Search

This paper proposes a complex boundary wave superposition method with a unique solution of full wavenumber based on the similarity between the acoustic wave superposition method (WSM) and the external excitation response of dynamic systems and combined with the idea that a damping system has a unique solution in dynamic theory. By placing the virtual equivalent source on the virtual boundary of complex space, the conventional WSM acquires damping properties comparable to those of the dynamical system. This approach successfully addresses the non-uniqueness of the solution at the eigenfrequency and is more efficient than the conventional combined layer potential method. The paper presents a comprehensive description of the proposed method, with a focus on theory, modeling, and parameter selection. The effectiveness of this method is evaluated by applying it to two types of acoustic problems, namely, radiation and scattering. The numerical results indicate that this method effectively addresses the non-unique problems encountered in conventional WSM. Furthermore, the proposed method is as accurate and efficient as the conventional WSM. [ABSTRACT FROM AUTHOR]

This document is a publication from Acoustics Australia that provides a collection of abstracts from various articles related to acoustics research. The articles cover a range of topics, including noise control in different environments, acoustic characterization of religious buildings, and virtual augmentation of sound systems. The document also includes information about the Australian Acoustical Society and upcoming conferences. Additionally, there are advertisements for acoustic equipment and information on accessing the full papers online. This document aims to provide library patrons with a concise overview of recent research in the field of acoustics. [Extracted from the article]

Inhomogeneous damping distribution leads to the occurrence of complex modes of structures. Complex modes' vibration and acoustic radiation characteristics are different from real modes. This paper studies the complex modal characteristics of inhomogeneously damped plates for forced vibration. We used the state space method to obtain the complex eigenvalues and eigenvectors of the vibration system and calculated the relationship between modal coordinates and frequency under unit force. The results show that the absolute values of the modal coordinates of two conjugate complex eigenvectors are different, and the structure's vibration is dominated by the eigenvectors corresponding to eigenvalues with positive imaginary parts near natural frequencies. When investigating the structural sound radiation in the vibration mode space, each mode's acoustic radiation is not independent but coupled with each other. The influence of the coupling between complex modes on the calculation results of the acoustic radiation power of the plate is studied in this paper. The results show that the coupling effect between modes cannot be ignored when calculating the acoustic radiation power based on complex modes. Finally, the error of calculating acoustic power using the decoupling approximation instead of the complex mode method is analyzed. [ABSTRACT FROM AUTHOR]

The differences between the acoustic tones generated by impinging jets with laminar and highly-disturbed nozzle-exit boundary layers are investigated. For that, jets at Mach numbers between 0.6 and 1.3 impinging on a flat plate at a distance of 8 nozzle radii from the nozzle exit are computed using large-eddy simulations. The amplitudes of the tones generated by the jets through feedback loops establishing between the nozzle and the plate are found to be significantly affected by the exit turbulent disturbances. In the present study, overall, they are lower for the initially laminar jets than for the initially disturbed ones. The level decrease varies from a few dB up to 15 dB, depending on the tones, which can change the frequencies of the dominant tones and the numbers and azimuthal structures of their associated feedback modes. For Mach numbers 0.75 and 0.8, for instance, the dominant tone frequencies are approximately two times lower for the initially laminar jets than for the other ones, yielding a better agreement with experiments of the literature in the former case. For a Mach number of 1.1, as a second example, the dominant tone is associated with the axisymmetric third feedback mode in the laminar case but with the helical fifth feedback mode in the disturbed case. The differences in the tone amplitude are finally discussed by estimating the power gains of the shear-layer instability waves between the nozzle and the plate using linear stability analysis for the axisymmetric mode. In most cases, at the frequency of a specific tone, the higher the gain, the stronger the acoustic tone. [ABSTRACT FROM AUTHOR]

In this study, we present the first numerical evidence of multiple bifurcation processes occurring in a multi-element model liquid rocket engine before and after the longitudinal thermoacoustic instability regime, as we vary the oxidizer inlet temperature within the range of 400–1400 K. To accurately capture the non-premixed turbulent combustion process, a comprehensive three-dimensional compressible detached eddy algorithm was employed, incorporating a two-step methane/oxygen chemical reaction kinetic mechanism based on OpenFOAM. After validating the numerical framework and achieving grid independence, we focus on (1) investigating the transition routes of system dynamics and (2) analyzing the spatiotemporal evolution of multiple jet combustion flow fields during the multi-bifurcation process. Our results indicate that the system dynamics undergoes two successive bifurcating processes. During the first bifurcation (400 K ≤ T ≤ 800 K), the system dynamics transitions into a full period-1 oscillation through intermittency. In the second bifurcation (1200 K ≤ T ≤ 1400 K), the system shifts from a limit cycle state back to a combustion noise state. The complex coupling mechanism between injectors is further elucidated through frequency spectrum results of radial velocity and temperature near the initial shear layer in the wakes of different injectors, especially the symmetry-breaking response between different injector jets. The analysis of snapshots and flame index also reveals the spatiotemporal evolution of combustion flow fields, specifically highlighting vortex dynamics, heat release, and combustion modes that potentially contribute to thermoacoustic instability. [ABSTRACT FROM AUTHOR]

The vortex-induced vibration of a step cylinder comprising two coaxially arranged cylinders of different diameters with a step between them is simulated numerically. The purpose is to investigate the impact of the interaction between the two cylinders on the vibration and the wake mode of the step cylinder. In this study, the Reynolds number, diameter ratio, and mass ratio are fixed at 150, 0.5, and 2, respectively. Two distinct lock-in regimes are observed, which are named larger cylinder (LC) lock-in regime and smaller cylinder (SC) lock-in regime. In the SC lock-in regime (for reduced velocities between 2.25 and 2.75), the vortex shedding of the SC synchronizes with the vibration, while the vortex shedding of the LC does not. The lift coefficient of the LC has dual frequency components, a lower-frequency and smaller-amplitude component and a higher-frequency and larger-amplitude component associated with vortex shedding and vibration, respectively. In the LC lock-in regime (for reduced velocities between 4 and 7), the vortex shedding of the LC synchronizes with the vibration, while the vortex shedding frequency of the SC increases with increasing reduced velocity, with reduced velocities of 4 and 5 being exceptions, at which the vortex shedding of both the LC and the SC locks in with the vibration frequency. The dual lock-in at reduced velocities of 4 and 5 results in a periodic chainlike wake behind the step where all the vortices from the LC are linked together by N-N loops. At the reduced velocity of 7, a very small difference between the vortex shedding frequency of the SC and twice the vibration frequency causes a low-frequency beating of the lift coefficient. The wake is in the indirect mode with an N-cell in the SC lock-in regime but changes to the direct mode without an N-cell in the LC lock-in regime. It is confirmed that in either of the lock-in regimes, the lock-in cylinder excites the vibration, whereas the non-lock-in cylinder damps the vibration. The damping effect of the non-lock-in cylinder results in a vibration amplitude lower than that in the lock-in regime of a uniform lock-in cylinder. [ABSTRACT FROM AUTHOR]

