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Terrestrial microwave links are increasingly being used to estimate path-averaged precipitation by determining the attenuation caused by rainfall along the link path, mostly with commercial microwave links from cellular telecommunication networks. However, the temporal resolution of these rainfall estimates and the method to derive them are often determined by the temporal sampling strategy that is employed by the mobile network operators. Currently, the links are most often sampled at a temporal resolution of 15 min with a recording of the minimum and maximum values, while more recently, a form of instantaneous sampling with possible intervals up to 1 s has also been set up. For rainfall research purposes, often high temporal resolutions in combination with averaged values are preferred. However, it is uncertain how these various temporal sampling strategies affect the estimated rainfall intensity. Here we aim to understand how temporal sampling strategies affect the measured rainfall intensities using microwave links. To do so, we use data from three collocated microwave links, two 38 GHz and one 26 GHz, sampled at 20 Hz and covering a 2.2 km path over the city of Wageningen, the Netherlands. We aggregate the microwave link power levels to multiple time intervals (1 s to 60 min) and use a mean, instantaneous, and minimum and maximum value to characterize the signal. Based on the aggregated data, we compute rainfall intensities and compare these with 20 Hz rainfall estimates, such that we isolate errors and uncertainties caused by the sampling strategies from instrumental effects, such as different biases between instruments and representativeness errors. In general, our results show that for all sampling strategies, an increase in sampling time interval reduces the performance of the rainfall estimates, which especially holds for the instantaneous sampling strategy. Even the mean sampling strategy, which generally performs best of all strategies, is sensitive to this reduction in temporal resolution and could lead to significant underestimations. This sensitivity of the mean sampling to the temporal resolution seems to be largely affected by the non-linear relation between attenuation and rainfall. The min–max sampling strategy is mostly prone to minor underestimations or large overestimations of the path-averaged rainfall intensities. Moreover, our results, including a comparison with theoretical events, show that the attenuation due to wet antennas not only affects the comparison between the rainfall estimates obtained with a microwave link and another reference instrument but also has a significant influence on the performance of the rainfall retrieval algorithm, especially for devices with relatively long duration of the wet-antenna attenuation combined with the longer sampling time intervals. Overall, this study demonstrates the effect a selected sampling strategy can have on rainfall intensity estimates using (commercial) microwave links. [ABSTRACT FROM AUTHOR]

In this study, we introduce an innovative model for evaluating the impact of environmental factors on drone-to-ground control station datalink communications. Our approach integrates both deterministic and stochastic processes to account for small-scale and large-scale fading effects, encompassing propagation attenuation, the Rician fading model, and Gaussian noise to accurately reflect real-world conditions. The model is implemented on signals transmitted using spread spectrum modulation. Through a comparative analysis of the model's predictions against actual signals received in three distinct environments, the model's efficacy in diverse scenarios is affirmed. Error metrics obtained from Monte Carlo simulations are employed to validate the theoretical results against experimental data. The proposed approach is pivotal for predicting the transmission range and understanding the electromagnetic susceptibility of the datalink, offering a substantial contribution to the optimization of remote drone control. [ABSTRACT FROM AUTHOR]

Reducing fall-related injuries is difficult due to the multi-factorial nature of falls, and challenges in implementing injury-preventative strategies. While safety floors are effective at absorbing energy and reducing fall-related impact forces, the low stiffness component of these floors may impair an individual's balance and mobility, thereby increasing fall risk. Research question: Therefore, the objective of this study was to investigate the influence of compliant flooring (i.e., safety flooring) on balance and mobility in young and older adults. Methods: Kinematics were measured with inertial measurement units from 20 young and 10 older adults. Static balance was evaluated during quiet stance on three flooring surfaces (traditional, safety, foam) with three stance positions (regular, tandem, one-legged). Mobility was evaluated using the 3 m timed-up-and-go test on two flooring surfaces (traditional, safety). Results: All participants were able to complete quiet standing trials on normal and safety flooring surfaces; however, most older adults could not complete one-legged stance trials or standing on foam. Significant age-related effects were observed for several balance and mobility tasks, particularly during the more challenging tandem stance condition, and the dynamic timed-up-and-go mobility test. In contrast, the introduction of safety flooring (compared to traditional flooring) had limited effects on balance/mobility (1 of 16 outcome variables showed negative effects). Significance: Overall, the findings demonstrate minimal effects of a novel safety floor compared to the age-related differences, and provide insights to assist researchers, consumers, and industry stakeholders in the development of environments that support safe movement and maintained independence for older adults. • Young and older adults were compared while standing/walking on compliant flooring. • Significant age-related effects were observed for balance and mobility tasks. • Minimal effects of novel safety flooring compared to the age-related differences. • This safety floor, designed for impact attenuation, had limited effects on balance and mobility. [ABSTRACT FROM AUTHOR]

In this paper, we present a consistent methodology for the reliable design of 6G-oriented filters with enhanced endurance to construction imperfections. The systematic formulation does not depend on the filter's operating frequency and employs a robust strategy for obtaining new roots and poles of the filtering function. Essentially, it requires that all the local maxima of the filtering function do not fluctuate beyond the design attenuation levels for a set of predefined roots/poles distortions. To this purpose, two novel algorithms for the derivation of the appropriate filtering functions are developed, in the prior basis, together with a versatile optimization criterion and a heuristic comparison approach that guarantee optimal outcomes. Specifically, the principal idea of the first technique is to accurately extract the roots of the new polynomial from a system of equations on condition that the maximum local peaks of the distorted (due to imperfections) initial polynomial are below a prefixed threshold, such as the unit. Conversely, the second method develops an alternative polynomial, compressed in the amplitude and frequency range, so that a similar prerequisite regarding the maximum local peaks, is satisfied. It is stressed that both methods are fully generalized and may be applied to any polynomial combination, without increasing the overall complexity. The proposed framework is successfully verified in terms of theoretical examples and the numerical simulation of realistic waveguide and mictrostrip line filters, operating at frequencies from 2 GHz to 65 GHz, which unveil its superiority over existing schemes and implementations. [ABSTRACT FROM AUTHOR]

