Mode Attenuation Research Articles

Underwater sound propagation over a layered seabed with weak shear rigiditya).

The shear wave speed is often small compared to the compressional wave speed in the top part of the seabed, where acoustic normal modes penetrate. In sediments with weak but finite shear rigidity, the strongest conversion from compressional to shear waves occurs at interfaces within the sediment. Shear wave generation at such interfaces and interference within sediment layers lead to first-order perturbations in the normal mode phase speed and contributions to sound attenuation, which vary rapidly with frequency. Weak shear rigidity is shown to lead to unexpectedly strong mode group speed perturbations that retain finite magnitudes for very small shear speeds in range-independent waveguides. Variation of the waveguide parameters with range affects shear-induced attenuation and mode travel time perturbations in a different manner, depending on whether shear wave interference conditions vary appreciably along the propagation path. In horizontally inhomogeneous ocean, weak shear magnifies the horizontal refraction of adiabatic normal modes due to sloping intra-sediment interfaces. In contrast to normal modes, attenuation of lateral waves with range is insensitive to weak shear. Concurrent measurements of normal mode and lateral wave attenuation can be potentially used to identify and separate the contributions of dissipation and shear waves into observed sound attenuation.

An Electronic “Tongue” Based on Multimode Multidirectional Acoustic Plate Wave Propagation

This paper theoretically and experimentally demonstrates the possibility of detecting the five basic tastes (salt, sweet, sour, umami, and bitter) using a variety of higher-order acoustic waves propagating in piezoelectric plates. Aqueous solutions of sodium chloride (NaCl), glucose (C6H12O6), citric acid (C6H8O7), monosodium glutamate (C5H8NO4Na), and sagebrush were used as chemicals for the simulation of each taste. These liquids differed from each other in terms of their physical properties such as density, viscosity, electrical conductivity, and permittivity. As a total acoustic response to the simultaneous action of all liquid parameters on all acoustic modes in a given frequency range, a change in the propagation losses (ΔS12) of the specified wave compared with distilled water was used. Based on experimental measurements, the corresponding orientation histograms of the ΔS12 were plotted for different types of acoustic waves. It was found that these histograms for different substances are individual and differ in shape, area, and position of their extremes. Theoretically, it has been shown that the influence of different liquids on different acoustic modes is due to both the electrical and mechanical properties of the liquids themselves and the mechanical polarization of the corresponding modes. Despite the fact that the mechanical properties of the used liquids are close to each other, the attenuation of different modes in their presence is not only due to the difference in their electrical parameters. The proposed approach to creating a multi-parametric multimode acoustic electronic tongue and obtaining a set of histograms for typical liquids will allow for the development of devices for the operational analysis of food, medicines, gasoline, aircraft fuel, and other liquid substances without the need for detailed chemical analysis.

High extinction ratio TE-Pass polarizer using the effect of superstrate layer in Ge-Clad optical waveguide

Attenuation characteristics of germanium (Ge) film clad planar optical waveguide are theoretically studied at the spectral wavelength of 0.6328 μm. Thin films of Ge are found to possess greater attenuation values than the other recognized materials. The existence of these greater attenuations is caused by lossy modes that are sustained by these films. It has been shown that the attenuation of the TM mode can be greatly increased by adding a high-index buffer layer between the Ge layer and the dielectric guide. It occurred because of the resonant coupling between the lossy modes supported by the Ge layer and the waveguide modes. Moreover, it is claimed that by adding a dielectric superstrate layer above the Ge thin film, the strength of the TM mode in the proposed structure can be further attenuated to an ultra-high value. In this study, a TE pass polarizer is proposed having a high extinction ratio of 30582.15 dB. Attenuation results are presented, after optimization of several parameters like thicknesses of Ge, buffer, and superstrate layers along with environmental stability of the suggested structure. The generated field distribution profiles are also in good agreement with the obtained attenuation results.

Study on optical properties of hexagonal lattice photonic crystal fibers infiltrated with heavy water

In this paper, we analyzed a PCF made from fused silica glass, with a core filled with heavy water. The guiding properties of proposed fibers in terms of effective refractive index, attenuation, and dispersion of the fundamental mode were studied and optimized setups were selected and analyzed in detail. After 25 simulations, we determined two structures possessing optimal dispersion with the lattice constant (Ʌ) and the filling factor as follows: Ʌ = 1.1 µm, d/Ʌ = 0.92 for #F1 and Ʌ = 1.4 µm, d/Ʌ = 0.92 for #F2. Besides, high nonlinearity and low confinement loss are also outstanding points in our model. Thanks to these advantages, the proposed fibers have been targeted for flat and smooth broadband supercontinuum (SC) generation for near-infrared applications.

