Complex Acoustic Impedance Research Articles

The Kirkwood–Bethe hypothesis for bubble dynamics, cavitation, and underwater explosions

Pressure-driven bubble dynamics is a major topic of current research in fluid dynamics, driven by innovative medical therapies, sonochemistry, material treatments, and geophysical exploration. First proposed in 1942, the Kirkwood–Bethe hypothesis provides a simple means to close the equations that govern pressure-driven bubble dynamics as well as the resulting flow field and acoustic emissions in spherical symmetry. The models derived from the Kirkwood–Bethe hypothesis can be solved using standard numerical integration methods at a fraction of the computational cost required for fully resolved simulations. Here, the theoretical foundation of the Kirkwood–Bethe hypothesis and contemporary models derived from it are gathered and reviewed, as well as generalized to account for spherically symmetric, cylindrically symmetric, and planar one-dimensional domains. In addition, the underpinning assumptions are clarified and new results that scrutinize the predictive capabilities of the Kirkwood–Bethe hypothesis with respect to the complex acoustic impedance experienced by curved acoustic waves and the formation of shock waves are presented. Although the Kirkwood–Bethe hypothesis is built upon simplifying assumptions and lacks some basic acoustic properties, models derived from it are able to provide accurate predictions under the specific conditions associated with pressure-driven bubble dynamics, cavitation, and underwater explosions.

Utilizing Shear Piezoelectricity of Chiral Lead‐Free Metal Halides for Electromechanical Sensing

AbstractChiral hybrid metal halides have emerged as a promising class of piezoelectric materials owing to their ease of synthesis, low acoustic impedance, and solution processibility. However, many known chiral halides crystalize in structures with only shear piezoelectricity which is less facile to be utilized compared with the longitudinal piezoelectricity, largely preventing their practical utility. In addressing this problem, chiral lead‐free S‐MPBiCl5 and R‐MPBiCl5 (MP = 2‐methylpiperazinium) with shear piezoelectricity are synthesized and the thin films orientating along the polarization direction are fabricated. These orientated films, characterized by numerous grains and compact grain boundaries, can effectively facilitate the grain boundary sliding to convert normal stress into shear stress, thus facilely activating the shear piezoelectricity. The resulting devices can accurately identify the position and type of ultrasound sources without the need for a complex acoustic impedance matching layer. Moreover, these devices can successfully sense delicate variations in momentum caused by table tennis balls. The findings open up a new pathway to utilize shear piezoelectricity that is normally considered unuseful of metal halides and other molecular piezoelectrics.

Numerical calculation of the phase of complex acoustic impedance of air in a cylindrical closed volume

Numerical calculation of the phase of complex acoustic impedance of air in a cylindrical closed volume

Numerical calculation of the phase of the complex acoustic impedance of air in a cylindrical closed volume

As a result of primary pressure calibration (by reciprocity technique or by pistonphone method) of LS-type microphones, their corresponding complex sensitivity is determined. However, one of the problems of this procedure is the need to theoretically determine the complex acoustic impedance of air enclosed in a closed volume. As experiments and various theoretical works have shown for almost 100 years of studying the above-mentioned problem, the adiabatic approximation of acoustic oscillations, adopted at the beginning, is not correct. The most signifi cant (in the fi rst approximation) infl uencing factors, due to which the adiabatic approximation alone is not correct, are the heat exchange of air inside a closed volume with the external environment (through the walls of a closed volume) and refl ected waves that appear at high frequencies (as the length of the closed volume and the wavelength of oscillations are compared). Numerical simulation is proposed to study these factors. The numerical algorithm is based on the regularized NavierStokes equations with quasi-gas-dynamic approach, taking into account viscosity, thermal conductivity and compressibility of air. In this paper, the phase of the complex acoustic impedance of air in a closed volume with heat-conducting and heat-insulated walls is determined. The results of the study are relevant both for calibration of measurement microphones at low and infrasound frequencies by the pressure reciprocity technique and the pistonphone method, and for studying acoustic processes in liquid and gaseous media using numerical modeling. Measurement devices that was transmitted the unit of sound pressure in the air from measurement microphones calibrated by the primary method are used, for example, when monitoring noise from various sources (industrial activity, transport),

Correction to: Modulus of Complex Acoustic Impedance of Air in a Cylindrical Closed Volume: Calculation Using Numerical Simulation

Correction to: Modulus of Complex Acoustic Impedance of Air in a Cylindrical Closed Volume: Calculation Using Numerical Simulation