The airflow generated noise inside a simple expansion chamber muffler is predicted by combining large eddy simulation and Morhing acoustic analogy in the present work, and a good agreement is observed between the prediction and measurement. Research indicates that wall pressure fluctuations are dominated by hydrodynamic pressure fluctuations at the distance of first three pipe diameters in the outlet pipe, and wall pressure fluctuations at the distance of six pipe diameters downstream are dominated by sound pressure fluctuations. The airflow generated noise is mainly attributed to the vortex generated by structural change in the muffler, and one observes strong influences at the longitudinal resonance frequency and antiresonance frequency of the expansion chamber. In addition, the effects of expansion chamber lengths, extensions of inlet/outlet, filleted structure, conical tube, and perforated tube on airflow generated noise are studied. Predicted results show that the filleted structure, conical tube, and perforated tube structure may reduce the airflow generated noise effectively. [ABSTRACT FROM AUTHOR]

Serrations on the owl wings' leading edge (LE) are considered one of the critical characteristics leading to their silent flight. Inspired by this, LE sawtooth was innovatively induced on ultra-thin centrifugal fan blades, and the morphological effects of these teeth on the vortex evolution and aeroacoustic characteristics of the fan were studied using large eddy simulation and the Ffowcs Williams–Hawkings analogy. A single-passage model was adopted to finely simulate the flow mechanism between blades with an acceptable scale. Five sawtooth schemes with relative tooth width λ/b from 7.96% to 29.84%, as well as the prototype, were calculated and analyzed. It is found that the optimal λ/b ranges from 8% to 17.05%, which reduces the overall sound pressure level (SPL) by over 1 dB without impacting the blade pressure and efficiency. These sawteeth inhibited the LE separation, shattered the leading-edge vortex (LEV) into small vortices, and consequently weakened the pressure fluctuations on the blades. However, more prominent teeth (λ/b > 23.8%) intensify the interactions between LEV and other passage vortices, changing the dominant pressure pulsations to high frequency, in turn raising the overall SPL. Too small sawteeth are challenging to process on such ultra-thin blades, so the largest sawtooth among the suggested range was considered the optimal scheme (λ/b = 17.05%) and was manufactured to measure. The results show that the SPL of the fan with LE sawtooth is 0.24–0.57 dB lower than that of the prototype under the same flow rates, even though its rotational speed is increased. [ABSTRACT FROM AUTHOR]

High-frequency signals like vibration and acoustic emission are crucial for condition monitoring, but their high sampling rates challenge data acquisition, especially for online monitoring. Our research developed a novel method for condition identification in undersampled signals using a modified convolutional neural network integrated with a signal enhancement approach. A frequency-domain filtering is applied to suppress similar sidebands and obtain more discriminative features of different conditions, followed by an interpolation-based upsampling in the time domain to restore the signal length and strengthen the low-frequency harmonic information. Enhanced signals are converted into two-dimensional grayscale images for neural network analysis. Tested on bearing datasets and real-world data from regenerative thermal oxidizer lift valve leakage, our method effectively extracts features from low-frequency signals, achieving over 95% fault identification accuracy. • This study introduces a novel 2DCNN-based method for condition identification. It reveals a significant accuracy decline when the sampling frequency falls below the Nyquist rate. • A novel signal enhancement approach is presented, suppressing sidebands to enhance feature discrimination in the frequency domain and bolstering low-frequency harmonic information via cubic interpolation in the time domain. • Tested on the CWRU bearing dataset and real-world regenerative thermal oxidizer data, it achieves over 95% accuracy in condition recognition with undersampled signals. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) sensors in tunable oscillator configuration, with a deposited polymeric layer, were used to investigate the layer's impact on the oscillator's resonant frequency. The SAW oscillators were tuned by means of variable loop amplification. Full-range amplification variation led to a resonant frequency increase of ~1.7 MHz due to the layer's nonlinear reaction. The layer's morphology and location resulted in a specific resonant frequency–amplitude dependence. Five types of layers were used to test the causal linkage between the layers' morphological parameters or positioning and the SAW oscillator's resonant frequency. The frequency variation trend is almost linear, with a complex minute variation. Small amplitude sigmoids occur at certain attenuation values, due to layer acoustic resonances. Multiple sigmoids were linked with layer resonances of different orders. A good correlation between the layer's thickness and resonance position was found. [ABSTRACT FROM AUTHOR]

Recent advancements in transfer learning have revolutionized predictive maintenance, enabling cross-domain generalization for components with varying characteristics and operating under different conditions. While traditional transfer learning approaches require labeled data in both source and target domains, unsupervised transfer learning strives for a more cost-effective alternative for which only labels are available in the source domain. This study investigates adversarial transfer learning between two different sensor modalities: vibration and acoustic. The goal is to enable bearing monitoring using microphones, which are, in general terms, cheaper and easier to deploy than vibration sensors; and without the need to label data in the target domain. The research goal is to identify the operating speed of a bearing testbed. The source domain data correspond to vibration measurements taken from an attached sensor, while the target domain uses a microphone array at distance. Artificial Neural Networks are used as the base architecture. Transferability is assessed with two unsupervised adversarial learning techniques: gradient reversal and deep correlation alignment. Their performance is compared to traditional supervised transfer learning via fine-tuning. Experimental results demonstrate that gradient reversal outperforms deep correlation alignment and is able to achieve results similar to those obtained with supervised transfer learning. These findings highlight the feasibility of speed identification using a microphone array and establish a baseline for future condition monitoring research with such sensors. [ABSTRACT FROM AUTHOR]

Ship-radiated noise separation is critical in both military and economic domains. However, due to the complex underwater environments with multiple noise sources and reverberation, separating ship-radiated noise poses a significant challenge. Traditionally, underwater acoustic signal separation has employed blind source separation methods based on independent component analysis. Recently, the separation of underwater acoustic signals has been approached as a deep learning problem. This involves learning the features of ship-radiated noise from training data. This paper introduces a deep time-domain network for ship-radiated noise separation by leveraging the power of parallel dilated convolution and group convolution. The separation layer employs parallel dilated convolution operations with varying expansion factors to better extract low-frequency features from the signal envelope while preserving detailed information. Additionally, we use group convolution to reduce the expansion of network size caused by parallel convolution operations, enabling the network to maintain a smaller size and computational complexity while achieving good separation performance. The proposed approach is demonstrated to be superior to the other common networks in the DeepShip dataset through comprehensive comparisons. [ABSTRACT FROM AUTHOR]