Experimental study of ultrasonic wave propagation in a long waveguide sensor for fluid-level sensing

This work reports an ultrasonic long waveguide sensor for measuring the fluid level utilizing longitudinal L(0,1), torsional T(0,1), and flexural F(1,1) wave modes. These wave modes were transmitted and received simultaneously using stainless-steel wire. A long waveguide (12 m) covers a broader region of interest and is suitable in the process industry's hostile environment applications, "fluid levels and temperature measurements." In this work, we used fluids "diesel, water, and glycerin" for measuring fluid levels based on the sensor's reflection factors from time domain and frequency domain signals. We examined the impact of wave modes' attenuation effects for long waveguide sensor design while changing the waveguide lengths. Initially, we obtained the L(0,1) and T(0,1) modes reflections from the 12.6 m waveguide length when one end of the long waveguide was fixed with a shear transducer at 45° orientation. Subsequently, we want to study and identify all wave modes'' (especially F mode) travel distances. Hence, we would like to investigate the guided wave propagation characteristics (attenuation, ultrasonic velocity, and frequency of all wave modes) in the long waveguide while cutting systematically at intervals of 1 meter, starting from its original length of the waveguide 12.6 meters by analyzing the A-scan signals of various lengths of a single waveguide. This simple and cost-effective technique can monitor the high fluid depths and temperature in power plants, oil, and petrochemical industries while designing a long waveguide sensor with appropriate ultrasonic parameters.

Composite sub-wavelength acoustic metasurfaces for acoustic mode attenuation

This paper reports an experimental investigation of a phase-gradient acoustic metasurface for duct acoustic applications, to evaluate the potential for attenuating acoustic modes and to understand the associated mechanism. The metasurface is a composite configuration where melamine foam as the main part includes a tunable wall. Given a target sound-absorbing frequency, a deeply sub-wavelength metasurface with a thickness-to-wavelength ratio of 1/6.86 is achieved. The unique way of assembling annular metasurfaces offers the possibility of fabricating three different configurations, which are then tested in a duct acoustic rig with artificially generated modes. The performance is assessed through in-duct modal analysis and far-field measurements. The results indicate excellent mode attenuation performance of the designed metasurface at broadband frequencies. The numerical simulation suggests that the mechanism can be related to the conversion from the incident mode to the evanescent waves due to the metasurface. In addition, the effects of the mode suppression are enhanced with the increase of the mode order, which can be attributed to the fact that the performance of the metasurface is influenced by the modal incidence angle. Overall, the present work provides a fascinating noise control method for ducted propulsion systems, and aeroengines in particular.

Variety of attenuation of RF suppression filters

Differential mode attenuation of RF suppression filters can be measured directly. Alternatively, this attenuation can be derived as modal S-Parameters from the S-Parameters measured for the single multiport paths which in fact the filter is. This paper outlines the differences between the two approaches. The first consists in direct measurement with separation transformers and the second with calculation from single ended measurement. In addition, the paper presents the method of determining the differential mode attenuation for the case of input and output impedance different from those used in direct measurements, i.e. by 50Ω/50Ω. At the same time, the presented method of determining the differential mode attenuation for different input and output impedances will require a change in the assumptions of the CISPR 17 document entitled ”Methods for measuring the attenuation characteristics of passive EMC filtering devices”, since the modal S-Parameter formulas presented in this document are only valid for the case when the RF suppression filter is in perfect balance. Otherwise, for different impedances it should be done taking into account the modification of the modal S-Parameters, as shown in this paper.The inclusion of this innovative change in the CISPR 17 document will allow the approach presented in this document to be used for various cases of the RF suppression filter, which is undoubtedly a significant progress in determining its attenuation.Frequency span by measurement of attenuation of RF Suppression filter is spanned from 10 kHz to 30 MHz.The comparison presented in this paper confirms that the S parameters are identical only if the filter is in equilibrium (ZL=ZN).From the results, three frequency areas can be distinguished. In the first interval between 10 kHz and 150 kHz the filter is in balance, which was demonstrated with identical measurement results. Between 150 kHz and 1.5 MHz, the attenuation is superimposed on the dynamics of the measurement system and therefore on the random frequency dependence of both measurements. Above 1.5 MHz there is a clear filter asymmetry, so the curves move away from each other.

