Band Attenuation Research Articles

Insertion loss prediction of sonic crystal noise barriers covered by porous concrete using the Method of Fundamental Solutions

Noise attenuation by sonic crystal noise barriers occurs mainly in specific frequency bands (bandgaps), due to a mechanism called Bragg scattering, which is the result of destructive interference between multiple reflections. To improve their performance, sound-absorbing materials may be used to coat the rigid scatterers, increasing attenuation in other frequency bands. In this work, the Method of Fundamental Solutions (MFS) is used to evaluate the performance of sonic crystal noise barriers with cylinders covered by porous and granular materials simulating the volume of the absorbent material using equivalent fluid models for porous or granular materials. The proposed numerical models were validated by experimental tests and, afterwards, these numerical models were verified through the comparison with results obtained using the Finite Element Method (FEM). Finally, several numerical tests were performed in order to understand/predict the acoustic behavior of the sonic crystal noise barriers covered with porous concrete.

New low-frequency broadband metamaterials based on inerter and novel large-linear negative stiffness mechanism

Elastic metamaterials are recently emerging structural–functional materials, which provide a new way for the control of elastic waves. However, the current low-frequency broadband performance is yet to be further improved. Herein, a novel large-linear negative stiffness mechanism is first proposed, which is capable of generating constant negative stiffness; the influences of the relevant structural parameters are discussed, and a design method for this mechanism is also given. Subsequently, a new type of elastic metamaterial is designed by combining the inerter and the proposed negative stiffness mechanism; a parametric programming method with general characteristics is proposed to guide the selection of unit-cell parameters, and it is revealed that only at most one negative stiffness spring is allowed to exist in the system. Finally, the low-frequency broadband characteristics of the metamaterial are investigated. It is found that the proposed metamaterial can produce a basin-like attenuation band, i.e., the attenuation curve at the bottom of the attenuation band is a stable flat line; in a given frequency range, the introduction of negative stiffness can further increase the attenuation strength of the metamaterial basin-like band.

Band gaps in an acoustic metamaterial composed of resonator with elastic support

In this paper, the band gaps in a mass-spring structure composed of resonator with elastic support are investigated. The band structure, effective parameters, and transmission spectra of the acoustic metamaterials are calculated numerically. The numerical results show that the elastic support and resonator in the structure generate the first and the second band gap, respectively. The effective parameters are analyzed to reveal the nature of this phenomenon and calculated to obtain the edge frequencies of band gaps. The transmission spectra are in accordance with the complex band structure. It is found that the attenuation factor is non-zero in band gap, and it determines the shape and magnitude of transmission ratio in band gap. The influences of the structural parameters on the band structure and attenuation factor are investigated numerically. Numerical results show that the band structure can be modulated by changing the structural parameters, and the topological structure will be changed when those parameters change greatly.

The Impact of Gamma Irradiation on Optical Fibers Identified Using Long Period Gratings

This paper compares the impact of gamma irradiation on various optical fibers, where the evolution in their optical properties could be identified using long period gratings (LPG) there induced. The LPGs were fabricated in broad spectrum of commercially available single-mode optical fibers - from standard to unconventional ones - using the electric arc discharge method. The fused silica fiber material contained such dopant as Ge, F, B/Ge and P. The gamma exposure has been performed with a dose rate of 2.6 kGy/h for 20 h (a total dose of 52 kGy). Subsequently, the recovery effect was monitored during the following 48 h. The wavelength shift and power change of the LPG attenuation bands during irradiation were investigated in real time. Moreover, to identify the impact of gamma treatment on the fiber properties, the thermal response of the gratings was studied before and after the irradiation. Depending on the fiber, significant differences have been observed in the grating responses. The highest radiation-dependent resonance wavelength shift has been found for B/Ge fiber (∼10 nm at maximum dose). Moreover, for these LPGs no response saturation within the applied dose levels has been observed together with very low recovery effect, what differentiate these LPGs from the other tested in this experiment. Finally, concerning the changes in optical power at the resonance wavelength, the LPG induced in P-doped fiber has shown a strong irradiation-induced attenuation reaching 18 dB with a negligible recovery effect. The findings reported in this work are crucial for optical fiber and optical fiber sensors application in environments exposed to radiation.

