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Reservoir computing (RC) is a bio-inspired framework suited for temporal data processing. Here we propose an all optical coherent RC for the equalization of the impairments of fiber optic (FO) system based on coherent detection. We compare the performances of the RC systems based on semiconductor saturable absorber mirror (SESAM) and highly nonlinear waveguide (HNLW). For a dispersion managed long haul FO system in which the nonlinear penalty is dominant, we find that the SESAM outperforms the HNLW due to its larger nonlinear memory. In contrast, for the equalization of dispersive impairments in a short haul FO system such as data center networks, we find that the HNLW has a much superior performance due to its larger linear memory.

In this paper we present a dual band low cross-polarized periodic microstrip leaky wave antenna (LWA) based on the multi mode resonator concept (MMR). The structure is capable of frequency dependent backward dual-beam steering and fast forward beam scanning in the upper and lower operating band, respectively. A gap loaded microstrip line is used as a host transmission line to feed the combination of the periodic patch radiators on the top and the bottom etched slots leading to the generation of the forward and the backward space harmonics. The etched ring slots at the bottom surface of the structure are not only responsible for steering the beam in the backward direction in the bottom hemisphere in its upper band but also adds radiation diversity in the overall radiation mechanism in its two operating bands. The potential use of this antenna resides in its ability to produce in-plane fast forward beam steering suitable for autonomous vehicle navigation systems in its lower band and out-of-plane backward-symmetric dual beam steering in the upper operating bands, suitable for tracking in relay systems.

Compact slow light devices are essential components for performing data caching and signal processing in photonic integrated loops. In this article, an integrated ultra-low-dispersion slow light device with a novel method is proposed. The device consists of three parts (hexagonal resonator with elliptical core, stub cavity, and tooth cavities) coupled to the waveguide, respectively. Dual Fano resonances occur in the structure, and transmission characteristics of the structure are investigated in detail by temporal coupled-mode theory. Finite-difference time-domain simulations reveal that the transmission bandwidth, group index, and delay time can be manipulated by adjusting the separation between two Fano resonances, which is related to the eccentricity of the oval core. At the 850.7 nm window, transmission bandwidth and average group index are optimized to 21.1 nm and 12.19, respectively. Moreover, multiple dispersionless wavelengths within the slow light bandwidth are obtained based on dual Fano resonances. Furthermore, feasibility of the device to perform slow light function in different channels is researched, and device performance is presented and analyzed. This device has a great impact on improving the quality of signals on chips, and the method introduced is of great significance for designing other photonic devices. [ABSTRACT FROM AUTHOR]

Surface wave tomography is performed by first estimating surface wave dispersion curves and then inverting them. The objective of this letter is the efficient and reliable estimation of the group velocity dispersion curves of surface waves. In this letter, group velocity dispersion curves of surface waves recorded at a single station with a known location of seismic source or between a pair of stations are estimated using continuous wavelet transform (CWT). The advantage of CWT is its multiresolution property and flexible choice of analyzing function. In the proposed method, the number of CWT filters used is almost half of the total number of filters used in the conventional frequency–time analysis (FTAN) method. The CWT coefficients of the seismogram are the functions of time and scale (analogs to wave period). The arrival time to reach the peak of the envelope function of CWT coefficients is estimated to calculate the group velocity of the surface waves. The group velocity dispersion curve of the surface waves is the plot of the change of group velocity with the period. Synthetic test data and ambient noise recordings of MesoAmerica seismic experiment (MASE) stations are acquired to investigate the performance of the proposed method. It is observed that the proposed method effectively retrieves the weaker surface waves and results in the broader band group-velocity dispersion curve when compared to the conventional FTAN method. The proposed method is also found to be computationally efficient. [ABSTRACT FROM AUTHOR]

The dispersion induced by fluid flow is a useful characteristic of hydrocarbon reservoirs and can be deduced from frequency-dependent amplitude versus offset (FAVO) inversion. However, FAVO inversion strongly depends on the spectral decomposition method, which directly affects the resolution of inversion results. In this letter, we propose a new time–frequency analysis method, named modified window-parameter-optimized S-transform (MWPOST), for improving the resolution of FAVO inversion. In MWPOST, the optimized scale parameter of the window function can be adaptively obtained according to the amplitude spectra of actual signals. Synthetic signal analysis indicates that the method has excellent performance with higher time–frequency resolution. Then, we present a high-precision FAVO inversion method using MWPOST for high gas-saturation reservoir delineation. The field seismic data application illustrates that the dispersion factor inverted by the proposed method has a higher time resolution and exhibits better performance for delineating the reservoir boundary with high gas saturation. The proposed method can improve the precision of FAVO and it is feasible to detect the location and spatial distribution of high gas-saturation reservoirs. [ABSTRACT FROM AUTHOR]

Intensity modulation/direct detection (IM/DD) and coherent schemes are two kinds of promising solutions to achieve the evolution for B5G/6G fronthaul networks. IM/DD has more mature commercial deployment applications for short-reach applications with lower costs and simpler configurations compared with coherent solutions. In this article, we experimentally demonstrate a local area network-wavelength division multiplexing (LAN-WDM) IM/DD access system with a record bit rate of 2 Tb/s (250 Gbit/s × 8) probabilistic shaping eight-pulse amplitude modulation (PS-PAM-8) signal with joint equalization techniques to support the evolution of future B5G/6G mobile fronthaul networks. Considering the 20% Soft Decision Forward Error Correction (SD-FEC) threshold with the bit error rate (BER) of 2 × 10−2, we realize a record net bit rate of 1.6 Tb/s over 5 km fiber. This system can potentially support a 12-wavelengths transmission with the total line rate of 3 Tb/s (250 Gbit/s × 12). Moreover, we analyze the challenges of the evolution, usage scenarios, digital signal processing (DSP) implementation, transmission rate and distance, and the tolerance of dispersion with different wavelengths. The LAN-WDM can be considered as a feasible and potential candidate scheme to meet the evolution and deployment of B5G/6G Terabit/s fronthaul networks.