Circular lattice benzene-core PCFs with flat near-zero dispersion for low-power broad-spectrum supercontinuum generation

A circular photonic crystal fiber infiltrated with benzene with different air-hole diameters is proposed as a new supercontinuum light source. Optical properties related to dispersion, effective mode area, nonlinear coefficient, and attenuation of the fundamental mode are investigated numerically. Two optimized structures are selected and verified against supercontinuum generation (SCG) in detail. The first structure (#F1) possesses all-normal dispersion, while the second (#F2) has a zero-dispersion wavelength. The possibility of coherent, octave-spanning SCG is proved by a 40 fs pulse, 1.064 μm wavelength, and 0.45 kW of power in-coupled into the core of #F1. Otherwise, injecting a 90 fs duration, 1.5 μm wavelength, and 0.555 kW peak power pump pulse into #F2 generates a broad SC spanning 0.76–4.23 μm. With the advantages of flat near-zero dispersion, high nonlinearity, low attenuation, and low input power used for SCG, the proposed fibers may lead to new low-cost all-fiber optical systems.

Sound designing classical guitars through metamaterials

An approach is presented to alter the sound of a classical guitar using a metamaterial structure. By adding additional masses using magnets in a row between the bridge and the soundhole, a bandgap of around 300 Hz appears. Alternation of magnet masses and placement determine the location and strength of the bandgap. A similar approach was presented with a frame drum [R. Bader, J. L. Fischer, M. Münster, and P. Kontopidis, “Metamaterials in musical acoustics: A modified frame drum,” JASA 145(5), 3086–3094 (2019)]. There, the lower and upper limits of the bandgap are caused by the relations between the frequency wavelength and the magnet distances. With the guitar, the bandgap is caused by a shifting and attenuation of modes. Interestingly, the added masses cause a decrease in the guitar top plate mode frequencies, which is similar to membrane behavior and contrary to the expectancy of a plate. Such a guitar sound is unique due to the strong bandgap and cannot be achieved with typical alternations of changed fan bracing or top plate thickness. Magnets can easily be applied by guitarists within minutes and, therefore, qualify as a guitar sound design chosen by players.

An Intelligent Charging Scheme for Lithium-Ion Batteries of Electric Vehicles Considering Internal Attenuation Modes

Charging control is one of the essential functions of battery management systems. Battery charging involves behavioral changes such as electricity, heat, and aging. Balancing these factors is crucial for the safe and efficient operation of batteries. This work proposes an intelligent charging scheme for lithium-ion batteries that considers charging time, temperature rise, and health losses. Firstly, charging aging experiments are conducted to investigate the effect of charging rate on battery aging. Specifically, half cell experiments are carried out to construct an electrode open circuit voltage model to explore battery aging modes. The aging mode attenuation model is proposed based on empirical formulas. Then, the charging multi-objective function is established based on the equivalent circuit, thermal, and aging empirical models. A multi-stage constant current charging optimization scheme has been developed based on the multi-objective grey wolf optimizer. Finally, the feasibility of three targets and dual targets fast charging schemes is verified through simulation and experiments.

Frequency reduction and attenuation of the tire air cavity mode due to a porous lining

The tire air cavity mode is known to be a significant source of vehicle structure- borne road noise near 200 Hz for current generation passenger vehicles, and a porous lining placed on the inner surface of a tire has proven to be an effective countermeasure. The two noticeable effects of such a lining are the reduction in the cavity resonance frequency and the attenuation of the air cavity mode. In the present work, through both theoretical and numerical analysis, the mechanisms underlying the effects of a porous lining were studied. A two-dimensional duct-shaped theoretical model and a two-dimensional torus-shaped numerical model were created to investigate the lined tire in conjunction with the Johnson- Champoux-Allard model describing the viscous and thermal dissipative effects of the porous material. The design parameters of the porous lining were varied to study their impact and to identify optimal ranges of the design parameters, in particular, the flow resistivity. Finally, in an experimental analysis, the sound attenuation and the frequency drop were observed in measurements of force, acceleration, and sound pressure. In conclusion, it was demonstrated that the suggested theoretical and numerical models successfully predict the effects of porous linings and that the frequency reduction results from the decreased sound speed within the tire owing to the presence of the liner.

Higher-order mode filtering by a resistive layer.