Modulus of Complex Acoustic Impedance of Air in a Cylindrical Closed Volume: Calculation Using Numerical Simulation

Modulus of Complex Acoustic Impedance of Air in a Cylindrical Closed Volume: Calculation Using Numerical Simulation

Modulus of complex acoustic impedance of air in a cylindrical closed volume: calculation using numerical simulation

Modulus of complex acoustic impedance of air in a cylindrical closed volume: calculation using numerical simulation

Acoustic Attenuation Performance of Two-Pass Perforated Hybrid Mufflers with Mean Flow

The one-dimensional (1-D) analytical approach is developed to predict and analyze the acoustic attenuation performance of two-pass perforated hybrid mufflers in the presence of mean flow. The expressions of complex acoustic wavenumber and impedance of long fiber glass wool are presented by using the impedance tube measurement and curve fitting. The 1-D approaches as well as the fitting expressions are validated by comparing the predicted and measured transmission loss of two-pass perforated hybrid mufflers with a different Mach number. Results illustrate that the 1-D predictions agree well with measurements below the plane wave cut-off frequency and deviate in higher frequency range. The influences of geometric parameters including the lengths of extended tubes, perforations on the right bulkhead and the outlet tube, and mean flow on the acoustic attenuation behavior of the hybrid mufflers are examined.

Experimental realization of aqueous double negative metamaterials in near-megahertz range

Ultrasound is strongly attenuated and aberrated by the skull, principally due to the complex structure and acoustic impedance mismatch of skull which generates strong scattering. Analytical models and finite element methods have shown that negative index metamaterials matching skull properties can enable the transmission of US which enhances bidirectional transmission of ultrasonic signal for imaging. However, it is difficult to realize double-negative metamaterials in near-megahertz range experimentally because of the limitation of fabrication and characterization methods. Here we show the experimental realization of waterborne double negative acoustic metamaterials by coupling micrometer-size membrane-based negative density metamaterials with Helmholtz resonator-based negative modulus materials. Numerical simulation and experimental verification consistently exhibit the double negative behavior between 230 kHz and 410 kHz. We demonstrated the feasibility of creating ultrasonic-range metamaterials for non-invasive ultrasound imaging and neuron stimulation.

Verification of complex acoustic mismatch model in sub-THz regime

An acoustic mismatch model is used to describe the reflection and transmission of acoustic waves at interfaces of two materials with mismatched impedances. Acoustic attenuation is typically ignored for calculating acoustic impedance, and the parameters in the acoustic mismatch model are thus all real numbers instead of complex numbers. However, acoustic attenuation up to the THz regime is significant. The validity and potential applications of the complex acoustic mismatch model have not been investigated in the sub-THz regime. We report the verification experiments of this model in a complex form. We experimentally measured the amplitude and phase of subpicosecond acoustic pulses, reflected from the interface of GaN and silica. Based on the acoustic mismatch model, the frequency dependence of complex acoustic impedance of silica, which includes the information of sound velocity and attenuation, was experimentally obtained in the sub-THz regime. The acoustic properties of silica were compared with the conventional method, which analyzes the acoustic pulses traveling inside the same silica film. Agreement of sound velocity from two methods was confirmed. The attenuations of the silica film, obtained through using the acoustic mismatch model to analyze the reflected acoustic pulses from silica, were validated by a typical method up to 0.3 THz. This work demonstrates potential applications for characterizing the sub-THz acoustic properties of thick and highly damped materials, which could be challenging by using conventional methods.

A fast automatic multichannel blind seismic inversion for high-resolution impedance recovery

The inversion of seismic reflection data for acoustic impedance (AI) is a common and accepted method for the interpretation of poststack seismic data. The original mathematical problem is nonlinear due to the nonlinearity of relation between the AI and the earth reflectivity series and also the insufficiency of information about the source wavelet. Furthermore, the problem is ill posed due to the lack of low and high frequencies in the data. We have developed a multichannel blind inversion and solved it for obtaining the AI model and the wavelet directly from seismic reflection data. We found a solution to the overall problem by alternating between two subproblems, corresponding to the AI and wavelet recovery. Having an estimation of the wavelet, the algorithm directly inverts multichannel data for a high-resolution AI model, having blocky structures in the sense of total variation (TV) regularization, while satisfying a priori low-frequency information. The advantages of the split Bregman technique and the discrete cosine transform are used to build a fast and efficient algorithm for solving the nonlinear impedance inversion with TV regularization. Having an estimate of the AI model, the wavelet is updated by restricting it to have a sparse representation in a wavelet transformation domain while predicting the observed data. Numerical tests using simulated 2D data obtained from the benchmark Marmousi model and also 2D field data confirm that the proposed algorithm stably generates accurate estimates of complex AI models and complicated wavelets, simultaneously.