Investigating the conveying and mixing characteristics of high‐viscosity fluids in an inclined flow channel under the excitation of acoustic vibration using computational fluid dynamics methods. As the intensity of the acoustic vibration excitation increases, the free surface of the liquid transitions from generating Faraday waves to generating disordered jets. Continued increase in the amplitude leads to the liquid filling most of the vessel space, causing a blockage. However, slowly increasing the amplitude alleviates the blockage phenomenon. When high‐viscosity materials are subjected to high‐intensity acoustic vibration, the flow field is dominated by shear flow, which is accompanied by efficient stretching and folding. Changing the amplitude or frequency alone can cause blockage, and increasing the frequency of vibration excitation alone will not alleviate the blockage. Instead, increasing the amplitude can generate more mixing‐promoting reflux, effectively relieving blockage while maintaining stable conveying capacity. [ABSTRACT FROM AUTHOR]

Bandgaps of phononic crystals dominating the propagation of evanescent waves have received significant attention recently, which can be determined and tuned by the topology of a unit cell. Predicting a band structure and designing topological structures with desirable characteristics have become a research hotspot. In this study, a data-driven deep learning framework is applied to arrive at the prediction of the band structure and the inverse design of topology. A convolutional neural network is trained to predict band structures of phononic crystals. After training a generative adversarial network, the generator is concatenated with the convolutional neural network for inverse design. Meanwhile, a complex band structure of phononic crystals is computed by the periodic spectral finite element method to present the spatial decay of evanescent waves. The topology with the greater spatial attenuation is screened from the ground truth topology and the inversely designed topology. Finally, an optimized topological phononic crystal with an anticipated bandgap is obtained, which has the potential for better acoustic insulation and vibration isolation. [ABSTRACT FROM AUTHOR]

Quantitative imaging technologies for in-situ non-destructive testing (NDT) demand high-resolution, wide-field, and stable metrology capabilities. Moreover, live processing and automation are vital for real-time quality control and inspection. Conventional methods use complex optical setups, resulting in large, immobile systems which can solely operate within controlled environmental conditions due to temporal instabilities, rendering them unsuitable for in-situ measurements of micro-to nano-scale physical phenomena. This article delves into the multiphysics application of lensless digital holography, emphasizing its metrological capacity for various in-situ scenarios, while acknowledging and characterizing the differing constraints imposed by various physical phenomena, both transient and steady-state. The digital reconstruction of holograms is computed in real-time, and numerical focusing capabilities allow for instantaneous retrieval of the optical phase at various working distances without the need of complex optical setups, making lensless digital holography well-suited for in-situ quantitative imaging under various types of environments. Current NDT capabilities are demonstrated, including high-resolution and real-time reconstructions, simultaneous measurements for comparative metrology, and practical applications ranging from vibrations and acoustics to thermo-mechanics. Furthermore, methodologies to enhance overall metrology capabilities are exploited, addressing the study of existing physical phenomena, thereby expanding the applicability of holographic techniques across diverse industrial sectors. [ABSTRACT FROM AUTHOR]

A single type of sensor is susceptible to interference and limited degradation information can be extracted. Therefore, a multi-information fusion-based bearing remaining useful life prediction method using the dual-channel convolutional neural network (DCCNN) and the gated recurrent unit (GRU) is proposed. Firstly, vibration sensors are utilized as a basis for signal collection, while acoustic emission sensors are introduced as a complement to obtain more comprehensive degradation information. Secondly, the time domain, frequency domain and time-frequency domain features of the vibration signal and acoustic emission signal were extracted respectively to construct a comprehensive bearing degradation feature set. Third, multiple evaluation indicators are used to comprehensively evaluate the degradation features, and effective degradation features that are highly related to bearing degradation are selected for feature fusion. Subsequently, the DCCNN-GRU model was established, which captures and comprehensively utilizes different degradation feature information in each channel through the DCCNN network structure, and employs GRU to process the time relationships and dependencies in sequence data to solves the vanishing gradient problem. Finally, an experimental bearing test bench was constructed to collect data, and this data was used to experimentally validated the model and compared with other methods to demonstrate its feasibility and effectiveness. [ABSTRACT FROM AUTHOR]

Magnesium foam is a promising material in industry and medicine due to its low density, high damping properties, ability to absorb acoustic and electromagnetic vibrations, and biocompatibility with the human body. The methods developed for producing products from porous magnesium by filtering the liquid melt through soluble granules ensure the production of porous magnesium with a pore size of at least 4 mm. To reduce the pore size by increasing the fluidity and fillability of the granular filling during the production of porous magnesium, vibration treatment of the melt during pouring has been proposed. The conducted studies have shown that vibration treatment allows increasing the fluidity of the Mg90 magnesium melt. In addition, a refinement of the magnesium structure and an increase in hardness are observed. Vibration treatment during the pouring and forming of porous magnesium contributes to an increase in the depth of impregnation of the granular filling and creates conditions for producing products from porous magnesium with a pore size of up to 2 mm, a density of 0.55–0.75 g/cm3, and a porosity of 57–68%. [ABSTRACT FROM AUTHOR]

Exact analytical solution of the Navier–Stokes equations, that describes, in the Boussinesq approximation, the flow of an incompressible liquid in the horizontal, plane layer with solid boundaries, rotating about a vertical axis, is presented. The flow of the liquid in this layer is advective and thermoacoustic in nature, and it is due to the constant longitudinal temperature gradient at the boundaries of the layer and to the acoustic wave propagating in it. The length of this wave is assumed to be comparable with the thickness of the layer, and the period of acoustic vibrations of the liquid in it is small compared to the characteristic convection times. Because of this, it is advantageous to define the averaged liquid flow in the layer. The properties of the solution obtained are investigated and the influence of the Taylor number of the liquid flow on its velocity and temperature profiles at constant Grashof, Reynolds, and Prandtl numbers is determined. [ABSTRACT FROM AUTHOR]

