Sound Field Distribution Research Articles

Theoretical analysis and experiment verification in improvement of the new micro contour mode ultrasound transducer

Commercialized micro ultrasonic transducer generally adopts thickness mode to produce ultrasound radiation of thickness direction. The miniaturization of low-frequency transducer is a problem due to frequency inversely proportional to thickness of transducer. A new micro contour mode ultrasound transducer is proposed for satisfying miniaturization design. Theory analysis, FEM analysis and experimental investigation are carried out to verify the principle and improve the sound field distribution of contour mode transducer. Three kinds of contour transducers with width 300 μm, 600 μm, and 900 μm are fabricated and the reflecting house is added to improve lateral resolution. The performance is evaluated by electrical impedance, pulse-echo response tests and B-mode imaging tests with a 25 µm tungsten wire phantom. The corresponding experiment result of center frequency, −6 dB bandwidth and sensitivity are 4.1 MHz@37 %@4.5Vpp, 2.5 MHz@37 %@3.4Vpp, and 1.8 MHz@29 %@2.0Vpp respectively. Wire phantom imaging showed the lateral resolution has been markedly promoted with reflecting house. Compared with traditional thickness mode transducer, the proposed transducer can achieve smaller size with simplifying fabricated structure. It has a good application prospect in the fields of intervention image and therapy.

Analytical modelling techniques for efficient broadband noise prediction of high-speed trains

Analytical modelling techniques are presented for broadband noise prediction of high-speed trains. For interior noise problems, train body structures are modelled exactly by the dynamic stiffness method (DSM); whereas the interior acoustic cavities of the train body are modelled by the SDSM where the boundary conditions are described by modified Fourier series with a rapid convergence rate. Finally, the vibro-acoustic coupling model of the train body structures is constructed. For exterior noise problems, exterior train noise models are first formed by experimental data considering the Doppler effect; then both the DSM and theoretical attenuation formulas are used to build noise radiation models for different external environment conditions. The performance of the method is evaluated by predicting the interior sound field distribution of typical cross sections of the train body and the external radiated noise in a tunnel, or in an environment where the acoustic barrier or buildings along railways exist. Numerical results are in good agreement with the those obtained by the finite element method. Thus, the proposed methods can achieve broadband noise prediction highly accurately and efficiently, which can also serve as the benchmark for predicting the radiated noise generated by high‐speed trains.

Certification considerations and sound field simulation of civil aircraft cabin passenger address

Abstract In the design of a civil aircraft cabin passenger address system, it is quite necessary and very important to sufficient consider and demonstrate the system design architecture, equipment selection and arrangement to ensure that the system sound quality complies with the requirements of CCAR25.1423(c). In the design phase, the certification considerations of the passenger address system should be researched in advance to comply with CCAR25.1423(c). The cabin sound field distribution and STI of the civil aircraft cabin passenger address system should be simulated through professional tools to predict, demonstrate and judge the sound quality before the system preliminary design review (PDR). In this paper, the certification considerations of passenger address are developed and elaborated from the system equipment arrangement, automatic gain design, and inhibit method of the Larsen effect. Based on two loudspeaker arrangement options, the cabin sound field distribution and STI of the passenger address are simulated to indicate its compliance with CCAR 25.1423(c) from the proposal design level theoretically.

Simulated analysis and experimental validation of sound field distribution regularity for a large-scale non-anechoic harbor pool

