts is of practical interest for use in the control of noise in, for example, aero-engines, automotive exhaust and heating or ventilation systems. The purpose of our experiments was to test the acoustic energy transmission of duct modes based on studies carried out by the sound intensity technique. Sound intensity patterns in circular duct are discussed of modal energy analysis with particular reference to proper orthogonal decomposition and dynamic mode decomposition. The authors try to justify some advantages of the sound intensity experimental research in this area. In the paper, the wide-band sound signal propagated from source approximated with loudspeaker in hard-walled duct is imaged using a sound intensity - based approach. For a simple duct geometry, the sound intensity field is examined visually and by performing a modal decomposition greater insight into the acoustic structures is obtained. The image of sound intensity fields below and above “cut-off” frequency region are found to compare acoustic modes which might resonate in duct.

Current techniques for measuring normal incidence sound transmission loss with a modified impedance tube, or transmission tube, require setting up two different absorbing termination loads at the end of the downstream tube [ASTM E2611-09, Standard Test Method for Measurement of Normal Incidence Sound Transmission of Acoustical Materials Based on the Transfer Matrix Method (American Society for Testing and Materials, West Conshohocken, 2009)]. The process of physically handling the two required passive absorbing loads is a possible source of measurement errors, which are mainly due to changes in sample test position, or in test setup re-assembly, between measurements. In this paper, a modified transmission tube apparatus is proposed for non-intrusively changing the downstream acoustic load by means of a combined passive-active termination. It provides a controlled variable sound absorption which simplifies the setup of standard two-load techniques, without the need of physically handling the apparatus during the tests. This virtually eliminates the risk of errors associated with the physical manipulation of the two passive terminations. Transmission loss measurements in some representative test conditions are reported, showing improvements over current implementations, in reducing by approximately 50% the measurement variations associated with the setup of the two required absorbing terminations. Measurement results agree within 0.4 dB (maximum difference in high resolution broadband), and 0.04 dB (mean difference in 1/3-octave bands), with those obtained using standard passive two-load methods.

A new method of wireless data telemetry used by oil industry uses compressional acoustic waves to transmit downhole information from the bottom hole to the surface. Unfortunately, acoustic echoes and drilling vibration noises in periodic drillstring are a major issue in transmission performance. A combined acoustic echo and noise suppression method based on wave motion characteristic in drillstring is adopted to enhance an upward-going transmitted acoustic signal. The presented scheme consists of a primary acoustic echo canceller using an array of two accelerometers for dealing with the downward-going noises and a secondary acoustic insulation structure for restraining the upward-going vibration noises. Furthermore, the secondary acoustic insulation structure exhibits a banded and dispersive spectral structure because of periodic groove configuration. By using a finite-differential algorithm for the one-dimensional propagation of longitudinal waves, acoustic receiving characteristics of transmitted signals are simulated with additive Gaussian noise in a periodic pipe structure of limited length to investigate the effects on transmission performance optimization. The results reveal that the proposed scheme can achieve a much lower error bit ratio over a specified acoustic isolation frequency range with a 30–40 dB reduction in the average noise level compared to traditional single-receiver scheme.

The sound transmission loss (STL) of the acoustic parts in the vehicle was proposed to be computed using the Sound Pressure Level measured at the several locations inside the vehicle and the transmitted Sound Intensity Level on the vehicles exterior panel, which the acoustic treated vehicle passenger compartment is assumed as a small reverberation room. The necessary parts retrofits and acoustic treatments for Sound transmission loss tests of the acoustic parts in the vehicle were listed. The values of the appropriate number and positions of the loud speakers, microphones and sound intensity probes for Sound transmission loss of the acoustic parts in the vehicle were recommended. The in vehicle sound transmission loss tests of the acoustic parts such as the doors, carpets, wheel house etc. were achieved in the semi-anechoic room. Based on the door system, the correlation work has been done among the methods of the proposed in vehicle STL test, the reverberation - semi-anechoic chamber buck STL test and SEA analysis.