Feature Extraction of a Non-Stationary Seismic–Acoustic Signal Using a High-Resolution Dyadic Spectrogram

Using a novel mathematical tool called the Te-gram, researchers analyzed the energy distribution of frequency components in the scale–frequency plane. Through this analysis, a frequency band of approximately 12 Hz is identified, which can be isolated without distorting its constituent frequencies. This band, along with others, remained inseparable through conventional time–frequency analysis methods. The Te-gram successfully addresses this knowledge gap, providing multi-sensitivity in the frequency domain and effectively attenuating cross-term energy. The Daubechies 45 wavelet function was employed due to its exceptional 150 dB attenuation in the rejection band. The validation process encompassed three stages: pre-, during-, and post-seismic activity. The utilized signal corresponds to the 19 September 2017 earthquake, occurring between the states of Morelos and Puebla, Mexico. The results showcased the impressive ability of the Te-gram to surpass expectations in terms of sensitivity and energy distribution within the frequency domain. The Te-gram outperformed the procedures documented in the existing literature. On the other hand, the results show a frequency band between 0.7 Hz and 1.75 Hz, which is named the planet Earth noise.

Computing dispersion diagrams and forced responses of arbitrarily varying waveguides

Periodic structures can be used for vibration control thanks to their vibration attenuation stop bands. The dispersion diagram obtained for the structural unit cell can be used to characterize such wave attenuation bands. Several designs using spatially varying unit cells have recently been reported in the literature. Spatially varying properties can also be used to investigate the effect of variability on finite structures. Therefore, various methodologies to model spatially varying structures have been recently developed. This work presents new numerical methodologies to compute (i) dispersion diagrams and (ii) forced responses of one-dimensional spatially varying periodic waveguides. The first method extends previous work using a state-space formulation to compute dispersion relations using a linear time-varying system dynamics approach. The methodology is applied to elementary rods, Saint-Venant shafts, Euler–Bernoulli beams, and Timoshenko beams, and the results are validated with discretized spectral element models and the plane wave expansion method. The proposed approach is shown to be more efficient in cases where the plane wave expansion method presents a slow convergence. The second method is a recursive dynamic condensation to compute forced responses using the dynamic stiffness matrix of the unit cell. The results and computational times of the proposed recursive condensation are compared with the direct assembly of a global dynamic stiffness and its standard dynamic condensation. The two proposed methods are shown to be more efficient and accurate in the computation of dispersion diagrams and forced responses of one-dimensional structures for which the elastodynamic equations are known.

A high-resolution extinction mapping technique for face-on disc galaxies

ABSTRACT We present a new dust extinction technique with which we are able to retrieve parsec-scale gas surface density maps for entire nearby galaxies. The method measures the dust attenuation in optical bands on a pixel-by-pixel basis against a smoothed, reconstructed stellar distribution. The contribution of foreground light along the line-of-sight is calibrated using dust emission observations, assuming that the dust sits in a layer close to the mid-plane of the face-on galaxy. Here, we apply this technique to M51 (NGC 5194) as a proof-of-concept, obtaining a resolution of 0.14 arcsec (5 pc). Our dust (and gas) surface density map is consistent with independent dust- and CO-based studies at lower resolution. We find that discrepancies between our estimates of surface density and other studies stem primarily from the choice of dust model (i.e. different dust absorption coefficients). When assuming the same dust opacity law, our technique produces surface densities that are consistent with independent studies. This dust extinction technique provides us with gas surface density maps at an unprecedented resolution for full disc coverage studies of nearby galaxies. The resulting well-resolved spatial information opens the possibility for more in-depth examination of the influence of large-scale dynamics (and also stellar feedback mechanisms) on the interstellar medium at parsec-scales, and consequently star formation in nearby galaxies.