Ultralow-frequency band gaps are realized to suppress the ultralow-frequency flexural wave propagation in the beams with periodically attached quasi-zero-stiffness (QZS) resonators, which are designed by inserting quasi-zero-stiffness systems into the mass-in-mass structures. The band structure and the transfer matrix of the QZS locally resonant beam are derived by the transfer matrix method to quantify the wave attenuation performance of band gaps. Then, the effect of the stiffness ratio on the bandgap characteristic is studied. It is shown that, thanks to the introduction of the QZS system, the band gaps can be easily transferred to lower frequency or even ultralow frequency without weakening the static stiffness of the resonators. Finally, the flexural wave propagation in locally resonant beam consisting of multiple periodic arrays of QZS resonators is investigated. The result shows that differential design of the bandgap frequencies can be easily realized by adjusting the negative stiffness coefficient of the QZS resonators, so as to obtain broadband flexural wave suppression performance. [ABSTRACT FROM AUTHOR]

We present the theoretical investigation on the flexural wave propagation and vibration attenuation characteristics in a Euler–Bernoulli beam-type metastructure with double-sides inertial amplified resonators. Based on Bloch theory, the dispersion relation and propagation characteristics of flexural waves are calculated by the spectral element method. The influences of system parameters on the flexural wave attenuation of the proposed beam-type metastructures are analyzed. Results show that broadband low-frequency flexural wave attenuation can be achieved by the proposed double-sides beam-type metastructures. The tunability of flexural wave band gap and vibration suppression performance significantly enhances. In addition, the low-frequency flexural wave band gap can be effectively modulated and optimized by changing the system parameters. [ABSTRACT FROM AUTHOR]

There has been a rising interest in utilizing metamaterials to manipulate the propagation of surface waves, including Rayleigh waves. These novel materials have a diverse range of applications, from micro-scale sensors and actuators to macro-scale seismic protection systems. In the field of seismic engineering, they are commonly referred to as seismic metamaterials. While various linear seismic metamaterials have been developed, incorporating nonlinearity into the design of seismic metamaterials could reveal novel phenomena and greatly expand their potential applications. In the present study, we propose a nonlinear metamaterial to block the propagation of low-frequency Rayleigh waves. The proposed metamaterial consists of a linear elastic substrate and nonlinear resonant units periodically attached to the surface of the substrate. Each resonant unit has two Duffing oscillators connected in series. We use the first-order harmonic balance method to derive analytical solutions for the dispersion of Rayleigh waves, considering both linear and various nonlinear cases. Our findings demonstrate that by coupling the motion of an elastic substrate with the dynamics of attached masses, a linear metamaterial with serial-connected resonators can achieve two band gaps. Furthermore, introducing softening nonlinearity can facilitate the attainment of a low-frequency band gap, while introducing hardening nonlinearity may result in the closure of the original linear band gaps. Our study broadens the range of applications for elastic metamaterials and potentially contributes to the development of more effective seismic wave blockers. [ABSTRACT FROM AUTHOR]

Telecommunications companies are constantly chasing continuous technological advances with their management methods of Operations & Maintenance (O&M) that still struggle to turn their eye toward innovation and simplification of processes. In a future that aims at fully fiber-optic networks, the objective of the research is to propose guidelines and provide data to support the Wholesale Operator for the definition of the acceptable attenuation threshold on the Passive Optical Network Fiber-To-The-Home (PON FTTH) infrastructure to determine the Service Level Agreements (SLA) to be contracted with Retail Operators. Following exceeding the threshold, the Retail Operator has the right to open a Trouble Ticket to request the resolution of the anomaly. Consequently, the definition of the attenuation threshold strongly affects the number of Trouble Tickets to be managed and the related costs the Wholesale Operator bears. This paper analyzes a specific case of the PON FTTH network of the Italian wholesale operator Open Fiber. The studied infrastructure, with a length of 11 km, allows a maximum attenuation of 37 dB without degrading the service. An economic model has been proposed to assess the cost impact of moving the attenuation threshold in the SLA. [ABSTRACT FROM AUTHOR]

This paper addresses the consensus control problem in multi‐agent systems under the influence of diffusively coupled disturbances. Two different types of systems are considered regarding the homogeneity of the disturbance coupling parameters. The main goal is to derive conditions that guarantee the prescribed performance of the designed control system on disturbance attenuation. To estimate the disturbance attenuation performance of the controller, the ℋ∞$$ {\mathscr{H}}_{\infty } $$ norm of the transfer function from the redefined disturbance vector to the disagreement vector is measured. Then the sufficient conditions for the system to achieve consensus within the desired performance are derived in terms of linear matrix inequalities (LMI). Numerical examples of both one‐ and multi‐dimensional consensus control systems are provided to check the validity of the derived LMI feasibility test along with the illustration of consensus behavior in time domain. [ABSTRACT FROM AUTHOR]

Periodic structures have gained attention in the research community since they show attenuation zones in their frequency response, called bandgaps. In this paper, the interactions of two mechanisms of bandgap formation in mono-coupled periodic structures are examined, i.e., Bragg scattering and local resonators. With reference to longitudinal elastic waves, an analytical study is carried out to describe in detail the formation of bandgaps. Local resonators are implemented via piezoelectric inserts shunted with a resonating electrical circuit for which a non-traditional model is needed since the study concerns higher frequencies with respect to those of the subwavelength regime. Design maps and tuning formulas are developed not only for the case of infinite structures, but also for the finite case, highlighting the role of the number of unit cells and that of resonances in the attenuation zones. Among the possible tuning strategies of local resonators, it is shown that the mutual influence between elastic and electric parameters is able to produce a wider attenuation zone, bridging Bragg scattering bandgaps thanks to the effect of local resonators. The analytical findings of this paper are validated with numerical results in an example application. [ABSTRACT FROM AUTHOR]

Piezoelectric metamaterials with inductance shunt circuits connected to the transducers have attractive potential for guiding and attenuating elastic waves. However, it is challenging to evaluate their wave attenuation capability experimentally because the signals of transmitted waves within the bandgap have extremely small amplitudes and are submerged in noise. The present paper reports a method for revealing the wave attenuation features of a piezoelectric metamaterial beam by taking advantage of the physical correlation between the excitation and the transmitted and incident waves. Correlations between the excitation and the measured waves are calculated in real time to eliminate noise. It is demonstrated that wave attenuation features within the bandgap can be recovered from noise with an amplitude that is 69.1 dB larger than that of the transmitted wave. The transmission diagram is presented, and wave attenuation of up to −50.7 dB can be observed. Also, the correlation-based signal processing procedure is effective for illustrating the resistance-load-based wave attenuation behavior of the piezoelectric metamaterial beam. This method can be extended to the experimental analysis of many other types of metamaterials and phononic crystals. [ABSTRACT FROM AUTHOR]

