Sound Pressure Distribution Research Articles

Super-resolution in sound field recording and reproduction based on sparse representation

Sound field recording and reproduction enables us to construct more realistic audio systems. In practical systems, sound pressure is obtained with microphones in a recording area, and then the sound field is reproduced with loudspeakers in a target area. Therefore, a signal conversion algorithm for obtaining the driving signals of the loudspeakers from the signals received by the microphones is necessary. Most of the current methods are based on the sound field analysis and synthesis in the spatial frequency domain. Although these methods make it possible for stable and efficient signal conversion, artifacts originating from spatial aliasing notably occur, which depends on the intervals of microphones and loudspeakers. We have proposed a signal conversion method based on sparse sound field decomposition, which enables sound field recording and reproduction above the spatial Nyquist frequency. By using sparse decomposition algorithms, the sound pressure distribution can be represented using a small number of fundamental solutions of the Helmholtz equation, such as Green's functions. Group sparse signal models are also required for accurate and robust decomposition. In this presentation, we reports on comparisons between several group sparse signal models and decomposition algorithms as well as their relation to reproduction performances.

Applying the cellular automaton model in speech production process simulation

This study investigates the dynamic simulation of the speech production process. When an utterance occurs, the sound pressure and the particle velocity distribution of the vocal tract space changes from word to word. The author examined and visualized this change to illustrate how it happens. The author used the cellular automata as a model to calculate the acoustic characteristics of the vocal tract in each region. This study takes a different approach from the traditional z-transform to the cellular automata to calculate the dynamic sound pressure at each site of the vocal tract space. To simplify the calculation, an acoustic cylindrical tube model was used. Dynamic calculations were made even more manageable by changing the physical model from a three-dimensional to a one-dimensional cellular automaton model. Consequently, this study demonstrates that the relationship between the words and the sound pressure distribution can be examined dynamically using the cellular automata model.

Non-contact acoustic manipulation in microchannel

Noncontact micromanipulation technique is needed in micromachine technology, biotechnology, and other fields. In the present paper, a standing wave field is generated in a microchannel and a geometric space, and it is possible to trap small objects at nodes of the sound pressure distribution in the medium. A microchannel and a geometric space were made at the center of a glass plate of 50 mm x 50 mm x 5 mm. In the experiment, when the liquid water containing alumina particles was injected into the microchannel on glass plate irradiated by ultrasound, the particles flowed along several layers in the microchannel. In the geometric space, the particles were trapped in the sound pressure nodes of the standing wave field. By changing the frequency, the geometric pattern of particles aggregation interestingly changed. When the geometric space is a triangular space, the particle moved toward the top from the base of the triangle. When the microchannel is branched at the half circular geometric space, it was able...

Sound source separation using image signal processing based on sparsity of sound field

Microphone arrays have been used to separate sound sources to improve speech recognition in a noisy environment. We propose a method using image signal processing to achieve highly accurate sound source separation. The microphone array is 1-m long and consists of eight microphones. Temporal sequences of the sound pressures obtained from the eight microphones are converted into sequences of luminance. These are arranged in parallel in an image, which is referred to as aspatio-temporal sound pressure distribution image. Sparse modeling using L1 regularization (Lasso) is applied to the image for restoring a high-resolution image. The spatial spectrum of the restored image is obtained using a two-dimensional fast Fourier transform (FFT) algorithm. In this spectrum, the angle of a line through the center denotes the arrival direction of sound, and the distance from the center indicates its frequency. By extracting a line from the spectrum, the sound source can be separated. A computational experiment revealed that high-resolution sound field obtained by a 512-microphone array could be restored using the proposed method. Moreover, SNR was improved by 32.1 dB when two sounds arrived 45° apart, indicating sufficient performance to extract a desired sound. [Work supported by JSPS KAKENHI Grant (16K06384).]