The large-scale underwater space, such as large water pool or large-scale harbor pool can provide a good experimental environment for the measurement of the underwater radiated noise of vessel. However, it's not as simple as measuring the sound power of a small machine in the air, the measurement and evaluation of the low frequency mechanical noise and radiated sound power of vessel requires a specific reverberation environment in the large-scale underwater space. Therefore, in this paper, the reverberant sound field characteristics of large-scale underwater space are simulated and calculated by finite element analysis, and experimental measurements are carried out in the large-scale harbor pool. It was found the cut-off frequency of large-scale underwater space depends on the depth of the water pool, and the lower limit frequency depends on the volume of the water pool. The dock door does not reduce the spatial average sound pressure in the reverberation sound field, the floating box platform does not effect on the cut-off frequency but has an effect on the sound energy of the reverberant sound field. It is possible to select the appropriate underwater experimental environment for the measurement and evaluation of different mechanical noise sources. The sound pressure level obtained by calculating the sound source at different locations in the reverberation area is basically the same, and in a 16 × 22 hydrophone arrays, more than 160 array elements are selected, each between 0.25 m and 1 m, a stable sound pressure level can be obtained through spatial averaging. Through experimental measurement verification in the large-scale harbor pool, low-frequency sound sources are emitted from 6 different positions, three hydrophone arrays data are collected, and the measured sound pressure level error is within 1.4 dB. These conclusions are conducive to the actual measurement and evaluation of noise sources of vessel.

Numerical and experimental study on the aerodynamic noise characteristics of 600-km/h high-speed maglev trains

Abstract High-speed maglev trains represent a new mode of transportation; however, their 600-km/h traveling speed causes serious aerodynamic noise problems, with very little research on the aerodynamic noise of such trains. To clarify the aerodynamic noise source and radiation characteristics of high-speed maglev trains, both large eddy simulations and wind tunnel experiments with a 1:8 scale three-train model were conducted to obtain the aerodynamic noise source spectrum and spatial distribution characteristics of the maglev train at different speeds; the contribution of the dipole noise source was also analyzed. The results revealed that the train shape has a significant impact on the frequency distribution of the far-field aerodynamic noise below 1 kHz, with the highest sound power concentrated on the train head, especially in the areas around the track joint and streamlined sections. The surface dipole sound source energy increases linearly with speed and is mainly distributed at the bottom of the train head and tail train body. A short-streamlined train exhibited the highest ratio, especially in the trailing edge area, up to 1.42×1011 dB. The far-field sound pressure level of the short-streamlined maglev train is significantly higher, with a maximum difference of about 10 dB(A). The distribution pattern of far-field sound pressure level is influenced by the train type, reflected in the tail train and wake area. Different frequency intervals have different relationships between the acoustic pressure level and frequency; long-streamlined models may enhance broadband features in the sound field distribution of high-speed maglev trains. These findings could be used to guide the aero-acoustic design of maglev trains with a designed speed of 600 km/h.

FDTD simulation of beamforming shape of a woolly horseshoe bat (Rhinolophus luctus)

Abstract The practicality of the Finite-Difference Time-Domain (FDTD) method is employed to calculate the bat biosonar beamforming shape obtained from the three dimensional (3D) digital model of a woolly horseshoe bat (Rhinolophus luctus), as well as to acquire the nearfield sound pressure distribution of the transient sound field. The multiple sound pressure amplitude can be obtained by Fourier transform of the instantaneous sound pressure in the nearfield FDTD region. According to Kirchhoff integral, the far field normalized directivity pattern is obtained. The single point source is positioned at the center of the computational region, which is surrounded by four different number of perfectly matched layer (PML). The FDTD method is utilized to calculate the absorption of waves by the PML. The trustworthiness of the algorithm is authenticated by the outcomes. It demonstrates that FDTD can produce satisfactory outcomes for biosonar calculations on the woolly horseshoe bat.

Vibration and noise mechanism of a 110 kV transformer under DC bias based on finite element method

Global energy and environmental issues are becoming increasingly problematic, and the vibration and noise problem of 110 kV transformers, which are the most widely distributed, have attracted widespread attention from both inside and outside the industry. DC bias is one of the main contributing factors to vibration noise during the normal operation of transformers. To clarify the vibration and noise mechanism of a 110 kV transformer under a DC bias, a multi-field coupling model of a 110 kV transformer was established using the finite element method. The electromagnetic, vibration, and noise characteristics during the DC bias process were compared and quantified through field circuit coupling in parallel with the power frequency of AC, harmonic, and DC power sources. It was found that a DC bias can cause significant distortions in the magnetic flux density, force, and displacement distributions of the core and winding. The contributions of the DC bias effect to the core and winding are different at Kdc = 0.85. At this point, the core approached saturation, and the increase in the core force and displacement slowed. However, the saturation of the core increased the leakage flux, and the stress and displacement of the winding increased faster. The sound field distribution characteristics of the 110 kV transformer under a DC bias are related to the force characteristics. When the DC bias coefficient was 1.25, the noise sound pressure level reached 73.6 dB.