A solution to the problem of acoustic source depth discrimination in a downward refracting, shallow-water ocean waveguide is presented for the case of a horizontal line array at endfire. The approach exploits the phenomenon of mode trapping, wherein a shallow acoustic source cannot excite the lowest order waveguide modes due to its evanescent amplitude dependence near the surface. The important implication of this "trapping" behavior is that, given sufficient spatial aperture, it provides a mechanism for differentiating a shallow acoustic noise source from one at depth. The method does not require array cant, or physical vertical aperture of any kind, but instead relies only on the sensitivity of a line array at endfire to differences in horizontal wave number to resolve low and high order mode subspace excitations. The only inputs to the algorithm are an approximate sound speed profile, water depth, and bottom type. The theoretical basis for the test statistic is first reviewed, followed by discussion of key requirements, and illustration of the concept using results from a RAM PE simulation for a downward refracting environment. Finally, the algorithm is experimentally demonstrated using data from a bottom-mounted HLA deployed in the moderately cluttered continental shelf environment of the Florida Straits.

An acoustic couplant layer plays an integral role in many ultrasonic nondestructive testing and material characterization applications. It is important to account for this layer for accurate time-delay measurements. In pulse-echo measurements, the couplant layer can be accounted for by modeling the frequency dependence of phase delay. In this paper, two such models are evaluated for robustness in determining an accurate phase velocity: a simple linear relationship and the acoustic transmission line with its associated nonlinear expression. For this evaluation, measurements of acoustic phase delay in an aluminum sample were made by the pulse-echo method using tone bursts of 1800 different carrier frequencies between 35 and 125 MHz. The transmission line model was fit to the measured data using an unconstrained nonlinear least squares fitting routine with two free parameters: the acoustic phase velocity in the sample and the couplant thickness. It was found that this nonlinear model was extremely sensitive to the initial parameter guesses and could not unambiguously determine both the couplant layer thickness and acoustic phase velocity. In contrast, the faster and simpler linear least squares fit to the delay data determines a unique phase velocity in agreement with resonant ultrasound spectroscopy, an independent measurement technique.

The wave propagation characteristics of an acoustic metamaterial composed of periodically repeated one-dimensional Helmholtz resonator array was investigated considering the effects of dimensional changes of the resonator geometry on the transmission coefficient and band gap. The effective impedance and transmission coefficient of the acoustic metamaterials are obtained based on the acoustic transmission line method. The designed acoustic metamaterials exhibit band gaps and negative bulk modulus that are non-existent properties in the nature. The band gap of the acoustic metamaterial is strongly dependent on the geometry parameters of Helmholtz resonators and lattice spacing. Also, a new type of metamaterial that is periodically constructed with two different resonators was designed to open the local resonance band gap without change of Bragg scattering.

An acoustic source identification technique with single layer pressure measurement is presented to reconstruct normal velocities of target sources in noisy environments. The theory for this reconstruction is developed from the inverse patch transfer functions method which is supposed to combine measurements of pressure and velocity on a surface surrounding the source. The rigid microphone array is called an acoustic mask, which is designed to obtain pressure on the Neumann boundary condition and realized by microphones flush mounted on the aluminum plate. The validity of the proposed method is demonstrated by giving the normal velocities of two baffled loudspeakers in a noisy environment in the simulation and experiment. Another experiment of a clamped steel plate is further presented to illustrate the ability of the acoustic mask to obtain the partial velocity field of interest without reconstruction of the whole source surface velocity. The accuracy of this technique is demonstrated by comparison with the accelerometer method.

We report an extraordinary acoustic transmission through two layer annuluses made of metal cylinders in air both numerically and experimentally. The effect arises from the enhancement and reconstruction of the incident source induced by different Mie-resonance modes of the annuluses. The proposed system takes advantages of the consistency in the waveform between the input and output waves, the high amplitude amplification of output waves, and the easy adjustment of structure. More interestingly, we investigate the applications of the extraordinary acoustic transmission in the acoustic beam splitter and acoustic concentrator. Our finding should have an impact on ultrasonic applications.

