Distribution Of Acoustic Energy Research Articles

Active nonreciprocal acoustic metamaterials using a switching controller.

A class of active acoustic diodes and metamaterials is developed to control the flow and distribution of acoustic energy in acoustic cavities and systems. Such development departs radically from the currently available approaches where the non-reciprocities are generated by hard-wired designs, favoring one transmission direction which is dictated by the arrangement of the hardware and hence it cannot be reversed, or without the presentation of rigorous control theory analysis. The proposed active nonreciprocal acoustic metamaterial (ANAM) cell consists of a one-dimensional acoustic cavity provided with active flexible boundaries. These boundaries are made from piezoelectric bimorphs interacting with the cavity to monitor the pressures of the propagating acoustic waves. The outer layers of the bimorphs provide the necessary control actions by direct application of the appropriate control voltage on each layer or by proper connection of nonlinearly activated shunted networks of switching resistors. The control of the switching is carried out using a Switching Mode Control (SMC) strategy. In this strategy, a lumped-parameter model of the ANAM cell is developed to predict the nonreciprocal characteristics of the cell by proper selection of the slope of the switching surfaces. Numerical examples are presented to demonstrate the merits of the proposed SMC.

Analysis of foldable acoustic arrays from piecewise linear, conformal, and tessellated topologies

Arrays of acoustic sources distributed over the tessellated frameworks of origami-inspired folding patterns demonstrate exceptional and straightforward adaptivity of acoustic wave guiding architecture to contrast to the challenges manifest in digital wave guiding control methods. Yet, when the concept of folding arrays is applied to tessellations formed by single patterns, acoustic fields with distinct distributions of energy delivery cannot be realized. To overcome this limitation, here multiple folding patterns are assembled by piecewise geometries that permit the array to conform to unique topologies when reconfigured by physical folding actions. An analytical model is developed to predict the acoustic pressure radiated from the acoustic sources arranged on piecewise-continuous surfaces, while experiments are conducted to demonstrate the concept and validate the model. Parametric investigations are then undertaken to uncover the relations of modularity and folding of the acoustic array and the resulting acoustic energy delivery and distributions. The results find that the assembly of tessellated arrays from multiple distinct folding pattern sub-elements may replicate the acoustic wave guiding of complex acoustic sources that traditionally do not enable adaptive wave radiation properties.

An Experimental Study on the Radiation Noise Characteristics of a Centrifugal Pump with Various Working Conditions

To investigate the radiation noise characteristics of a centrifugal pump under various working conditions, a noise measurement system is established; afterwards, the distribution of different points and intervals, as well as the overall level of noise, are studied. The total sound pressure level distribution for different points manifests the dipole and asymmetric directivity characteristics. Additionally, the acoustic energy is introduced to compare the noise of different intervals to reveal the asymmetric characteristics, and it is found that variation in working conditions has little impact on the acoustic energy distribution, and the ratio of the acoustic energy in the direction facing the tongue, as well as that in the direction against the tongue, to total acoustic energy fluctuate around 0.410 and 0.160, respectively, under various working conditions. Also, the A-weighted average sound pressure level (LpA) is applied to describe the overall level of noise, and LpA increases gradually with the growth of rotational speed, but the growth slope decreases. While in the operation of throttling regulation, LpA shows the trend that first increases, then remains stable, and increases again with the growth of flow rate. This study could provide guidance for optimizing the operating conditions and noise control of centrifugal pumps.

High-Performance SAW Resonator on New Multilayered Substrate Using LiTaO3 Crystal.

To develop the high-performance filters and duplexers required for recent long-term evolution frequency bands in mobile handsets, a surface acoustic wave (SAW) resonator is needed that has a higher quality (Q) and a lower temperature coefficient of frequency (TCF). To achieve this, the authors focused on acoustic energy confinement in the depth direction for a rotated Y-X LiTaO3 (LT) substrate. Characteristics of multilayered substrates with low-impedance and high-impedance layers under LT layer were studied numerically in terms of acoustic energy distribution, phase velocity, coupling coefficient, and temperature characteristics employing a finite-element method simulation. After several calculations, a novel multilayered structure was developed that uses SiO2 for a low-impedance layer and AlN for a high-impedance layer under the thin LT layer. A one-port resonator using the new substrate was fabricated, and its experimental results showed that the developed resonator had a Bode-Q over 4000 and TCF of -8 ppm/°C, which are four times higher than and one-fifth as small as those of a conventional 4° YX-LT SAW resonator, respectively. By applying this technology, a band 25 duplexer with very narrow duplex gap was successfully developed, which shows extremely low insertion loss, steep cutoff characteristics, and stable temperature characteristics.