We propose a novel Dispersion Minimisation framework for event-based vision model estimation, with applications to optical flow and high-speed motion estimation. The framework extends previous event-based motion compensation algorithms by avoiding computing an optimisation score based on an explicit image-based representation, which provides three main benefits: i) The framework can be extended to perform incremental estimation, i.e., on an event-by-event basis. ii) Besides purely visual transformations in 2D, the framework can readily use additional information, e.g., by augmenting the events with depth, to estimate the parameters of motion models in higher dimensional spaces. iii) The optimisation complexity only depends on the number of events. We achieve this by modelling the event alignment according to candidate parameters and minimising the resultant dispersion, which is computed by a family of suitable entropy-based measures. Data whitening is also proposed as a simple and effective pre-processing step to make the framework’s accuracy performance more robust, as well as other event-based motion-compensation methods. The framework is evaluated on several challenging motion estimation problems, including 6-DOF transformation, rotational motion, and optical flow estimation, achieving state-of-the-art performance. [ABSTRACT FROM AUTHOR]

A novel microfluidic sensor based on quarter-mode localized surface equipartition excitations for liquid detection is proposed in this article. The sensor has a compact size and ultrahigh sensitivity. With the excellent properties of field enhancement and field confinement of the localized surface plasmon (LSP), a double-interdigitated structure is employed to further improve the sensitivity. The proposed sensor is validated in a microwave frequency regime, and the confined electric field is fully employed by placing a microfluidic channel etched on polydimethylsiloxane (PDMS), which is aligned on top of the internal interdigitation. The results show that the simulated results are in good agreement with the experimental measurements. The ultrahigh sensitivity with 0.34% is excited by the addition of interdigitated structure. The ultrahigh sensitivity and compact size make it a good choice for sensing applications, which can be widely used in environmental monitoring, medical health, and other fields and have great potential in the microwave and terahertz regions. [ABSTRACT FROM AUTHOR]

In this article, the relation between corporate R&D and industry pay gap is tested. We further test the relation between CEO pay and R&D. We find positive bidirectional influence between corporate R&D and industry pay gap. We further find positive bidirectional influence between CEO pay and corporate R&D, and between corporate R&D and industry pay dispersion. CEO pays rise in an industry as competitive dynamics come into play as other firms respond to the focal firm's investment in R&D, thereby increasing industry pay dispersion, which widens the industry pay gap. Moreover, investment opportunities increase CEO pay that further increases the firm's R&D investment. CEO pay thus drives greater R&D investment. The positive association between R&D and industry pay gap is stronger for more proactive and aggressive firms. A higher uncertainty makes a firm's growth options embedded in R&D investments more valuable, enhancing the firm value that increases the CEO pay. R&D lowers the firm's stock undervaluation that increases the CEO pay. Our results suggest CEO pays increase R&D investments that further increase industry pay dispersion and industry pay gap. The board of directors increases CEO pay in line with the industry pay gap, which drives greater investment in R&D. [ABSTRACT FROM AUTHOR]

This article demonstrates the application of a novel multiagent modeling approach to support supply network configuration (SNC) decisions toward addressing several challenges reported in the literature. These challenges include: enhancing supply network (SN)-level performance in alignment with the goals of individual SN entities; addressing the issue of limited information sharing between SN entities; and sustaining competitiveness of SNs in dynamic business environments. To this end, a multistage, multiechelon SN consisting of geographically dispersed SN entities catering to distinct product-market profiles was modeled. In modeling the SNC decision problem, two types of agents, each having distinct attributes and functions, were used. The modeling approach incorporated a reverse-auctioning process to simulate the behavior of SN entities with differing individual goals collectively contributing to enhance SN-level performance, by means of setting reserve values generated through the application of a genetic algorithm. A set of Pareto-optimal SNCs catering to distinct product-market profiles was generated using Nondominated Sorting Genetic Algorithm II. Further evaluation of these SNCs against additional criteria, using a rule-based approach, allowed the selection of the most appropriate SNC to meet a broader set of conditions. The model was tested using a refrigerator SN case study drawn from the literature. The results reveal that a number of SNC decisions can be supported by the proposed model, in particular, identifying and evaluating robust SNs to suit varied product-market profiles, enhancing SC capabilities to withstand disruptions and developing contingencies to recover from disruptions. [ABSTRACT FROM AUTHOR]

The scanning rate of a composite right/left-handed (CRLH) leaky-wave antenna (LWA) is usually determined by the dispersive behavior of the corresponding CRLH unit cell. In this letter, a novel CRLH unit cell with high dispersive behavior is proposed and investigated. The unit cell is formed by four stubs embedded in a rectangular ring patch, which is grounded with several metal vias. The right-handed characteristic is enhanced by the ring patch, while the left-handed characteristic is reduced by the vias and the gaps between the patch and the stubs. Then, the unit cell is applied to design an LWA with high scanning rate. The measured result shows that the seamless scanning angle of the antenna prototype is 130° (−65° to +65°) within a frequency range from 9.3 to 9.93 GHz (i.e., 6.6% for fractional bandwidth). Therefore, the proposed LWA antenna is with a high scanning rate up to 19.7°/%BW. [ABSTRACT FROM AUTHOR]

This letter presents a single-layer, wide-angle, low-cost frequency beam scanning leaky-wave antenna (LWA) based on spoof surface plasmon polaritons (SSPPs). Here, two rows of Sierpinski prefractal parasitic patches are placed near an ultrathin planar SSPP waveguide, which can achieve continuous backfire to nearly endfire beam scanning with increasing frequency. The overall width of the proposed antenna is only 0.75 $\lambda _{\text{0}}$ (with $\lambda _{\text{0}}$ being the wavelength of the lowest operating frequency). This SSPP LWA provides high-performance backfire and broadside radiations due to applying prefractal units. Simulated results show that the proposed SSPP LWA achieves a wide scanning range from −90 $^{\circ }$ to +58 $^{\circ }$ within the frequency range of 3–8 GHz. The average gain and radiation efficiency of the antenna are 10.9 dBi and 88%, respectively. An antenna prototype is fabricated and measured. The measured results agree reasonably well with the simulated ones. [ABSTRACT FROM AUTHOR]