This paper reports a numerical study of a novel methodology for passive suppression of deep cavity noise by means of strategically designed and arrangements of multiple elastic panels and examines its underlying aeroacoustic–structural interaction physics. The study is conducted with a freestream, at Mach number 0.09 and Reynolds number of 4 × 104 based on the cavity length, past a two-dimensional cavity by means of direct aeroacoustic simulation coupled with a panel dynamic solver in monolithic fashion. For each cavity-panel configuration, the fluid-loaded panel natural frequencies are harmonized with the characteristic aeroacoustic processes of the original/modified cavity aeroacoustic feedback loop. This promotes panel aeroacoustic-structural resonance for absorption of feedback flow and acoustic fluctuation energy for achieving less eventual cavity noise. The most effective configuration gives a remarkable noise power reduction by 15 dB from a rigid cavity. Inadvertently, it reduces cavity drag by almost 15%. Simultaneous reduction of both cavity noise and drag is unprecedented among similar attempts in the literature. In-depth spatiotemporal analyses of aeroacoustic–structural interaction results elucidate the intricate interplay between cavity flow, panel vibration responses, and cavity acoustic modes, leading to noise reduction in all cavity-panel configurations studied. Essentially, the vertical panel acts to curtail the efficacy of coupling between growing shear layer and cavity acoustic modes whose sustenance is further impeded by an acoustically induced resonant panel at the cavity bottom. The proposed methodology is confirmed to be feasible yet effective, which holds great potential for fluid-moving applications in which a quiet and energy-efficient cavity configuration is desired. [ABSTRACT FROM AUTHOR]

Turbulent kinetic energy (TKE) is a quantity of primary importance in shock–turbulence interaction (STI). Linear interaction analysis (LIA) serves as a theoretical method to predict the amplification of TKE in STI. LIA is constrained by low-amplitude fluctuations and neglects nonlinear effects. In this paper, we explore the nonlinear amplification of the kinetic energy of fluctuations in the interaction between a vorticity wave and a shock wave that serves as a building block flow for STI. A weakly nonlinear framework (WNLF) is introduced to analyze nonlinear effects in fluctuation kinetic energy (FKE) and identify the dominant physical mechanisms driving its amplification. The theoretical framework is validated through high-accuracy numerical simulations of shock–vorticity wave interactions. The simulation results are compared with the predictions derived from the WNLF for a range of intensities and inclinations of shock-upstream vorticity fluctuations at different Mach numbers, and WNLF is found to successfully scale the numerical data for FKE, thus confirming the validity and applicability of the framework. According to WNLF findings, at lower supersonic Mach numbers, the intermodal interaction between vorticity–vorticity modes is important, whereas the interaction between vorticity and acoustic modes becomes dominant at higher Mach numbers. Using the intermodal interactions, a model based on WNLF is proposed to predict TKE amplification in STI. In comparison to direct numerical simulation, the WNLF based model predicts the TKE amplification for moderate turbulent Mach number and lower supersonic flow Mach numbers. This is a significant improvement over the LIA results available in the literature. [ABSTRACT FROM AUTHOR]

When exposed to an intermediate level of noise, dynamical systems near a Hopf bifurcation can reveal deterministic information about the impending oscillatory mode. Known as the coherence resonance, this phenomenon can be used as a precursor to thermoacoustic instability, which is detrimental to practical combustors. In this study, we apply a spatiotemporal dimensionality reduction method, namely the sparsity-promoting dynamic mode decomposition, to detect coherence resonance in a combustor that exhibits a transition toward thermoacoustic instability. We stochastically excite the annular model gas-turbine combustor and acquire its high-speed image for spatiotemporal analysis. As a result, we find that the impending mode of instability is best identified with a maximum clustering level at the intermediate noise amplitude, implying the existence of coherence resonance. To the best of our knowledge, this is the first time that an image-based method has been used for the detection of coherence resonance, opening new possibilities for the prediction of combustion instability without requiring embedded sensors. [ABSTRACT FROM AUTHOR]

Acoustic measurements were performed using microphone downstream of a 2-D wind turbine blade section in wind tunnel. The experiments have been carried out in both static and oscillatory pitching cases. The latter is usually experienced by the blades in actual circumstances. The microphone was 1.5 chords downstream of the airfoil and the measurements were conducted at three transverse positions, i.e. behind the trailing edge, midway between the trailing edge and the ground and very close to the ground. A CFD simulation of the flowfield has also been conducted using Fluent to correlate the acoustic behavior to the phenomena observed in the flowfield around the blade. The results show that the acoustic noise heard by a listener located on the ground is higher and stronger than that positioned downstream of the trailing edge, showing the ground effect on acoustic noise reverberation. The aerodynamic noise heard by the listener, changes from a treble to bass sound as the angle of attack increases. Beyond stall, the flow is dominated by the vortices shed into wake and the acoustic noises would be at very low frequencies which would result in a bass sound accompanied by structural vibration. In high angle of attack range, such noises can hardly be heard by a normal person but have a very destructive role on blade structure. [ABSTRACT FROM AUTHOR]

The open-frame multi-cabin structure is a common structure for deep-sea underwater vehicles. The numerical method on the vibration and acoustic radiation characteristics of the open-frame multi-cabin structure is of great significance for the prediction and control of underwater vehicles noise radiation. In this work, an engineering calculation method based on dynamic load identification in frequency domain was proposed for the acoustic radiation of structures excited by complex vibration sources. The dynamic model of the open-frame multi-cabin structure was established by using the finite element method (FEM). The vibration source was replaced by an equivalent load model, and the equivalent load was identified through the vibration response and the dynamic model of the structure. The key to the equivalent load identification is the selection of vibration measurement point. A method for selection of vibration measurement point in load identification process is proposed by predicting vibration response of the accelerometer validation channel. The identified loadwas loaded on the structural finite element model as an input to calculate the structural dynamic vibration and acoustic radiation. The equivalent load model was proposed for eccentric motors, and the load identification was verified on the stiffened plate structure. Using this method, the acoustic radiation of the open-frame multi-cabin structure was calculated and compared with experimental results. The results show that the sound pressure level at the excitation frequency of the vibration source and the overall sound pressure level are in good agreement with the experimental results. This research provides a practical engineering calculation method for radiation noise prediction of underwater vehicles. [ABSTRACT FROM AUTHOR]

Passive harmonic mode-locking of a soliton fiber laser locked to optoacoustic resonance (OAR) in the cavity fiber ensures high-frequency laser operation, high pulse stability, and low timing jitter. However, the pulse repetition rate (PRR) of such lasers is limited to ∼1 GHz for standard fibers due to the available acoustic modes. Here, we address these limitations by demonstrating a soliton fiber laser built from standard fiber components and subjected to double harmonic mode-locking (DHML). As an example, the laser adjusted to operate at the 15th harmonic of its cavity matching the OAR at ∼199 MHz could be driven to operate at a high harmonic of this particular OAR frequency, thus reaching ∼12 GHz. This breakthrough is made possible through controllable optoacoustic interactions in a short, 50 cm segment of unjacketed cavity fiber. We propose that the precise alignment of the laser cavity harmonic and fiber acoustic modes leads to a long-lived narrow-band acoustic vibration. This vibration sets the pace for the pulses circulating in the cavity by suppressing modes that do not conform to the Vernier principle. The surviving modes, equally spaced by the OAR frequency, in cooperation with the gain depletion and recovery mechanism, facilitate the formation of stable high-frequency pulse sequences, enabling DHML. In this process, the OAR rather than the laser cavity defines the elementary step for laser PRR tuning. Throughout the entire PRR tuning range, the soliton fiber laser exhibits enhanced stability, demonstrating supermode suppression levels better than ∼40 dB and picosecond pulse timing jitter. [ABSTRACT FROM AUTHOR]