A method for filtering higher-order acoustic modes using a resistive layer is proposed and applied to a two-dimensional rectangular waveguide with a quiescent fluid. An analogue of Cremer's criterion is discussed and used to obtain the optimal modal attenuation of the non-planar waves while the plane wave is preserved. Numerical validation of the concept is performed for a straight waveguide and an abrupt expansion in a waveguide.

Numerical study of generation mechanisms of narrow spectral modes, emerging in a raman fiber laser with randomly distributed feedback

The present paper discusses possible influence of nonlinear effects, namely – the degenerate four-wave mixing process – upon the build-up and attenuation of narrow spectral modes, emerging in radiation of a Raman fiber laser with randomly distributed feedback.

Dynamic properties and the roton mode attenuation in liquid 3He: ab initio study within the self-consistent method of moments.

The dynamic structure factor and the eigenmodes of density fluctuations in liquid 3He are studied using a novel non-perturbative approach. This new version of the self-consistent method of moments invokes up to nine sum rules and other exact relations, the two-parameter Shannon information entropy maximization procedure, and the ab initio path integral Monte Carlo simulations which provide necessary reliable input information on the system static properties. Detailed analysis is performed of the collective excitations dispersion relations, the modes' decrements and the static structure factor of 3He at the saturated vapour pressure. The results are compared to available experimental data by Albergamo et al. (Albergamo et al. 2007 Phys. Rev. Lett. 99, 205301. (doi:10.1103/PhysRevLett.99.205301)) and Fåk et al. (Fåk et al. 1994 J. Low Temp. Phys. 97, 445-487. (doi:10.1007/BF00754303)). The theory reveals a clear signature of the roton-like feature in the particle-hole segment of the excitation spectrum with a significant reduction of the roton decrement in the wavenumber range [Formula: see text]. The observed roton mode remains a well-defined collective mode even in the particle-hole band, where it is strongly damped. The existence of the roton-like mode in the bulk liquid 3He is confirmed like in other quantum fluids. The phonon branch of the spectrum is in a reasonable agreement with the same experimental data. This article is part of the theme issue 'Dynamic and transient processes in warm dense matter'.

Frequency reduction and attenuation of the tire air cavity mode due to a porous lining

The tire air cavity mode is known to be a significant source of vehicle structure-borne road noise near 200 Hz. A porous lining placed on the inner surface of a tire is an effective countermeasure to attenuate that resonance. The two noticeable effects of such a lining are the sound pressure attenuation and the frequency reduction of the air cavity mode. In this paper, through both analytical and numerical methods, the mechanism of the effects of porous lining was studied. A two-dimensional duct-shaped analytical model and a tire-shaped numerical model were built to investigate the lined tire in conjunction with the Johnson-Champoux-Allard model describing the visco-inertial dissipative effects of the porous material. Design parameters of the porous lining were controlled to study their impact and optimal ranges of the design parameters were suggested. Finally, in experimental analysis, the sound attenuation and the frequency drop were observed in measurements of force, acceleration, and sound pressure. In conclusion, it was demonstrated that the suggested analytical and numerical models successfully predict the effect of porous lining and that the frequency reduction results from the decreased sound speed within the tire owing to the presence of the liner.

Laser Doppler vibrometry measurements of acoustic attenuation in optical fiber waveguides.

Fiber Bragg grating (FBG) sensors have been widely applied for structural health monitoring applications. In some applications, remote bonding of the optical fiber is applied, where ultrasonic waves are coupled from the structure to the optical fiber and propagated along the fiber to the FBG sensor. The distance that this signal can propagate along the optical fiber without decaying below a threshold value can be critical to the area of the structure that can be monitored per sensor. In this paper, we develop a method to measure the acoustic mode attenuation of fiber waveguides based on laser Doppler vibrometry (LDV) that is independent of the fiber type. In order to validate the method, we compare attenuation measurements on single-mode optical fibers using both the LDV and FBG sensor methods. Once the method is validated, experimental measurements of different coated and uncoated optical fibers are performed to quantify the role of the fiber diameter on the attenuation coefficient. As the radius of the waveguide decreases, the signal attenuation increases exponentially.

Resonant spin Hall effect of light in random photonic arrays

It has been recently shown that the coherent component of light propagating in transversally disordered media, the so-called coherent mode, exhibits an optical spin Hall effect (SHE). In non-resonant materials, however, this phenomenon shows up at a spatial scale much larger than the mean free path, making its observation challenging due to the exponential attenuation of the coherent mode. Here, we show that in disordered photonic arrays exhibiting Mie resonances, the SHE on the contrary appears at a scale smaller than the mean free path if one operates in the close vicinity of the lowest transverse-magnetic resonance of the array. In combination with a weak measurement, this gives rise to a giant SHE that should be observable in optically-thin media. Furthermore, we show that by additionally exploiting the cooperative emission of a flash of light following the abrupt extinction of the incoming beam, one can achieve a time-dependent SHE, observable at large optical thickness as well.

