Acoustic Phenomena Research Articles

Unconventional Quantum Sound-Matter Interactions in Spin-Optomechanical-Crystal Hybrid Systems.

We predict a set of unusual quantum acoustic phenomena resulting from sound-matter interactions in a fully tunable solid-state platform in which an array of solid-state spins in diamond are coupled to quantized acoustic waves in a one-dimensional optomechanical crystal. We find that, by using a spatially varying laser drive that introduces a position-dependent phase in the optomechanical interaction, the mechanical band structure can be tuned insitu, consequently leading to unconventional quantum sound-matter interactions. We show that quasichiral sound-matter interactions can occur, with tunable ranges from bidirectional to quasiunidirectional, when the spins are resonant with the bands. When the solid-state spin frequency lies within the acoustic band gap, we demonstrate the emergence of an exotic polariton bound state that can mediate long-range tunable, odd-neighbor, and complex spin-spin interactions. This work expands the present exploration of quantum phononics and can have wide applications in quantum simulations and quantum information processing.

Experimental Evidence of the Existence of Bound States in the Continuum and Fano Resonances in Solid-Liquid Layered Media

Bound states in continuum (BICs) are resonances with zero width (infinite lifetime) without any leakage into the surrounding media. Their fascinating properties and potential applications have attracted a great deal of interest. In this paper, we give an analytical, numerical, and experimental demonstration of BICs in simple acoustic structures based on either a single solid layer or a triple solid-liquid-solid layer inserted between two liquids. These modes are an intrinsic property of the inserted structure (solid layer or solid-liquid-solid triple layer) with free surfaces and are independent of the surrounding media. Two kinds of BICs are discussed: (i) Fabry-Perot (FP) BICs exist as the consequence of the intersection of the local resonances induced by inserted structure intersect the transmission zeros induced by the solid layers. (ii) Symmetry-protected (SP) BICs occur when appear at normal incidence due to the decoupling of the transverse modes in the solid layer from the longitudinal modes that propagate in the solid and solid-liquid multilayer media. When the incidence angle departs slightly from the BIC conditions, the latter transform into Fano resonances characterized by an asymmetric line shape in the transmission spectra. In addition, we show that the transmission zeros give rise to negative delay times and therefore acoustic superluminal effect. The theoretical results are obtained by means of the Green's function method, whereas the experimental measurements are carried out in ultrasonic domain using plexiglass plates in water. These results may have important applications to realize subsonic and acoustic superluminal phenomena as well as acoustic filters and sensors.

Non-extensive statistical mechanics for acoustic emission in disordered media: Entropy, size effect, and self-organization

The present work explores acoustic emission phenomenon of concrete like disordered material within the framework of non-extensive statistical mechanics. The aim of the study is threefold. At first, we re-derive the non-extensive distribution function using the power-function and exponential-function ansatzes. We assert that the power-function ansatz based distribution model, compared to exponential-function based model, is superior due to its ability to recover the exponential distribution in the limit when the tail index q→1 and due to its higher sensitivity for long-tail. The ability of recovering exponential distribution in the limit q→1 preserves the essence of Tsallis non-extensive statistical mechanics formulation and retains the pertinent meaning of entropic index q of the distribution. Second, we study the size effect on the various parameters of the distribution models and discover the size-independence of the entropic index. Thirdly, the self-organization phenomenon often observed in the complex dynamic systems is commented. The existence of criticality near failure for quasi-static loading of concrete beams appear speculative and the criticality might exist in midway of damage progress.

An Overview of Acoustic Impedance Measurement Techniques and Future Prospects

In order to progress in the area of aeroacoustics, experimental measurements are necessary. Not only are they required for engineering applications in acoustics and noise engineering, but also they are necessary for developing models of acoustic phenomenon around us. One measurement of particular importance is acoustic impedance. Acoustic Impedance is the measure of opposition of acoustical flow due to the acoustic pressure. It indicates how much sound pressure is generated by the vibration of molecules of a particular acoustic medium at a given frequency and can be a characteristic of the medium.The aim of the present paper is to give a synthetic overview of the literature on impedance measurements and to discuss the advantage and disadvantage of each measurement technique. In this work, we investigate the three main categories of impedance measurement techniques, namely reverberation chamber techniques, impedance tube techniques, and far-field techniques. Theoretical principles for each technique are provided along with a discussion on historical development and recent advancements for each technique.

