Airborne Sound Waves Research Articles

The evolution of the various structures required for hearing in Latimeria and tetrapods

Sarcopterygians evolved around 415Ma and have developed a unique set of features, including the basilar papilla and the cochlear aqueduct of the inner ear. We provide an overview that shows the morphological integration of the various parts needed for hearing, e.g., basilar papilla, tectorial membrane, cochlear aqueduct, lungs, and tympanic membranes. The lagena of the inner ear evolved from a common macula of the saccule several times. It is near this lagena where the basilar papilla forms in Latimeria and tetrapods. The basilar papilla is lost in lungfish, certain caecilians and salamanders, but is transformed into the cochlea of mammals. Hearing in bony fish and tetrapods involves particle motion to improve sound pressure reception within the ear but also works without air. Lungs evolved after the chondrichthyans diverged and are present in sarcopterygians and actinopterygians. Lungs open to the outside in tetraposomorph sarcopterygians but are transformed from a lung into a swim bladder in ray-finned fishes. Elasmobranchs, polypterids, and many fossil fishes have open spiracles. In Latimeria, most frogs, and all amniotes, a tympanic membrane covering the spiracle evolved independently. The tympanic membrane is displaced by pressure changes and enabled tetrapods to perceive airborne sound pressure waves. The hyomandibular bone is associated with the spiracle/tympanic membrane in actinopterygians and piscine sarcopterygians. In tetrapods, it transforms into the stapes that connects the oval window of the inner ear with the tympanic membrane and allows hearing at higher frequencies by providing an impedance matching and amplification mechanism. The three characters-basilar papilla, cochlear aqueduct, and tympanic membrane-are fluid related elements in sarcopterygians, which interact with a set of unique features in Latimeria. Finally, we explore the possible interaction between the unique intracranial joint, basicranial muscle, and an enlarged notochord that allows fluid flow to the foramen magnum and the cochlear aqueduct which houses a comparatively small brain.

Orb-Web-Inspired Polymer-Carbon Nanocomposite Mesh Film for Acoustic Sensing

Thin films are ideal building blocks for hyperacute sensors and flexible electronic devices. However, most thin films either lack strength for practical applications or are not compatible with mass-production processes. Here, we reported an orb-web-inspired polymer-carbon nanocomposite-based, strong, lightweight, flexible mesh-type film that was compatible with standard microfabrication and suitable for high-performance acoustic sensing. Taking advantage of the superior mechanical strength of the three-dimensional (3D) heterogeneous nanocomposites constructed by one-dimensional (1D), two-dimensional (2D) carbon-based nanoparticles and polymer matrixes, we fabricated a 564-nm-thick mesh-type film that could be suspended freely both in liquid and air, and folded and stretched repeatedly over a macroscale opening. The sensing application of the mesh-type nanocomposite film was further demonstrated, which could even detect weak airborne sound waves with high fidelity, large dynamic range (>115 dB), and fine frequency resolution (<0.05 Hz) over the audible range. This work provides an approach to manufacturing designable, thin film-based flexible devices across scales with superior performance.

Nonlocal interaction engineering of 2D roton-like dispersion relations in acoustic and mechanical metamaterials

The interior of the synthetic unit cells and their interactions determine the wave properties of metamaterials composed of periodic lattices of these cells. While local interactions with the nearest neighbors are well appreciated, nonlocal beyond-nearest-neighbor interactions are often considered as a nuisance. Here, by introducing a versatile effectively two-dimensional metamaterial platform for airborne sound and elastic waves, we exploit nonlocal effects as a powerful design tool. Within a simplified discrete model, we analytically show that the lowest band can be engineered by Fourier synthesis, where the N-th order Fourier coefficient is determined by the N-th nearest-neighbor interaction strength. Roton-like dispersion relations are an example. The results of the discrete model agree well with a refined model and with numerical calculations. In addition, we engineer the passage of waves from a local metamaterial into a nonlocal metamaterial by carefully tailoring the transition region between the two.

Experimental demonstration of Willis coupling for elastic torsional waves

While Willis coupling has been originally proposed as the analog bianisotropy for elastic waves in a bulk solid, its realizations are currently limited to airborne sound and flexural waves on an elastic beam. Here, we experimentally demonstrate Willis coupling for elastic torsional waves on a thin beam. The design is achieved by breaking mirror symmetry for a metamaterial atom with local resonance for the particular type of elastic waves, which also serves as a universal approach in generating Willis coupling. The investigations will be useful for non-destructive testing on pipes and beam structures with torsional waves.