Slow electrons (with energy below 10 eV) play an important role in nature and technology. For instance, they are believed to initiate solubility change in extreme ultraviolet resists. Depending on their mobility, such secondary electrons can lead to image blur and degradation of patterning resolution. Hence, it is important to characterize the transport of slow electrons by measuring parameters such as the effective attenuation length (EAL). We present a technique that allows for prompt characterization of EAL in polymer films. In this experiment, slow electrons are generated in a substrate upon absorption of x-ray photons. The attenuation of electron flux by a polymer film is measured as a function of film thickness, allowing for the determination of EAL for slow electrons. We illustrate this method with poly(hydroxy styrene) and poly(methyl metacrylate) films. Furthermore, we propose an improvement for this technique that would enable the measurement of EAL as a function of electron kinetic energy. [ABSTRACT FROM AUTHOR]

For developing a reliable Power Line Carrier Communication (PLCC) system, it is extremely important to know the characteristics of different subsystems in PLCC and power lines. The circuit used to superimpose carrier signal from the transmitter with high potential power lines is termed as line tuners. The design and simulation of a capacitive type line tuner meeting IEC 60481:1974 and IEEE Std C93.4-2012 are included in this article. The wave trap allows the power signal to pass through but blocks the high-frequency carrier signal to reach terminal equipment which works at 50/60 Hertz. Three types of wave traps are studied as part of this paper: single frequency, dual frequency, and wideband wave traps. Impedance characteristics obtained in simulation show effective rejection of carrier signal as desired. The distribution power transformers are an inevitable part of the power line network which offers high attenuation to carrier signal as being inductive it functions as low pass filter. To overcome this problem a bypass circuit which could be incorporated in future power transformers is proposed in this article. The Resistance, Inductance, and Capacitance (RLC) parameter of the power line cable used in the simulation model are derived based on the experimental values observed on an actual 11 kV underground cable and thus replicates actual field conditions. A complete PLCC system with all the above components is presented in this article and can be used as a testbed by designers to validate the MODEM for communication in different topologies by modifying the elements according to actual field conditions. [ABSTRACT FROM AUTHOR]

The use of mmWaves for achieving 5G networks is increasingly being seen as a necessity due to the vastly improved bandwidth and data rates at these frequencies. These waves suffer from severe attenuation and their use may, however, be restricted, in the immediate future, to short-range networks, such as personal area networks (IEEE 802.11ad) or vehicular and mobile adhoc networks operating in proximity. MmWaves require directional antennas which have the added advantage of allowing spatial reuse. Even though the high gain in a given direction in such antennas allows us to extend the range, there are several factors, such as error in antenna orientation, fading, blockage which show that an optimum beamwidth can be obtained to maximize the network throughput. The treatment of transmissions, during Line-of-Sight transmission conditions and during Non-Line-of-Sight, is completely different. The paper has evaluated the optimum beamwidth for successful mmWave transmissions in mmWave adhoc networks at 60 Ghz in short-range mmWave networks (IEEE 802.11ad). [ABSTRACT FROM AUTHOR]

In the era of continuous advancement in wireless technologies, path loss, also known as channel attenuation, is a drop in signal strength from the transmitter to the receiver. Path loss modelling is critical in designing fixed and mobile communication systems for various applications. This paper focuses on the received power (dBm) and free space path loss (FSPL) on various distances and frequencies such as 5240 MHz for wireless local area network (WLAN) and frequency such as 2100 MHz for the mobile network such as Celcom. As a result, able to analyze the correspondence between received power (dBm) and distance of each related frequency and the correspondence between FSPL (dB) and distance of each corresponding frequency and able to analyze the effect of obstacle on received power (dBm) and frequency. [ABSTRACT FROM AUTHOR]

One of the largest earthquakes in the Zagros region occurred on November 12, 2017, in Sarpol-e Zahab with Mw=7.3. We considered the aftershocks of this event and collected the S-wave amplitude spectra from 87 strong-motion records to determine the source, path, and site effects using a non-parametric generalized inversion technique. The grid-searching method based on Brune's X2 model was employed to determine some of the source parameters. The corner frequency and seismic moment vary from 1.11 to 5.14 Hz and from 9.12×1014 to 1.36×1017 N.m, respectively. Also, The seismic moment and the cube of corner frequency are inversely related to each other. The stress drop of earthquakes is determined with the e indicator. In this study e is equal to 1.91; thus this value indicates that frictional overshoot has occurred with the dynamic frictional stress larger than the final stress. The S-wave quality factor is estimated as Q=101f0.67. The value of Q0 is small, which is characteristic of an active tectonic environment. We compared the site effects that were calculated by GIT and H/V methods. In most cases, a very good agreement was observed and the small difference between them is mainly due to the constraints and assumptions of these methods. [ABSTRACT FROM AUTHOR]

Summary: Paper has considered multiple reconfigurable intelligent surfaces (RISs) assisted downlink non‐orthogonal multiple accesses (NOMA) system, referred to as MR‐NOMA. Multiple RISs create a line‐of‐sight (LOS) channel between BS and users to improve network coverage, especially in high frequencies and severe path attenuation scenarios. In MR‐NOMA, all RISs are in series and activated simultaneously; therefore, multiplicative beamforming gain from the inter‐RIS channels is achieved. Bit error probability (BEP) under the Rician fading channel is derived and compared with simulation results. It is observed that BEP performance depends on the number of passive reflecting elements, Rician factor, and positions of RISs panels in the MR‐NOMA. [ABSTRACT FROM AUTHOR]

Underwater Wireless Optical Communication (UWOC) offers significant research prospective with major challenges in the design and implementation. UWOC is capable of providing high rate of data transmission across large distances. This paper attempts to focus on the intricacies of practical implementations and open research issues of UWOC systems. Critical advances and progresses made in the field, modelling techniques and link design challenges are summarised. The purpose of this review is to give suggestions towards feasible and reliable UWOC design with improved performance. Finally the major points are summarized so that it will assist the future research in UWOC. [ABSTRACT FROM AUTHOR]