High-sensitivity trace gas detection based on differential Helmholtz photoacoustic cell with dense spot pattern

A high-sensitivity photoacoustic spectroscopy (PAS) sensor based on differential Helmholtz photoacoustic cell (DHPAC) with dense spot pattern is reported in this paper for the first time. A multi-pass cell based on two concave mirrors was designed to achieve a dense spot pattern, which realized 212 times excitation of incident laser. A finite element analysis was utilized to simulate the sound field distribution and frequency response of the designed DHPAC. An erbium-doped fiber amplifier (EDFA) was employed to amplify the output optical power of the laser to achieve strong excitation. In order to assess the designed sensor's performance, an acetylene (C2H2) detection system was established using a near infrared diode laser with a central wavelength 1530.3 nm. According to experimental results, the differential characteristics of DHPAC was verified. Compared to the sensor without dense spot pattern, the photoacoustic signal with dense spot pattern had a 44.73 times improvement. The minimum detection limit (MDL) of the designed C2H2-PAS sensor can be improved to 5 ppb when the average time of the sensor system is 200 s.

Quantitative Measurement and Evaluation of High-Resolution Ultrasonic Sound Fields using a Novel Automated Ultrasonic Immersion Scanner

Ultrasonic probes are an integral part of the automated ultrasonic non-destructive testing and evaluation (NDT&E) systems to detect and size the defects in a wide range of structural materials in production lines. A complete quantitative assessment of the performance characteristics of an application-specific UT probe is needed to be evaluated on the basis of the international standard DIN EN ISO 22232-2. This requirement of full assessment not only improves the quality assurance of the manufactured probes by evaluating the acceptance criteria but also provides the useful technical information to the end-user to optimize the automated ultrasonic testing on-site. In addition, the evaluation of probe characteristics should be carried periodically throughout their service life. In this work, we developed a novel high-precision ultrasonic immersion scanner to evaluate the full ultrasonic probe characteristics which include the squint angle measurement in three different reference planes (XY, XZ, and YZ), RF-signal and its frequency spectrum at water-steel interface, focal distance, focal range, focal width, focal length and also the angle of beam divergence in different planes of the sound field distribution. In the newly developed UT immersion scanner, for the first time, we successfully integrated the high-precision Hexapod with six axes to achieve a few micrometer (~15 µm) spatial-resolution in the measured sound field patterns and a good angular resolution (~0.05°) in the squint angle measurement. In addition, we used a verified UT instrument in accordance with the standard DIN EN ISO 22232-1 to obtain more accurate amplitude values (±0.5 dB) while scanning a test block. The automated scanning, data acquisition, evaluation, visualization and the automated test report generation are carried based on the standard DIN EN ISO 22232-2. The measured sound beam characteristics of both focused and non-focused application-specific ultrasonic probes with center frequencies ranging from 0.2 - 15 MHz using the pulse-echo technique on a 3 mm half-ball steel reflector are presented. In addition, the measured sound beams of an application-specific 5 MHz multi-element transmit-receive (TR) probe using the 3 mm flat-bottomed-hole (FBH) reflector in a steel reference plate are discussed. Finally, the quantitative analysis of the measured sound field results and the acceptance criteria in accordance with DIN EN ISO 22232-2 are discussed.