Local resonance – Helmholtz lattices with simultaneous solid-borne elastic waves and air-borne sound waves attenuation performance

Traditional metamaterial designs can only be applied to a single medium, such as air or resin. Inspired by the local resonators and Helmholtz resonators, a novel configuration called the local resonance – Helmholtz (LRH) lattices is proposed in this paper. This metamaterial is designed to suppress the propagation of both solid-borne and air-borne sound waves simultaneously. Numerical simulations are adopted to obtain the dispersion curves, transmission characteristics, and mechanical properties. The experimental samples are fabricated through the stereo lithography appearance (SLA)-based 3D-printing technology to test the actual vibration isolation and sound insulation performances. The results show that both mechanical vibrations and air sound waves are attenuated, meaning the concept of LRH lattices is feasible. The proposed metamaterial provides new possibilities for the design of advanced material with simultaneous sound and vibration attenuation performances.

An elastic higher-order topological insulator based on kagome phononic crystals

Recently, the novel bulk–edge–corner correspondence of higher-order topological states had attracted increasing attention. Past research studies on higher-order topological insulators, however, have mainly concentrated on the topological multipole states within the low-frequency bandgap for airborne sound waves. In this paper, we propose a higher-order topological insulator with kagome symmetry based on two-dimensional elastic phononic crystals (PNCs), which can operate in the high-frequency bandgap. Topological corner and edge states are both achieved in well-designed finite PNCs. In addition, we demonstrate the robust characteristics of elastic topological corner and edge states in PNCs with different defects (e.g., cavities, disorders, and bends). As the analog counterpart for classical waves, the proposed PNCs provide an alternative scheme for research into the topological phases of matter in macroscopic systems.

Ultra-High Sensitive Quasi-Distributed Acoustic Sensor Based on Coherent OTDR and Cylindrical Transducer

Highly sensitive distributed acoustic sensor is required in various practical applications. In this article, an ultra high sensitive quasi distributed acoustic sensor based on coherent detection and cylindrical transducer is proposed and demonstrated. As the acoustic sensing medium, distributed microstructured optical fiber (DMOF) is utilized to improve the signal to noise ratio (SNR) of the signal, which contains backscattering enhanced points (BEPs) along the longitudinal direction of the fiber. In order to increase the acoustic sensitivity, the hollow cylindrical structure is developed for acoustic wave transduction. In addition, coherent phase detection is adopted to achieve the high precision phase signal demodulation, and thus to realize high-fidelity recovery of the airborne sound wave. Consequently, the spatial distributed acoustic sensing can be realized, which integrates a series of high-sensitive sensing units in a single fiber. The field test results of the airborne sound detection illustrate an excellent phase sensitivity of −112.5 dB ( re 1 rad/μPa) within the flat frequency range of 500 Hz–5 kHz and a peak sensitivity up to −83.7 dB ( re 1 rad/μPa) at 80Hz. The waveform comparison between the measurement result and the standard signal shows the maximum error of only 3.07%. Besides, distributed audio signal recovery and spatial acoustic imaging are demonstrated, which can be further applied in the field of fiber distributed microphone and urban noise intensity holography.

Numerical prediction of passenger cabin noise due to jet noise by an ultra–high–bypass ratio engine

Within the framework of the Collaborative Research Center 880, future civil transportation aircraft are investigated. One major aim is a drastic reduction of the noise emission to the ground and an appropriate noise immission into the passenger cabin. The latter forms the focus of this contribution with the aim to ensure an equal or lower noise level in the cabin for new aircraft configurations. Numerical methods are applied to establish a multidisciplinary modeling chain resulting in a prediction of cabin noise due to jet noise by two different engine configurations. An ultra–high–bypass ratio engine is compared to a conventional engine on the basis of a preliminary aircraft design used for both configurations. On the basis of flow calculations in cruise flight as operation point, the hybrid Computational Aeroacoustics solver PIANO combined with the Fast Random Particle Mesh method is applied to compute the pressure fluctuations due to jet noise on the outer skin of the fuselage. These loads are applied to a finite element model considering the structure and the fluid of the aircraft cabin. The acoustic model resolving the structure-borne and airborne sound waves is derived from the design data. The results show a lower sound pressure level induced by the ultra–high–bypass ratio engine in the entire frequency range on the outer skin. Within the cabin, the modern engine is still much quieter, though this fact is not generally valid for the entire frequency range as transmission effects of the double wall occur.