Stealth technology plays an important role in modern military conflicts, and because of its many practical advantages, plasma stealth technology has gained a lot of attention. In this paper, we describe our study of the reflection and absorption characteristics of waves propagating in multilayer plasma slabs. Our results show that positive effects on the attenuation can be obtained by optimizing the plasma parameters and by increasing the number of plasma layers. We also found that multilayer plasma slabs can effectively widen absorption bands, especially for low frequency bands. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new multi-resonator metamaterial (MRM) for attenuating impact stress waves. Theoretical analyses show that the MRM has wider bandgaps than those of a single-resonator metamaterial (SRM) and a dual-resonator metamaterial (DRM), and numerical studies are conducted to compare the performances of the MRM, SRM, and DRM in mitigating impact forces. The influences of the number of unit cells, the spring stiffnesses, and the resonator masses on the mitigation of impact force are analyzed by studying a one-dimensional impact wave model. In addition, the calculation results of a three-dimensional crash model clearly confirm the outstanding features of the MRM, which can provide a thin and light structure with a wider attenuation region of the frequency spectrum and a better mitigation effect of the impact force. [ABSTRACT FROM AUTHOR]

Ducts with membranes in their sidewalls have been used for noise control due to their remarkable ability to reflect sound waves at low frequencies. To obtain a broader attenuation band, combining several membranes is one possible way, which leads to yet another branch of engineering called phononic crystals or acoustic metamaterials. This study analyzes sound wave propagation and attenuation in a duct with periodic membranes embedded in its sidewalls. For each cell, an analytical, fully coupled vibro-acoustic model is proposed via energy formulation, and then the interference among multiple membrane cells is treated using the cell transfer matrix. Our study provides an efficient means to predict, and eventually optimize, the acoustic bandgap structure. Results from the current model fit well with those simulated using a two/three-dimensional finite element method. The 2D membrane with free lateral edges was found to perform almost as well as its 1D counterpart. Moreover, a better bandgap can be achieved via coupling of resonance and Bragg reflection. The effects of periodic distance and membrane tension force on the bandgap structure are then discussed and analyzed to determine their appropriate parameters. Some optimal designs are implemented through artificial disorder, which shows promising potential in attenuating bandwidth expansion compared with the original periodic configuration. [ABSTRACT FROM AUTHOR]

A Green function-based analytic solution of pressure diffusive wave motion is introduced for investigating the transient pressure response in fluid saturated matrix-fracture media. One-dimensional solutions are presented for a time-harmonically forced problem with internal damping and are used to analyze the propagation and attenuation of pressure pulse in a semi-infinite spatial domain. The concise form of the solutions simplifies the calculation of pressure diffusion with arbitrary forcing functions at fixed boundaries. It indicates that the periodically forced function with internal damping has remarkable effects on pressure diffusion-wave motions. It is found that the characteristic delay-frequency separates the pressure diffusion-wave domain into matrix-dominated, transition, and fracture-dominated zones. The Green functions could physically predict any transient response of pressure fluctuations due to hydro-fracturing in geological reservoirs given proper physical parameters. [ABSTRACT FROM AUTHOR]

Unknown multiple tonal noise and band-limited random noise can be both generated in ductwork systems. This article has constructed a LQG controller with an augmented Youla (Q) parameterized adaptive regulation approach to minimize the residual error at the end of the duct segment where both types of noise signals are supposed to be attenuated. The construction approach of the Youla parameterized controller based on a LQG controller is first presented. Then, the recursive least squares adaptive algorithm is developed, and the convergence of the algorithm and the robustness of the closed-loop control system are analyzed. The effectiveness of the proposed adaptive control approach is experimentally evaluated in a duct noise attenuation testbench platform. The results illustrate that the proposed adaptive noise control method can effectively attenuate the unknown multiple tonal noise and band-limited random noise simultaneously in the ductwork system. [ABSTRACT FROM AUTHOR]

This article investigates the conducted-emission (CE) suppression characteristics of electromagnetic interference (EMI) filters used in power-electronic equipment by time-domain circuit simulation. An operational definition of insertion attenuation is introduced by comparing the CE in the absence and in the presence of the EMI filter. For the sake of exemplification, the analysis focuses on switched-mode dc–dc converters. It is shown that the EMI-filter attenuation behaves differently from the standard insertion loss (IL) and exhibits peculiar properties in these circuits. Namely, its response is known at discrete frequencies where the converter generates CE and may strongly depend on the harmonic index so to jump between quite different levels from a harmonic component to the next one, with a pseudoperiodic behavior, which can be related to the duty cycle. This effect is caused by circuit nonlinearity and is partially mitigated if the simulation accounts for two practically relevant aspects: random instability of the duty cycle and resolution bandwidth of the EMI receiver. The dependence of the common-mode (CM) and differential-mode attenuations on the loading conditions and duty cycle is analyzed, and it is shown that linear IL models provide reasonable predictions of CM attenuation only. Finally, experimental evidence of the unveiled phenomena is presented. [ABSTRACT FROM AUTHOR]

Accurate aircraft positioning is the key to construct a reliable network topology when aircrafts are used to assist 6G cellular networks in ground communications. Distance Measuring Equipment (DME) has been widely used in aircraft positioning with the help of multiple ground-based radar stations. In this paper, a learning-based health prediction method for airborne DME receiver is proposed by using signal processing techniques to achieve quantitative health status assessment and failure degradation trend prediction, when the DME is used to measure the distance between ground-based radar stations and airborne DME. First, a quantitative airborne DME device receiving channel health evaluation model is established, which takes the Automatic Gain Control (AGC) attenuation value and the collected distance between the ground beacon station and the airborne DME receiver with DME device as input, to calculate the receiving channel AGC attenuation value deviation and gain loss. The model can be used to build the mapping relationship between the receiver channel gain loss and the DME function range, and further establish the calculation model of the receiving channel's health index. Second, a multi-model fusion fault prediction framework based on the Deep Belief Network (DBN) techniques is proposed. In this framework, the problem of insufficient generalization and robustness of the traditional DBN model is solved by introducing the Dropout mechanism into the DBN structure, and an improved weighted voting method is utilized as a model fusion algorithm to eliminate the deviation of prediction results caused by environmental load differences and improve the accuracy of fault prediction. Finally, extensive experiments are conducted to show the feasibility of the proposed method, and the results show that the proposed method has a good performance. [ABSTRACT FROM AUTHOR]