Mathematical justification of the acoustic method for measuring the impedance of the respiratory tract.

A new method for measuring a complex frequency-dependent acoustic impedance of the respiratory tract based on two-microphone method was developed. The measuring device consists of a waveguide connected through a mouthpiece to the patient's mouth. A sound field with a frequency range from 5 to 100 Hz is created in the waveguide. The impedance of the respiratory tract is determined at free respiration of the patient in the set frequency range; the duration of examination does not exceed 15 s. The criteria for the recognition of respiratory tract pathologies are proposed.

The effect of subglottal acoustics on vocal fold vibration

Acoustic pressures above and below the vocal folds produce a push-pull action on the vocal folds which can either help or hinder vocal fold vibration. The key variable is acoustic reactance, the energy-storage part of the complex acoustic impedance. For the subglottal airway, inertive (positive) reactance does not help vocal fold vibration, but helps to skew the glottal airflow waveform for high frequency harmonic excitation. Compliant (negative) reactance, on the contrary, helps vocal fold vibration but does not skew the waveform. Thus, the benefit of subglottal reactance is mixed. For supraglottal reactance, the benefit is additive. Inertive supraglottal reactance helps vocal fold vibration and skews the waveform, whereas compliant supraglottal reactance does neither. The effects will be demonstrated with source-filter interactive simulation.

Thermal Boundary Resistance between GaN and Cubic Ice and THz Acoustic Attenuation Spectrum of Cubic Ice from Complex Acoustic Impedance Measurements

A phonon nanoscopy method, based on the picosecond ultrasonics technique, capable of studying the complex acoustic reflection coefficient at frequency up to 1 THz is proposed and demonstrated. By measuring the reflection coefficient at the same surface location at the interface between GaN and air, and between GaN and the material to characterize, we get access to the THz amplitude and phase spectra of the acoustic phonon reflection. The retrieval of both these pieces of information then allows the calculation of the attenuation in a wide range of frequency and gives new insight into the Kapitza anomaly. This method is then applied to cubic ice, and the measurements of the elastic properties, the phonon anharmonic decay spectrum up to 1 THz, as well as the measurements of the thermal phonon lifetime at 150 K are all achieved.

Characterizing the ear canal acoustic impedance and reflectance by pole-zero fitting

This study characterizes middle ear complex acoustic reflectance (CAR) and impedance by fitting poles and zeros to real-ear measurements. The goal of this work is to establish a quantitative connection between pole-zero locations and the underlying physical properties of CAR data. Most previous studies have analyzed CAR magnitude; while the magnitude accounts for reflected power, it does not encode latency information. Thus, an analysis that studies the real and imaginary parts of the data together, being more general, should be more powerful. Pole-zero fitting of CAR data is examined using data compiled from various studies, dating back to Voss and Allen (1994). Recent CAR measurements were taken using the Mimosa Acoustics HearID system, which makes complex acoustic impedance and reflectance measurements in the ear canal over a 0.2–6.0 [kHz] frequency range. Pole-zero fits to measurements over this range are achieved with an average RMS relative error of less than 3% with 12 poles. Factoring the reflectance fit into its all-pass and minimum-phase components estimates the effect of the residual ear canal, allowing for comparison of the eardrum impedance and admittance across measurements. It was found that individual CAR magnitude variations for normal middle ears in the 1–4 [kHz] range often give rise to closely-placed pole-zero pairs, and that the locations of the poles and zeros in the s-plane may systematically differ between normal and pathological middle ears. This study establishes a methodology for examining the physical and mathematical properties of CAR using a concise parametric model. Pole-zero modeling accurately parameterizes CAR data, providing a foundation for detection and identification of middle ear pathologies.This article is part of a Special Issue entitled “MEMRO 2012”.

Acoustic impedance measurements of pulse tube refrigerators

Complex acoustic impedance is determined in a prototype refrigerator that can mimic orifice-type, inertance-type, and double inlet-type pulse tube refrigerators from simultaneous measurements of pressure and velocity oscillations at the cold end. The impedance measurements revealed the means by which the oscillatory flow condition in the basic pulse tube refrigerator is improved by additional components such as a valve and a tank. The working mechanism of pulse tube refrigerators is explained based on an electrical circuit analogy.