Preliminary attempts to isolate ground-radiated noise from exploding balloons

Seismo-acoustic coupling occurs when seismic wave propagation creates air-borne acoustic signals. Research is ongoing to determine methods to distinguish between sound due to seismo-acoustic coupling and purely air-borne transmission. In a field experiment, we detonated 17 in. balloons filled with a stoichiometric oxy-acetylene mix placed both on and in the ground. We attempted to isolate ground-radiated waves by constructing a portable soundproof box to deaden air-borne sound wave. The box was constructed from mass-loaded vinyl, soundproofing composite board, liquid nails, and Green Glue. This design incorporated soundproofing through decoupling, absorption, and insulation techniques. Signals observed from a microphone placed in the box are compared with those obtained on microphones outside the box at various heights. The initial blast wave was not evident inside the box. However, the loudest sound measured in the box matches a subsequent portion of signals on microphones near the ground. Testing in a reverberation chamber is done to measure the frequency response in the transmission loss through the box. These results could suggest a viable technique for isolating ground-borne acoustic waves, which could be useful in experiments where calculating the coupling effect is impractical.

Acoustic Imaging with Metamaterial Luneburg Lenses

The Luneburg lens is a spherically symmetrical gradient refractive index (GRIN) device with unique imaging properties. Its wide field-of-view (FoV) and minimal aberration have lead it to be successfully applied in microwave antennas. However, only limited realizations have been demonstrated in acoustics. Previously proposed acoustic Luneburg lenses are mostly limited to inherently two-dimensional designs at frequencies from 1 kHz to 7 kHz. In this paper, we apply a new design method for scalable and self-supporting metamaterials to demonstrate Luneburg lenses for airborne sound and ultrasonic waves. Two Luneburg lenses are fabricated: a 2.5D ultrasonic version for 40 kHz and a 3D version for 8 kHz sound. Imaging performance of the ultrasonic version is experimentally demonstrated.

The defect detection algorithm that combined spectrum entropy with vibrational energy ratio for acoustic inspection method

We have studied the non-contact and non-destructive acoustic inspection method using airborne sound wave and a laser Doppler vibrometer. Internal defects (crack, peeling etc.) of concrete near the surface are excited by vibrational energy of acoustic radiation. The resonance frequency of flexural vibration of the defect (inside to depth 8-10 cm) of concrete can be measured. By our technique, a non-destructive test is possible from a long distance more than 5 m max to 30 m. The two-dimensional vibration velocity data are measured and processed numerically. An image of the defect is reconstructed by vibrational energy ratio. There was a problem of an optical noise resulting from the leakage of light reception depending on surface state of concrete. To solve it, we introduced “Spectrum Entropy.” The data under influence of an optical noise show a frequency characteristic similar to a white noise. Spectrum entropy is calculated as an information entropy and express white nature of a signal. Therefore, we propose an algorithm that combines spectrum entropy with vibrational energy ratio. Our technique was applied to an experiment with a real concrete structure (bridge). The defective part was extracted as an image and the validity of our method was confirmed.

Innovative pharmaceutical approaches for the management of inner ear disorders.

The sense of hearing is essential for permitting human beings to interact with the environment, and its dysfunctions can strongly impact on the quality of life. In this context, the cochlea plays a fundamental role in the transformation of the airborne sound waves into electrical signals, which can be processed by the brain. However, several diseases and external stimuli (e.g., noise, drugs) can damage the sensorineural structures of cochlea, inducing progressive hearing dysfunctions until deafness. In clinical practice, the current pharmacological approaches to treat cochlear diseases are based on the almost exclusive use of systemic steroids. In the last decades, the efficacy of novel therapeutic molecules has been proven, taking advantage from a better comprehension of the pathological mechanisms underlying many cochlear diseases. In addition, the feasibility of intratympanic administration of drugs also permitted to overcome the pharmacokinetic limitations of the systemic drug administration, opening new frontiers in drug delivery to cochlea. Several innovative drug delivery systems, such as in situ gelling systems or nanocarriers, were designed, and their efficacy has been proven in vitro and in vivo in cochlear models. The current review aims to describe the art of state in the cochlear drug delivery, highlighting lights and shadows and discussing the most critical aspects still pending in the field.