The accurate analysis and the characterization of guided-wave structures are important steps in the design of microwave and optical systems. A numerical methodology based on a three-dimensional discontinuous Galerkin time-domain (DGTD) finite element method is used to estimate the resonant frequencies of various structures in a single run, with several polychromatic sources (dipole, plane wave, etc). The proposed approach leads to simulations that are fast and accurate, this being the result of the local discretization strategy of the full-wave time-domain Maxwell’s equations on unstructured tetrahedral meshes that is easy to parallelize. The stability of the overall numerical scheme is obtained using an upwind numerical flux and an implicit second-order accurate time integration scheme. The numerical methodology is verified based on two problems with closed-form solutions. First, homogeneous and non-homogeneous waveguides are studied using the proposed methodology. The WR-284 waveguide is used, and cut-off frequencies of the first 7 modes are computed and compared with analytical solutions. Propagation characteristics of mode-selective transmission lines (MSTL) are then investigated. These MSTL simulation results are verified using measurement results of fabricated MSTL, microstrip, and RWG prototypes up to 110 GHz. Simulation results show the flexibility, the robustness, and the high accuracy of the proposed numerical strategy.

Metasurfaces are artificial sheets with sub-wavelength thickness and they are two-dimensional equivalents of metamaterials. The generalized sheet transition conditions (GSTCs) have been recently proposed for electromagnetic analysis of the metasurfaces. In GSTCs, the metasurface is generally modeled as a sheet with zero-thickness. However, the conventional finite-difference time-domain (FDTD) method is not straightforwardly applied to analyze electromagnetic wave propagation in the metsurface by harnessing GSTCs because GSTCs exhibit electric and magnetic discontinuities. Alternatively, the GSTC-FDTD formulation is highly suitable for analyzing the electromagnetic properties of metasurfaces by introducing electric and magnetic virtual grids. Meanwhile, metasurfaces can be realized by using 2-D materials such as black phosphorus and thus the dispersion characteristics of metasurfaces should be considered. In this work, we propose an efficient dispersive GSTC-FDTD algorithm by employing the Drude dispersion model. Moreover, for the first time, the numerical surface susceptibility inherent to the dispersive GSTC-FDTD formulation is derived and its numerical accuracy is investigated. Numerical examples illustrate high efficiency of the proposed Drude-dispersive GSTC-FDTD algorithm.

The theoretical foundations of a metamaterial (MM) liner for the MRI bore that facilitates the propagation of reduced-cutoff cylindrical waveguide modes are presented in the Part 1 companion paper to this work. Here, in Part 2, the practical design and modelling of the novel MM liner is applied to a body MRI radio-frequency (RF) transmitter for 4.7T. An equivalent network mesh model is developed to reduce the distributed structure of the MM to one that uses lumped discrete tuning elements. The close match between full-wave simulation and the network model is demonstrated by comparison of the longitudinal propagation dispersion curves and input impedance. The application of the methods developed for analysis of the MM liner behavior are demonstrated in the design of a practical MM liner as an effective MRI RF transmitter. The liner’s simulated performance was evaluated using three key metrics of MR radio-frequency (RF) coil performance: transmit efficiency, the variation of the transmit field (a measure of homogeneity), and the 10g averaged local specific absorption rate (SAR). These metrics are compared to those of the commonly used birdcage (BC) coil. The main advantage of the MM liner is the 29.6% reduction in maximum SAR normalized to transmit field relative to the BC coil, with comparable transmit efficiency and homogeneity. Thus, the liner can potentially replace the BC coil as an RF transmitter and provide an enhanced safety margin, or allow the use of faster, more SAR-aggressive imaging sequences.

The upconversion detection is a promising method to detect infrared radiation. It is proved that the focused beam makes a contribution to improving the upconversion efficiency. A near-infrared detector at room-temperature based on sum frequency generation(SFG) with focused beams is demonstrated. To enhance the upconversion efficiency, the signal and pump beams are tightly focused by the same focal lens. To reduce that the dispersion of the focal lens has a negative effect on upconversion efficiency in a tightly focusing system, the relation between the upconversion efficiency and the focused beams in our system is investigated. In the setup, the signal and pump beams are combined by a polarization maintaining wavelength division multiplexer (PMWDM) that is connected on a collimator. The mixed beam is focused into a periodically poled lithium niobate (PPLN) bulk by a lens of 35 mm focal length. The signal pulse at 1550 nm is converted to 863 nm with a 172 mW continuous-wave pump beam at 1950 nm. The converted signal is measured by a photomultiplier tube(PMT) and results shows the maximum upconversion efficiency is $5.23 \times 10^{-4}$ while the pump power is 172 mW.

A novel low-cost high-gain beam-steering antenna terminal topology for global data connectivity with low-earth-orbit satellite constellations in the UHF 900 MHz ISM band is reported. It is shown how a simple printed-circuit-board half-width microstrip leaky-wave antenna (LWA) with passive frequency-beam scanning capacity provides an energy-efficient scanning method avoiding more power-demanding and expensive beam-steering techniques (such as electronic scanning, mechanical rotation, or beam switching). For that, iridescent channel-agile operation and cross-layer optimization are needed. As an example, two single-element LWAs and an LWA array are designed to scan the celestial vault with an angular elevation scanning range of 130° and using the available LoRaWAN protocol channels from 902 to 928 MHz. It is reported a scanned-beam peak gain above 9 dBi for the compact printed-circuit LWA array design with 55 cm × 27 cm aperture dimensions. [ABSTRACT FROM AUTHOR]