Odd Willis coupling induced by broken time-reversal symmetry

When sound interacts with geometrically asymmetric structures, it experiences coupling between pressure and particle velocity, known as Willis coupling. While in most instances this phenomenon is perturbative in nature, tailored asymmetries combined with resonances can largely enhance it, enabling exotic acoustic phenomena. In these systems, Willis coupling obeys reciprocity, imposing an even symmetry of the Willis coefficients with respect to time reversal and the impinging wave vector, which translates into stringent constraints on the overall scattering response. In this work, we introduce and experimentally observe a dual form of acoustic Willis coupling, arising in geometrically symmetric structures when time-reversal symmetry is broken, for which the pressure-velocity coupling is purely odd-symmetric. We derive the conditions to maximize this effect, we experimentally verify it in a symmetric subwavelength scatterer biased by angular momentum, and we demonstrate the opportunities for sound scattering enabled by odd Willis coupling. Our study opens directions for acoustic metamaterials, with direct implications for sound control, non-reciprocal scattering, wavefront shaping and signal routing, of broad interest also for nano-optics, photonics, elasto-dynamics, and mechanics.

From the Reef to the Ocean: Revealing the Acoustic Range of the Biophony of a Coral Reef (Moorea Island, French Polynesia)

The ability of different marine species to use acoustic cues to locate reefs is known, but the maximal propagation distance of coral reef sounds is still unknown. Using drifting antennas (made of a floater and an autonomous recorder connected to a hydrophone), six transects were realized from the reef crest up to 10 km in the open ocean on Moorea island (French Polynesia). Benthic invertebrates were the major contributors to the ambient noise, producing acoustic mass phenomena (3.5–5.5 kHz) that could propagate at more than 90 km under flat/calm sea conditions and more than 50 km with an average wind regime of 6 knots. However, fish choruses, with frequencies mainly between 200 and 500 Hz would not propagate at distances greater than 2 km. These distances decreased with increasing wind or ship traffic. Using audiograms of different taxa, we estimated that fish post-larvae and invertebrates likely hear the reef at distances up to 0.5 km and some cetaceans would be able to detect reefs up to more than 17 km. These results are an empirically based validation from an example reef and are essential to understanding the effect of soundscape degradation on different zoological groups.

Experimental evidence of a hiding zone in a density-near-zero acoustic metamaterial

This paper examines the feasibility of cloaking an obstacle using Plate-type Acoustic Metamaterials (PAMs). We present two distinct strategies to cloak this obstacle, using either the near-zero-density regime of a periodic arrangement of plates or the acoustic doping phenomenon to achieve simultaneous zero-phase propagation and impedance matching. The strong limitations induced by viscothermal and viscoelastic losses that cannot be avoided in such a system are studied. A hiding zone is reported analytically, numerically, and experimentally. In contrast to cloaking, where zero-phase propagation must be accompanied by total transmission and zero reflection, the hiding configuration requires that the scattering properties of the hiding device must not be affected by the presence of the obstacle embedded in it. Contrary to cloaking, the hiding phenomenon is achievable even with a realistic PAM possessing unavoidable losses.

Propagation characteristics of low-frequency acoustic wave in full waveguide of shallow water based on time-domain finite element method

In order to clarify the propagation mechanism and characteristics of low-frequency sound signals in shallow sea with elastic bottom, using the Time-domain Finite Element Method (TDFEM), a time-domain numerical calculation model of the low-frequency sound field in shallow sea full-waveguide under the action of a point sound source is established. With this model, The influence of seabed acoustic parameters’ and seabed topography’ changes on the sound propagation characteristics in full-waveguide is simulated and analyzed. The results show that when there is a shear wave effect on the seabed, low-frequency sound waves will excite the Scholte wave propagating on the bottom boundary of the seabed. The greater the seabed acoustic impedance, the faster the excited Scholte wave velocity and the large the amplitude. At the same time, there will be acoustic energy leakage phenomenon in the inclined seabed.