Metastructures and phononic crystals could have several unique physical properties, such as effective negative parameters, tunable band gaps, negative refraction, and so on, which allow them to improve multi-physical performances at the materials level. Motivated by the elastic negative mass metastructures, this work reports the enhancement of bandwidth and vibration suppression while achieving better energy harvesting via non-linear attachments. We propose to consider the effect of spring softening and spring hardening simultaneously along with exploiting the coupled influence of multiple variables, such as spring stiffness, damping, number of unit cells, electro-mechanical coupling coefficient and masses. A mathematical model of the metastructure having linear spring with nonlinear attachments is developed and analyzed numerically including the effect of functional gradation. Dimensionless parametric study is performed to tune two-cell and multi-cell models to enhance vibration suppression and energy harvesting performances. In an eight-cell model, the non-linear characteristic parameter is functionally graded from softening to hardening using exponential and power law to explore the dual functionality further. It is revealed that the resonant peak can be reduced by non-linear softening characteristics. For enhanced energy harvesting, a smaller value of mass ratio is preferred, while a larger value of damping characteristic is suitable for vibration suppression. Under certain configurations, band structure of the phononic metastructure is capable of achieving absolute band gaps, resulting in frequency ranges, where waves cannot propagate. The comprehensive analysis presented here on the effect of various system parameters would lead to the design of non-linear multi-resonator metamaterials for the dual functionality of vibration attenuation and energy harvesting that can be applied in a wide range of automated systems and self-powered devices including the capabilities of real-time monitoring and active behaviour. [ABSTRACT FROM AUTHOR]

Monte Carlo simulations are at the heart of many high-fidelity simulations and analyses for radiation transport systems. As is the case with any complex computational model, it is important to propagate sources of input uncertainty and characterize how they affect model output. Unfortunately, uncertainty quantification (UQ) is made difficult by the stochastic variability that Monte Carlo transport solvers introduce. The standard method to avoid corrupting the UQ statistics with the transport solver noise is to increase the number of particle histories, resulting in very high computational costs. In this contribution, we propose and analyze a sampling estimator based on the law of total variance to compute UQ variance even in the presence of residual noise from Monte Carlo transport calculations. We rigorously derive the statistical properties of the new variance estimator, compare its performance to that of the standard method, and demonstrate its use on neutral particle transport model problems involving both attenuation and scattering physics. We illustrate, both analytically and numerically, the estimator's statistical performance as a function of available computational budget and the distribution of that budget between UQ samples and particle histories. We show analytically and corroborate numerically that the new estimator is unbiased, unlike the standard approach, and is more accurate and precise than the standard estimator for the same computational budget. • Parameter uncertainty and Monte Carlo solver noise both contribute to output variance. • The brute-force approach is to over-resolve the stochastic solver noise towards zero. • The introduced estimator is more accurate and efficient than the brute-force approach. • The bias and variance of both estimators are characterized and compared. • Resource allocation analysis shows that over-resolution is not necessary. • Results are discussed for an example energy-independent radiation transport problem. [ABSTRACT FROM AUTHOR]

This paper reports the dynamic effects leveraged into one-dimensional metastructures by Duffing- and Nonlinear Energy Sink (NES)-type piezoelectric attachments. The versatility of the nonlinear piezoelectric attachments enables the exploitation of their rich dynamic features under low amplitude excitation regimes. Numerical and experimental results show that this class of nonlinear metastructures present reconfigurable attenuation bands as a function of the strength of nonlinearity. Broadband and multimode vibration attenuation become enhanced due to the wave supratransmission phenomenon, as the strength of nonlinearity increases in the piezoelectric attachments. While the experimentally investigated metastructure with Duffing-type piezoelectric attachments presents normalized bandwidths, Δ Ω , of 0.84 around the underlying linear resonating frequency, it is shown for the first time in the literature that the finite beam with NES-type piezoelectric attachments exhibits impressive Δ Ω values in excess of 1.90, including strong attenuation of several linear transmissibility peaks. The results open new avenues for fully tunable metastructures with enhanced broadband and multimode vibration attenuation features, based on nonlinear piezoelectric shunt circuits. • Experimentally verified numerical model for a nonlinear piezoelectric metamaterial. • Nonlinear piezoelectric metamaterial exhibits broadband vibration attenuation. • First experimentally investigated piezoelectric metamaterial with NES attachments. • NES-type piezoelectric metamaterial exhibits normalized bandwidths larger than 1.90. [Display omitted] [ABSTRACT FROM AUTHOR]