The mechanical characteristics and sliding friction behaviors of AA7075 samples were studied in regard to structural states formed in them by ECAP and depending on the ECAP pass number. In addition, the effect of a counterbody's material on the tribological characteristics of the samples was investigated by the examples of AISI 52100 steel, alumina Al2O3 and silicon nitride Si3N4. Vibration acceleration and acoustic emission signals with parameters such as acoustic emission energy and median frequency were used for characterizing the sliding regimes. The structural state and mechanical properties of the ECAPed AA7075 samples significantly affected their wear behaviors in dry sliding. The counterbody material had a significant influence on the formation of a transfer layer and the subsurface deformation of samples. The dynamic behavior of the tribosystem was studied and the relationship between the sliding parameters, vibrometry and acoustic emission signals was established. [ABSTRACT FROM AUTHOR]

In the process of the intelligent inspection of belt conveyor systems, due to problems such as its long duration, the large number of rollers, and the complex working environment, fault diagnosis by acoustic signals is easily affected by signal coupling interference, which poses a great challenge to selecting denoising methods of signal preprocessing. This paper proposes a novel wavelet threshold denoising algorithm by integrating a new biparameter and trisegment threshold function. Firstly, we elaborate on the mutual influence and optimization process of two adjustment parameters and three wavelet coefficient processing intervals in the BT-WTD (the biparameter and trisegment of wavelet threshold denoising, BT-WTD) denoising model. Subsequently, the advantages of the proposed threshold function are theoretically demonstrated. Finally, the BT-WTD algorithm is applied to denoise the simulation signals and the vibration and acoustic signals collected from the belt conveyor experimental platform. The experimental results indicate that this method's denoising effectiveness surpasses that of traditional threshold function denoising algorithms, effectively addressing the denoising preprocessing of idler roller fault signals under strong noise backgrounds while preserving useful signal features and avoiding signal distortion problems. This research lays the theoretical foundation for the non-contact intelligent fault diagnosis of future inspection robots based on acoustic signals. [ABSTRACT FROM AUTHOR]

This study investigates the characterization of acoustic cavitation in a water-filled, opaque chamber induced by ultrasonic waves at 20 kHz. It examines the effect of different acoustic radiator geometries on cavitation generation across varying electrical power levels. A cost-effective piezoelectric sensor, precisely positioned, quantifies cavitation under assorted power settings. Two acoustic radiator shape configurations, one with holes and another solid, were examined. The piezoelectric sensor demonstrated efficacy, corroborating with existing literature, in measuring acoustic cavitation. This was achieved through the Fast Fourier Transform (FFT) analysis of voltage data, specifically targeting sub-harmonic patterns, thereby providing a robust method for cavitation detection. Results demonstrate that perforated geometries enhance cavitation intensity at lower power levels, while solid shapes predominantly affect cavitation axially, exhibiting decreased activity at minimal power. The findings recommend using two different shape geometries on the acoustic radiator for efficient cavitation detection, highlighting intense cavitation on radial walls and cavitation generation on the bottom. Due to the stochastic nature of cavitation, averaging data is critical. The spatial limitation of the sensor necessitates prioritizing specific areas over complete coverage, with multiple sensors recommended for comprehensive cavitation pattern analysis. [ABSTRACT FROM AUTHOR]

Introduction: As an important part of ship manufacturing, parts are of great significance in the calculation of its reliability level. Methods: To achieve rapid damage detection of ship parts, amethod for measuring the reliability level of ship casting and forging parts based on spectral subtraction and vibration-acoustic principles was proposed. This method improves the spectral subtraction method by adding a percussion vibration signal and time-frequency analysis, and uses the principle of resonance acoustics to complete the construction of the test platform to obtain the natural frequency of the part and achieve nondestructive testing of the part. Results: The results show that using the Fabric data set as the task data set for experiments, the accuracy of the research method is 98.54%; the uncertainty is 5.58; the sensitivity detection is 0.26 µm. In the comparison of the spectrogram of the sound signal after noise reduction, this method has fewer yellow spots remaining on the spectrogram of the noise reduction sound signal, and almost no excess noise remains. In the comparison of modal simulation data of ship parts, the maximum relative error between the simulation data obtained by this method and the natural frequency value obtained from the experimental data is 2.3%, and there is no value exceeding 2.5%, so the error is small. Discussion: The above results show that this method can obtain more accurate natural frequencies of parts, can effectively calculate the reliability level of ship casting and forging parts, and provides a new method reference for the safe operation of ships. [ABSTRACT FROM AUTHOR]

In recent years, worldwide research on fruit and vegetable quality detection technology includes machine vision, spectroscopy, acoustic vibration, tactile sensors, etc. These technologies have also been gradually applied to fruit and vegetable grading and sorting lines in recent years, greatly improving the income of farmers. There have been numerous reviews of these techniques. Most of the published research on fruit and vegetable quality detection technology is still carried out in the laboratory. The emphases have been on quality feature extraction, model establishment and experimental verification. The successful application in the fruit and vegetable sorting production line proves that these studies have high application potential and value, and we look forward to the performance of these sensing technologies in the fruit and vegetable picking field. Therefore, in this paper, based on the future highly automated fruit and vegetable picking mode, we will focus on three kinds of fruit and vegetable quality detection technologies including machine vision, tactile sensor and spectroscopy, to provide some reference for future research. Since there are currently limited cases of detecting quality during the fruit and vegetable picking, experiments performed on prototypes of manipulator, or devices such as Nanocilia sensors, portable spectrometers, etc., which are compact and convenient to mount on manipulator will be reviewed. Several tables and mosaics showing the performance of the three technologies in the detection of fruit and vegetable quality over the past five years have been listed. The performance of each sensing technology was relatively satisfactory in the laboratory in general. However, in the picking scenario, there are still many challenges to be solved. Different from industrial environments, agricultural scenarios are complex and changeable. Fragile and vulnerable agricultural products pose another challenge. The development of portable devices and nanomaterials have become important breakthroughs. Optical and tactile detection methods, as well as the integration of different quality detection methods, are expected to be the trends of research and development. [ABSTRACT FROM AUTHOR]