We are aiming to develop a puncture-type ultrasound microscope by which less invasive settled diagnosis can be executed. To provide in vivo high-resolution imaging of a tumor, we need to scan high frequency ultrasound by rotating an acoustic mirror or an ultrasound oscillator at the tip of a probe. As a driving source device for rotating those, we can use our miniature ultrasonic motor. To narrow the probe while maintaining a smooth rotation of the ultrasonic motor, ultrasound energy for the motor has to be efficiently transmitted from a sound source placed outside the body. In this study, we propose an innovative method for propagating ultrasound using an acoustic transmission line.

We present a novel surface acoustic wave sensor, incorporating the advantages of multi-frequency and multi-mode operation in a single acoustic device structure. SAW sensors are commonly based on the change of the effective elastic constants or the mass loading of the device due to a different sensor environment. Usually, single acoustic modes at a fixed frequency are employed allowing for the detection of a certain chemical species, depending on the coating of the wave's propagation path. Analyzing multiple acoustic modes or multiple excitation frequencies that are each reacting differently on a particular load, allows for the multi-parameter analysis of gases and liquids. We present a sensor system that is based on floating electrode unidirectional transducers (FEUDTs) allowing for the excitation of a set of 48 equally spaced frequencies and at least two acoustic modes (depending on the material system) in a single transducer structure. FEUDTs allow for the efficient excitation of acoustic waves at GHz frequencies without the use of sophisticated nanofabrication techniques. Higher frequencies, on the other hand, are advantageous for the sensitivity of the device. We tested the basic operation of our sensor system by applying it to humidity sensing without a sensitive layer.

This paper presents a theoretical study of sound propagation in a duct with a tube array flush-mounted periodically. The underlying wave interaction is analyzed by the transfer matrix method, and validated by the numerical simulation. With identical tubes, a particular situation is observed that the periodic distance and the tube length are “matched,” leading to a strong coupling effect by Bragg reflection and tube resonance, resulting in a wide stopband in low frequency. Even when the tubes in the array are not identical, the Bragg reflection can still work to broaden the stopband which was originally contributed by tube resonances.

A transmission-line acoustic metamaterial is an engineered, periodic arrangement of relatively small unit-cells, the acoustic properties of which can be manipulated to achieve anomalous physical behaviours. These exotic properties open the door to practical applications, such as an acoustic leaky-wave antenna, through the implementation of radiating channels along the metamaterial. In the transmitting mode, such a leaky-wave antenna is capable of steering sound waves in frequency-dependent directions. Used in reverse, the antenna presents a well defined direction-frequency behaviour. In this paper, an acoustic leaky-wave structure is presented in the receiving mode. It is shown that it behaves as a sound source direction-finding device using only one sensor. After a general introduction of the acoustic leaky-wave antenna concept, its radiation pattern and radiation efficiency are expressed in closed form. Then, numerical simulations and experimental assessments of the proposed transmission-line based structure, implementing only one sensor at one termination, are presented. It is shown that such a structure is capable of finding the direction of an incoming sound wave, from backward to forward, based on received sound power spectra. This introduces the concept of sound source localization without resorting to beam-steering techniques based on multiple sensors.

The paper presents acoustic borehole depth-gauge with a new method of determining the temporal position of the received signal and the description of the mathematical apparatus method. The algorithm of measuring distance by means of ultrasound two-frequency method is given as well.

A variety of applications require the mixing and/or heating of a slurry made from a powder/fluid mixture. One of these applications, Sub Critical Water Extraction (SCWE), is a process where water and an environmental powder sample (sieved soil, drill cuttings, etc.) are heated in a sealed chamber to temperatures greater than 200 degrees Celsius by allowing the pressure to increase, but without reaching the critical point of water. At these temperatures, the ability of water to extract organics from solid particulate increases drastically. This paper describes the modeling and experimentation on the use of an acoustic resonant chamber which is part of an amino acid detection instrument called Astrobionibbler [Noell et al. 2014, 2015]. In this instrument we use acoustics to excite a fluid- solid fines mixture in different frequency/amplitude regimes to accomplish a variety of sample processing tasks. Driving the acoustic resonant chamber at lower frequencies can create circulation patterns in the fluid and mixes the liquid and fines, while driving the chamber at higher frequencies one can agitate the fluid and powder and create a suspension. If one then drives the chamber at high amplitude at resonance heating of the slurry occurs. In the mixing and agitating cell the particle levitation force depends on the relative densities and compressibility’s of the particulate and fluid and on the kinetic and potential energy densities associated with the velocity and pressure fields [Glynne-Jones, Boltryk and Hill 2012] in the cell. When heating, the piezoelectric transducer and chamber is driven at high power in resonance where the solid/fines region is modelled as an acoustic transmission line with a large loss component. In this regime, heat is pumped into the solution/fines mixture and rapidly heats the sample. We have modeled the piezoelectric transducer/chamber/ sample using Mason’s equivalent circuit. In order to assess the validity of the model we have built and tested a variety of chambers. This paper describes the experimental results which are in general agreement with theory within the limitations of the modeling.