Acoustic liners, consisting of a perforated panel affixed to a honeycomb core with a rigid back plate, are widely used for noise attenuation purpose. In this study, by exploiting inhomogeneous impedance properties, we report an experimental and numerical study on a liner-type acoustic metasurface, which possesses the functionality of both reflected wave manipulation and sound energy attenuation simultaneously. To realize the inhomogeneous acoustic impedance, an acoustic metasurface constructed by varying-depth acoustic liners is designed and fabricated. The reflected sound pressure fields induced by the metasurface are obtained in both experiments and simulations. A complete characterization of this metasurface is performed, including the effects of depth gradient, incident angle, and incident frequency. Anomalous reflection, apparent negative reflection, and conversion from an incident wave to a surface wave with strong energy dissipation are achieved by the structure. Moreover, our proposed structure can overcome the single frequency performance limitation that exists in conventional metasurfaces and performs well in a broadband frequency range. The proposed acoustic metasurface offers flexibility in controlling the direction of sound wave propagation with energy dissipation property and holds promise for various applications of noise reduction. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) MXene materials have potential applications in electromagnetic pollution elimination and energy conversion fields owing to their high carrier mobility, specific surface area and unique layered features. Here, we demonstrated a controlled self-assembly strategy to construct multifunctional nano/microstructured 2D Ti 3 CNT x MXene-based composites for efficient electromagnetic attenuation and Joule energy conversion application. The multiple compositions and novel architecture endowed the layered porous Ti 3 CNT x /Ni@C composites with enhanced electromagnetic wave absorption and EMI shielding performances. Notably, the optimized nanocomposites achieved a high-performance electromagnetic wave absorption with a low loading (8 wt%), a broad effective absorption bandwidth (5.4 GHz) and a strong absorption (−65.7 dB) at a thickness of only 1.5 mm. The high electromagnetic shielding efficiency reached 66.7 dB. The underlying mechanism of electromagnetic shielding and absorption was the synergistic effects among electronic transport, abundant interfacial/dipolar polarization, strong magnetic coupling and multiple reflections in the layered porous structure. In addition, the efficient Joule energy conversion with favorable flame-retardant and high infrared shielding versatility broadened the practical application range of Ti 3 CNT x /Ni@C composites in harsh environments. Therefore, this assembly strategy inspires the construction and application of the 2D Mxene-based composites to promote the development of energy conversion and green electromagnetic environments. Owing to the rational-designed components and novel nano/microstructure, the layered MXene/Ni@C composites achieved efficient electromagnetic wave absorption and EMI shielding performance with favorable Joule heating, flame-retardant and infrared shielding properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Ultra-high-frequency (UHF) partial discharge (PD) monitoring is gaining popularity because of its advantages over electrical methods for onsite/online applications. One such advantage is the possibility of three-dimensional PD source localization. However, it is necessary to understand the signal propagation and attenuation characteristics in transformers to improve localization. Since transformers are available in a wide range of ratings and geometric sizes, it is necessary to ascertain the similarities and differences in UHF signal characteristics across the different designs. Therefore, in this contribution, the signal attenuation and propagation characteristics of two 300 MVA transformers are analyzed and compared based on experiments. The two transformers have the same rating but different internal structures. It should be noted that the oil is drained out of the transformers for these tests. Additionally, a simulation model of one of the transformers is built and validated based on the experimental results. Subsequently, a simulation model is used to analyze the electromagnetic wave propagation inside the tank. Analysis of the experimental data shows that the distance-dependent signal attenuation characteristics are similar in the case of both transformers and can be well represented by hyperbolic equations, thus indicating that transformers with the same rating have similar attenuation characteristics even if they have different internal structures. [ABSTRACT FROM AUTHOR]

A family of three phase, polymer-ceramic-metal (Poly-cer-met) electrically conducting composites was developed via cold sintering for acoustic matching application in medical ultrasound transducers. A range of acoustic impedance (${Z}$) between $5 < {Z} < 21$ MRayl with low attenuation (<3.5 dB/mm, measured at 10 MHz) was achieved in composites of zinc oxide, silver, and in thermoplastic polymers like Ultem polyetherimide (PEI) or polytetrafluoroethylene (PTFE) at sintering pressure less than 50 MPa and temperature of 150 °C. Densities exceeding 95% were achieved, with resistivities less than $1~ \Omega $ -cm. The acoustic velocity was homogeneous across the part (variations <5%). The acoustic velocities exceeded 2500 m/s for ${Z}$ above 12 MRayl. The experimentally measured acoustic impedance of ZnO/Ag/PEI composites was observed to be in close agreement with the theoretical logarithmic model developed for different volume fractions of individual phases at the percolation limit for Ag. Thus, the acoustic properties of this family of matching layers (MLs) can be predicted to a good approximation before experimental realization. Additionally, a non-conducting low ${Z}$ (5 MRayl $< {Z} < 12$ MRayl) with acoustic velocities exceeding 2000 m/s was achieved using hydrozincite as the ceramic component. Scaling of the composites to $2{^\prime}{^\prime}$ diameter was demonstrated. A −6 dB bandwidth greater than 85% was measured for a three ML ultrasound transducer, fabricated using a single cold sintered layer (${Z} = 19$ MRayl) and two other commercial layers in the stack. Finally, a co-cold sintered graded prototype consisting of three tape-casted formulations corresponding to ${Z} = 5$ , 9, and 19 MRayl, while still retaining the correct distributions of the components was demonstrated. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) cavities have been widely applied as electronic bandpass filters, sensors, microfluidic tweezers, and, in recent years, as devices for coupling with quantum systems. Here we propose a novel method of analyzing acoustic Fabry–Pérot spectra, by analogy with optical cavities, to determine the free surface velocity and attenuation of SAW waves, as well as the reflection of interdigital transducers (IDTs), all of which are crucial design parameters. In our experiment, two-port SAW resonators, consisting of two IDTs laterally separated by a free surface cavity length, are used to generate SAWs on 128° Y-X lithium niobate that are trapped between the two IDTs which also act as Bragg reflectors. Resonant cavity peaks can be observed through the electrical ${S}_{{11}}$ (reflection) spectrum measured on one IDT. The free spectral range and linewidths of cavity peaks are then measured to obtain the free surface SAW velocity, SAW propagation attenuation coefficient, and IDT reflection phase and amplitude. Our method of analyzing Fabry–Pérot spectra provides an intuitive approach for determining key characteristics of SAW waves and cavities. [ABSTRACT FROM AUTHOR]

In this paper, we propose a general design concept for acoustic metamaterials that introduces a ubiquitous synergetic behavior into the design procedure, in which the structure of the design is driven by its functional requirements. Since the physical properties of the widely used, resonanttype metamaterials are mainly determined by the eigenmodes of the structure, we first introduce the design concept through the modal displacement distributions on two typical plate-type structures. Next, by employing broadband sound attenuations that involve both the insulation and absorption as the typical targets, two synergetic coupling behaviors are systematically revealed among the dense resonant modes and multi-cell. Furthermore, through plate-type multiple-cell structures assembled from nine oscillators, the design is shown to realize strong broadband attenuations with either the average sound transmission loss (STL) below 2000 Hz higher than 40 dB or the absorption approximately 0.99 in the range of 400-700 Hz wherein the average absorption below 800 Hz remains higher than 0.8. Finally, two multi-cell plate-type samples are fabricated and then used experimentally to measure the STLs in support of the proposed synergetic coupling design method. Both the computational and experimental results demonstrate that the proposed synergetic design concept could effectively initiate a design for metamaterials that offer a new degree of freedom for broadband sound attenuations. [ABSTRACT FROM AUTHOR]