Acoustic energy distribution in microfluidics chip via a secondary channel

Acoustic energy is commonly utilized in microfluidic technology enabling the use of minute volume of fluid for diagnosis and analysis in biology research. However, the milli-micrometer scaled acoustic sensors and actuators are low in surface power density. We simulate the output response in a secondary microfluidic channel with multiple output ports sealed by a thin flexible membrane to demonstrate the use of frequency control for distribution of acoustic vibration. As a verification, a two output-location sample is fabricated, tested, and compared to our model simulation. The present methodology employs the application of larger acoustic actuator without compromising the volume of sample fluid required. The differential vibration response between two components of >1 order is shown experimentally. The design of secondary channel is analyzed as an RLC circuit and a quality factor of >6 is required to minimize damping.

Absorption scaling theory applied to an energy-intensity boundary element method for prediction of broadband acoustic fields in enclosures

Insight into the acoustic energy distribution in enclosures is gained by applying Absorption Scaling Theory. Broadband high-frequency acoustic fields within 3D rectangular enclosures are modeled with an energy-intensity boundary element method (EIBEM) that replaces the enclosure boundary with a distribution of broadband uncorrelated directional intensity sources to simulate either diffuse or specular reflection. Assuming a highly reflective enclosure, the boundary panel strengths are expanded in a power series with the spatially-averaged absorption as a small parameter. For diffuse reflection fields, where the theory is well developed, a matrix formulation is derived for each of the expansion coefficients that must be solved in sequential order. The leading order term in the expansion is inversely proportional to the scaling parameter and estimates the average level inside the enclosure, the next term gives spatial variation independent of average absorption level, while higher order terms account for the spatial variation of energy due to the distribution of absorption and the location of sources. For a highly reflective enclosure, only a few terms are needed to accurately predict the mean-square pressures. Similar behavior is demonstrated for specular reflection using numerical simulations. Applications include theoretical and empirical enclosure design and assessment, and solving the inverse problem.

Power-Law Distribution of Acoustic Emission Energy of Coal Samples in Brazilian Test

Power-Law Distribution of Acoustic Emission Energy of Coal Samples in Brazilian Test

Mechanical and energy release characteristics of different water-bearing sandstones under uniaxial compression

This paper presents the experimental results of calcium argillaceous cemented sandstones with different water contents under uniaxial and cyclic loading conditions. The effects of the water content status on peak strength, deformation, and dissipated energy are discussed. Meanwhile, the acoustic emission energy is also studied based on the accelerating energy release theory and energy distribution density function. The experimental results show that the water content has remarkable effects on the peak strength and elastic modulus by a decrease of 37–58% and 15.7–21% after being saturated, respectively. Both the accumulated dissipated energy and dissipated energy generating ratio of dry specimens are higher than those of the saturated specimens. The acoustic emission energy release rate of dry specimens is higher than those of the saturated specimens, which means a high tendency of sudden failure for dry specimens. Moreover, the distributions of acoustic emission absolute energy are consistent with the normal density distribution function, and the AE energy expectations of dry specimens are higher than those of the saturated ones in the loading process and they show an obvious increasing trend on approaching failure. These conclusions will be helpful for the illumination of water-weakening effects on the mechanics parameters and failure mechanism analysis in view of the releasing energy.

Design of Fresnel Lens-Type Multi-Trapping Acoustic Tweezers.

In this paper, acoustic tweezers which use beam forming performed by a Fresnel zone plate are proposed. The performance has been demonstrated by finite element analysis, including the acoustic intensity, acoustic pressure, acoustic potential energy, gradient force, and particle distribution. The acoustic tweezers use an ultrasound beam produced by a lead zirconate titanate (PZT) transducer operating at 2.4 MHz and 100 Vpeak-to-peak in a water medium. The design of the Fresnel lens (zone plate) is based on air reflection, acoustic impedance matching, and the Fresnel half-wave band (FHWB) theory. This acoustic Fresnel lens can produce gradient force and acoustic potential wells that allow the capture and manipulation of single particles or clusters of particles. Simulation results strongly indicate a good trapping ability, for particles under 150 µm in diameter, in the minimum energy location. This can be useful for cell or microorganism manipulation.