A study on calculation method for mechanical impedance of air spring

This paper proposes an approximate analytic method of obtaining the mechanical impedance of air spring. The sound pressure distribution in cylindrical air spring is calculated based on the linear air wave theory. The influences of different boundary conditions on the acoustic pressure field distribution in cylindrical air spring are analysed. A 1-order ordinary differential matrix equation for the state vector of revolutionary shells under internal pressure is derived based on the non-moment theory of elastic thin shell. Referring to the transfer matrix method, a kind of expanded homogeneous capacity high precision integration method is introduced to solve the non-homogeneous matrix differential equation. Combined the solved stress field of shell with the calculated sound pressure field in air spring under the displacement harmonic excitation, the approximate analytical expression of the input and transfer mechanical impedance for the air spring can be achieved. The numerical simulation with the Comsol Multiphysics software verifies the correctness of theoretical analysis result.

Tunable broadband unidirectional acoustic transmission based on a waveguide with phononic crystal

In this paper, a tunable broadband unidirectional acoustic transmission (UAT) device composed of a bended tube and a superlattice with square columns is proposed and numerically investigated by using finite element method. The UAT is realized in the proposed UAT device within two wide frequency ranges. And the effectiveness of the UAT device is demonstrated by analyzing the sound pressure distributions when the acoustic waves are incident from different directions. The unidirectional band gaps can be effectively tuned by mechanically rotating the square columns, which is a highlight of this paper. Besides, a bidirectional acoustic isolation (BAI) device is obtained by placing two superlattices in the bended tube, in which the acoustic waves cannot propagate along any directions. The physical mechanisms of the proposed UAT device and BAI device are simply discussed. The proposed models show potential applications in some areas, such as unidirectional sonic barrier or noise insulation.

Ultrasonic heat transfer enhancement on different structural tubes in LiBr solution

A LiBr absorption refrigeration system that uses solar energy is a promising alternative to traditional air-conditioning systems. However, its overall efficiency is low due to the poor boiling heat transfer of the LiBr solution. This paper investigates the ultrasonic heat transfer enhancement on three different structural tubes (smooth, screwed and finned) in LiBr solution in the sub-cooled boiling regime. The pool boiling heat transfer performance of the LiBr solution is investigated, and the characteristics of the boiling heat transfer, which are driven by the ultrasonic field, are described using bubble dynamics, which are numerically determined by the Rayleigh–Plesset (R–P) equation. The effects of ultrasonic parameters (e.g., frequency, power) on the boiling heat transfer of the three different structural tubes are investigated, and the sound pressure distribution around the tested tubes that is calculated by a two-dimensional numerical model is used to describe the mechanism of the ultrasonic heat transfer enhancement. Additionally, a high-speed camera is used to take images of the bubbles in the structural tubes to help analyze the mechanism.

Noise generation mechanisms for a supersonic jet impinging on an inclined plate

Noise generation mechanisms for a perfectly expanded supersonic Mach number $M=1.8$ turbulent jet impinging on a $45^{\circ }$ inclined plate are investigated for a Reynolds number of $1.6\times 10^{6}$ employing a large-eddy simulation. Excellent comparisons with experimental acoustic far-field measurements and pressure measurements on the impingement plate are obtained. Two local maxima are identified in the far-field overall sound pressure levels in the $75^{\circ }$ and $120^{\circ }$ observer directions, which are associated with different noise generation mechanisms. The peak frequencies in the spectra with Strouhal numbers of $St=0.2$ for $75^{\circ }$ and $St=0.5$ for $120^{\circ }$ match the experimental measurements. The jet-impingement region generates pressure waves that propagate predominantly in the $120^{\circ }$ observer direction. The noise generation in this region is attributed to vortex stretching and tearing during shear-layer impingement, and shock oscillations that are induced by the motion of downstream convected vortical flow structures. The second peak in the overall sound pressure distribution at $75^{\circ }$ is associated with noise sources located in the wall jet. The noise generation in the wall jet is associated with supersonically convecting large-scale coherent flow structures that also interact with tail shocks in the wall jet causing large localized pressure fluctuations. Strongly coherent flow structures are identified by applying proper orthogonal decomposition (POD) to the unsteady flow field. The frequency characteristics of the most energetic POD modes are distinctly different based on which energy norm is chosen. The most energetic entropy-based POD modes contain a peak frequency of approximately $St=0.4{-}0.6$, while the most energetic turbulent kinetic-energy-based POD modes appear to be dominated by lower-frequency content. The causality method, based on Lighthill’s acoustic analogy, is used to link the acoustic noise signature to the relevant physical mechanisms in the source region. A differentiation is made between the application of normalized and non-normalized cross-correlation functions for noise source identification and characterization.