Portovenography Findings Following Partial Polypropylene Versus Thin Film Band Attenuation of a Single Congenital Extrahepatic Portosystemic Shunt: A Prospective Randomized Study in Dogs.

The objective was to conduct a prospective, randomized study to compare mesenteric portovenogram findings following partial polypropylene suture versus thin film band extrahepatic portosystemic shunt attenuation in dogs. Dogs with extrahepatic portosystemic shunts that could not tolerate complete acute shunt closure received a partial attenuation with either a polypropylene suture or synthetic polymer thin film band. At a routine second surgery three months after shunt patency, missed shunt branches and/or development of multiple acquired shunts were assessed using intra-operative mesenteric portovenography. Twenty-four dogs were enrolled, 12 received partial polypropylene suture ligation, and 12 received partial thin film band shunt attenuation. Intra-operative mesenteric portovenography three months later demonstrated that nine dogs (75%) in the thin film band group had achieved complete shunt closure versus two dogs (16.7%) in the polypropylene suture group, which was significantly different (p = 0.004). No dogs in the polypropylene suture group and two dogs (16.7%) in the thin film band group developed multiple acquired shunts. This is the first study directly comparing follow-up intra-operative mesenteric portovenography imaging findings between two methods of partial portosystemic shunt attenuation in dogs. The study provides accurate information on the rates of complete anatomical shunt closure and development of multiple acquired shunts following partial shunt attenuation with either synthetic polymer thin film band or polypropylene suture.

An investigation on the acoustic impedance of a viscously damped micro-perforated rectangular membrane

A theoretical method base on the zero-slip boundary and a finite element model with thermoviscous membrane-acoustic interaction are proposed for investigating a viscously damped micro-perforated rectangular membrane. Both the theoretical and finite element methods well predicted the sound absorption performance of a dielectric elastomer micro-perforated membrane, and the results agree with those from experiments. The thermoviscous membrane-acoustic interaction is further explored. The properties which lead to better acoustic performance are studied using the developed numerical model. With the optimized parameters, a duct silencer with high transmission loss (>10 dB) and broad noise attenuation band (from 300 Hz to 1700 Hz) is designed, fabricated, and tested. The potential engineering application and the background physical mechanism are also addressed.

Factors influencing the electromagnetic transmission of mercury vapor discharge plasma tube arrays

Low-pressure Mercury vapor discharge plasma tubes were used to form arrays to control electromagnetic transmission. The internal and external factors influencing a discharge tube array were adjusted to expand the electromagnetic wave manipulation ability. The plasma electron density (n e) is the key parameter for electromagnetic wave manipulation. Microwave transmission was used to diagnose n e under different working conditions. Simulations and electromagnetic transmission measurements were used to investigate the behavior of the effect of internal and external factors on electromagnetic transmission. Simulation results indicated that increasing n e increased the attenuation, widened the attenuation bandwidth, and shifted the attenuation band to higher fRequencies. The experimental results showed that increasing the discharge power significantly increased n e and widened the strong attenuation frequency band. n e first increased and then decreased when the gas pressure was increased. The tube diameter affected both n e and the plasma layer thickness, and the attenuation band of the plasma tube array moved to a low frequency with an increase in tube diameter. The primary and secondary order of the influence of external factors other than power on the attenuation bandwidth obtained via an orthogonal experiment is as follows: gas composition > tube diameter > pressure. The maximum attenuation bandwidth for 10 dB attenuation was 9.85 GHz. The results show that the attenuation control ability of the plasma tube array can be significantly improved by adjusting the external factors of the plasma tube.