Effect of internal waves on acoustic energy structure in the northern East China Sea

Relation between depth direction acoustic energy and sound speed fluctuation caused by internal wave activity observed during SAVEX15 experiment is investigated. In the SAVEX15 region (northern East China Sea with water depths around 100 m), underwater sound channel was observed during May 2015 along with extensive internal wave activities. When the source is near the sound channel axis, most of the acoustic energy is trapped in the channel. However, internal waves change the sound speed profile, which results in spreading the acoustic energy over depth. Measured data during the experiment is used to investigate the relation between acoustic energy structure and internal wave activity. Parameters reflecting their variabilities are defined. Two main parameters are standard deviation of the acoustic energy integrated over depth and the sound speed gradient at the channel axis, which reflects the internal wave activity. The correlation of two parameters is used to show the effect of internal waves on the changes of acoustic energy distribution.

Numerical and experimental evaluation of continuous ultrasonic sludge treatment system

Ultrasonic disintegration is a very promising sludge pretreatment method that leverages the cavitation effect to produce extreme physical environments characterized by high temperatures and high pressures. This process disintegrates sludge structure features, promotes sludge dewatering, and aides resource recovery. This paper presents a newly designed continuous ultrasonic sludge treatment device. The characteristics of the ultrasonic wave propagated in the activated sludge were simulated, with the results showing that at lower frequencies, the acoustic pressure energy distribution exhibits more local concentrations, whereas at 80kHz, the energy distribution is relatively uniform as a result of the interference of standing waves. Subsequently, activated sludge was ultrasonically treated with different exposure times and frequencies. The sludge’s capillary suction time, particle size, and moisture content were measured. The results showed different trends for each of the investigated parameters. The dewatering performance was best when the exposure time was 5–10s. Finally, different substances were added to the ultrasonically treated sludge to analyze the effects of ultrasonic treatment on anaerobic digestion. The gas production rate was higher when glucose was the added substance than it was for yeast. The highest total concentration of produced gas, including both hydrogen and methane, was 34% for an ultrasonic input power of 200W at a 25kHz frequency, an exposure time of 20s, and with 30g of added glucose. The gas production rate was found to be higher at the lower frequency when frequency was the only variable. These experiments demonstrate that ultrasonic treatment can change the structure of sludge particles and the moisture content of the sludge, improving sludge dewatering performance. Furthermore, after ultrasonic treatment can improve gas production.

Decoding Group Vocalizations: The Acoustic Energy Distribution of Chorus Howls Is Useful to Determine Wolf Reproduction.

Population monitoring is crucial for wildlife management and conservation. In the last few decades, wildlife researchers have increasingly applied bioacoustics tools to obtain information on several essential ecological parameters, such as distribution and abundance. One such application involves wolves (Canis lupus). These canids respond to simulated howls by emitting group vocalizations known as chorus howls. These responses to simulated howls reveal the presence of wolf litters during the breeding period and are therefore often used to determine the status of wolf populations. However, the acoustic structure of chorus howls is complex and discriminating the presence of pups in a chorus is sometimes difficult, even for experienced observers. In this study, we evaluate the usefulness of analyses of the acoustic energy distribution in chorus howls to identify the presence of pups in a chorus. We analysed 110 Iberian wolf chorus howls with known pack composition and found that the acoustic energy distribution is concentrated at higher frequencies when there are pups vocalizing. We built predictive models using acoustic energy distribution features to determine the presence of pups in a chorus, concluding that the acoustic energy distribution in chorus howls can be used to determine the presence of wolf pups in a pack. The method we outline here is objective, accurate, easily implemented, and independent of the observer's experience. These advantages are especially relevant in the case of broad scale surveys or when many observers are involved. Furthermore, the analysis of the acoustic energy distribution can be implemented for monitoring other social canids that emit chorus howls such as jackals or coyotes, provides an easy way to obtain information on ecological parameters such as reproductive success, and could be useful to study other group vocalizations.

Joint statistical moments of mode amplitudes at different frequencies in a random acoustic waveguide

This paper considers an approximate ray-based analytical approach for evaluating the joint statistical moments of mode amplitudes in an acoustic waveguide with large-scale sound speed fluctuations. Explicit analytic expressions for the statistical moments are derived from an approximate analytical solution of the mode-coupling equations. The analytic solution allows one to deduce a scaling law establishing the connection between amplitudes of modes with the same ratio of the mode number to frequency. The applicability of the ray-based approach for evaluating the joint statistical moments of modes amplitudes including the moments at different frequencies is demonstrated using the Monte Carlo simulation of sound fields in a model of the underwater acoustic waveguide in a deep ocean. Numerical simulation also shows different manifestations of the scaling law. In particular, it is shown how this law manifests itself in the acoustic energy distribution between normal modes, in the jump-like range variations of statistical moments, and in the shape of the correlation function between amplitudes of different modes at different frequencies.