A high-scanning rate leaky-wave antenna (LWA) working at Ka-band with continuous backward-to-forward beam-scanning capability, good open stopband (OSB) suppression and wide scanning angle is exhibited. The proposed LWA is made by etching an array of cascaded high-Q resonators and open discontinuities on the substrate integrated waveguide (SIW). The resonator is designed by combining two symmetrically unbalance split ring resonators (USRRs) on the top surface of the SIW. The LWA's working mechanics were thoroughly investigated through band structure theory. An in-depth interpretation of the LWA's characteristics is provided by studying the surface current distribution and the equivalent circuit model of the resonator structure. The LWA's OSB is effectively alleviated by properly selecting the length of the radiation slot. Yet, the antenna scanning rate is directly improved by the oscillation quality of the resonators (i.e., USRRs), which is realized by tuning the split gap of the USRR. In the experiments, a prototype of the proposed LWA was fabricated and measured. The simulated and measured data show good agreement in terms of the antenna's scanning range and radiation gain. The measured results indicates that a continuous beam scanning from −56° to +48° is rendered over the frequency band from 32 to 36 GHz, which implies a spectral scanning rate of 8.84° per percentage. Finally, it is shown that the average gain can reach up to 9.1 dBi. [ABSTRACT FROM AUTHOR]

Surface waves are demonstrated theoretically to propagate along periodically corrugated surfaces made of non-conductive lossless materials with positive permittivity. An analytic derivation of the surface wave dispersion relation is presented in the case of the deeply subwavelength period of a corrugated structure using impedance boundary conditions (IBCs) at the interfaces. Thus obtained dispersion relation is verified numerically and limitations as well as the physicality of IBCs when modeling surface waves are discussed. Finally, suitable materials, potential experimental realization, and sensing applications of surface waves in the terahertz spectral range are discussed. [ABSTRACT FROM AUTHOR]

This article presents the design and experimental characterization of microwave structures based on parity time-reversal duality symmetric bifilar edge waveguides (PTD-BEWs) realized through a parallel plate waveguide (PPW) loaded by a metasurface. The analyzed structures include transmission lines with bends and multiple line arrangements. Due to their unique symmetry properties, these structures are robust against backscattering, thus resembling the behavior of topological WGs, despite the fact they are reciprocal. This makes it possible to guide the electromagnetic (EM) waves along the edge with low insertion losses and unique matching properties. Measurements, performed in the frequency range between 24 and 32 GHz, have confirmed the feasibility of the theoretical concept. [ABSTRACT FROM AUTHOR]

Dynamic manipulation of the surface plasmon polariton (SPP) and wave steering is important in plasmonic applications. In this work, we excite a curved SPP in topological continua by applying a radial magnetic bias. We believe that it is a new technique to create a unidirectional SPP traveling along a curved trajectory. We also derive a Green’s function (GF) model for radially biased plasma, applicable to curved SPPs. We compare the properties of unidirectional curved SPPs with the usual case when an axial bias is applied. [ABSTRACT FROM AUTHOR]

Glide-symmetric (G-S) waveguides made of metallic metasurfaces are a wideband, low-loss, low-cost, and conformable alternative to dielectric materials for the design of antenna lenses at millimeter waves. However, computing the effective refractive index of glide-symmetric waveguides with existing full-wave analysis techniques results in cumbersome parametric studies for each new design. This article presents a new analytic homogenization technique for glide-symmetric holey parallel-plate waveguides (PPWs). The dispersion equation of these structures, found by way of mode-matching, is simplified at low frequency using the properties of the modes resonating within the holes, independently of the hole shape. This simplified equation yields a closed-form expression of the effective refractive index, relying on the eigenmodes of the hole cross section. This formula avoids solving a 3-D full-wave problem and is fully analytic in the case of canonical hole shapes. Although derived in the quasi-static regime, it characterizes propagation over an ultrawide band, due to the low dispersive properties of glide symmetric structures. It is a function of the angle of propagation within the waveguide and can thus be used to study anisotropic properties. Its efficiency is demonstrated with the example of glide-symmetric PPWs with rectangular and circular holes. [ABSTRACT FROM AUTHOR]

This article proposes a single-layered electronically tunable annular surface plasmon polariton (SPP)-based leaky-wave antenna at 60 GHz for continuous azimuthal beam scanning. Initially, the groundless annular SPP transmission line is designed having specialized feeding mechanism which is operational at 60 GHz under SPP mode. Periodic radiating semicircular patches are incorporated into the vicinity of the TL that form an additional momentum caused to convert the slow-wave SP mode to radiating leaky-mode and placement of extra metallic ground makes the radiated beam unidirectional. Furthermore, implementation of the varactor diodes with imposed suitable switching conditions make the geometry electronically tunable to achieve a continuous complete azimuth coverage. The theoretical predictions, numerical simulations and the experimental validations of the proposed structure show good agreement. The proposed antenna show an overall scanning range of 275°, peak gain of 19.9 dBi with average sidelobe level of −10 dB and minimum cross polar level of −20 dB. Availing the benefits from the low-profile compactness and improved performance, the proposed groundless LWA appears as a promising candidate for integration in 60-GHz mm-wave applications. [ABSTRACT FROM AUTHOR]

Rate-Splitting Multiple Access (RSMA) is an emerging flexible and powerful multiple access for downlink multi-antenna networks. In this paper, we introduce the concept of RSMA into short-packet downlink communications. We design optimal linear precoders that maximize the sum rate with Finite Blocklength (FBL) constraints. The relations between the sum rate and blocklength of RSMA are investigated for a wide range of network loads and user deployments. Numerical results demonstrate that RSMA can achieve the same transmission rate as Non-Orthogonal Multiple Access (NOMA) and Space Division Multiple Access (SDMA) with smaller blocklengths (and therefore lower latency), especially in overloaded multi-antenna networks. Hence, we conclude that RSMA is a promising multiple access for low-latency communications. [ABSTRACT FROM AUTHOR]

