Acoustic Tunnel Research Articles

Acoustic Streaming Tunnel Enables Particle Velocity Stretching in Multiplex Flow Cytometry.

Multiplexed flow cytometry, known for its powerful high-throughput identification capability, is widely applied across various biomedical and clinical fields. However, classical flow cytometry relies on multichannel lasers and detectors, which are significant in cost and size, limiting their application in miniaturized assays. Herein, we developed an acoustic streaming-based flow cytometry technique that focuses on multisized microbeads flowing sheathlessly. This method enables the discrimination of particle types and the quantification of target protein concentrations using only a single detector. Microbeads of different sizes exhibit distinct behaviors in the continuous acoustic streaming tunnel, leading to an increased velocity difference during their transition under the laser spot. Consequently, a size detection method based on "velocity stretching" has been established. A multiplex assay of three proteins: cardiac troponin I, creatine kinase-MB and myoglobin, in acute myocardial infarction is performed to validate the feasibility and evaluate the performance of the system. This new multiplexed flow cytometry strategy is expected to enable low-cost and onsite detection of multiple biomarkers.

Extreme near-field heat transfer between silica surfaces

Despite recent experiments exhibiting an impressive enhancement in radiative heat flux between parallel planar silica surfaces with gap sizes of about 10 nm, the exploration of sub-nanometric gap distances remains unexplored. In this work, by employing non-equilibrium molecular dynamics (NEMD) simulations, we study the heat transfer between two SiO2 plates in both their amorphous and crystalline forms. When the gap size is 2 nm, we find that the heat transfer coefficient experiences a substantial ∼30-fold increase compared to the experimental value at the gap size of 10 nm confirming the dependence on the distance inversely quadratic as predicted by the fluctuational electrodynamics (FE) theory. Comparative analysis between NEMD and FE reveals a generally good agreement, particularly for amorphous silica. Spectral heat transfer analysis demonstrates the profound influence of gap size on heat transfer, with peaks corresponding to the resonances of dielectric function. Deviations from the fluctuational electrodynamics theory at smaller gap sizes are interpreted in the context of acoustic phonon tunneling and the effects of a gradient of permittivity close to the surfaces.

Acoustic tunnel lining cavity detection using cepstral coefficients with optimized filter bank

Tunnels are an essential component of modern transportation infrastructure, and their structural health is critical to traffic safety, which can be seriously affected by tunnel lining cavities. In this paper, an acoustic-based detection approach for assessing the integrity of tunnel linings is studied. By tapping the tunnel lining surface, acoustic signals are sampled and analyzed using a novel feature parameter extraction algorithm-the energy-frequency cepstral coefficient, which uses wavelet packet decomposition to obtain energy distribution statistics in the frequency domain of the signal, and constructs a signal-dependent filter bank to achieve the cepstral coefficient extraction. Compared with the traditional Mel filter bank, this method can adaptively adjust the resolution of the filter bank according to the frequency characteristics of the classified samples. This allows for higher frequency resolution in regions where the energy distribution is concentrated. As a result, the extracted feature parameters achieve both dimensional compression and superior information retention. Experimental results show that the proposed energy-frequency cepstral coefficient feature outperforms the traditional Mel-frequency cepstral coefficient feature, resulting in a higher accuracy of tunnel lining detection. The convolutional neural network model achieves an accuracy of 99.2%, with a 78.9% reduction in error rate compared with the traditional Mel-frequency cepstral coefficient feature parameters. Additionally, a particle swarm optimization support vector machine model is trained to achieve an accuracy rate of 99.6% and an error rate reduction of 76.5%.

A football-like acoustic metamaterial with near-zero refractive index and broadband ventilated sound insulation

Acoustic metamaterial with negative or near-zero refractive index exhibits extraordinary acoustic transmission characteristics, including acoustic total reflection, acoustic stealth and acoustic tunneling. Based on the coiled-up space structure, a football like near-zero refractive index acoustic metamaterial (FNZIM) was proposed. The result reveals the formation of two transmission peaks at 1270 Hz and 2300 Hz from the equivalent parameters by using the transfer matrix method. The first peak exhibits excellent air impedance matching, while the second peak arising from the metamaterial’s near-zero refractive index. We then constructed an acoustic prism using 15 cells of FNZIM and calculated the dispersion curve, revealing that the near-zero refractive index supernormal transmission of metamaterials is attributable to multimode degeneracy. Furthermore, we find that the positions of the transmission peaks and transmission loss can be adjusted by appropriately altering the structural parameters. Finally, we tested two groups of samples by using impedance tube four-channel to verify the accuracy of the simulation and the validity of insulation performance of FNZIM. The broadband ventilation sound insulation coupled structure is constructed, and the average sound insulation performance of this structure is more than 25 dB in the range of 1140–2210 Hz.