Performance, aeroacoustics and feature extraction of an axial flow fan with abnormal blade angle

The effect of the deviation angle of an abnormal blade Δβ on the performance of an axial fan is investigated using 3D steady simulation. The sound pressure distribution in the time and frequency domains is examined using LES (large eddy simulation) and FW–H (Ffowcs Williams–Hawkings) noise model. The energy features of the sound pressure are extracted using WPD (wavelet packet decomposition) and EMD (empirical mode decomposition). The results show that under the abnormal condition, fan performance is lower than normal value and the noise rises. The main noise sources are concentrated on the leading edge and tip of the suction surface. The aerodynamic noise is generated mainly by low-frequency sound, and the impeller exhibits an obvious broadband sound feature. In the regions outside of the impeller, the wavelet packet energy in the fundamental frequency band under abnormal conditions is much lower than that under the normal condition, and the difference becomes significant with increasing Δβ. The EMD energy features appear as obvious changes in the relative percentages of the intrinsic mode function energies; the energy entropy is closely related to the deviation angle. The characteristics obtained by WPD and EMD provide significant references for detecting the deviation angle in axial flow fans.

Penetration state recognition based on the double-sound-sources characteristic of VPPAW and hidden Markov Model

A series of work is conducted to study the relationship between the welding sound and penetration states in VPPAW (variable polarity plasma arc welding), which are No-keyhole, Keyhole and Cutting Modes. The spatial distribution of sound pressure is measured and the optimal acquisition angle is determined as 150°. The mechanism, based on the special double-sound-sources characteristic of VPPAW, is proposed and demonstrated by a series of phenomena about sound of VPPAW. The sound source structure and sound generating mechanism are quite similar to those of speech. Five features, which are mean amplitude, mean energy, logarithm of energy, standard deviation and kurtosis, are extracted to depict the characteristics of each frame. Half of these feature vectors is employed to train a HMM (Hidden Markov Model) of 5 states, and the rest acts as the test samples. HMM is applied in VPPAW for the first time, and the recognition rate of prediction model, based on HMM, about acoustic signal and penetration states could reach up to 93.23%. The work shows that the acoustic signal of VPPAW is similar to speech to some extent, which establishes the theoretical basis for the application of speech process technology in VPPAW, and it is also practical, especially for HMM.

The acoustical role of vocal tract in the horseshoe bat, Rhinolophus pusillus.

The sound field distribution in the vocal tract with a single sound source in the glottis and the transfer function of the supraglottal vocal tract of the horseshoe bat, Rhinolophus pusillus, have been obtained using the finite-element method (FEM) technique. The models of vocal tracts used for FEM calculation are constructed by tomography scanning. These models are used to set up a finite-element model for calculating the sound field distribution by loading the unit sound source in the glottis. By changing the frequency of the unit sound source, the frequency response was figured out and the acoustic role of vocal tract chambers was examined by obtaining the transfer function and sound pressure distribution before and after filling the chambers using voxels. Sound pressures in the trachea and nostrils are recorded and some analysis of the acoustics of the subglottal and vocal tract was made to find the function of the construction in the vocal tract and subglottal parts. The results show nasal chambers can effectively improve the Q (quality factor) value near the second harmonic, and alternate the sound distribution in the supraglottal part. Whereas the tracheal chambers can reduce the amplitude second harmonic in the subglottal part, its function is like a notch filter which can block the second harmonic component of the back propagation sound under the glottis.