An Improved Boundary Element Method for Predicting Half-Space Scattered Noise Combined with Permeable Boundaries

The boundary element method is widely used in practical engineering problems, especially in the field of acoustics. For flow-induced noise, the main target of acoustic calculations is to solve the wave equation with the flow field information. However, the sound field distribution of noncompact structures in half-space is especially complex because of the strong scattering effect, while the object surface boundary integration often brings a large workload and generates numerical singularities. In this paper, an improved boundary element method for predicting the aeroacoustic noise of noncompact structures is proposed, which can consider the characteristic distribution of sound field induced by complex structures in half-space. The smooth permeable boundary surrounding the object is used as the integration boundary, while the scattering effect of the ground boundary is investigated by combining the mirror Green’s function method, and the numerical prediction of aeroacoustic noise is carried out for the dipole source and NACA0012 airfoil in half-space. Numerical results show that the far-field noise obtained by using the permeable surface is consistent with that obtained by integrating the direct object boundary under the influence of ground boundary scattering. The mirror image Green’s function method is able to finely capture the ground scattering effect, which has a significant effect on the sound field as the frequency increases.

Mesoscale Eddy Effects on Vertical Correlation of Sound Field and Array Gain Performance

To solve the problem of array detection performance in environments with mesoscale eddies, this study utilizes the Gaussian eddy model to describe the sound speed structure disturbed by eddies. Through numerical simulations, the corresponding sound field is obtained, and the transmission loss influenced by the eddy is analyzed. Furthermore, to investigate the relation between the array gain and spatial correlation in the eddy environments, the differences in vertical correlation at different positions and their effects on the vertical array gain of conventional beamforming (CBF) are studied. When the source is around the eddy center, the conclusions drawn are as follows: (1) The presence of an eddy changes the turning-point depth and the sound field distribution, significantly affecting the direct sound region and the first convergence zone, while having a minor impact on the first shadow zone. (2) In different eddy-induced environments, the first convergence zone maintains a high vertical correlation, but the vertical correlation of the direct sound region is greatly influenced by the eddy. (3) The array gain of CBF is consistent with the vertical correlation. When the correlation between each element of the sound field is great, the array gain increases with the number of array elements.

Numerical simulation study on noise pollution of the pressurized gas system in pumped storage power station

To Investigate the noise pollution caused by pneumatic whistling during the blowdown operation of a pressurized gas storage system in a pumped storage power station, the flow field and sound field distribution of the gas storage tank under blowdown operation are analyzed in detail through full-channel unsteady numerical simulation of the gas storage tank and its supporting facilities. Subsequently, a comprehensive analysis of the noise issue in the gas cylinder was conducted. While investigating the mechanism of noise generation based on the distribution of noise intensity, the precise location of the noise source was pinpointed, providing a reference for the stability research of the exhaust pressurized water system.

Study of the acoustic scattering characteristics of a rigid sphere in a vortex acoustic field

This paper investigates the scattering sound field of a rigid sphere positioned in a vortex beam generated by a phase-modulated circular transducer array. The effects of the dimensionless parameter ka, the number of array elements, the topological charge, the radius of the transducer array, the distance between the array and the sphere, and its offset position on the scattering sound field distribution of a sphere are studied. Simulation results show that as the ka increases, the incident wave intensity and the scattering sound field of a rigid sphere increase, and the angle between the two main lobes decreases. Once ka is determined, the number of the array elements has no effect on the scattering pattern. However, the topological charge of the vortex beam has greater effect on the scattering sound field. As the topological charge increases, the incident wave intensity decreases, but the angle between two main lobes of the scattering field increases. The radius of the array has an effect on the intensity of the scattering field and the larger the radius, the larger the area of low intensity radiation between the two main lobes. In addition, the distance between the sphere and the array has a weak effect on the scattering pattern when it exceeds a certain value. For an off-axis sphere, the scattering pattern becomes more complex as the topological charge changes. These results can be used to adjust the constituent factors of the transducer array and to investigate the advantages of the vortex beam for underwater target detection.