Advanced aerospace structures are subjected to extremely harsh working environment, including of mechanical, acoustic, thermal, and aerodynamic loads. These combined loads can make the structures exhibit complex response, which has already attracted increasing concern in the design of advanced aerospace structures. To tackle the problem, a finite element model (FEM) by discretizing the theoretical differential equation is established to calculate the dynamic response of thin-walled structures under combined thermal and acoustic loads. The numerical analysis indicates that three types of nonlinear responses of the thin plate under combined thermal-acoustic loads are obtained, and the mechanism of snap-through is revealed through two ways: thermal buckling analysis and thermal modal analysis. which can be used to explain the nonlinear response characteristics. [ABSTRACT FROM AUTHOR]

The emerging field of direct recycling for spent Li-ion batteries offers significant advantages, such as reduced energy expenses and minimized secondary pollution, when compared to traditional pyrometallurgical and hydrometallurgical methods. This is due to its direct utilization of the spent cathodes as raw materials. However, efficient harvesting of spent cathode particles remains a challenge. To address this issue, this technical brief is the first to incorporate resonant acoustic vibration technology (RAV) as an efficient method for stripping cathode powders from spent Li-ion batteries. Our findings indicate that RAV-based techniques can achieve a stripping efficiency of up to 92%. A comparative analysis with conventional stripping methods, such as magnetic stirring, sonication, and curling-uncurling, reveals that RAV coupled with heat treatment provides unparalleled scalability and efficiency, eliminating the need for post-processing. Furthermore, the resulting cathode powders retain their original polycrystalline particle structures, with no impurities, such as carbon black or small aluminum fragments detected. These findings highlight the promise of RAV technology for large-scale recovery of electrode powders and its potential role in direct recycling of spent Li-ion batteries. [ABSTRACT FROM AUTHOR]

Bubbles are widely used in industrial production, biomedical engineering, and many other fields. The analysis of the response of bubble clusters under acoustic waves is significant for the application of bubbles. In this paper, different bubble dynamics models are used to calculate the instantaneous radius of multi-bubbles, and the results corresponding to the different models are compared with those by the finite element method. In addition, the effect of bubble interactions on bubble pulsation is analyzed at different distances, and the effect of incident acoustic direction on the bubble's instantaneous radius is also investigated. The results show that time delays, which have often been neglected in previous work, should be considered except when the bubble spacing is minimal. The results calculated by the finite element method indicate that the attraction and repulsion between bubbles are alternating, which is related to the velocity field between bubbles. Moreover, the suppression or promotion of bubble interactions for bubble pulsation is affected by bubble distance under the same acoustic excitation conditions. Finally, for a bubble cluster with large bubble distances, its total scattered field relating to the incident acoustic wave can be approximated as the interference field of multiple secondary acoustic sources with the same waveform and different phases. If these bubbles are in random motion, the total scattered sound intensity of the bubble cluster is proportional to the number of bubbles. [ABSTRACT FROM AUTHOR]

Thornfish (Terapon jarbua) is a significantly commercial species inhabiting the shallow coastal waters of the Indo-Pacific Ocean. To achieve effective underwater acoustic (UWA) monitoring on the abundance and population dynamics of this species, the comprehensive target strength (TS) characteristics should be investigated and understood. In this study, the Kirchhoff-ray mode (KRM) model was adopted to evaluate and analyze the acoustic TS of T. jarbua and its variations with the sound wave frequency, pitch angle distributions as well as morphological characteristics in the South China Sea. A total of 19 samples were captured and evaluated at four types of frequencies of 38 kHz, 70 kHz, 120 kHz, and 200 kHz. The results demonstrated that the TS of T. jarbua varied with the pitch angle shifts, and the number of secondary TS peaks increased as the increasing frequency accordingly. Two classic pitch angle distributions that included N[−5°, 15°] and N[0°, 10°] were adopted to calculate the average TS of T. jarbua. The fitted TS-L regression formulations and the standard b20 form equations were determined at different pitch angle distributions as well as frequencies. These results could support the accurate and reliable UWA abundance estimation in the South China Sea to facilitate a better understanding of the abundance and population dynamics of T. jarbua. [ABSTRACT FROM AUTHOR]

Thin-walled connection structures are commonly used in the hot-end components of aerospace vehicles. Large deflection nonlinear responses and fatigue failure occur due to their discontinuous mass distribution and prominent cross-sectional changes under the action of complex thermal, aerodynamic, and noise loads. A thermoacoustic fatigue test was carried out to obtain the acoustic and vibration responses and fatigue life changes of the connection structure under heat flow conditions in engineering applications. The high-temperature acoustic fatigue test system of aviation thin-walled structures was used, taking the high-temperature alloy thin-walled plate-load-bearing frame bolted connection structure as the research object. As a result, the vibration response and fatigue life under different thermoacoustic loads were obtained. The contact finite element method was used to simulate the connection pre-tightening force, and the coupled finite element/boundary element method was used to calculate the acoustic and vibration response of the heat flow conditions. The changing rules of the frequency response peak value at the critical point of the thin-walled connection structure under the effects of different temperature fields, fluid fields, and sound fields were obtained through the processing and analysis of the calculation results. Considering the structural vibration fatigue damage mechanism, this study employed an improved rainflow counting method to compute the rainflow circulation matrix (RFM) and rainflow damage matrix (RFD) of the vibration stress time history at critical points within the structure framework. Said method was combined with Miner's linear cumulative damage theory to estimate the fatigue life under various thermal-fluid-acoustic coupled loads. A comprehensive analysis validates the accuracy of the established numerical simulation calculation model in identifying critical connection points within structures subjected to pre-tightening forces. This model effectively characterizes thermal, aerodynamic, and acoustic loads on high-temperature alloy thin-walled-load-bearing frame bolted connection structures. It delineates the relationship between vibration response and fatigue life while assessing the impact of three distinct load parameters. [ABSTRACT FROM AUTHOR]