The acoustic center of radiating sources is relevant to the modeling of radiation patterns and to their effective implementation in acoustical applications and computer models. However, the acoustic center of the sources may not be unique and therefore should be defined. Previously studied source centering algorithms used analytic methods for specific acoustic models, or applied post processing methods on a recorded sound from an acoustic source that was surrounded by a spherical microphone array. This work performs an acoustic centering of a radiating circular baffled piston that is formed by an open termination of a circular pipe. A signal processing based acoustic centering algorithm is redefined for this case and is shown to be correlated with the effective length of the pipe.

This paper presents a passive method to control low-frequency noise in a cylindrical structure by using multi-modal T-shaped acoustic resonators. The feasibility of noise transmission control on the cylindrical structure is investigated, including a detailed experimental evaluation of the control performance using a single resonator and a resonator array consisted of different resonators. Finally, six long T-shaped acoustic resonators are used to target the first four lowest cylindrical cavity resonances, and up to 9 dB noise reduction is achieved, and broadband improvement of noise reduction is also observed.

The Transmission Line loudspeaker is an audio loudspeaker enclosure topology devoted to extending the low frequency range near the loudspeaker frequency resonance. A few models based on physical properties of damped pipes have been proposed to characterize the Transmission Line loudspeaker systems. Unfortunately, Thiele/Small parameters, which are usually employed in enclosure designs, are not useful as parameters of design for these loudspeakers. In this paper, a comprehensive numerical formulation of a Transmission Line loudspeaker is presented, which is based in a finite difference approach of the governing equations, including the effects of the absorbing material allocated inside the pipe. The influence of the main empirical parameters is tested on the proposed model, which is also compared to a real prototype for validation purposes. © 2011 Elsevier Ltd. All rights reserved., Authors want sincerely thank to Daniel Garcia for his valuable collaboration performing simulations. Authors are also very grateful to Dr. Viciana for her thoughtful and critical comments about this work. This work has been supported by Spanish Ministry of Science and Technology (MCYT) under Project Ref. TEC2009-14414-C03-01 and FEDER funds.

Energy of high-amplitude sound that often appears in acoustic resonators with mean flow can be harnessed and converted into electricity for powering sensors and other devices. In this study, tests were conducted in a simple setup consisting of a pipe with a pair of baffles and a piezoelement. Tonal sound, corresponding to the second acoustic mode of the resonator, was excited due to vortex shedding/impinging on baffles in the presence of mean flow. Generated sound energy was partially converted into electrical energy by a piezoelement. About 0.55 mW of electric power was produced on a resistive electric load at acoustic pressure amplitudes in the pipe about 170 Pa and mean flow velocity 2.6 m/s.

A simulation method using the acoustic software SYSNOISE to study far-field acoustic performance in different angles of a planar phased array in broadside dome is performed. The planar array is installed parallel to the vessel centerline. The cases in which the acoustic window is parallel to the planar array and at an angle of 8 degrees are separately calculated. The simulation results show that the impact of the acoustic window to the far-field beams when the acoustic window is parallel to the array is smaller. When they are at an angle of 8 degrees, the impact of the acoustic window on the side lobes is more obvious than it on the main lobe. The cases when the acoustic window is fully transmissive and when it is with a titanium film are calculated. The titanium film introduces an obvious insertion loss, and the insertion loss of the side lobes is significantly larger than that in the case of the main lobe. The results have a practical significance to sonar installations in broadside domes.