Absolute total cross section (TCS) measurements for electron scattering from 1-propanol molecules are reported for impact energies from 40 to 500 eV. These measurements were obtained using a new apparatus developed at Juiz de Fora Federal University--Brazil, which is based on the measurement of the attenuation of a collimated electron beam through a gas cell containing the molecules to be studied at a given pressure. Besides these experimental measurements, we have also calculated TCS using the Independent-Atom Model with Screening Corrected Additivity Rule and Interference (IAM-SCAR+I) approach with the level of agreement between them being typically found to be very good. [ABSTRACT FROM AUTHOR]

The spin-Hall effect induced modification of the attenuation of propagating exchange-mode spin waves (SWs) is studied micromagnetically and analytically in heavy-metal/ferromagnet bilayers. Micromagnetic simulations of spin-wave propagation in Pt/NiFe show that at a relatively low current density of ~6×1011 A/m2, Gilbert damping is exactly balanced by the spin-Hall torque and long-distance SW transmission is possible. An analytical model is developed to explain the micromagnetic results and relate the current density to the characteristic attenuation length. The results suggest that the spin Hall effect can be used as an effective means to control the attenuation length of propagating spin waves in nanostructures. [ABSTRACT FROM AUTHOR]

This paper studies the adaptive event-based H ∞ control problem for a class of T-S fuzzy distributed parameter system with parameter uncertain and actuator faults. To overcome the drawback of the period control scheme, an event-triggered control scheme with adaptive threshold is proposed to minimize the number of unnecessary sampled data transmission and to reduce the update frequency of the controller. Furthermore, a T-S fuzzy controller based on the adaptive event-triggered sampled data is designed to ensure the stochastic exponential stability of the distributed parameter system with H ∞ disturbance attenuation performance. Based on a new Lyapunov functional and inequality technique, the stochastic exponential stability criterion of the closed-loop system is obtained, and the controller parameters are designed. The new developed inequality can reduce the conservatism of the stability criterion. Finally, the effectiveness of the theoretical calculation results is verified by numerical simulation, and the results are compared with the relevant literature in the simulation, showing that the methods and results in this paper are less conservative. [ABSTRACT FROM AUTHOR]

An analysis method for the detectability of defects on the TC4 (Ti-6Al-4V) diffusion bonding interface was proposed in this study. First, a semi-analytical model of the liquid–solid coupling acoustic field with attenuation characteristics was constructed. Based on this, a method for the selection of transducer parameters was investigated for effective focus on the diffusion bonding interface. Second, according to the characteristics of defects on the diffusion bonding interface, an acoustic response model for diffusion bonding defects was established based on Kirchhoff approximation. The detectability of defects on the diffusion bonding interface was analyzed using transducers of different frequencies with different diffusion bonding interface gaps. Finally, an experiment was conducted to verify the reliability of the simulation. The analysis method proposed shows the advantages in the selection of suitable parameters for detecting specific diffusion bonding interface gaps, providing theoretical predictions of the detectability of diffusion bonding interface defects. [ABSTRACT FROM AUTHOR]

This paper is devoted to H ∞ consensus design and online scheduling for homogeneous multiagent systems (MASs) with switching topologies via deep reinforcement learning. The model of homogeneous MASs with switching topologies is established based on switched systems theory, in which the switching of topologies is viewed as the switching among subsystems. By employing linear transformation, the closed-loop systems of MASs are converted into reduced-order systems. The problem of H ∞ consensus design can be transformed to the issue of H ∞ control. It is supposed that the consensus protocol is composed of two parts: dynamics-based protocol and learning-based protocol, where dynamics-based protocol is provided to guarantee the convergence and weighted attenuation and learning-based protocol is proposed to improve the transient performance. Then, the multiple Lyapunov function (MLF) method and mode-dependent average dwell time (MDADT) method are combined to ensure the stability and weighted H ∞ disturbance attenuation index of reduced-order systems. The sufficient existing conditions of dynamics-based protocol are given through the feasible solutions of linear matrix inequalities (LMIs). Moreover, the online scheduling is formulated as a Markov decision process, and the deep deterministic policy gradient (DDPG) algorithm in the framework of actor-critic is proposed for the compensation of disturbance to explore optimal control policy. The online scheduling of parameters of MASs is viewed as bounded compensation of dynamics-based protocol, whose stability can be guaranteed by nonfragile control theory. Finally, simulation results are provided to illustrate the effectiveness and superiority of the proposed method. [ABSTRACT FROM AUTHOR]

Sandwich structures are widely applied in modern industry such as aerospace, automobile as well as marine structures. However, the vibroacoustic properties of sandwich structures are adversely influenced by low effective mass. In this study, the flexural wave propagation characteristics and vibration mitigation performances of the periodic sandwich plate-type metastructures are investigated. The proposed sandwich plate-type metastructures are constituted of a sandwich plate with periodic thin-wall circular tube cores and periodically attached local stepped resonators. A finite element method combining Solid-Shell coupling numerical method and Bloch theory is presented to calculate the dispersion relations and the displacement fields of the eigenmodes of the infinite periodic sandwich plate-type metastructures. In addition, the acceleration frequency responses and vibration attenuation performances of finite periodic sandwich plate-type metastructures are numerically investigated and compared with the experimental measurements. Furthermore, the influences of geometric parameters on flexural wave band gaps are conducted. Results show that the sandwich plate-type metastructures can yield a low-frequency broad flexural wave band gap, in which the flexural wave propagation is conspicuously suppressed, resulting in significant flexural vibration attenuation. The flexural wave band gap and vibration attenuation performances can be effectively manipulated by designing geometric parameters of the sandwich plate-type metastructures. [ABSTRACT FROM AUTHOR]

The gravity flow in sewer systems may change to partially pressurized flow for reasons including rapid filling, and maintenance and repair. During this alteration, air can be entrapped and becomes highly pressurized, and this air pressure can negatively impact the sewer system and hydraulic infrastructure. The available mathematical models in this field mostly overestimate the peak pressures and underestimate the attenuation. In partially pressurized transient flows following air-pocket entrapment, the frictional force, similar to other forces, can be affected by the unsteady behavior of the flow and by the air-pocket size. Therefore, using a constant steady-state friction factor for the numerical simulation is a simplistic approximation. In this study, an additional friction factor, which has the same form as the steady-state Darcy–Weisbach friction factor, is proposed using dimensional analysis and calibrated by experimental data. Two well-known mathematical models, the rigid column and the method of characteristics models, were used for the numerical simulation. It was found that, compared with a constant steady-state friction factor, the additional friction factor can improve the numerical results significantly, including the overestimation of the pressure peak values, and can predict the attenuation behavior. [ABSTRACT FROM AUTHOR]