Scattering effect of submarine hull on propeller non-cavitation noise

This paper investigates the non-cavitation noise caused by propeller running in the wake of submarine with the consideration of scattering effect caused by submarine׳s hull. The computation fluid dynamics (CFD) and acoustic analogy method are adopted to predict fluctuating pressure of propeller׳s blade and its underwater noise radiation in time domain, respectively. An effective iteration method which is derived in the time domain from the Helmholtz integral equation is used to solve multi-frequency waves scattering due to obstacles. Moreover, to minimize time interpolation caused numerical errors, the pressure and its derivative at the sound emission time is obtained by summation of Fourier series. It is noted that the time averaging algorithm is used to achieve a convergent result if the solution oscillated in the iteration process. Meanwhile, the developed iteration method is verified and applied to predict propeller noise scattered from submarine’s hull. In accordance with analysis results, it is summarized that (1) the scattering effect of hull on pressure distribution pattern especially at the frequency higher than blade passing frequency (BPF) is proved according to the contour maps of sound pressure distribution of submarine׳s hull and typical detecting planes. (2) The scattering effect of the hull on the total pressure is observable in noise frequency spectrum of field points, where the maximum increment is up to 3dB at BPF, 12.5dB at 2BPF and 20.2dB at 3BPF. (3) The pressure scattered from hull is negligible in near-field of propeller, since the scattering effect surrounding analyzed location of propeller on submarine’s stern is significantly different from the surface ship. This work shows the importance of submarine׳s scattering effect in evaluating the propeller non-cavitation noise.

Numerical and experimental studies of hydraulic noise induced by surface dipole sources in a centrifugal pump

The influences of the four different surface dipole sources in a centrifugal pump on the acoustic calculating accuracy are studied in this paper, by using the CFD combined with the Lighthill acoustic analogy methods. Firstly, the unsteady flow in the pump is solved based on the large eddy simulation method and the pressure pulsations on the four different surfaces are obtained. The four surfaces include the volute surface, the discharge pipe surface, the inner surface of the pump cavity, and the interfaces between the impeller and the stationary parts as well as the outer surface of the impeller. Then, the software Sysnoise is employed to interpolate the pressure fluctuations onto the corresponding surfaces of the acoustic model. The Fast Fourier Transform with a Hanning window is used to analyze the pressure fluctuations and transform them into the surface dipole sources. The direct boundary element method is applied to calculate the noise radiated from the dipole sources. And the predicted sound pressure level is compared with the experimental data. The results show that the pressure fluctuations on the discharge pipe surface and the outer surface of the impeller have little effect on the acoustic simulation results. The pressure pulsations on the inner surface of the pump cavity play an important role in the internal flow and the acoustic simulation. The acoustic calculating error can be reduced by about 7% through considering the effect of the pump cavity. The sound pressure distributions show that the sound pressure level increases with the growing flow rate, with the largest magnitude at the tongue zone.

Simulations of cavity flow noise and turbulent jet noise using a hybrid method

A hybrid method was explored to investigate the generation and near-field radiation of aerodynamic sound from an unsteady turbulent flow over a two-dimensional open cavity and three-dimensional jet flow. A two-dimensional cavity model was established to study the unsteady flow and radiated jet sound. It was revealed that the radiated sound that generated by the boundary layer separation and vortex impact cavity wall intervened in the front of the cavity, and an obvious interference phenomenon appeared. The far-field radiated sound generated by the cavity presented obvious directivity, and the sound pressure in the area located at 45°–135° interval was much higher. Then, the unsteady turbulence jet noises of the elliptical and rectangular nozzles were analyzed. It was revealed that the scale and intensity of the vortexes generated by the elliptical nozzle were larger than those by the rectangular nozzle. The jet noise of the elliptical nozzle is lower than that of the rectangular nozzle. Besides, the sound pressure distributions of the two nozzles presented obvious directivity. The sound pressure in the short-axis direction of the nozzle section was higher than that in the long-axis direction.

Phased array simulation for evaluation of weld in offshore chain

Offshore chain may have the flaws such as the lack of fusion in the weld. The ultrasonic testing (UT) has performed to detect the lack of fusion in the weld. The conventional UT has been performed by the pulse-echo and/or tandem method; the probe is positioned on the straight part with cylindrical surface but has not completely secured the reliability of the flaw detection in the offshore chain. Phased array ultrasonic testing (PAUT) can generate the ultrasonic focused beam and sweep the ultrasonic beam with multiple angles, so it is possible to inspect the wide area on a fixed probe position. Therefore, PAUT can inspect the full area of the weld in the offshore chain as moved with single array probe in a finite area. The phased array probe is positioned off the straight part with the spherical surface. And, the procedure of PAUT and the criteria of the detection and sizing of the flaw are not established. In this study, ultrasonic beam generated with array probe in offshore chain is simulated with CIVA simulation software, and sound pressure distribution is analyzed for establishing the criteria of the flaw sizing.