The effect of fluid flow in the longitudinal fracture along a borehole axis on Stoneley wave propagation

The characterization of fractures is essential to increase the production of hydrocarbon and geothermal resources. In this study, we investigate the effect of the fluid flow in the longitudinal fracture along a borehole on the dispersion and attenuation behavior of Stoneley waves using numerical experiments. In general, incorporating a fracture with the aperture of several tens to hundreds of micrometers into 3D seismic modeling is challenging with high calculational costs. We develop a novel numerical scheme that includes a 2D fluid flow simulation embedded into a 3D wave propagation modeling to address this problem. We devise an approach for capturing the effects of the fluid flow in the fractures of arbitrary aperture widths, which could be much thinner than the grid spacing of a 3D wave propagation simulation. A comparison of the numerical results from our scheme with the analytical solution indicates good agreement, supporting the method’s validity. This developed scheme is applied to the coupled simulation between the Stoneley wave propagation along the borehole axis and induced fluid flow inside a longitudinal fracture with different fracture apertures, fluid viscosity, and dynamic hydraulic conductivity. The modified matrix pencil algorithm applied to the recorded waveforms estimates the dispersion and attenuation of the Stoneley mode. The numerical results reveal the effect of the fracture aperture and fluid viscosity on the dispersion and attenuation behavior of the Stoneley waves. Based on the results, we demonstrate our scheme is an innovative method for estimating the aperture of the fracture and viscosity of the fluid by analyzing the dispersion and attenuation properties of the Stoneley waves.

Complex dispersion relations and evanescent waves in periodic magneto-electro curved phononic crystal plates

This paper presents a novel semi-analytical method to consider complex dispersion relations and evanescent wave characteristics in periodic magneto-electro-electric curved phononic crystal plates, based on the plate theory and Bloch-Floquet theorem. Generalized elastodynamic wave equation considering the magneto-electric effects in cylindrical coordinate system is established and discretized with the curved higher-order spectral elements. Then, the proposed approach is validated by the analysis of accuracy and convergence. The influence of magneto-electro coupling effect on dispersion relations are discussed. Significant parameters of the periodic curved phononic crystal are studied systematically, which fundamentally determines the tunability of complex dispersion relations of various guided wave modes including propagative wave modes, purely evanescent wave modes, evanescent edge wave modes, and complex wave modes. It is witnessed that propagative wave modes lead the bandgap to the emergence, variation, and closure with the change of significant parameters. And evanescent wave modes dominate two individual patterns of bandgaps. When the radius angle or curvature changes, the polarization of bandgaps appears. Furthermore, complex wave modes are generated with the increase of curvature resulting in strengthening the attenuation of propagative wave modes. The variation of lattice ratio can separate the intersection point of two propagative wave modes, which induces the opening of two bandgaps and the attenuation of evanescent wave modes. The results of this work provides may benefit the multi-functional development and application of smart materials and structures.

Effects of weak shear rigidity of the seabed on sound propagation in a range-dependent ocean

The shear wave speed is often small compared to the compressional wave speed in unconsolidated marine sediments. Sediment stratification and especially mass density variation in the seabed enhance the effects of weak shear on acoustic normal modes in range-independent ocean and produce significant shear wave contributions to mode attenuation in shallow water [O. A. Godin, J. Acoust. Soc. Am., 149, 3586–3598 (2021)]. A distinctive feature of the shear-induced perturbations in the mode phase speed and attenuation is their rapid variation with sound frequency due to shear wave interference within a sediment layer. This paper investigates theoretically the shear wave-induced perturbations in normal mode phase, travel time, and attenuation when water depth and/or sediment layer thickness vary gradually with range. Frequency dependencies of the adiabatic normal mode travel time and attenuation are found to be highly sensitive to range dependence of the seabed layering. Gradual changes in the sediment layer thickness have an effect similar to frequency averaging or artificially increased shear wave attenuation. Implications of these findings for geoacoustic inversions will be discussed. Contributions of shear rigidity and cross-range gradients of the sediment layer thickness to horizontal refraction of normal modes will be also examined. [Work supported by ONR.]