Mechanism analysis and optimal design of sound-absorbing metastructure constructed by slit-embedded Helmholtz resonators

<sec>Low-frequency noise has always been a thorny problem in the field of noise control. In recent years, the development of sound-absorbing metastructures has provided new ideas for controlling low-frequency noise. In this work, we propose a low-frequency sound-absorbing metastructure constructed by Helmholtz resonators with embedded slit. Analytical and numerical models are established to analyze the sound absorption performance and mechanism of the proposed sound-absorbing metastructure, and optimization design is conducted to achieve low-frequency wideband absorption performance. The analytical modeling method and the performance of the proposed sound-absorbing metastructure are also experimentally verified. The main conclusions are summarized as follows.</sec><sec>1) By using transfer matrix method and finite element method, analytical and numerical models for calculating sound absorption coefficient are established. It is shown that analytical predictions are in good agreement with numerical calculations. It is demonstrated that a typical design of a 30-mm-thick single-cell metastructure can achieve a sound absorption coefficient of 0.88 at 404 Hz. Typical designs of two-cell parallel structure and the four-cell parallel structure (both with a thickness of 50 mm) can achieve two and four nearly perfect low-frequency sound absorption peaks in a frequency band of 200–400 Hz, respectively.</sec><sec>2) The low-frequency sound absorption mechanisms of the proposed metastructures are explained from four aspects: simplified equivalent model parameters, normalized acoustic impedance, complex-plane zero/pole distribution, and sound pressure cloud image and particle velocity field distribution. It is demonstrated that the main sound absorption mechanism is related to the thermal viscous loss of sound waves, caused by the inner wall of embedded slit.</sec><sec>3) The design for broadband low-frequency absorption performance is optimized by using differential evolution optimization algorithm. An optimized parallel-multi-cell coupled metastructure with multiple perfect sound absorption peaks below 500 Hz is realized. For a thickness of 90 mm, the sound absorption coefficient curve of an optimized metastructure exhibits 8 almost perfect sound absorption peaks and an average sound absorption coefficient of 0.86 in a frequency range of 170－380 Hz.</sec><sec>4) Experimental samples are fabricated to test sound absorption. Experimental results are basically consistent with the analytical predictions. The results from analytical model, numerical calculations and experimental measurements are mutually verified.</sec><sec>In summary, the sound-absorbing metastructures with a thickness of sub-wavelength, proposed in this work, exhibit outstanding sound absorption performance at low frequencies. We demonstrate that they are suitable for low frequency broadband sound absorption below 500 Hz. Owing to their thin thickness and relatively simple construction, they have broad application prospects in practical noise control engineering.</sec>

Dipole-like interface states in quasi-periodic elastic waveguide based on Fibonacci sequences

Abstract This paper investigates the dipole-like interface states in a quasi-periodic elastic waveguide structured according to Fibonacci sequences. The dipole-like distribution arises from the interaction of different transverse modes within the waveguide. Specifically, the non-Bragg bandgap resulting from the interaction between distinct transverse modes exhibits a stronger inhibitory effect compared to the traditional Bragg bandgap. Furthermore, our simulations reveal a notable sound field distribution on the surface of the waveguide, displaying two diametrically opposite regions with maximum sound pressures. This structure, characterized by a high Q factor, provides valuable insights into designing elastic wave applications such as filtering and wave enhancement.

Study on bandgap extension and defect states of hybrid primitive structure phononic crystals

Based on the two-dimensional square lattice phononic crystal of the steel-gas system, a hybrid primitive phononic crystal is constructed by replacing the single-cylinder primitive with a tangent double-cylinders primitive structure and inserting the tangent double-cylinders primitive in the center of the lattice. The plane wave expansion method is used to calculate the band structure according to the variation of the extremal positions of the band. It is found that compared with the simple single-cylinder primitive lattice structure, the new structure can significantly separate the degenerate states of the band, and obtain a huge bandgap with a width of 5 times the simple single-cylinder lattice at low filling ratios. Its mechanism can be revealed by the inconsistency of the sound pressure field in the boundary direction. Meanwhile, adding the double-cylinders primitive to the center of the simple single-cylinder lattice produces an effect similar to the interstitial impurity defect, which can excite high-quality localized states of defects in the bandgap. The filling ratio of the defect body mainly affects the position of the localized states and the locality of sound pressure, whereas the orientation of the defect body has almost no effect on the distribution of sound field and the position of defect states.