High-Q energy trapping of temperature-stable shear waves with Lamé cross-sectional polarization in a single crystal silicon waveguide

A multi-port electrostatically driven silicon acoustic cavity is implemented that efficiently traps the energy of a temperature-stable eigen-mode with Lamé cross-sectional polarization. Dispersive behavior of propagating and evanescent guided waves in a ⟨100⟩-aligned single crystal silicon waveguide is used to engineer the acoustic energy distribution of a specific shear eigen-mode that is well known for its low temperature sensitivity when implemented in doped single crystal silicon. Such an acoustic energy trapping in the central region of the acoustic cavity geometry and far from substrate obviates the need for narrow tethers that are conventionally used for non-destructive and high quality factor (Q) energy suspension in MEMS resonators; therefore, the acoustically engineered waveguide can simultaneously serve as in-situ self-oven by passing large uniformly distributed DC currents through its body and without any concern about perturbing the mode shape or deforming narrow supports. Such a stable thermo-structural performance besides large turnover temperatures than can be realized in Lamé eigen-modes make this device suitable for implementation of ultra-stable oven-controlled oscillators. 78 MHz prototypes implemented in arsenic-doped single crystal silicon substrates with different resistivity are transduced by in- and out-of-plane narrow-gap capacitive ports, showing high Q of ∼43k. The low resistivity device shows an overall temperature-induced frequency drift of 200 ppm over the range of −20 °C to 80 °C, which is ∼15× smaller compared to overall frequency drift measured for the similar yet high resistivity device in the same temperature range. Furthermore, a frequency tuning of ∼2100 ppm is achieved in high resistivity device by passing 45 mA DC current through its body. Continuous operation of the device under such a self-ovenizing current over 10 days did not induce frequency instability or degradation in Q.

Prediction of the vibroacoustic behavior of a submerged shell with non-axisymmetric internal substructures by a condensed transfer function method

The vibroacoustic behavior of axisymmetric stiffened shells immersed in water has been intensively studied in the past. On the contrary, little attention has been paid to the modeling of these shells coupled to non-axisymmetric internal frames. Indeed, breaking the axisymmetry couples the circumferential orders of the Fourier series and considerably increases the computational costs. In order to tackle this issue, we propose a sub-structuring approach called the Condensed Transfer Function (CTF) method that will allow assembling a model of axisymmetric stiffened shell with models of non-axisymmetric internal frames. The CTF method is developed in the general case of mechanical subsystems coupled along curves. A set of orthonormal functions called condensation functions, which depend on the curvilinear abscissa along the coupling line, is considered. This set is then used as a basis for approximating and decomposing the displacements and the applied forces at the line junctions. Thanks to the definition and calculation of condensed transfer functions for each uncoupled subsystem and by using the superposition principle for passive linear systems, the behavior of the coupled subsystems can be deduced. A plane plate is considered as a test case to study the convergence of the method with respect to the type and the number of condensation functions taken into account. The CTF method is then applied to couple a submerged non-periodically stiffened shell described using the Circumferential Admittance Approach (CAA) with internal substructures described by Finite Element Method (FEM). The influence of non-axisymmetric internal substructures can finally be studied and it is shown that it tends to increase the radiation efficiency of the shell and can modify the vibrational and acoustic energy distribution.

Ultrasonic Drying Processing Chamber

The design of a high intensity ultrasonic chamber for drying process was investigated. The acoustic pressure distribution in the ultrasonic drying chamber was simulated solving linear elastic models with attenuation for the acoustic-structure interaction. Together with the government equations, the selection of appropriate boundary conditions, mesh refinement, and configuration parameters of the calculation methods, which is of great importance to simulate adequately the process, were considered. Numerical solution, applying the finite element method (FEM), of acoustic-structure interactions involves to couple structural and fluid elements (with different degrees of freedom), whose solution implies several problems of hardware requirements and software configuration, which were solved. To design the drying chamber, the influence of the directivity of the drying open camera and the staggered reflectors over the acoustic pressure distribution was analyzed. Furthermore, to optimize the influence of the acoustic energy on the drying process, the average value of the acoustic energy distribution in the drying chamber was studied. This would determine the adequate position of the food samples to be dried. For this purpose, the acoustic power absorbed by the samples will be analyzed in later studies.