Concept for a study on community responses to low sonic boom in Europe

In 2018, NASA was the first to assess noise annoyance by low-sonic booms among a population not used to hearing any of the acoustical phenomena associated with an aircraft flying at supersonic speeds (QSF18 study). Meanwhile, within the EU-project RUMBLE, data are collected, and literature reviewed used for research on community responses to low sonic boom demonstrator overflights. We present recommendations for such a field study, comprising NASA and RUMBLE studies' findings and other European efforts emphasizing items discussed by NASA and European researchers in the aftermaths of the first QSF18 results. We propose a study design for the CRLSB study in different European climate zones. A low-fidelity simulation model has been developed to pre-select test sites, supplemented by a more detailed impact model (NENA) for final site selection and preparation of the survey. We identified an approach of mixed survey modes, including experience-sampling procedures, as the most desirable modus operandi for community response assessment. Further, we propose a method for calculating desired sample sizes when applying linear mixed-effects modeling to data collected from a continental field study. [This project has received funding from the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 769896.]

Automatic classification of normal and sick patients with crackles using wavelet packet decomposition and support vector machine

Auscultation of the respiratory system – a key system in a human body – is a complicated procedure and it requires a doctor to have good perception skills and profound experience. During auscultation, specific sounds are identified by the doctor who then associates the acoustic phenomena heard with pathological processes. This article is an attempt at developing a classification system, using wavelet packets, a genetic algorithm, and a Support Vector Machine (SVM), which distinguishes between healthy patients and patients with crackles caused by pneumonia, pulmonary fibrosis, Heart Failure (HF) or Chronic Obstructive Pulmonary Disease (COPD). The system is elaborated and tested over a dataset consisting of 62 healthy (166 recordings) and 58 sick patients (187 recordings). A reliable system is described, consisting of 5 wavelet classifiers, featuring approx. 95 % sensitivity and 91 % specificity, applying 10-fold cross-validation.

WindTrack: Leveraging Sound and Wind to Track Angular Position of Users on Commercial Internet-Connected Fans

A recent trend in electric fans is the support of smarter features based on Internet connectivity, such as remote control. This work opens new opportunities to make these devices more intelligent, particularly by proposing WindTrack, a novel angular positioning technique for electric fans. This would encourage the emergence of a new class of smart fans that use spatial information for automatic wind direction control. Many works have extensively studied angular positioning, but had limitations realizing such smart fans in terms of deployability (due to hardware requirements), accuracy, and usability. WindTrack overcomes these limitations by leveraging the acoustic phenomenon of refraction caused by wind. More specifically, it transmits and receives sound signals by using a smartphone located close to a user, while operating a fan in an oscillating mode. Therefore, WindTrack only requires Internet-connected fans for collaboration with smartphones. It then identifies the user’s angular position based on the relationship between the propagation characteristics of the received signals and the oscillating fan. We further improve the robustness of WindTrack by using multiple speakers and microphones built-in smartphones and listening to wind sounds captured when wind passes across microphones. Extensive experiments on a WindTrack prototype demonstrate that it can achieve an angular positioning accuracy of a few degrees, especially in various environments and with no modification to commercial smartphones and Internet-connected fans.

Flow-Induced Acoustic Resonance of Finned Cylinders With Varying Fin Heights

Abstract The flow-excited acoustic resonance phenomenon, which is instigated by periodic flow perturbation, leads to the generation of acute sound pressure. In this work, we investigated the characteristics of the flow-excited acoustic resonance for circular finned cylinders with different fin heights. The fin height is expressed as a normalized form considering the ratio of the fin diameter to the root cylinder diameter. The experiments are performed with finned cylinders having a range of diameter ratios between 1.5<Df/Dr<2.5. The diameter ratios are varied by changing the root diameter and fin diameter separately as well as simultaneously while keeping the fin pitch and the fin thickness constant. The results show that the excitation of acoustic resonance has profound dependence on the diameter ratio. Increasing the diameter ratios of the finned cylinder results in strong acoustic resonance excitation. The lock-in width and the onset of the acoustic resonance excitation also depend on the diameter ratio of the cylinders. Moreover, the results show that using an effective diameter based on the geometrical flow blockage does not take into account the changes occurring in the source of resonance excitation due to the addition of fins.