A 77.3-dB SNDR 62.5-kHz Bandwidth Continuous-Time Noise-Shaping SAR ADC With Duty-Cycled Gm-C Integrator

This article presents a first-order continuous-time (CT) noise-shaping successive-approximation-register (NS-SAR) analog-to-digital converter (ADC). Different from other NS-SAR ADCs in literature, which are discrete-time (DT), this ADC utilizes a CT Gm-C integrator to realize an inherent anti-aliasing function. To cope with the timing conflict between the DT SAR ADC and the CT integrator, the sampling switch of the SAR ADC is removed, and the integrator is duty cycled to leave 5% of the sampling clock period for the SAR conversion. Redundancy is added to track the varying ADC input due to the absence of the sampling switch. A theoretical analysis shows that the 5% duty-cycling has negligible effects on the signal transfer function (STF) and the noise transfer function. The output swing and linearity requirements for the integrator are also relaxed thanks to the inherent feedforward path in the NS-SAR ADC architecture. Fabricated in 65-nm CMOS, the prototype achieves 77.3-dB peak signal-to-noise and distortion ratio (SNDR) in a 62.5-kHz bandwidth while consuming <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$13.5~\mu \text{W}$ </tex-math></inline-formula> , leading to a Schreier figure of merit (FoM) of 174.0 dB. Moreover, it provides 15-dB attenuation in the alias band.

Performance of rubber-concrete composite periodic barriers applied in attenuating ground vibrations induced by metro trains

Recently, the use of periodic vibration isolation barriers (PVIBs) has emerged as a significant method for attenuating environmental vibrations along the propagation path. Previous studies have indicated that periodic infilled trenches and piles can effectively isolate low-frequency surface waves. However, a considerable number of these periodic structures require full-size shipments or cast-in-place construction, thus increasing the shipment difficulty or construction period. In addition, few experimental studies have reported on the performance of PVIBs under underground excitation. To solve these problems, this study proposes a novel periodic composite rubber-concrete barrier (PCRCB) with prefabricated assembly characteristics. A laboratory test was performed, in which the calculated frequency band gap (FBG) and attenuation zones of the optimised PCRCB were validated under ground-borne and underground hammering excitations. Then, a numerical model was developed to analyse the vibration mitigation effect of the optimised PCRCB considering the metro train loads. The results of the laboratory study demonstrated that the depth of the impact load affects ground vibration attenuation. The optimised PCRCB has been proven to exhibit good vibration isolation performance. The results of the numerical study demonstrate that the vibration mitigation effect of the PCRCB on the ground surface is good under underground metro train loads. The insertion loss (IL) increases, but its value is less than 2 dB, with the ratio of burial depth to tunnel base depth increases from 1 to 2 times. Accordingly, the ratio of the burial depth to the tunnel base depth is recommended to be 1 in the vibration isolation project of an underground metro train.

Composite collaborative acoustic metamaterials: Isolating shaft vibration of guide roller in printing machine

During the operation of the unit type gravure press, the violent mechanical vibration generated by the guide roller will seriously affect the stability of the unit operation, and causing transmission faults such as wrinkle, offset, scratch or fracture, and reducing the printing accuracy. To this problem, a novel multi-approach composite collaborative vibration isolator which combines the local resonator and multi-layer composite structure is proposed to solve the problems of vibration suppression in the single frequency and vibration energy dissipation in the full frequency band, respectively, and the theoretical model on the proposed isolator is established basing on dynamic stiffness method. For demonstrating isolation performance, the regularized normalized modal displacement, power loss density, elastic strain energy density, total kinetic energy, and vibration transmission ratio can be discussed. The results show that the composite vibration isolator has a wide vibration isolation band, and the vibration wave has two attenuation bands within 0–2000 Hz. The first attenuation band is 188–224 Hz and the width is 36 Hz; the second attenuation band is greater than 328 Hz. When the band of the vibration isolator is above 700 Hz, the vibration transmission ratio shows a monotonous decreasing trend. Furthermore, an experimental platform for the vibration isolation device of the guide roller is established to verify the vibration isolation performance. When the drive motor frequency is 20 Hz, the composite vibration isolator has the best vibration isolation effect. At the same time, the vibration isolation effect gradually decreases with the increase of the guide roller speed, but it still has preferable vibration isolation performance under various working conditions.