Low-frequency reverberant sound fields are usually suppressed by means of either adaptive feedforward control or Helmholtz resonator. Feedforward systems utilize a noise reference signal, error microphone, and loudspeaker to cancel sound propagating in one direction. Due to the requirement for multiple transducers and a powerful digital signal processor, feedforward systems are the most complex and expensive option for acoustic noise reduction. Helmholtz resonators, comprising auxiliary coupled acoustic chambers, are a popular passive technique for the control of dominant acoustic modes. Although lightly damped acoustic modes can be heavily attenuated, the resonators are difficult to tune and require unpractically large cavity volumes at frequencies below 200 Hz. This paper introduces a new technique for the control of low-frequency reverberant sound fields. By connecting an electrical impedance to the terminals of an acoustic loudspeaker, the mechanical dynamics, and hence, acoustic response can be made to emulate a sealed acoustic resonator. No microphone or velocity measurement is required. In some cases, the required electrical circuit is simply the parallel connection of a capacitor and resistor. With the addition of a single pressure microphone, a technique for online circuit adaptation is proposed. Experimental application to a closed acoustic duct results in 14-dB pressure attenuation of a single acoustic mode. Active impedances can be designed by viewing the system model from a feedback control perspective. The resulting electrical impedances, although not passive, are experimentally shown to attenuate four acoustic modes by up to 10 dB.

The acoustic transmission technology of information measured by MWD is an important research direction of underground information wireless transmission technology. The drill string as information transmission channel is composed by size difference drill pipe, so it is one of important issue to understand the relationship between the drill pipe size difference and acoustic wave propagation characteristics in the drill-string. That is related to the selected acoustic carrier and detection. A test device for testing the drill string acoustic propagation characteristics was established. Test and analysis of acoustic wave propagation characteristics in drill string which consisting by size differences drill pipe. The results showed that: When the drill size differences exist, the acoustic propagation characteristics in drill string have changed, performance in the number of the pass-band was reduces, some of the pass-band disappearance, and the pass-band width is narrowed, When acoustic waves through the drill string composition by size differences drill pipe, the attenuation is larger than the cyclical one, Less affected by differences in the drill pipe size is the low-frequency pass band acoustic waves, There is a separate arrangement, the effect can be reduced.

The paper describes a mathematical simulation of the acoustic signals. The propagation of signals in waveguides of circular section is simulated. For the analysis a linear model of ultrasound propagation is used. The purpose of mathematical modeling is accuracy increasing of distance measurement by acoustic methods.

Measurements and visualization of acoustic field around an organ pipe are presented. Sound intensity technique was applied for this purpose. Measurements were performed in free field. The organ pipe was activated with a constant air flow, produced by an external compressor, aimed at obtaining long-term steady state responses of generated acoustic signal. Sound energy distribution was measured in a defined fixed grid of points by means of multichannel acoustic vector sensor. For a precise positioning of the acoustic probe the specialized Cartesian robot was applied. Obtained results made it possible to produce visualizations of sound intensity distribution of radiated acoustic energy around the considered organ pipe.

This paper proposes a method of creating acoustic contrast control in an arc-shaped area using a linear loudspeaker array. The boundary of the arc-shaped area is treated as the envelope of the tangent lines that can be formed by manipulating the phase profile of the loudspeakers in the array. When compared with the existing acoustic contrast control method, the proposed method is able to generate sound field inside an arc-shaped area and achieve a trade-off between acoustic uniformity and acoustic contrast. The acoustic contrast created by the proposed method increases while the acoustic uniformity decreases with frequency.

Given data from a shallow-water acoustic communication experiment, the acoustic environmental parameters influencing the sound propagation conditions are estimated, particularly the sound speed p ...

The acoustic center of a reciprocal transducer is defined as the point from which spherical waves seem to be diverging when the transducer is acting as a source. This paper examines various ways of determining the acoustic center of a source, including methods based on deviations from the inverse distance law and methods based on the phase response. The considerations are illustrated by experimental results for condenser microphones.