Modular reverse design of acoustic metamaterial and sound barrier engineering applications: High ventilation and broadband sound insulation

A multi-gradient cavity acoustic metamaterial (MCAM) structure and a modular reverse design method (MRDM) that can realize high ventilation and broadband acoustic isolation are proposed. The method controls the deep neural network model of acoustic metamaterials through a particle swarm algorithm, and the optimized multi-gradient cavity acoustic metamaterial structure (OMCAM) can be reverse-designed by inputting only the constraints and the objective function such as the amount of noise reduction. Compared with the finite element method, the computational efficiency can be improved by about 500 times to achieve an optimized design. The acoustic simulation results show that the average noise reduction of the structure is 23.5 dB in the range of 0∼4000 Hz, and a broadband sound attenuation with 38 dB noise reduction is formed in the target frequency band of 500Hz∼2000 Hz. The acoustic experimental results of the 3D-printed structure are in agreement with the simulation results. Compared with the two existing ventilated acoustic metamaterials, the average noise reduction of OMCAM under equal ventilation capacity is improved by 10.6 dB and 17.4 dB, respectively. The sound barrier based on the proposed OMCAM design is implemented on an elevated rail transit line, showing an improvement of 9.4 dB of average noise reduction compared with existing upright railroad sound barriers. The noise reduction mechanism of the OMCAM structure was finally revealed by the sound field distribution in different modes.

Research on the Relationship between Vibration Noise and Magnetic Saturation of Magnetic Saturated Controllable Reactor Based on COMSOL

This article is based on a 2.2 kVar small magnetically saturated controllable reactor (MSCR) prototype and builds a three-dimensional three-field coupling model of its electromagnetic structure acoustics in the finite element simulation software COMSOL. The time-domain sound field distribution of MSCR under electromagnetic force and magnetostrictive effect is obtained through simulation, and DC bias is linearly added. The trend of changes in magnetic saturation and MSCR maximum sound pressure level are obtained, and finally, the relationship curve between MSCR maximum sound pressure level and its magnetic saturation is analyzed, which is similar to the magnetization curve. Taking the half-load working state as the knee point, this study provides a research idea for the design and monitoring of reactors based on the relationship between MSCR acoustics and the working state.

Acoustic propagation simulation of closed cavity with obstacles based on finite volume method

The propagation characteristics of sound in different cavities and cavity tube combinations are different. With reasonable design, sound will be dissipated in it to achieve noise elimination effect.Therefore, it is beneficial to optimize the structure design distribution to explore the sound field distribution inside the mechanical structure, so as to minimize the transmitted sound through the wall.Therefore, this paper mainly discusses the sound field distribution in closed cavity and the influence of obstacles on it, providing theoretical guidance for sound insulation design. Firstly, the advantages and disadvantages of different numerical simulation methods are discussed, and the feasibility of finite volume method in acoustic numerical simulation is expounded by comparing the methods used in commercial software. Secondly, based on the FVM, the influence of the location and number of obstacles in the closed cavity on the sound field distribution is emphatically analyzed. The simulation results show that acoustic waves are easy to overlap near obstacles with reflection boundaries. When the number of obstacles increases, the higher-order natural frequency increases. Therefore, in the internal design of the equipment, different sound absorbing materials can be laid on the internal obstruction to reduce the sound wave reflection.

Estimating the characteristic vibrations of a sound field in a room using coefficient of variation in the power spectrum of a decay-cancelled impulse response

Estimating the characteristic vibration distribution of a room sound field is difficult because the half-power bandwidth of the characteristic vibrations broadens due to room impulse response decay. Therefore, a coefficient of variation in a power spectrum of a decay-cancelled impulse response is proposed for estimating the characteristic vibrations of a room sound field. In the decay-cancelled impulse response, only the decay of the impulse response is cancelled. Cancelling the decay narrows the half-power bandwidth, thus enabling a clearer estimation of the characteristic vibration even in a sound field with a short reverberation time. In this study, sound fields with different characteristic vibration distributions were numerically simulated to investigate whether the coefficient of variation could estimate their difference.