Beamspace Channel Estimation for Wideband Millimeter-Wave MIMO: A Model-Driven Unsupervised Learning Approach

Millimeter-wave (mmWave) communications have been one of the promising technologies for future wireless networks that integrate a wide range of data-demanding applications. To compensate for the large channel attenuation in mmWave band and avoid high hardware cost, a lens-based beamspace massive multiple-input multiple-output (MIMO) system is considered. However, the spatial-wideband effect in wideband mmWave systems makes channel estimation very challenging, especially when the receiver is equipped with a limited number of radio-frequency (RF) chains. Furthermore, the real channel data cannot be obtained before the mmWave system is used in a new environment, which makes it impossible to train a deep learning (DL)-based channel estimator using real data set beforehand. To solve the problem, we propose a model-driven unsupervised learning network, named learned denoising-based generalized expectation consistent (LDGEC) signal recovery network. By utilizing the Stein’s unbiased risk estimator loss, the LDGEC network can be trained only with limited measurements corresponding to the pilot symbols, instead of the real channel data. Even if designed for unsupervised learning, the LDGEC network can be supervisingly trained with the real channel via the denoiser-by-denoiser way. The numerical results demonstrate that the LDGEC-based channel estimator significantly outperforms state-of-the-art compressive sensing-based algorithms when the receiver is equipped with a small number of RF chains and low-resolution ADCs.

Vibration Transmission Analysis in FGM Beams with Periodically Arranged Enhanced Multiple Dynamic Vibration Absorbers

Functionally graded material (FGM) beams are widely used in engineering as moving components. Nevertheless, their generated vibrations usually become annoying. To realize multi-broadband vibration reduction of FGM beams, an enhanced multiple dynamic vibration absorber (EMDVA), which utilizes an amplification mechanism, is proposed in this study. The devices are periodically arranged on the FGM beams. The dispersion and vibration transmission characteristics of the structure are investigated using the energy method and nullspace technique. The accuracy of the model is verified using the finite element method. The effects of parameter on its vibration damping performance are also analyzed. Finally, the relationship between the amplification coefficient and the operating performance of the EMDVA is revealed in terms of both the impedance principle and the energy method. The results show that the amplification mechanism can amplify the stiffness, damping, and mass of the MDVA by a factor of square of the amplification coefficient. Therefore, the proposed EMDVA has a wider damping band and stronger attenuation performance compared to the conventional MDVA. This study provides a simple and easy-to-implement solution for multi-band vibration reduction in FGM beams, which is useful for the engineering application of FGM beams in vibration and noise reduction.

Evanescent waves in a metabeam attached with lossy acoustic black hole pillars

In this paper, we suggest a metabeam having periodically distributed integrated acoustic black holes (IABHs). Compared to conventional embedded ABHs, the thickness of the base beam has not been modified, so it adapts well to application occasions with load-bearing requirements. The ABH pillars behave as dynamic vibration absorbers (DVAs) that not only provide abundant modes with high damping performance but also generate local resonance and Bragg scattering bandgaps to stop wave propagation. To characterize the evanescent waves, a wave and Rayleigh–Ritz method (WRRM) is proposed, based on the nullspace method (NSM) that assumes the response is constituted by the linear combination of the nullspace basis of the constraint matrix. The proposed WRRM is validated using numerical partial differential solutions. Analysis of the complex dispersion curves shows that multiple local resonance and Bragg scattering bandgaps take place in the whole frequency range of interest, and the damping effect can merge these bandgaps so as to form very wide attenuation bands. Not only that, remarkable evanescent waves are also observed in the passbands. The lattice constant and ABH length are studied parametrically. Results show that the larger the lattice constant, the more attenuation bands appear, and the longer ABH length can enhance the attenuation capability. Finally, the transmissibility and mean square velocity for a finite metabeam with 5 cells are investigated, indicating substantial wave damping in a broadband frequency range.