Distribution of sound pressure around a singing cricket: radiation pattern and asymmetry in the sound field

Male field crickets generate calls to attract distant females through tegminal stridulation: the rubbing together of the overlying right wing which bears a file of cuticular teeth against the underlying left wing which carries a sclerotized scraper. During stridulation, specialized areas of membrane on both wings are set into oscillating vibrations to produce acoustic radiation. The location of females is unknown to the calling males and thus increasing effective signal range in all directions will maximize transmission effectiveness. However, producing an omnidirectional sound field of high sound pressure levels may be problematic due to the mechanical asymmetry found in this sound generation system. Mechanical asymmetry occurs by the right wing coming to partially cover the left wing during the closing stroke phase of stridulation. As such, it is hypothesized that the sound field on the left-wing side of the animal will contain lower sound pressure components than on the right-wing side as a result of this coverage. This hypothesis was tested using a novel method to accurately record a high-resolution, three dimensional mapping of sound pressure levels around restrained Gryllus bimaculatus field crickets singing under pharmacological stimulation. The results indicate that a bilateral asymmetry is present across individuals, with greater amplitude components present in the right-wing side of the animal. Individual variation in sound pressure to either the right- or left-wing side is also observed. However, statistically significant differences in bilateral sound field asymmetry as presented here may not affect signalling in the field.

Modelado de transductores ultrasónicos piezoeléctricos para fisioterapia

Applications of ultrasound are well known in medical and aesthetic skin and subcutaneous fatty tissue mobilization treatments. The basic transducer used consists of a piezoelectric disk adhered to a metal delay line in capsule shape. The capsule design is critical since the two bonded elements have vibration modes which can cause very inefficient designs and vibration distributions very irregular if they are not properly studied and utilized. This must be known to avoid distributions of heat and sound pressure that could be ineffective or harmful.In this paper, using Finite Element Method and laser interferometric vibrational analysis, it has reached a piston-type solution that allows properly implement sound pressure vibration dose.

A radiation emission shielding method for high intensity focus ultrasound probes.

Electromagnetic compatibility (EMC) is a key issue in the design and development of safe and effective medical instruments. The treatment probes of high intensity focused ultrasound (HIFU) systems not only receive and transmit electromagnetic waves, but also radiate ultrasound waves, resulting in electromagnetic coupling. In this paper, an electromagnetic shielding method involving the enclosure of the probe in a copper wire mesh was introduced. First, sound pressure distribution simulations and measurements were performed using a hydrophone in order to evaluate the effects of the wire mesh on the acoustic performance of the HIFU system. The results indicated that the wire mesh did not disturb the normalized sound pressure field. In addition, the attenuation of the maximum pressure in the focal plane was equal to 6.2%. Then, the electronic emission level was tested in a chamber. After the implementation of the wire mesh, the 10-100 MHz frequency band radiation was suppressed, and the HIFU system satisfied the national EMC standards.

Vibration and acoustic responses of composite and sandwich panels under thermal environment

The paper is focused on the vibration and acoustic responses of the sandwich panels constituted of orthotropic materials applied a concentrated harmonic force in a high temperature environment. The natural frequencies together with corresponding modes are obtained under the thermal stresses by applying the piecewise low order shear deformation theory. The critical temperature is derived to prevent the thermal load excess. And the sound pressure distribution is derived by applying the Rayleigh integral. The analytical solution is verified by the numerical simulations. It is observed that the natural frequencies of the sandwich panel decrease with the increment of the temperature. The interchanges of the mode shapes occur because of the material anisotropy. The peaks of vibration and acoustic responses float to the low frequency domain due to the decrement of the natural frequencies. The influences caused by the high temperature environment on the sandwich panels are deeply discussed.

Lattice Boltzmann simulation of acoustic resistance in microchannels

Lattice Boltzmann method (LBM) is utilized to model the acoustic resistance in microchannels at mesoscopic scale in this paper. Sound pressure distribution at different positions are studied. A number of physical parameters, such as the wavelength, channel number, channel width and length are investigated to find their effects on pressure variation. Simulation results are compared with those obtained by traditional methods and demonstrate that the LBM is a helpful approach to study sound attenuation in microchannels at mesoscopic scale. These results have potential application for designing the high-efficiency sound absorbers.