Random pulsewidth modulation (RPWM) with variable carrier frequency generally disperses the dominant PWM harmonics more effectively than the RPWM with constant carrier frequency. But variable carrier frequency results in variable sampling frequency, which changes controller parameters and makes RPWM difficult to use in closed-loop applications. To significantly disperse dominant harmonic clusters located nearby the PWM frequency and its multiples, while maintaining constant sampling frequency, in this article, N-state random pulse position space vector pulsewidth modulation is proposed. This method randomly selects one of the N selected carrier patterns with equal probability in each carrier period, resulting in N different pulse position states. By applying two-dimensional Fourier analysis, the additional multiplication factor in the derivation results, named harmonic dispersion coefficient in this article, can intuitively explain the principle from the perspective of mutual cancellation of complex vectors in different directions. All dominant PWM harmonics are significantly dispersed except those located nearby the Nth PWM frequency and its multiples when using the proposed method. Besides, power losses and switching counts are detailed discussed. Both simulation and experimental results verify the effectiveness of the method at last. [ABSTRACT FROM AUTHOR]

We consider quadrature spatial modulation (QSM) schemes, which achieve high spectral efficiency (SE) via the dispersion of a relatively small number $P$ of $M$ -ary modulated symbols over a large number of combinations of $n_{T}$ transmit antennas and $T$ transmit instances. In particular, we design a new space-time block code (STBC)-based scalable QSM scheme combining high SE with maximum diversity and optimum coding gains. Deriving a closed-form expression for the optimum SE, we show that scaling the size $T$ with $n_{T}$ not only is required to achieve SE optimality, but also results in further gains in bit error rate (BER) performance. Building on the latter optimal parameterization, a fully optimized scalable QSM (OS-QSM) transmitter design is then obtained by introducing a new dispersion matrix index selection algorithm that ensures even utilization of spatial-temporal resources. Finally, a new greedy boxed iterative shrinkage thresholding algorithm (GB-ISTA) QSM receiver is proposed, which exploits the inherent sparsity of QSM signals and while detecting spatially and digitally modulated bits in a greedy fashion. The resulting low complexity of the new receiver, which is linear on $n_{T}$ , enables the utilization of OS-QSM in systems of previously prohibitive dimensions. [ABSTRACT FROM AUTHOR]

The advanced non-destructive tests (NDT) have become increasingly popular in the structural performance evaluation of transportation infrastructures including pavements. Among them, Falling Weight Deflectometer (FWD) and Spectral Analysis of Surface Waves (SASW) are the two most widely used methods in modulus measurement. Although popularly used, FWD methods base the analysis purely on the deflection characteristics of the pavement and the back-calculated modulus values are usually not unique for different data processing methods. SASW is based on fundamental spectral analysis of the Rayleigh waves but is practically limited in field operation due to its efficiency concern. On the other hand, the impact loading applied by the FWD will generate the Rayleigh wave, and the geophones used in FWD can capture Rayleigh wave fluctuation and measure the particle motion for phase velocity calculations. It is theoretically possible to use the deflection-time history collected by FWD to perform dispersion analysis based on the Rayleigh wave propagation theory, as used in the SASW method. Inspired from that, the main objective of this paper is to propose a new approach of using the deflection-time history collected by FWD to develop the dispersion curves and thus obtain the in-situ modulus of the layered asphalt pavement. This approach is referred as the FWD dispersion curve method. Two in-service semirigid base asphalt pavement segments were used as case studies to explain the new methodology. The results of layered modulus from the FWD dispersion curve method were compared with the traditional FWD and SASW method, as well as the laboratory Indirect Tensile (IDT) testing results using field cores. Findings demonstrated the feasibility of the FWD dispersion curve method in accurately capturing the layered modulus profile of the asphalt pavements. [ABSTRACT FROM AUTHOR]

Multiband elastic optical network (MB-EON) technology can help to sustain exponential traffic growth in the optical backbone network. However, multiband operation creates high inter-channel stimulated Raman scattering, leading to a high nonlinear impairment (NLI) that may severely affect the optical signal-to-noise ratio (OSNR) of a lightpath. Additionally, the severity of NLI on the channel of interest depends upon the choice of allocated wavelength. Hence, appropriate channel allocation may cumulatively lead to a higher network capacity. This paper proposes a quality-aware resource provisioning scheme in the context of MB-EON that selectively chooses the available channels from different bands in order to achieve the maximum network capacity in the long run. A deep neural network-assisted quality of transmission estimator is considered to estimate the OSNR of a lightpath with accuracy of 99.65% and 0.012 dB variance in estimation error. The performance of our algorithm in the proposed scheme, namely, optical signal-to-noise ratio adaptive first–last-fit (OA-FLF), is analyzed for two geographically diverse networks, namely, BT-UK and the 24-node USA network, in terms of traffic admissibility, quality of established lightpaths, and contiguous aligned available slot ratio (CAASR), and compared with four state-of-the-art baseline algorithms: first fit, last fit, route adaptive first–last-fit, and distance adaptive first–last-fit. Numerical results indicate that the proposed algorithm outperforms all of the baseline algorithms in terms of traffic admissibility. Reported results show that, compared to the baseline algorithms, consideration of the effect of NLI before resource allocation in the OA-FLF algorithm can provide a maximum gain of nearly 30% in terms of traffic admissibility for smaller networks such as BT-UK, whereas, for longer geography such as the 24-node USA network, this traffic admissibility gain becomes close to 61% till 1% blocking. [ABSTRACT FROM AUTHOR]

An air-filled mode selective transmission line (AF-MSTL) consisting of an opened groove gap waveguide (GWG) and an inverted coplanar waveguide (CPW) is proposed in this letter. By using the electromagnetic band gap (EBG) structure, the electrical contacts of AF-MSTL are not required during the assembly process. To verify the design, the AF-MSTL prototype, connected to two designed grounded-CPW (GCPW) to AF-MSTL transitions to build a back-to-back structure, has been fabricated and measured. A measured insertion loss of 0.2857 dB/mm at 110 GHz is achieved, which is lower than the dielectric filled (DF) MSTL of 0.5012 dB/mm at 110 GHz. [ABSTRACT FROM AUTHOR]