Application of a Deep Neural Network for Acoustic Source Localization Inside a Cavitation Tunnel

Navigating with low noise is the key capability in the submarine design considerations, and noise reduction is also one of the most critical issues in the related fields. Therefore, it is necessary to identify the source of noise during design stage to improve the survivability of the submarines. The main objective of this research is using the supervised neural network to construct the system of noise localization to identify noise source in the large acoustic tunnel. Firstly, we started our proposed method by improving the Yangzhou’s method and Shunsuke’s method. In the test results, we find that the errors of the both can be reduced by using the min-max normalization to highlight the data characteristics of the low amplitude in some frequency. And Yangzhou’s method has higher accuracy than Shunsuke’s method. Then, we reset the diagonal numbers of the cross spectral matrix in Yangzhou’s method to zero and replace mean absolute error to be the loss function for improving the stability of training, and get the most suitable neural network construction for our research. After our optimization, the error decreases from 0.315 m to 0.008 m in cuboid model test. Finally, we apply our method to the cavitation tunnel model. A total of 100 data sets were used for training, 10 sets for verification, and 5 for testing. The average error of the test result is 0.13 m. For the model test in cavitation tunnel in National Taiwan Ocean University, the length of ship model is around 7 m. And the average error is sufficient to determine the noise source position.

Acoustic transmissive cloaking with adjustable capacity to the incident direction

Zero-refractive-index (ZRI) phononic crystals (PhCs), in which acoustic waves can be transmitted without phase variations, have considerable potential for engineering wavefronts and thus are applicable to invisibility cloaking. However, the creation of the transmissive cloaking achieved by ZRI-PhCs is challenging under an oblique incidence, which substantially hinders their practical applications. Here, we experimentally demonstrate acoustic transmissive cloaking with the adjustable capacity to the incident direction. Acoustic transmissive cloaking of arbitrarily shaped obstacles can be obtained through a hybrid acoustic structure consisting of one outer layer of a programmable phase-engineered metasurface (PPEM) and one inner layer of a double zero-refractive-index (DZRI)-PhC. The DZRI-PhC is functionally the same as an equiphase area and can guide acoustic waves around the obstacle, a process known as acoustic tunneling. The PPEM perpendicularly transfers the incident acoustic waves to the DZRI-PhC and allows the emergent waves from the DZRI-PhC to transmit along the original incident direction. The DZRI-PhC is made of an array of iron squares in the air. The reciprocal of the effective bulk modulus and the effective mass density is approximately zero at a frequency of 3015 Hz (0.5187 v0/a) originating from the zeroth-order Fabry–Pérot (FP) resonance that possesses infinite phase velocities. Each meta-atom of the outer metasurface consists of a line channel and four shunted Helmholtz resonators, which have effective masses that are engineered by a mechanics system. The amplitude and phase of the sound waves propagating through each meta-atom can be controlled continuously and dynamically, enabling the metasurface to obtain versatile wavefront manipulation functions. Acoustic cloaking is visually demonstrated by experimentally scanning the acoustic field over the hybrid structure at a frequency of 3000 Hz (0.5160 v0/a). Our work may provide applications with great potential, including underwater ultrasound, airborne sound, acoustic communication, imaging, etc.