A microelectromechanical system (MEMS) sound waveguide is considered as a transmission line for RF signals. We analyze a device geometry of a straight one-dimensional microsize silicon rod, where a longitudinal acoustic wave is generated and detected using capacitive transducers. Linear, isotropic, and nondispersive acoustic-wave propagation is assumed. Based on the calculation of the electromechanical impedance, an electrical equivalent model is derived for the acoustic transmission line. A numerical example and a comparison to measured properties of a MEMS-transmission-line resonator shows that the characteristic impedance level of the waveguide is typically high, which causes challenges for matched termination. Solutions to overcome the matching problems are discussed.

This paper reports a method to focus sound in liquid to a desired point using a PDMS-based varifocal acoustic mirror. We used PDMS-air boundary as a sound reflector to concentrate sound. By adjusting the curvature radius of the acoustic mirror, we could change the position where sound was concentrated. We confirmed that our method was able to improve the output of the acoustic sensor for different sound source positions.

This paper presents a model suitable to design and characterize broadband thin film sensors based on piezoelectric polymers. The aim is to describe adequately the sensor behavior, with a reasonable number of parameters and based on well-known physical equations. The mechanical variables are described by an acoustic transmission line. The electrical behavior is described by the quasi-static approximation, given the large difference between the velocities of propagation of the electrical and mechanical disturbances. The line parameters include the effects of the elastic and electrical properties of the material. The model was validated with measurements of a poly(vinylidene flouride) sensor designed for short-pulse detection. The model variables were calculated from the properties of the polymer at frequencies between 100 Hz and 30 MHz and at temperatures between 283 K and 313-K, a relevant range for applications in biology and medicine. The simulations agree very well with the experimental data, predicting satisfactorily the influence of temperature and the dielectric properties of the polymer on the behavior of the sensor. Conversely, the model allowed the calculation of the material dielectric properties from the measured response of the sensor, with good agreement with the published values. Fil: González, Martín Germán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentina Fil: Sorichetti, Patricio Aníbal. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentina Fil: Cardozo Santiago, Gustavo David. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentina

Since the mid 1990s, acoustics research has been undertaken relating to the sound zone problem—using loudspeakers to deliver a region of high sound pressure while simultaneously creating an area where the sound is suppressed—in order to facilitate independent listening within the same acoustic enclosure. The published solutions to the sound zone problem are derived from areas such as wave field synthesis and beamforming. However, the properties of such methods differ and performance tends to be compared against similar approaches. In this study, the suitability of energy focusing, energy cancelation, and synthesis approaches for sound zone reproduction is investigated. Anechoic simulations based on two zones surrounded by a circular array show each of the methods to have a characteristic performance, quantified in terms of acoustic contrast, array control effort and target sound field planarity. Regularization is shown to have a significant effect on the array effort and achieved acoustic contrast, particularly when mismatched conditions are considered between calculation of the source weights and their application to the system.

A class of active acoustic metamaterial (AAM) is presented. The proposed AAM consists of an acoustic transmission line connected in parallel to an array of Helmholtz resonators that are provided with actively controlled boundaries. In this manner, the AAM is in effect an assembly of periodic cells, each of which consists of a Helmholtz resonator connected in parallel to two sections of the transmission line. The two sections meet the Helmholtz resonator at its neck. The local control action at each Helmholtz resonator of a unit cell is generated by using a Fractional Derivative (FD) controller that relies in its operation on the measurement of the flow resulting from the deflection of the resonator boundary and the flow rates inside the two transmission line sections before and after the resonator. Such a single local control action is shown to be capable of controlling the local effective density and elasticity of each unit cell. A lumped-parameter model is developed to model the dynamics and control characteristics of the AAM under different gains and exponents of the FD controller. The model is exercised to demonstrate the ability of the FD controller in generating metamaterials with double negative effective density and elasticity over broad frequency ranges as compared to conventional Proportional and Derivative (PD) controllers. With such capabilities, the development of AAM with FD control action may provide viable means for generating desirable spatial distributions of density and elasticity over broad frequency band using a small number of control actuators.