Resonance mode analysis of finite plate strip with acoustic black holes: the gap between bandgap and attenuation band

Acoustic Black Hole (ABH) lattice structures show promise for achieving broadband bandgap in lightweight design. Existing ABH lattice research usually assumes that the bandgaps of infinite periodic structure are roughly the same as the attenuation band with strong energy attenuation in the finite counterpart. This work is concerned with comparison of the real attenuation bandwidth of finite periodic ABH structures and the bandgap of the infinite counterpart. The plate strips consisting of different numbers of periodic ABH elements are considered. It is observed that the bandgap-predicted attenuation band is split into two narrow attenuation bands, so that the periodic ABHs fails to ensure a broadband and continuous attenuation in the finite scenarios. Results show that there are resonance modes of finite plate strips with ABHs falling into the bandgap due to the boundary reflection and would result in high transmission peaks within the bandgap-predicted attenuation band. This unexpected phenomenon suggests the gap between the attenuation bandwidth of finite periodic structure and the bandgap of the corresponding infinite one. Analysis shows that the resonance mode of finite plate strips, which reduces the bandgap-predicted attenuation bandwidth, can be tuned by geometrically disturbing the periodicity and symmetry of the finite periodic configuration.

Two-step optimization design of a periodic beam with acoustic black holes

This paper presents a two-step optimization method to design the acoustic black holes (ABH) profiles according to local property in the target frequency region. In the first step, the concept of 'local index' is used to identify the position of local vibration. Then, as the second step, the ABH parameters are multi-objective optimized. The numerical examples indicate that the two-step optimization provide a set of Pareto solutions for lightweight ABH design with board bandgaps. To reveal the mechanism of the attenuation band, the vibration modes of the structure are analyzed and the local property of the ABH is shown. Using dynamic and static characteristics as objective functions, the proposed method provides a way to merge physical meaning in the process of data-based optimization.

Magnetic crystallite-decorated hollow multi-cavity carbon nanosheet spheres for superior electromagnetic absorption

Carbonaceous-magnetic composites have emerged as the most attractive absorbers in recent years, and creating hierarchically porous structures in composites is generally considered an indispensable strategy to enhance overall performance. Herein, we design a series of carbonaceous-magnetic composites with superior electromagnetic absorption performance. Via simple spray-drying of a solution containing metal/carbon precursors and a water-removal salt template (i.e., NaCl), the as-made materials feature a complex hierarchical architecture with a hollow interior and a multi-cavity shell, which is assembled from ultrathin carbon nanosheets decorated with magnetic crystallites. The proposed method is generally applicable and can integrate various magnetic crystallites (e.g., Fe3O4, Ni, FeCo, and CoFe2O4) into hollow multi-cavity carbon spheres. The optimal Fe3O4-based absorber achieves effective absorption bandwidth (7.7–13.4 GHz) covering the entire X band and excellent electromagnetic attenuation capability (−51.1 dB) with a thin thickness of 2.7 mm. Furthermore, a simulation demonstrates that an absorbing coating with the optimal absorber enables remarkably reduced radar cross section lower than −10 dBm2 over the whole measurement range. These results indicate that proposed microwave absorbing materials have practical feasibility in civilian and military stealth applications.

Базовые конструкции СВЧ балансных фильтров на оттекающих поверхностных акустических волнах

Ladder filters on leaky surface acoustic waves (LSAW) with electrical connection of resonators provide the lowest insertion loss IL=0.6-1.2 dB as compared with other types of LSAW filters, such as longitudinally coupled resonator filters. A drawback of ordinary nonsymmetrical ladder filters on LSAW is their limited selectivity (or minimal attenuation in the stop band) about UR=40-45 dB. In addition some problems arise when matching nonsymmetrical ladder filters to balanced or differential microcircuits. The present paper describes basic symmetric П-type and Т-type sections as well as various structures of ladder filters that allow to achieve a high selectivity thanks of parasitic electromagnetic signal (EMS) suppression. An extra advantage of balanced LSAW filters is their possibility to work with high impedance symmetric loads. The results of our study have been illustrated by few examples of balanced filters constructions on frequency 1217 MHz with selectivity UR=55-7- dB and low insertion loss IL=1,5-2,0 dB. Filters exhibiting high selectivity UR=55-70 dB and small insertion loss IL=1,2-4,0 dB. The described constructions may be used as basic for application on TV tuners, receivers of communication and navigation systems in frequency range 600-2000 MHz.