An invisible acoustic sensor based on parity-time symmetry.

Sensing an incoming signal is typically associated with absorbing a portion of its energy, inherently perturbing the measurement and creating reflections and shadows. Here, in contrast, we demonstrate a non-invasive, shadow-free, invisible sensor for airborne sound waves at audible frequencies, which fully absorbs the impinging signal, without at the same time perturbing its own measurement or creating a shadow. This unique sensing device is based on the unusual scattering properties of a parity-time (PT) symmetric metamaterial device formed by a pair of electro-acoustic resonators loaded with suitably tailored non-Foster electrical circuits, constituting the acoustic equivalent of a coherent perfect absorber coupled to a coherent laser. Beyond the specific application to non-invasive sensing, our work broadly demonstrates the unique relevance of PT-symmetric metamaterials for acoustics, loss compensation and extraordinary wave manipulation.

Study on the Non-contact Acoustic Inspection Method for Concrete Structures by using Strong Ultrasonic Sound source

Hammering test is widely used to inspect the defects in concrete structures. However, this method has a major difficulty in inspect at high-places, such as a tunnel ceiling or a bridge girder. Moreover, its detection accuracy is dependent on a tester's experience. Therefore, we study about the non-contact acoustic inspection method of the concrete structure using the air borne sound wave and a laser Doppler vibrometer. In this method, the concrete surface is excited by air-borne sound wave emitted with a long range acoustic device (LRAD), and the vibration velocity on the concrete surface is measured by a laser Doppler vibrometer. A defect part is detected by the same flexural resonance as the hammer method. It is already shown clearly that detection of a defect can be performed from a long distance of 5 m or more using a concrete test object. Moreover, it is shown that a real concrete structure can also be applied. However, when the conventional LRAD was used as a sound source, there were problems, such as restrictions of a measurement angle and the surrounding noise. In order to solve these problems, basic examination which used the strong ultrasonic wave sound source was carried out. In the experiment, the concrete test object which includes an imitation defect from 5-m distance was used. From the experimental result, when the ultrasonic sound source was used, restrictions of a measurement angle become less severe and it was shown that circumference noise also falls dramatically.

Biomechanics of hearing in katydids.

Animals have evolved a vast diversity of mechanisms to detect sounds. Auditory organs are thus used to detect intraspecific communicative signals and environmental sounds relevant to survival. To hear, terrestrial animals must convert the acoustic energy contained in the airborne sound pressure waves into neural signals. In mammals, spectral quality is assessed by the decomposition of incoming sound waves into elementary frequency components using a sophisticated cochlear system. Some insects like katydids (or bushcrickets) have evolved biophysical mechanisms for auditory processing that are remarkably equivalent to those of mammals. Located on their front legs, katydid ears are small, yet are capable of performing several of the tasks usually associated with mammalian hearing. These tasks include air-to-liquid impedance conversion, signal amplification, and frequency analysis. Impedance conversion is achieved by a lever system, a mechanism functionally analogous to the mammalian middle ear ossicles, yet morphologically distinct. In katydids, the exact mechanisms supporting frequency analysis seem diverse, yet are seen to result in dispersive wave propagation phenomenologically similar to that of cochlear systems. Phylogenetically unrelated katydids and tetrapods have evolved remarkably different structural solutions to common biophysical problems. Here, we discuss the biophysics of hearing in katydids and the variations observed across different species.

Proposal of Non Contact Inspection Method for Concrete Structures Using High-Power Directional Sound Source and Scanning Laser Doppler Vibrometer

Maintenance for concrete structures such as buildings, bridges, and tunnels is necessary, because it is thought that a lot of them show deterioration. As a periodic inspection, a hammering test is the most popular method. However, it has several problems. One of the problems is that it is difficult to inspect the places where people cannot reach. Therefore, non contact inspection methods have been developed. As a non-contact inspection method, we propose a system consisting of a high-power directional sound source and a scanning laser doppler vibrometer (SLDV). In this method, an air-borne sound wave is used for the excitation of a concrete wall, and then the vibration velocities on the concrete wall are measured two-dimensionally by the SLDV. From the vibration velocity, defective parts can be detected. In this paper, we describe two types of experiment on the feasibility of our proposed method. In these experiments, concrete wall test pieces, which have artificial defects, are used. From the experimental results, we confirmed the effectiveness of our proposed method as a non contact inspection method for concrete structures.