Purpose: This research numerically investigates the free vibration characteristics and sound radiation responses exhibited by a novel partially biodegradable hybrid composite material. Methods: The composite synthesis involves NaOH-treated animal-based (human hair) and plant-based (Luffa cylindrica) fibers, epoxy resin, and variable proportions of Incense stick ash (ISA) as filler. The synthesis process involved stirring of the individual constituents using an ultrasonicator, and the composites are produced through hand lay-up method. Experimental assessments of densities precede the determination of elastic properties, employing a non-destructive impulse excitation technique (IET). Utilizing the experimentally acquired composite material properties, a higher order finite-element (FE) model is derived and executed within the MATLAB programming environment to compute the free vibration responses. The model is expanded in conjunction with the indirect boundary-element method (IBEM) to achieve coupling between the structure and its surroundings. Sound radiation responses are computed by solving the Helmholtz wave equation. Results: The efficacy of the developed model is evaluated by comparing the outcomes with the data obtained from laboratory experiments. From the parametric investigation, moderate ISA filled (10 wt.%) composites with higher aspect ratio and lower thickness ratio are observed to provide more significant resistance to resonant vibrations and less susceptible to sound radiation. Conclusion: The functional inferences derived from this study will assist in designing imminent hybrid natural fiber composite structures for high-performance engineering applications where minimizing sound radiation into the surrounding medium is a critical design consideration. [ABSTRACT FROM AUTHOR]

Introduction: An effective data-driven bearing fault diagnosis has been moving away from traditional reliance on statistical features toward a focus on raw time-domain analysis. This transition is driven by the need to preserve the critical information contained within the signals. Purpose: In machinery maintenance, a challenge arises when attempting to detect bearing faults under extremely low operating conditions. This is due to the minimal interaction between the rolling element and the fault at such speeds. In response to this, the research aims to tackle the issue of bearing fault detection under these low-speed operating conditions by introducing an advanced fault diagnosis approach. Method: The proposed method involves the utilization of acoustic emission and vibration sensors to capture the vibration behavior of the bearing component at low operating conditions. Importantly, a data fusion strategy is adopted to fuse the raw signals obtained from both sensor types. These fused signals are then directly input into the novel one-dimensional optimized convolutional neural network (1D-CNN). To further enhance the model's performance, a differential evolution algorithm is leveraged for the optimization of its hyperparameters. To validate the effectiveness of the approach, a preliminary analysis is initially conducted using the CWRU dataset, comparing the diagnosis accuracy of the proposed model to existing literature results. Subsequently, the model's performance is evaluated using experimental data collected under low operating speed conditions, spanning a range from 48 rpm (extremely low speed) to 300 rpm (low speed). Result: The results showcase the remarkable capability of the DE-1D-CNN model to diagnose the presence of bearing faults under low-speed conditions, with the highest achieved accuracy standing at an impressive 100%. Through the judicious optimization of hyperparameters, the proposed 1D-CNN model proves its competence in bearing fault diagnosis even when the signal was collected under challenging low-speed operating conditions. [ABSTRACT FROM AUTHOR]

Noise pollution is a major threat to the health and well-being of the entire world; this issue forces researchers to find new sound absorption and insulating material. In this paper, the sound absorption coefficient and vibration damping factor of panels manufactured from Cyperus pangorei rottb and ramie fiber reinforced with epoxy resin are explored. Cyperus pangorei rottb grass fiber and ramie fiber are widely available natural fibers. Cyperus pangorei rottb grass fiber is used in mat manufacturing, whereas ramie is widely used as a fabric. Using both of these fibers, six variant panels using a vacuum resin infusion process (VRIP) were fabricated. The panels were named C, R, CR, RCR-Flat, RCR-Curved, and RCR-Perforated. All the panels were tested for the sound absorption coefficient using an impedance tube with a frequency ranging up to 6300 Hz. Modal analysis was carried out by using the impulse hammer excitation method. A micro X-ray computed tomography (CT) scan was used to study the voids present in the panels. The results were compared among the six variants. The results show that the RCR-curved panel had the highest sound-absorbing coefficient of 0.976 at a frequency range between 4500 Hz to 5000 Hz. These panels also showed better natural frequency and damping factors. The presence of internal voids in these panels enhances sound absorption properties. These panels can be used at higher frequencies. [ABSTRACT FROM AUTHOR]

This study presents a predominantly numerical and theoretical investigation into the balance of tonal and broadband noise due to an isolated propeller in uniform motion. The predicted trends in the balance between tonal and broadband noise radiation with varying blade number and speed of rotation is supported by preliminary experimental measurements. Here, we assume that the dominant noise generation mechanisms are the tones due to steady loading and blade thickness, while the broadband noise is due to boundary layer scattering at the trailing edge. The study also provides a detailed comparison between the tonal and broadband formulations to highlight their similarities and differences. In this paper, we show that the main differences in the behaviour and character of the tonal and broadband spectra and directivities are due to the number of acoustic modes that can be excited. This paper presents a parametric study in which the variation in tonal and broadband noise is investigated as a function of blade tip Mach number (M t ) and blade number (B) whilst maintaining constant solidity and thrust. This study is repeated for three NACA airfoil profiles. It is found that tonal noise dominates at low blade number and low frequency and/or higher tip speeds, while broadband noise is the major contributor at high-frequencies and at high blade number and low tip speeds. The results show a clear distinction between the combinations of M t and B that are dominated by tonal and by broadband noise. These results are interpreted from fundamental principles relating to modal radiation efficiencies. We confirm this trend of balance between tonal and broadband noise with measured noise at different B and M t . The results of this paper will serve as useful guidelines for preliminary propeller design. [ABSTRACT FROM AUTHOR]

This numerical simulation study has been performed to investigate the dynamic characteristics, oscillation characteristics, and sound pressure of direct contact condensation at low steam mass flux. The volume of fluid model, Ffowcs Williams and Hawkings model, and condensation model are used to simulate the acoustic signal, which is produced during the steam injection process. The simulation results are verified by the experimental results to keep the applicability and accuracy of the model. The results show that the acoustic signal is related to the steam flow patterns. The vibration of the bubble volume, caused by the separation of bubbles, is the important factor for the generation of the acoustic signal. When the subcooled temperature is large, the chugging regime appears during the injection process. The sound pressure amplitude of the steam injection process increases significantly, with the increase in subcooled temperature. In the low-frequency region, which is below 10 Hz, the larger the subcooled temperature increases, the greater the sound pressure amplitude becomes. [ABSTRACT FROM AUTHOR]

A computational and theoretical investigation of acoustical and vibrational properties of rigid thin fiberglass material was carried out for different boundary conditions. Fiberglass materials could be applied in industries varying from the aircraft and automotive sectors to the built environment and construction sectors. Plate vibration and acoustic radiation were applied to predict the deflection of the thin fiberglass material and sound radiation efficiency at different locations on its surface, while a study-controlled equation of motion known as the Kirchhoff thin plate theory was applied for a COMSOL simulation of the thin material to determine the deflection of the plate and to obtain stress distribution, velocity contour, displacement, and acoustic pressure at the first resonance of the material. The results of this paper show that thin fiberglass material could be applied to sandwich building elements to form panels for reducing airborne noise and to lessen the sound transmission of structural borne noise, to cover noise barriers to make them more sustainable and weather resistant, to dampen the vibration of machines, and to reduce the structural vibration of buildings. [ABSTRACT FROM AUTHOR]