NUMERICAL INVESTIGATION OF ROD-AIRFOIL CONFIGURATION AEROACOUSTIC CHARACTERISTICS USING FFOWCS-WILLIAMS-HAWKINGS EQUATIONS

The rod-airfoil configuration is a fundamental study to understand sound generation processes and the acoustic phenomena in the application of turbines, fans, and airfoils. In the present research, the noise that is originated by the rod-airfoil configuration is examined using numerical methods which are Large Eddy Simulation (LES), and Reynolds Averaged Navier Stokes (RANS) models, coupled with an FFOWCS-WILLIAMS-HAWKINGS (FW-H) technique. For the RANS method, k-ω SST and Spalart Allmaras (S-A) turbulence models are utilized in order to investigate the capability of different models for the analysis of the aeroacoustic flow field. The ANSYS FLUENT solver is chosen to carry out the numerical simulations. The examined rod and chord diameter Reynolds numbers are 48000 and 480000, respectively and the Mach number is 0.2. Results are obtained for both in the near field and acoustic far-field. The obtained numerical results are verified with an experimental study from the literature, and the results of both approaches are compared with each other and the experiment. Comparisons are performed for mean velocity profiles in the rod and airfoil wakes, pressure spectra and power spectral density. The results obtained show that LES is preferable for this problem as it is capable of capturing the flow separation, reattachments, vortex street, and various length scales of turbulence. Although both RANS and LES methods provide a consistent flow field with experimental methods, the RANS approach overestimates the vortex shedding frequency and Strouhal number. The RANS model predicts the flow field well; however, it overestimates the noise spectra. The LES model predicts satisfactory acoustic spectra.

Acoustic holograms for directing arbitrary cavitation patterns

Cavitation is an important phenomenon in biomedical acoustics. It can produce both desired outcomes (i.e., local therapeutic effects in vivo) and undesired outcomes (i.e., tissue damage), and it is, thus, important to both understand and direct cavitation fields. Through the use of three-dimensional-printed acoustic lenses and cavitation-sensitive acoustic phantoms, we demonstrate the generation of arbitrary shape two-dimensional (2D) microbubble cavitation fields. In this study, we demonstrate shaping a 1 MHz acoustic beam as the character “7” on a target plane that contains a higher mechanical index than the cavitation threshold for encapsulated microbubbles in a gelatin phantom. The lens pattern is first designed by calculating the phase map of the desired field using an angular spectrum approach. After lens implementation, acoustic pulsing through the lens generated the target acoustic field in a phantom and produced a cavitation map following the intended 2D pattern. The cavitation pattern was similar (with the structural similarity of 0.476) to the acoustic pressure map of the excitation beam.

Acoustics Apps: Interactive simulations for digital teaching and learning of acoustics.

This paper presents the Acoustics Apps, an e-learning platform that offers an interactive and playful environment for teaching and learning the principles of acoustics and vibration. The Acoustics Apps address the increasing demand for digitized teaching methods, which might be suitable for home schooling or as a complement to physical experiments by adding interactive simulation. The apps combine learning by experimenting, observing, and exploring using state-of-the-art scientific methods and numerical simulations. The ability to visualize and control acoustic phenomena facilitates understanding of the relevant physical principles. The apps are designed to be used intuitively and can be tailored to suit the existing knowledge of the user. As such, a wide range of users can benefit from this learning aid. It has been developed to allow barrier-free access to modern educational tools, requiring only a device with a browser and Internet access. The necessary computing power is provided by an external server using the COMSOL ServerTM technology. The Acoustics Apps are freely available for academic and teaching purposes at apps.vib.mw.tum.de.