Mapping thunder sources by inverting acoustic and electromagnetic observations

AbstractWe present a new method of locating current flow in lightning strikes by inversion of thunder recordings constrained by Lightning Mapping Array observations. First, radio frequency (RF) pulses are connected to reconstruct conductive channels created by leaders. Then, acoustic signals that would be produced by current flow through each channel are forward modeled. The recorded thunder is considered to consist of a weighted superposition of these acoustic signals. We calculate the posterior distribution of acoustic source energy for each channel with a Markov Chain Monte Carlo inversion that fits power envelopes of modeled and recorded thunder; these results show which parts of the flash carry current and produce thunder. We examine the effects of RF pulse location imprecision and atmospheric winds on quality of results and apply this method to several lightning flashes over the Magdalena Mountains in New Mexico, USA. This method will enable more detailed study of lightning phenomena by allowing researchers to map current flow in addition to leader propagation.

Frequency-domain model of tonal blade thickness and loading noise

A tonal thickness noise and loading noise model of rotating blades has been developed as an extension of the exact frequency-domain solutions for rotating monopole and dipole point sources. The present model has two advantages over the previous methods and models for noise prediction. The first is the unified expression for sources in subsonic and supersonic rotation even at rest. The second is that the present model has no limit on the location of the observer and no interpolation error. Two test cases are carried out to validate the present model and emphasize its advantage at the noise prediction for sources in supersonic rotation. Moreover, as a specified application of the present model for the rotating blades whose tip radius is acoustically compact, acoustic energy distribution at different frequencies and in different directions is analyzed. Result shows that the acoustic energy of acoustically compact rotating blades is mainly concentrated at the source frequency while propagating along the axial direction, leaving the rest propagating along the radial direction at the other frequencies.

Visualization of Long-duration Acoustic Recordings of the Environment

Acoustic recordings of the environment are an important aid to ecologists monitoring biodiversity and environmental health. However, rapid advances in recording technology, storage and computing make it possible to accumulate thousands of hours of recordings, of which, ecologists can only listen to a small fraction. The big-data challenge addressed in this paper is to visualize the content of long-duration audio recordings on multiple scales, from hours, days, months to years. The visualization should facilitate navigation and yield ecologically meaningful information.Our approach is to extract (at one minute resolution) acoustic indices which reflect content of ecological interest. An acoustic index is a statistic that summarizes some aspect of the distribution of acoustic energy in a recording. We combine indices to produce false-color images that reveal acoustic content and facilitate navigation through recordings that are months or even years in duration.

The use of acoustic indices to determine avian species richness in audio-recordings of the environment

Interpreting acoustic recordings of the natural environment is an increasingly important technique for ecologists wishing to monitor terrestrial ecosystems. Technological advances make it possible to accumulate many more recordings than can be listened to or interpreted, thereby necessitating automated assistance to identify elements in the soundscape.In this paper we examine the problem of estimating avian species richness by sampling from very long acoustic recordings. We work with data recorded under natural conditions and with all the attendant problems of undefined and unconstrained acoustic content (such as wind, rain, traffic, etc.) which can mask content of interest (in our case, bird calls).We describe 14 acoustic indices calculated at one minute resolution for the duration of a 24hour recording. An acoustic index is a statistic that summarizes some aspect of the structure and distribution of acoustic energy and information in a recording. Some of the indices we calculate are standard (e.g. signal-to-noise ratio), some have been reported useful for the detection of bioacoustic activity (e.g. temporal and spectral entropies) and some are directed to avian sources (spectral persistence of whistles). We rank the one minute segments of a 24hour recording in descending order according to an “acoustic richness” score which is derived from a single index or a weighted combination of two or more. We describe combinations of indices which lead to more efficient estimates of species richness than random sampling from the same recording, where efficiency is defined as total species identified for given listening effort. Using random sampling, we achieve a 53% increase in species recognized over traditional field surveys and an increase of 87% using combinations of indices to direct the sampling.We also demonstrate how combinations of the same indices can be used to detect long duration acoustic events (such as heavy rain and cicada chorus) and to construct long duration (24h) spectrograms.