The term acoustics can mean sound or the science of sound. It is in the latter sense that it is used here. Acoustics thus covers all aspects of sound waves, from low-frequency sound waves to ultrasound waves and beyond to what are simply called acoustic waves. As a means of sensing and actuation, acoustic waves have developed in a number of directions. The most obvious is the use of sound waves in the audible range for the sensing of sound (microphones, hydrophones, dynamic pressure sensors) and for actuation using loudspeakers. Another direction that has contributed greatly to the development of sensors and actuators is the extensive work in sonar - the generation and detection of acoustic energy (including infrasound and ultrasound) in water, initially for military purposes and later for the study of oceans and life in the oceans, and even down to fishing aids. Out of this work has evolved the newer area of ultrasonics, which has found applications in the testing of materials, material processing, ranging, and medicine. The development of surface acoustic wave (SAW) devices has extended the range of ultrasonics well into the gigahertz region and for applications that may not seem directly connected to acoustics, such as oscillators in electronic equipment. SAW devices are important not only in sensing, especially in mass and pressure sensing, but also in a variety of chemical sensors.

A small thermoacoustic sound source device has been built and tested. It uses a flame or electrical heat source at 308 °C to produce sound pressure levels as high as 149 dB SPL at 930 Hz. The heat power to radiated sound power efficiency has been measured to be 2.8%. Sufficient information has been included so that others may construct the device.

The results of calculations performed in the framework of the approximate approach developed by the authors are presented for the diffraction of sound waves by a stiff spheroid in an acoustic waveguide. The scattered sound field is analyzed as a function of the following parameters of the problem: the spheroid dimensions, its position relative to the sound source and the receiver, the vertical profile of sound velocity in the waveguide, and the acoustic parameters of the waveguide bottom.

This paper describes an analytical and experimental investigation which compares the feedforward control of harmonic and random sound transmission into an acoustic cavity. A rectangular enclosure is considered that has five acoustically rigid walls and a flexible plate on the remaining side through which a plane acoustic wave is transmitted into the enclosure. The control systems are designed to reduce the acoustic potential energy inside the enclosure when the incident sound is either harmonic or random. Three control configurations classified by the type of actuators are investigated both theoretically and experimentally. They are (i) use of a single point-force actuator, (ii) use of a single acoustic piston source and (iii) simultaneous use of both a point-force actuator and an acoustic piston source. It is shown that the configuration of both acoustic and structural actuators is desirable for the active control of both harmonic and random sound transmission into a coupled structural–acoustic system whose response is governed by plate and cavity-controlled modes.

Targeted ultrasonic contrast systems are designed to enhance the reflectivity of selected tissues in vivo [Lanza et al., Circulation 94, 3334 (1996)]. In particular, these agents hold promise for the minimally invasive diagnosis and treatment of a wide array of pathologies, most notably tumors, thromboses, and inflamed tissues. In the present study, acoustic microscopy was used to assess the efficacy of a novel, perfluorocarbon based contrast agent to enhance the inherent acoustic reflectivity of biological and synthetic substrates. Data from these experiments were used to postulate a simple model describing the observed enhancements. Frequency averaged reflectivity (30-55 MHz) was shown to increase 7.0 +/- 1.1 dB for nitrocellulose membranes with targeted contrast. Enhancements of 36.0 +/- 2.3 dB and 8.5 +/- 0.9 dB for plasma and whole blood clots, respectively, were measured between 20 and 35 MHz. A proposed acoustic transmission line model predicted the targeted contrast system would increase the acoustic reflectivity of the nitrocellulose membrane, whole blood clot, and fibrin plasma clot by 2.6, 8.0, and 31.8 dB, respectively. These predictions were in reasonable agreement with the experimental results of this paper. In conclusion, acoustic microscopy provides a rapid and sensitive approach for in vitro chracterization, development, and testing of mathematical models of targeted contrast systems. Given the current demand for targeted contrast systems for medical diagnostic and therapeutic use, the use of acoustic microscopy may provide a useful tool in the development of these agents.