Acoustic emission entropy: An innovative approach for structural health monitoring of fracture‐critical metallic components subjected to fatigue loading

AbstractThe paper presents an innovative approach for structural health monitoring of metallic components under fatigue crack phenomena. The methodology is based on the evaluation of the information entropy of the acoustic emission (AE) data. AE testing of fatigue crack growth (FCG) is performed on metallic components is performed within an extremely noisy testing environment. Basic AE data analysis is demonstrated to be inefficient with regard to the specific testing conditions. AE entropy is proven to be a reliable damage‐sensitive feature for real‐time assessment despite both significant noise disturbance and complexity/randomness of the acoustic phenomena. This was also confirmed for (time‐)discontinuous monitoring processes over random‐based data detections. An innovative monitoring protocol is finally developed according to the experimental evidence also considering the recommendations of the current monitoring. The protocol is found to be promising for structural health monitoring of metallic fracture‐critical components of structures under fatigue.

A benchmark for room acoustical simulation. Concept and database

Room acoustical simulations are usually evaluated by comparing them to measurements in corresponding physical environments as a benchmark. However, it proved to be challenging to provide a precise representation of the room geometry, the source and receiver characteristics, and the absorption and scattering coefficients to be re-modeled in the simulation. We aim to overcome these shortcomings by providing a database that can serve as a Benchmark for Room Acoustical Simulations (BRAS) and which is expandable and permanently available to researchers and developers of simulation software. The database includes a selection of reference scenes such as “single reflection”, or “diffraction around an infinite wedge” which isolate specific acoustic phenomena. This article introduces the concept of the BRAS along with the description of the currently contained acoustic scenes and discusses the implication of measurement errors. The acquisition of impulse responses for omnidirectional and binaural receivers, the identification of the boundary conditions, and the data structure is detailed in the database itself. The BRAS is publicly available11https://dx.doi.org/10.14279/depositonce-6726.3.. The free license under which it is provided allows for future extensions such as additional scenes or improved data due to advanced measurement techniques.

Air Injection as a Solution to the Problem for Reducing High-Frequency Acoustic Noise in Some Operating Modes of Francis Hydro Turbines

During operation of Francis hydro turbines at the regimes of 70–95 % of Nrated, high-frequency acoustic phenomena (noise) were recorded. In order to study and identify the causes of these phenomena, special field tests were conducted. The main objectives of the tests were: determination of the main frequencies of acoustic phenomena, comparison with natural frequencies of the turbine water passages elements and the search for solutions to reduce acoustic phenomena. During the tests, the natural frequencies of the elements of turbine water path were investigated. Several methods of air injection to the turbine water path were also tested. The most effective way (including by the amount of air) to reduce acoustic phenomena was the air injection from industrial air piping into the spiral case and into the area of guide vanes.

Food cries, historical city sounds, and the twentieth century silencing of street vendors

ABSTRACT This article explores historical street cries, the sounds, calls, and music of peddlers, hawkers, and vendors who sold food, provisions and services, and their changes within global soundscapes and urban communities. It considers food cries as an acoustic, socio-economic, and cultural phenomenon associated for centuries with street selling as a key constituent of culinary provisioning and subaltern livelihoods. It examines how and why from the mid-nineteenth century, such cries were perceived negatively by many urban residents and how the sounds of selling food that were historically integral to culinary provisioning systems were portrayed as an undesirable and backward aspect of urban life and virtually relegated to the realm of nostalgia.

Study on the Sound Radiation Efficiency of a Typical Distribution Transformer

In the realm of power grids environmental protection, low-frequency harmonic noise radiated from transformers has always been the focus of attention for decades. The existing noise control technologies, such as traditional noise barriers, sound insulation enclosures, and damping panels, not only occupying a large space but also causing difficulties in heat dissipation and daily maintenance of transformers. Therefore, explorations on the theory and design of low-noise power transformers become particularly necessary. In this paper, we started from the concept of acoustic radiation efficiency and discussed the radiation efficiency of a typical distribution transformer with radiators. It is found that the overall radiation efficiency is reduced below 230 Hz (low-frequency band) due to radiator barriers compared with that of the flat transformer tank. Furthermore, the phase effect of vibration distribution was also studied with a validated BEM code, inspired by the “acoustic short circuit” phenomenon. It is verified that the acoustic short circuit phenomenon truly exists for a typical transformer enclosure and affects its sound radiation. These supporting results might lead to a promising noise reduction technology from the perspective of radiation control of transformer tanks, i.e., acoustic metamaterials for noise source phase control.