The geometric parameters of periodic units, which influence the refractive/reflective behaviors of grating waveguides, are usually designed using intuition combined with meticulous trial-and-error, making the design extraordinarily time-consuming and computationally intensive. In this work, we proposed an effective method based on deep learning to meet this challenge. Concretely, we employed fishbone slow-light waveguides as the object to be optimized, whose unit cell has multiple degrees of freedom, and trained a deep neural network (DNN) to predict their geometric parameters with the given discrete group index curves as the input. Our design is oriented for high group index and near-zero group velocity dispersion (GVD). To verify this functionality, we performed the controllable inverse design of GVD while keeping the group index at the same level (about 24), which made the bandwidth increase by 53.8% at the same time, and further explored near-zero GVD structures with a group index of 30.76/41.30/51.90. Our results lay the groundwork for the rapid design of complex slow-light grating waveguides. [ABSTRACT FROM AUTHOR]

In this communication, we present a longitudinally slotted substrate integrated slot (SIS) leaky-wave antenna (LWA) for point-to-point communication. To mitigate the dispersion of traditional substrate integrated waveguide (SIW) LWAs, an SIS is proposed by etching a long straight slot along the SIW. The loaded slot mitigates the dispersion of SIW due to the special electric field distribution. Anti-TE10 mode is excited inside the SIS. Then, longitudinal slots are symmetrically loaded on both sides of the long slot. The prototype of SIS LWA is validated by the simulated and experimental results. A frequency bandwidth of 10.3% is realized with the beam squinting within 7° and realized gain of 13.9 ± 0.7 dB at a fixed angle of −7°. The proposed antenna is intended for point-to-point communication. [ABSTRACT FROM AUTHOR]

We present a new approach to the study of the telegraph equation, which is based on analyzing the equation in phase space. We consider the phase space of time and frequency, as well as of position and spatial frequency (or wavenumber). We show that considerable simplification, both conceptual and mathematical, results from this approach. The basic reason why a phase space approach is fruitful is that when there is dispersion, the group velocity is not constant but changes with frequency, and therefore the wave changes as it propagates over space and time. Simple but effective and insightful phase space approximations to the solution of the telegraph equation are presented, with examples. [ABSTRACT FROM AUTHOR]

A periodic leaky-wave antenna (LWA) with unidirectional horizontal radiation and wide-angle beam-scanning capacity through broadside is presented. The proposed antenna is made of a slow wave coplanar strips line with open-ended slots and short-ended slots etched on the two strips, respectively. The energy leaks mainly from the open-ended slots, contributing to the horizontal radiation of the antenna. Consequently, the constraint of the ground plane on the radiation patterns is reduced, suggesting the potential of the proposed structure to break the scanning range limitation of the traditional LWAs. The scanning range of LWAs is determined theoretically by the normalized phase constant. Therefore, the slow wave structure is utilized to ensure the normalized phase constant of the $n = -1$ harmonic varying from −1 to 1. Subsequently, a pair of extended slots are introduced to the slow wave LWA unit cell to eliminate the open-stopband (OSB) effect. As a validation of the proposed antenna, a prototype with broadside frequency of 10 GHz is designed, fabricated, and measured. The measured results are in good agreement with the simulated results. It is shown that the fabricated antenna scans from −75° to 83° in the horizontal plane with eliminated OSB and measured gain variation of 2.65 dB. [ABSTRACT FROM AUTHOR]

High-speed digital signaling can cause various signal integrity and electromagnetic interference problems. Signal attenuation and distortion can be observed in the gigahertz band owing to the frequency dispersion of substrates. In this article, we propose a frequency-dependent finite-difference time-domain (FDTD) approach for the numerical analyses of flame-retardant type-4 (FR-4) substrates. The proposed FDTD approach provides accurate broadband solutions because it can take into account the frequency dispersion of the substrate. First, the broadband complex permittivity of FR-4 substrates was measured using a balanced-type circular disk resonator and fitted into a Djordjevic model for the FR-4 substrates. Second, we adapted the fast inverse Laplace transform and Prony methods to find the z-domain expressions and incorporate them into the FDTD formulation.The validity of the proposed approach was demonstrated by comparing the numerical and experimental results of the differential insertion loss and phase constant of differential microstrip lines. Both results were in good agreement, indicating the validity and usefulness of the proposed approach for simulations of broadband signal transmission in FR-4 substrates. [ABSTRACT FROM AUTHOR]

This article proposes a method to engineer degenerate band-edge conditions in periodic substrate-integrated waveguides (SIWs). A degenerate band edge (DBE) is a fourth-order exceptional point originating from the coupling of four Floquet–Bloch modes; it leads to a dispersion relation flatter than a regular band edge (RBE) and is suitable to design slow wave structures and high $Q$ -factor resonators. Design guidelines to achieve a DBE point are given based on Bloch analyses of unit cells. An oblique line of vias in SIW is proposed to form a suitable modal coupling between adjacent waveguides enabling a degenerate band-edge condition. The effect of losses and the robustness to parameter variations are discussed by means of rigorous Bloch analyses. A unit cell showing the best behavior concerning the losses and geometric tolerances is selected and prototypes of finite-length resonators are realized. Measurements validate simulated results and confirm the typical $N^{5}$ scaling of the loaded $Q$ -factor to the number of cells $N$ of the resonator. [ABSTRACT FROM AUTHOR]

This letter presents a systematic method to regulating the response of an artificial impedance surface. The method is based on governing the dispersion diagram to control the depth of modulation so that a meaningful pattern of scatterers is obtained on the structure. The method is applied on a holographic-based large reflective metasurface to achieve a dual-beam radiation pattern with tilt angles of $\pm 45^{\circ }$ in the azimuth plane at $f=3.5$  GHz. The structure is fabricated and the measured data concur with the simulation results. [ABSTRACT FROM AUTHOR]