Reproducibility experiments on measuring acoustical properties of rigid-frame porous media (round-robin tests)

This paper reports the results of reproducibility experiments on the interlaboratory characterization of the acoustical properties of three types of consolidated porous media: granulated porous rubber, reticulated foam, and fiberglass. The measurements are conducted in several independent laboratories in Europe and North America. The studied acoustical characteristics are the surface complex acoustic impedance at normal incidence and plane wave absorption coefficient which are determined using the standard impedance tube method. The paper provides detailed procedures related to sample preparation and installation and it discusses the dispersion in the acoustical material property observed between individual material samples and laboratories. The importance of the boundary conditions, homogeneity of the porous material structure, and stability of the adopted signal processing method are highlighted.

Finite-difference modeling of the piano

The construction of a complete computational model of the piano is described. This model treats the three major subsystems of the instrument: the hammers and strings, the soundboard, and the air (the sound radiation). Hammer nonlinearities and hysteresis are included, along with realistic stiff strings with frequency-dependent damping, following the work of Chaigne and Askenfelt. [Chaigne and A. Askenfelt, ‘‘Numerical simulations of piano strings. I. A physical model for a struck string using finite difference methods,’’ J. Acoust. Soc. Am. 95, 1112–118 (1994); A. Chaigne, J. Acoust. 5, 181 (1992)]. The strings are coupled to a soundboard model that includes the added thickness and stiffness of ribs and bridges. The vibrating soundboard drives the room air, with walls modeled through a complex acoustic impedance following Botteldooren. [D. Botteldooren, ‘‘Acoustical finite-difference time-domain simulation in a quasi-Cartesian grid,’’ J. Acoust. Soc. Am. 95 2313–2319 (1994); 98, 3302 (1995)]. All of the calculations take a finite difference approach, producing a time domain computation. Calculated tones are presented and future directions discussed. [Work supported in part by NSF grant PHY-9988562.]

A three-dimensional finite element approach for predicting the transmission loss in mufflers and silencers with no mean flow

A three-dimensional finite element method has been implemented to predict the transmission loss of a packed muffler and a parallel baffle silencer for a given frequency range. Iso-parametric quadratic tetrahedral elements have been chosen due to their flexibility and accuracy in modeling geometries with curved surfaces. For accurate physical representation, perforated plates are modeled with complex acoustic impedance while absorption linings are modeled as a bulk media with a complex speed of sound and mean density. Domain decomposition and parallel processing techniques are applied to address the high computational and memory requirements. The comparison of the computationally predicted and the experimentally measured transmission loss shows a good agreement.

Study of layer-by-layer self-assembled viscoelastic films on thickness-shear mode resonator surfaces.

We describe quartz crystal electroacoustic admittance studies in thickness shear mode resonators loaded with self-assembled multilayers composed of alternate layers of glucose oxidase (GOx) and poly(allylamine) covalently attached to [Os(bpy)2ClPyCOH]- , (PAH-Os), deposited on a 3-mercaptopropanesulfonic acid (MPS)-modified gold on the quartz crystal. The complex acoustic impedance parameters, R(S) and X(LS) of a lumped-element Butterworth-Van Dyke (BVD) resonator have been determined for organized thin films of different thickness obtained by varying the number of enzyme layers, n, in (PAH-Os)n(GOx)n structures. The ellipsometric film thickness and mass for dry enzyme multilayer films and films in contact with water were evaluated, and the average film density was estimated. By combination of the estimated film thickness and density, the expression for the surface mechanical impedance of the lumped-element modified resonator (Granstaff and Martin model), and the liquid density and viscosity, we simulate the layer-by-layer film growth on the basis of the measured electroacoustic impedance. The complex impedance X(LS) and R(S) increase with film thickness and the enzyme films can be regarded as acoustically thin in the reduced state for films thinner than 600 nm. We have also measured electroacoustic parameters for PAH-Os/GOx self-assembled multilayers under electrochemical perturbation in a buffer electrolytic solution. The electrostatically self-assembled multilayers behaved as lossy viscoelastic films at 10 MHz with G'f and G''f on the order of 10(6) Pa. The films became viscoelastic upon oxidation to Os(III), resulting in an increase of R(S) and X(LS) in the oxidized state with the number of (PAH-Os)(GOx) bilayers due to film swelling and an increase in the shear moduli during oxidation.