Non-negative matrix factorization (NMF) has been used in various applications, including local damage detection in rotating machines. Recent studies highlight the limitations of diagnostic techniques in the presence of non-Gaussian noise. The authors examine the impact of non-Gaussianity levels on the extraction of the signal of interest (SOI). The simple additive model of the signal is proposed: SOI and non-Gaussian noise. As a model of the random component, i.e., noise, a heavy-tailed α -stable distribution with two important parameters (σ and α) was proposed. If SOI is masked by noise (controlled by σ), the influence of non-Gaussianity level (controlled by α) is more critical. We performed an empirical analysis of how these parameters affect SOI extraction effectiveness using NMF. Finally, we applied two NMF algorithms to several (both vibration and acoustic) signals from a machine with faulty bearings at different levels of non-Gaussian disturbances and the obtained results align with the simulations. The main conclusion of this study is that NMF is a very powerful tool for analyzing non-Gaussian data and can provide satisfactory results in a wide range of a non-Gaussian noise levels. [ABSTRACT FROM AUTHOR]

Through the advancement of Data Science methodologies, a new era in output-only identification techniques has been inaugurated, driven by the integration of data-driven methodologies within the realm of Structural Health Monitoring (SHM). This study endeavors to introduce a simplified data-driven approach catering to System Identification (SI) and Response Estimation (RE). This is realized through the utilization of a summation of sine functions, fashioned as a model to harmonize with time domain vibration and acoustic responses. The fidelity of the findings is subsequently authenticated through the application of the Frequency Domain Decomposition (FDD) technique. In addition to the identification process, the proposed approach extends its applicability to predicting time domain responses at novel locations. This augmentation is achieved by harnessing an enhanced methodology founded on the principles of the Dynamic Mode Decomposition (DMD) technique. The veracity of these predicted outcomes is underscored through a comparison with measurements recorded at the same locations, alongside concurrent analysis of DMD-derived results. In order to affirm the efficacy of the proposed methodology, a case study involving a building grappling with enigmatic vibration issues is meticulously selected. The findings underscore that the proposed technique not only adeptly discerns unidentified vibrations without resorting to frequency domain transformation techniques, but also facilitates precise estimation of time domain responses. [ABSTRACT FROM AUTHOR]

This document is an editorial piece discussing the increasing interest in philosophy in the field of acoustics, particularly in Germany. The authors highlight the interdisciplinary applicability of philosophical methods and their potential to provide objective and reliable solutions to technical challenges. They also emphasize the importance of ethics and responsibility in acoustics, particularly in relation to issues such as climate change, data privacy, and the impact of sound on human and animal well-being. The authors argue for the development of an ethics of responsibility in acoustics and hope to encourage international discussions and research on the philosophical aspects of the field. [Extracted from the article]

Wound rotor induction machine (WRIM) has been extensively used in different applications such as medium-power wind turbines and traction systems. Since these machines work under harsh and difficult conditions, condition monitoring of such systems is crucial. Different electrical and mechanical signatures of machines were used for electrical and mechanical fault detection in electrical machines such as vibration, acoustic emission, stray flux, and stator current signature. In recent years, stator current signature analysis due to simplicity, cost-effectiveness, and availability has been considered for fault detection process in comparison with previous conventional methods such as acoustic and vibration. In this paper, a high-resolution technique based on the chirp-Z transform is used for rotor asymmetry fault (RAF) detection in induction machines through stator current signature analysis. In this regard, the Teager-Kaiser energy operator (TKEO) technique for demodulation fault characteristic frequency is used as a pre-processing stage to avoid leakage of the supply frequency. The method has better accuracy due to better spectral resolution and resolvability. Furthermore, computational complexity in the proposed method will be reduced in comparison to the previous conventional ones which have used the Fast Fourier transform (FFT). The proposed technique is tested through synthetic and experimental stator current of WRIM in healthy and faulty conditions with different rotational speeds and fault severities. The results show the validity of the proposed method in rotor asymmetry fault detection through the stator current signature of WRIM. [ABSTRACT FROM AUTHOR]

Purpose: This paper studies the low-frequency vibration control mechanism of a finite locally resonant beam with elastic supports. Methods: A theoretical model of the finite locally resonant beam consisting of periodic resonators attached to a beam with elastic support boundaries is established, and the power flow of the elastic supported beam is calculated by the modal superposition and harmonic-balance methods. In addition, the study investigates the influence of the periodic number of resonators on the isolation performance of the elastic supported beam, and the difference between local resonance and anti-resonance is determined. Finally, the equivalent Young's modulus of the locally resonant beam is obtained using the parameter inversion method. Results: The periodic number of resonators can affect the bandgap characteristics, and the anti-resonance of the resonators dominates the attenuation performance when the number of resonators is not sufficient to form a locally resonant bandgap. The bandgap created by the local resonance has a wider frequency range than the anti-resonance, and the periodic resonators will change the equivalent Young's modulus of the beam in a pattern consistent with the bandgap. Conclusion: It is shown that the periodicity of the resonators has a significant effect on the low-frequency bandgap characteristics and equivalent parameters of the elastic supported beam. [ABSTRACT FROM AUTHOR]

Photoacoustic imaging systems offer a platform with high resolution to explore body tissues, food, and artwork. On the other hand, plasmonics constitutes a source of resonant heating and thermal expansion to generate acoustic waves. However, its associated techniques are seriously limited to laser penetration and nonspecific hyperthermia in the sample. To address this issue, the present work adopts a paradigm shift in photoacoustics. By simulating microparticles made of random composites, the calculated pressure can be made similar or superior to that calculated via plasmonic optoacoustics. The improvement is due to a phenomenon called double or triple resonance, which is the excitation of one or both electric and magnetic plasmons within radiofrequency range and the simultaneous excitation of the particle's acoustic mode. Given that electromagnetic pulses are restricted to nanosecond pulse widths and MHz frequencies, the proposed method overcomes the poor penetration in tissues and reduces thermal damage, thereby offering a noninvasive technique of theragnosis. Moreover, the resonant pressure obtained lasts longer than with conventional photoacoustic pressure, providing a central feature to enhance detection. To fully comprehend the multi-resonance framework, we develop a complete photoacoustic solution. The proposed approach could pave the way to thermoacoustic imaging and manipulation methods for sensitive materials and tissues with micrometer resolution. [ABSTRACT FROM AUTHOR]