A novel digital signal processing (DSP)-based scheme for physical layer security in coherent optical communication systems is proposed and numerically investigated. The optical layer signal encryption is accomplished by two dispersive elements and one phase modulator (PM) driven by a DSP-generated encryption key, whilst signal decryption uses similar components but with inverted dispersion values and security keys. A critical aspect of the DSP-based physical layer security is that the security keys, driving the PMs to hide/recover the data signals, must be highly unpredictable and noise-like, thus orthogonal frequency division multiplexing (OFDM) signals are employed as they possess these characteristics, they can also be easily generated and cover a suitably wide range of unique keys. Numerical simulations are conducted to determine optimum system parameters for achieving a high level of security, the key parameters requiring optimization are the dispersion of the dispersive elements and the bandwidth of the security keys. Using these determined optimum parameters, in-depth investigations are undertaken of encryption/decryption induced transmission performance penalties, sensitives to various parameter offsets and operation over various transmission distances. To observe any data signal dependencies, various performance metrics are investigated for different combinations of modulation formats (DQPSK and 16QAM) and baud rates (40 Gbaud and 100 Gbaud) for the transmitted data signals. The proposed DSP-based physical layer security scheme is shown to have the potential to achieve, in a low-cost and highly effective manner, a high level of physical layer security with acceptable performance penalties for existing coherent optical communication systems. [ABSTRACT FROM AUTHOR]

This paper proposes a belief propagation (BP)-based algorithm for sequential detection and estimation of multipath component (MPC) parameters based on radio signals. Under dynamic channel conditions with moving transmitter/receiver, the number of MPCs, the MPC dispersion parameters, and the number of false alarm contributions are unknown and time-varying. We develop a Bayesian model for sequential detection and estimation of MPC dispersion parameters, and represent it by a factor graph enabling the use of BP for efficient computation of the marginal posterior distributions. At each time step, a snapshot-based parametric channel estimator provides parameter estimates of a set of MPCs which are used as noisy measurements by the proposed BP-based algorithm. It performs joint probabilistic data association, and estimation of the time-varying MPC parameters and the mean number of false alarm measurements, by means of the sum-product algorithm rules. The algorithm also exploits amplitude information enabling the reliable detection of “weak” MPCs with very low component signal-to-noise ratios (SNRs). The performance of the proposed algorithm compares well to state-of-the-art algorithms for high SNR MPCs, but it significantly outperforms them for medium or low SNR MPCs. Results using real radio measurements demonstrate the excellent performance of the proposed algorithm in realistic and challenging scenarios. [ABSTRACT FROM AUTHOR]

A novel dual-beam fixed-beam leaky-wave antenna (LWA) is proposed in this article. This antenna has a very simple structure, which is basically a grounded coplanar waveguide (GCPW) printed on a specially shaped printed circuit board (PCB). Its working principle is that, for a GCPW with no ground vias (leaky GCPW), there will be a parallel plate waveguide (PPW) mode between its two ground layers, which couples with its GCPW mode. Because the GCPW mode has a phase velocity higher than that of the PPW mode, leaky-wave radiation will be generated from the GCPW to the PPW. This radiation is then radiated into the free space through a metal flare. Since the GCPW is nearly non-dispersive, the beam direction of this radiation is inherently not frequency scanning. Besides its simplicity, the proposed antenna has a pretty good performance. Measured results show a 3 dB realized gain bandwidth and −10 dB impedance bandwidth of larger than 26–40 GHz, a peak gain of 17.5 dBi, and a negligible beam scanning range of only 2.5° (±1.25°) across 26–40 GHz. [ABSTRACT FROM AUTHOR]

A novel concept of combining the advantages of pseudospark (PS)-sourced electron beam (high beam current density), multiple-sheet-electron-beams (large total beam cross-sectional area), and high-order mode (HOM) slow wave structure (SWS) (high power capacity) to produce high-power terahertz signals is presented in this article. As an example, a sub-terahertz backward wave oscillator (BEO) driven by PS-sourced dual-sheet-electron-beams is designed. Measured results of the interaction circuit, including transmission/reflection coefficients and the dispersion relation, were in good agreement with simulation predictions. Beam-wave interaction simulations having considered the plasma effect and conductor loss predicted stable output signals with radiation power of 167.4–255.4 W over a tunable bandwidth of 234.4–241.0 GHz. [ABSTRACT FROM AUTHOR]

This article aims to improve nanofiller dispersion in epoxy resins by using an electrostatic disperser (ED), as well as reduce costs by using a combination of microfillers and nanofillers. The ED method aids in homogenized mixing of nanofillers in epoxy resin, due to its jet elongation and shearing effect on a polymer mix. In this article, two concentrations (7.5 wt% and 5 wt%) of nanosilica are used with resin, and the rheological properties of hybrid composites are tested before and after the addition of 50 wt% microsilica. It is observed that the electrostatic dispersion method aids in the network formation of nanosilica, unlike the high shear (HS) method, wherein clusters of nanosilica are formed. Hence, the ED method aids in reducing the viscosity values with the addition of microsilica, which is helpful in the product molding process. A plausible mechanism of filler dispersion is explained for ED and HS methods. The morphological analysis showed that the composites are brittle due to the high silica content, and that the silica fillers are dispersed well within the epoxy matrix. The flexural strength lies in the same range for both composites prepared using ED and HS methods. Thermal conductivity depends both on nanosilica and epoxy matrix dispersion, while heat deflection temperature, thermal diffusivity and specific heat depend on the dispersion method. [ABSTRACT FROM AUTHOR]