Manipulation of single cells via a Stereo Acoustic Streaming Tunnel (SteAST)

At the single-cell level, cellular parameters, gene expression and cellular function are assayed on an individual but not population-average basis. Essential to observing and analyzing the heterogeneity and behavior of these cells/clusters is the ability to prepare and manipulate individuals. Here, we demonstrate a versatile microsystem, a stereo acoustic streaming tunnel, which is triggered by ultrahigh-frequency bulk acoustic waves and highly confined by a microchannel. We thoroughly analyze the generation and features of stereo acoustic streaming to develop a virtual tunnel for observation, pretreatment and analysis of cells for different single-cell applications. 3D reconstruction, dissociation of clusters, selective trapping/release, in situ analysis and pairing of single cells with barcode gel beads were demonstrated. To further verify the reliability and robustness of this technology in complex biosamples, the separation of circulating tumor cells from undiluted blood based on properties of both physics and immunity was achieved. With the rich selection of handling modes, the platform has the potential to be a full-process microsystem, from pretreatment to analysis, and used in numerous fields, such as in vitro diagnosis, high-throughput single-cell sequencing and drug development.

Acoustic wave tunneling across a vacuum gap between two piezoelectric crystals with arbitrary symmetry and orientation

It is not widely appreciated that an acoustic wave can ``jump'' or ``tunnel'' across a vacuum gap between two piezoelectric solids, nor has the general case been formulated or studied in detail. Here, we remedy that situation, by presenting a general formalism and approach to study such an acoustic tunneling effect between two arbitrarily oriented anisotropic piezoelectric semi-infinite crystals. The approach allows one to solve for the reflection and transmission coefficients of all the partial-wave modes, and is amenable to practical numerical or even analytical implementation, as we demonstrate by a few chosen examples. The formalism can be used in the future for quantitative studies of the tunneling effect in connection not only with the manipulation of acoustic waves, but with many other areas of physics of vibrations such as heat transport, for example.

Acoustic manipulation of fractal metamaterials with negative properties and near-zero densities

Acoustic metamaterials have high potential in diverse applications, including acoustic cloaking, sound tunneling, wavefront reshaping, and sound insulation. In the present study, new metamaterials consisting of spatially coiled units are designed and fabricated to manipulate sound waves in the range of 0–1600 Hz. The effective acoustic properties and band diagrams of the metamaterials are studied. The simulation and experimental results demonstrate that the metamaterials provide an effective and feasible approach for designing acoustic devices such as sound cloaking and insulators.

Acoustic Tunneling Study for Hexachiral Phononic Crystals Based on Dirac-Cone Dispersion Properties

Acoustic tunneling is an essential property for phononic crystals in a Dirac-cone state. By analyzing the linear dispersion relations for the accidental degeneracy of Bloch eigenstates, the influence of geometric parameters on opening the Dirac-cone state and the directional band gaps’ widths are investigated. For two-dimensional hexachiral phononic crystals, for example, the four-fold accidental degenerate Dirac point emerges at the center of the irreducible Brillouin zone (IBZ). The Dirac cone properties and the band structure inversion problem are discussed. Finally, to verify acoustic transmission properties near the double-Dirac-cone frequency region, the numerical calculation of the finite-width phononic crystal structure is carried out, and the acoustic transmission tunneling effect is proved. The results enrich and expand the manipulating method in the topological insulator problem for hexachiral phononic crystals.

TUNABLE CONTROL AND FUNCTIONAL SWITCH OF TRANSMITTED ACOUSTIC WAVES BY AN ARCH-SHAPED METASURFACE

A tunable transmitted three-tunnel helix unit cell is designed based on the working principle of the “screw-nut”. The length of the acoustic tunnel is changed by the screw-in depth of the screw, and then the phase of the transmitted waves can be tuned accordingly. The variations of the phase shift and transmittance of the unit cell with the screw-in depth and frequency are calculated by the finite element method. The generalized Snell's law of an flat surface is extended to an arc-shaped surface in this paper. The arch-shaped and toroidal metasurfaces are designed to regulate the wavefront of the transmitted acoustic wave. According to the presupposed acoustic function and the working frequency, the phase gradient of the metasurface and the screw-in depth of every unit can be determined by the generalized Snell's law of the arc-shaped surface and the variation of the phase shift of the unit cell with the screw-in depth. And the screw-in depth will be modified according to the variation of the transmittance of the unit cell in order to obtain the high transmission. The functional switch between the directional refraction, beam splitting and beam focusing for the arch-shaped metasurface is realized in a broadband frequency region. And the functional switch between the three-way splitting of wave beam, spiral wave generation and virtual movement of the source position is also realized for the toroidal metasurface. The full-field numerical simulations are performed by using the finite element method. And the experimental measurements are also carried out for both arch-shaped and toroidal metasurfaces. The experimental results have a good agreement with the numerical ones, which shows that the metasurfaces we designed are effective for the wavefront modulation of the transmitted acoustic waves. The study in this paper is relevant to the development of tunable irregular non-planar conformal acoustic devices.