Topology Optimized Cloak for Airborne Sound

Directional acoustic cloaks that conceal an aluminum cylinder for airborne sound waves are presented in this paper. Subwavelength cylindrical aluminum inclusions in air constitute the cloak design to aid practical realizations. The positions and radii of the subwavelength cylinders are determined by minimizing scattering from the cloak-structure and cylinder using the gradient-based topology optimization method. In the final optimization step, the radii of the subwavelength cylinders are constrained to three discrete values. A near-perfect narrow-banded and angular cloaking effect is obtained by optimizing for one target frequency. To get a larger bandwidth, the acoustic cloak is optimized for three frequencies at the cost of reduced peak cloaking performance at the center frequency.

Sound propagation in a pipe with dynamically rough boundary

The surface pattern of the water flow in partly filled circular pipe contains information on some key characteristics which are important for a better understanding of the hydraulic energy losses and turbulent processes. Surface pattern variation is a dynamic and nonstationary process which is difficult to measure directly. In this sense, airborne sound waves provide an attractive statistical mean which describes the apparent boundary roughness, its spatial correlation function, and frequency spectrum. These parameters can then be linked to key hydraulic characteristics of the flow. This work presents new experimental setup, which is used to study these characteristics under controlled laboratory conditions and allows for simultaneous measurements of the acoustic field in the pipe and water surface roughness. The acoustic technique makes use of Gaussian pulses which are transmitted in air above the turbulent flow of water over a carefully instrumented section and recorded on an intensity probe. The result...

Efficient Modelling of Absorbing Boundaries in Room Acoustic FE Simulations

Thanks to the rapidly increasing computational power of contemporary computer systems, acoustic finite element (FE) applications are nowadays widely used to predict the modal behaviour of airborne and structure-borne sound waves in enclosed cavities. In room acoustics it is by now mostly possible to simulate the whole frequency range below the Schroeder frequency using FEM in reasonable simulation times, thus making it a promising contender for extending the validity of typically ray-based room acoustic simulations to lower frequencies. However, while contemporary CAD and meshing tools facilitate the design of high quality geometric models with regular and sufficiently fine meshes, the Achilles' heel of room acoustic FEM simulations appears to be the realistic representation of the room boundaries. The present study investigates the influence of different boundary representations of porous absorbers on the simulated sound field in small rooms. Therefore measurements and FE simulations of the sound field in a scale model room with a well defined geometry and variable boundary conditions are conducted. Two different approaches are followed to model the porous absorbers on the room boundaries. Firstly the absorber layers are modelled with their exact 3D dimensions using an 'equivalent homogeneous fluid' (EHF) model. Secondly the acoustic characteristics of a porous absorber are modelled by an acoustic surface impedance for either normal or field/diffuse incidence, which is determined by measurement or model calculation. The paper clearly points out the limitations of the applied boundary models and also brings out the differences between these models. As a conclusion the paper shows that by using field incidence impedances instead of normal incidence impedances the quality of room acoustic FE simulation results can in some cases be increased considerably and comparable results to those obtained with a 3D absorber model can be achieved even for non-locally reacting materials.

Fast acoustic landmine detection using multiple beam laser Doppler vibrometry

An acoustic method of buried landmine detection consisting of excitation of the ground using airborne sound or seismic waves in the frequency range from about 50 Hz to 1000 Hz, and obtaining a velocity image of the ground surface with a laser Doppler vibrometer (LDV) has been developed and successfully tested in the laboratory and field experiments. The presence of a buried landmine can be detected by an abnormality in the velocity image. Initially, the scanning single‐beam LDV created a velocity image of the ground through point‐by‐point measurements, which resulted in a long measurement time. To reduce this measurement time, a multiple beam LDV having 16 beams configured in a linear array was developed and successfully used in field experiments. To further reduce the time of measurement, a full‐field LDV capable of making 256 vibration measurements in parallel on the target, configured as 16x16 square array of points equally separated in x‐ and y‐directions has been recently developed. The system is capable of creating a two‐dimensional vibrational velocity image of the ground surface in the time defined by the required frequency resolution. The parallel measurement makes the system a unique tool to measure transient vibrations.