A high‐gain, low‐cost empty substrate integrated waveguide (ESIW)‐fed circularly polarized (CP) antenna array is demonstrated for millimetre‐wave 5G applications in this letter. The ESIW is formed by metallized FR4 printed circuit boards. By stacking the metallic aluminium z‐shaped radiating slots atop the ESIW feeding network, CP radiation is achieved. The proposed 1 × 8 antenna array offers a high measured gain of 17.8 dBic and high measured radiation efficiency of 89.1%. The measured impedance bandwidth for |S11| ≤ −10 dB and measured axial ratio (AR) bandwidth for AR ≤ 3 of the proposed 1 × 8 array are 11.4% (36.5–40.9 GHz) and 7.8% (37–40 GHz), respectively. [ABSTRACT FROM AUTHOR]

Based on the same blasting vibration signal, the S transform and HHT method have been applied for the time and frequency analysis. Both the S transform and HHT method are analyzed and compared from the point of decomposition path and analysis function. It expressed that these two methods are complete and effective and have the characteristics of adaptive multiresolution. Especially, the time resolution of the HHT method is invariable and its accuracy is high. Moreover, its frequency resolution can be adaptively adjusted with the inherent characteristics of the signal. However, the time and frequency resolution of the S transform are limited by the uncertainty principle, and the resolution improvement is at the cost of reducing the resolution of another. Furthermore, the HHT method has much more adaptability and is superior to S transform in the analysis of nonstationary signals. In advance, the waveform curve and power spectral density of each detonator are extracted, which indicates that it is not scientific to use different segment detonators for the same circle of the auxiliary hole. Under the premise of the same charge quantity, the vibration energy peak value produced by the same segment detonator is less than that of several segments of detonators. Therefore, it is believed that the HHT method has broad application prospects in the study of wave propagation, attenuation law, structural dynamic response characteristics, and blasting vibration damage in rocks. [ABSTRACT FROM AUTHOR]

Chemically functionalized or coated sensors are by far the most employed solution in gas sensing. However, their poor long term stability represents a concern in applications dealing with hazardous gases. Uncoated sensors are durable but their selectivity is poor or non-existent. In this study, multi-parametric discrimination is used as an alternative to selectivity for uncoated capacitive micromachined ultrasonic transducers (CMUTs). This paper shows how measuring simultaneously the attenuation coefficient and the time of flight under different nitrogen mixtures allows to identify hydrogen, carbon dioxide and methane from each other and determine their concentration along with identification of temperature and humidity drifts. Theoretical comparison and specific signal processing to deal with the issue of multiple reflections are also presented. Some potential applications are monitoring of refueling stations, vehicles and nuclear waste storage facilities. [ABSTRACT FROM AUTHOR]

To solve the problem of high NOx emission of 600‐MWe boilers in power plants, we established a cold gas–solid modeling testbed scaled by 1:5 for two‐channel overfire air (OFA). A phase‐Doppler anemometer was used to measure the characteristics of the outlet flow field of the two‐channel OFA under different OFA rates. We also verified the industrial feasibility of this testbed under loads of 300 and 600 MWe. The influence of the OFA rate on the divergence angle of the outlet jet was small: When the OFA rate was increased from 15% to 35%, the divergence angle only increased by 2.2°. The attenuation of the axial velocity of the outlet jet increases with increasing OFA rate. For OFA rates of 15% and 25%, the jet penetration depth was between 1.5d and 2.5d (where d is the cone diameter of the OFA model in the cold‐flow experiments). When the OFA rate was 35%, the jet penetration depth was between 2.5d and 3.5d. The jet maintained about 17% O2 concentration at 1.4 m (about 11d) in the furnace under different boiler loads, and the concentration of emitted NOx increased with decreasing load. Based on these findings, we propose the use of two‐stage OFA: The jet at the outlet of the first‐stage OFA ports should have a larger jet‐divergence angle, and the other stage should have a larger jet‐penetration depth to realize full mixing with the flue gas and to ensure high burnout and low NOx emission. [ABSTRACT FROM AUTHOR]

A filtering power divider (FPD) with low-pass property and wideband harmonic suppression is presented in this paper. The microstrip structure of the FPD is designed based on elliptic function. The open stubs are embedded in the transmission line to obtain low-pass effect. An isolation resistor of 100Ω is connected between the two output ports to achieve good isolation. The operating frequency of the power divider is 2.9 GHz and the low-pass filter (LPF) has the cut-off frequency of 3 GHz with a sharpness factor of 55 dB/GHz. The attenuation band is extended up to 20 GHz (simulated) with a suppression of −19 dB. The maximum insertion loss in the passband for the FPD is −3.6 dB and the structure occupy an area of 0.7 λ g × 0.21 λ g . A lumped equivalent circuit of the LPF structure is also proposed. The LPF and the FPD both are fabricated using low-cost substrate FR4 of height (h) of 0.8 mm, a dielectric constant (εr) of 4.4, conductor thickness (t) of 0.04 mm and loss tangent (δ) of 0.02. For experimental verification, the measured data are compared with the simulated ones. [ABSTRACT FROM AUTHOR]

In recent years, special attention has been given to the effects of underground spaces and structures on the seismic response of adjacent ground. Nevertheless, to the best of the authors' knowledge, no method has yet been considered to reduce these effects in technical literature. The present study aims to investigate the role of geofoam as the cover material in cut and cover tunnels on the seismic response of the ground surface. For this purpose, a numerical study was performed using FLAC 2D, a finite difference software, and verified against previous studies. The effects of parameters such as the geofoam type, thickness of the geofoam blocks and interfaces between the blocks, on the ground surface amplification pattern were investigated. Parametric studies demonstrate that the geofoam has a strong potential to attenuate the seismic horizontal movements of the ground surface. As the thickness of the geofoam blocks is decreased, its attenuation ability is increased. It was also determined that the interface between the geofoam blocks plays a key role in the attenuation of the aboveground seismic responses. Based on the results, it was concluded that geofoam is a proper material to attenuate seismic amplifications at the ground surface, induced by underground tunnels. [ABSTRACT FROM AUTHOR]