Dissipation and acoustic tunnelling about the sonic horizon of Bondi accretion

Viscous dissipation, as a small perturbative effect about the Bondi flow, shrinks its sonic sphere. An Eulerian perturbation on the steady flow gives a wave equation and the corresponding dispersion relation. The perturbation is a high-frequency travelling acoustic wave, in which small dissipation is taken iteratively. The wave, propagating radially outwards against the bulk inflow, is blocked just within the sonic horizon, where the amplitude of the wave diverges because of viscosity. The blocked acoustic wave can still tunnel outward through the horizon with a viscosity-dependent decaying amplitude, scaled by the analogue Hawking temperature. The escape of acoustic waves (analogue Hawking phonons) through the sonic horizon is compatible with the radial contraction of the sonic sphere.

Realization of acoustic supercoupling through a density-near-zero metamaterial

The supercoupling effect, which enables wave transmission through a subwavelength tunnel, has various applications, including subwavelength focusing and energy harvesting and sensing. We constructed a metamaterial with a density near zero using a membrane as a lumped element and created a subwavelength acoustic tunnel. Although this tunnel has a diameter of λ/40 and a cross-sectional area of only 2.25% of that of the normal waveguides connected to the channel, the tunnel acts as a nearly perfect acoustic supercoupler by transmitting 95.1% of the incident acoustic energy without a phase delay. These results could open up new possibilities for developing various devices in fields that use acoustic waves such as noise control, signal processing and medical imaging.

Skin Friction Measurements of Transition in High Reynolds Number, Adverse Pressure Gradient Flow

Abstract A combined experimental and analytical modeling effort has been carried out to measure the skin friction response of the boundary layer in high Reynolds number adverse pressure gradient flow. The experiment was conducted in the United Technologies Research Center (UTRC) Acoustic Research Tunnel, an ultra-low freestream turbulence facility capable of laminar boundary layer research. Boundary layer computational fluid dynamics and stability modeling were used to provide pre-test predictions, as well as to aid in interpretation of measured results. Measurements were carried out at chord Reynolds numbers 2–3 × 106, with the model set at multiple incidence angles to establish a range of relevant leading edge pressure gradients. The combination of pressure gradient and flight Reynolds number testing on a thin airfoil has produced a unique data set relevant to propulsion system turbomachinery.

Acoustic transmissive cloaking using zero-index materials and metasurfaces

A design of acoustic transmissive cloaking is proposed using a hybrid cloaking shell. The shell consists of one layer of metasurface to manipulate both the incident and exit acoustic wavefronts and one layer of zero-index metamaterial to achieve acoustic energy tunneling. Incident acoustic wave will remain its wavefront after propagating through our hybrid cloaking shell constructed by experimentally realizable acoustic metamaterials. As there is no intrinsic limit to the object to be cloaked, the strategy of our transmissive cloaking geometry has wide potential applications in both airborne sound and underwater ultrasound.

Acoustic Tunnelling of Internal Gravity waves in the stratified fluids

This paper focuses on the study of acoustic propagation of internal gravity waves which generates small scale variations through propagation and hence can obtain transmission co-efficients using N2 buoyancy frequency variation of a compressible stratified fluid for a small regions. We have also analysed the results using the asymptotic expansions for large compressible limits. The reduction of the transmission in the N2-barrier region for the density layers sandwiched along with acoustic waves is obtained through graphs for different density barrier regions. The dispersion characteristics shows the contours of the transmission in the wave number plane. The curves for ! < N0 are hyperbolic, representing internal gravity waves as these become the dispersionwaves for an incompressible fluid and the curve with ! > N0 are ellipsoids which represent the acoustic gravity or infrasonic waves for the cut off frequency

Instantaneous Incident Detection System Based on Analysis of Acoustic Signal from Crash and Skid in Tunnel

Introduction:An acoustic signal-based tunnel accident detection system was developed in this study. In a tunnel environment, the sound diffusion effect is minimized and thanks to that, discrimination of accident sounds (crash and skid) from other noises can apparently be accomplished.Discussion:The system is composed of three parts: algorithm, field device, and center system. To distinguish accident-related acoustic signals such as a crash or skid among various other sounds in a tunnel, a delicate algorithm that can discriminate those signals from other normal signals generated from moving vehicles was created.Conclusion:The developed algorithm processes acoustic signals to filter out noises and to identify accident-related signals. The field device, installed in a tunnel, collects analog sounds, transforms them into digital signals, and transmits the digital signals to the server in the tunnel traffic management center. Lastly, in the tunnel traffic management center, the acoustic signal processing algorithm described above, installed in a server system, can instantaneously detect accidents. Once confirmed by the system operators, the information on the detected accidents is intended to be provided to drivers following behind as well as relevant agencies to prevent secondary accidents and to respond promptly. The developed system was evaluated in a real tunnel environment using traffic accident sounds acquired from real crash tests. The detection rates were 95, 91, and 80% at distances of 10, 30, and 50 m, respectively with a detection duration less than 1.4 s. Compared to conventional detection systems using loop detectors or video images that have a long detection time of around 1 min, the developed system can be regarded as superior in that it has an extremely short detection time, which, of course, is one of the most important factors for automatic incident detection systems.

Dirac cones in two-dimensional acoustic metamaterials

Dirac cones show many extraordinary properties, including Klein tunneling, pseudo-diffusive behavior, phase reconstruction, and topological edge states, and are thus attracting increasing research attention. However, no studies of Dirac cones on a subwavelength scale have been reported to date. In this paper, subwavelength-scale Dirac cones are realized using acoustic metamaterials that consist of hexagonal arrays of hexagonal columns with Helmholtz resonators. We have calculated the band structures of the three types of unit cells that are yielded by space group symmetry operations of the triangular Helmholtz resonators. The results show that these acoustic metamaterials with Helmholtz resonators can be used successfully to reduce the Dirac cone frequencies. Subwavelength Dirac cones of acoustic metamaterials with p6 mm or p6 symmetries are robust to rotation, while subwavelength Dirac cones of acoustic metamaterials with p31m symmetry are sensitive to rotation. In addition, the Dirac cone frequency decreases gradually with increasing filling ratio, which indicates a possible way to control wave propagation on the subwavelength scale. Numerical simulation results show that acoustic metamaterials can behave like zero-refractive-index media and can be applied to acoustic tunneling. The acoustic metamaterials designed in this work offer a route towards the design of functional acoustic devices operating on subwavelength scales.

Double Dirac cone in two-dimensional phononic crystals beyond circular cells

A double Dirac cone plays a significant role in the design of zero-refractive-index metamaterials without phase variation and topological insulators with pseudospin states. We present a study on the formation of a double Dirac cone in two-dimensional phononic crystals consisting of either hexagonal or triangular columns in air. We arranged hexagonal and triangular columns separately in a honeycomb lattice to explore the influence of phononic crystal symmetry on the formation of the double Dirac cone. The results show that phononic crystals forming a honeycomb lattice with C6v or C6 symmetry induce an accidental degeneracy, but C3v and C3 cannot. We also demonstrate that by varying the filling ratio of the hexagonal columns, a topological phase transformation induced by energy band inversion with dipolar and quadrupolar states occurs near the double Dirac cone. Transmission properties for acoustic tunneling and waveform shaping are confirmed in two numerical simulation examples. A discussion is given on the formation of the double Dirac cone in different phononic crystal symmetries in a honeycomb lattice. The conclusions suggest a new route for designing topological and zero-refractive-index acoustic devices.

Broadband Focusing Acoustic Lens Based on Fractal Metamaterials.

Acoustic metamaterials are artificial structures which can manipulate sound waves through their unconventional effective properties. Different from the locally resonant elements proposed in earlier studies, we propose an alternate route to realize acoustic metamaterials with both low loss and large refractive indices. We describe a new kind of acoustic metamaterial element with the fractal geometry. Due to the self-similar properties of the proposed structure, broadband acoustic responses may arise within a broad frequency range, making it a good candidate for a number of applications, such as super-resolution imaging and acoustic tunneling. A flat acoustic lens is designed and experimentally verified using this approach, showing excellent focusing abilities from 2 kHz and 5 kHz in the measured results.