In most communication scenarios, antennas are often required to achieve broadband and directional radiation, and beam squint with frequency is unfavorable for broadband signal transmission. The traditional leaky-wave antennas (LWAs) have beam squint with frequency. In this letter, an LWA with fixed beam direction in a broadband is designed with consistent gain over the band. A ridge gap waveguide (RGW) is adopted to construct a nondispersive structure, and one lateral side is connected to a parallel plate filled with dielectric slab. Thus, leakage radiation is produced at the interface between the RGW and the parallel plate, generating a beam with fixed direction and high gain. The novelty is that in theory the fixed beam can be realized in infinite band owing to the nondispersive waveguide. Finally, a broad band of up to 58% (from 22 to 40 GHz) is achieved due to the limitations of the stopband structure and feeding port. The measured beam is fixed at 41° over the whole band, with a slight beam deviation of 2.6°. The realized gain is consistent over the band with a peak gain of 19.3 dBi. The designing method provides a simple and efficient way to realize the broadband fixed-beam LWAs. [ABSTRACT FROM AUTHOR]

This letter presents a novel dual-polarized two-dimensional (2-D) Luneburg lens operated at millimeter-wave band with a low-profile and planar structure. Based on a dual-mode unit cell that supports TE/TM surface wave modes with orthogonal polarizations, the proposed 2-D Luneburg lens with gradient refractive index distribution compresses the beamwidth in one dimension and achieves fan-shaped beams for both of the two polarization modes. To verify the proposed Luneburg lens, a prototype is fabricated using the printed circuit broad process with low cost, weight, and profile. The measured peak gain of H- and V-pol mode is 17.0 dBi and 17.2 dBi, respectively. Because the surface wave modes are applied to both polarizations of the proposed Luneburg lens, the electromagnetic waves transform from the lens to the air smoothly, without the need for additional radiation structures, which reduces the profile further and increases the antenna aperture. [ABSTRACT FROM AUTHOR]

This letter presents an analysis of channel characteristics for an outdoor scenario at the frequency band of 28–30 GHz. A geometry-based clustering algorithm is proposed to group the measured multipath components (MPCs) from the interaction points on the surrounding walls or objects according to ray-tracing three-dimensional (3-D) simulations, giving results that are more physically interpretable than the traditional clustering algorithms. The cluster-level characteristics at 15 positions along a predefined route covering both line-of-sight (LoS) and non-LoS (NLoS) scenarios are investigated. Moreover, power contributions of MPCs with multiple bounces (up to seven bounces in NLoS scenario) from the interaction objects are also investigated. [ABSTRACT FROM AUTHOR]

In this letter, we propose a design of rectangular waveguide-fed surface-wave frequency-scanning antenna utilizing the principle of wavevector mismatch. First, the transition from a side-fed rectangular waveguide mode to spoof surface plasmon polariton (SSPP) is achieved. Then the SSPP propagating on the metal-dielectric interface is modulated through wavevector mismatching that induces the SSPP to spatial radiating wave conversion. Theoretical deduction proves the frequency scanning nature of the generated radiating beam. Phase gradient metasurface (PGM) is used to realize the wavevector engineering that causes artificial wavevector mismatch. Simulated and experimental results, agreeing well with each other, showed that the antenna can realize beam scanning from −8° to 11.6° across 6.8 to 7 GHz, with realized gain varying from 5 to 5.98 dBi. [ABSTRACT FROM AUTHOR]

Entropy is a powerful tool for nonlinear analysis of time series. We have recently introduced dispersion entropy (DispEn), which has widely drawn attention from researchers in a variety of settings in data analysis. However, DispEn is sensitive to its parameters, especially number of classes (quantization level). Additionally, in some cases, a small change in the signal amplitude due to noise changes the quantized series and so entropy value. To address these limitations, we develop fuzzy dispersion entropy (FuzzDispEn) on the basis of fuzzy membership functions for the quantization of a signal and Shannon entropy (ShEn). In FuzzDispEn, the concept of fuzzification in ShEn-based methods is introduced for the first time. Several straightforward concepts in signal processing using a set of time series were utilized to show the advantages of FuzzDispEn over DispEn in terms of the detection of the dynamical variability of signals. The results showed that FuzzDispEn has lower sensitivity to noise and signal length compared to DispEn. FuzzDispEn was also applied to five real world applications: mechanical fault detection in gearbox, fault diagnosis of rolling element bearings, damage level detection of bearings, detection of blood pressure in salt-sensitive rats, and detection of seizure and seizure-free electroencephalographics (EEGs). The results suggest that FuzzDispEn outperforms DispEn as well as popular sample entropy and permutation entropy in distinguishing different kinds of dynamical patterns in synthetic and real data. [ABSTRACT FROM AUTHOR]

The diffusion of toxic gas, biochemical material, and radio-active contamination – known as continuous objects – endangers the safe production of the petrochemical and nuclear industries. To mitigate these well known hazards, the new paradigm of industrial wireless sensor networks (IWSNs) shows great potential in monitoring evolving hazardous phenomena in unfriendly industrial fields. In order to prolong the lifetime of these networks, existing research focuses on energy-efficient boundary nodes selection. However, sensor state cannot be scheduled proactively, due to the difficulty in predicting the spatiotemporal evolution of diffusive hazards. In this article, we propose a motion behavior learning predictive tracking (MBLPT) algorithm for continuous objects in IWSNs. Considering the relatively unpredictable patterns exhibited by continuous objects, the MBLPT uses a data-driven approach for motion state recognition, and then utilizes Bayesian model averaging (BMA) for future boundary prediction. The prediction of the MBLPT provides the knowledge for establishing a wake-up zone, in which standby nodes are activated in advance to participate in tracking the upcoming boundary. Simulation results demonstrate that the MBLPB achieves superior energy efficiency while keeping effective tracking accuracy. [ABSTRACT FROM AUTHOR]

Frequency-multiplexing metasurfaces are typically attributed to the integration of multiple resonators, where mode coupling may significantly affect their performances. In this communication, we develop a dispersion-assisted dual-phase hybrid strategy for dual-frequency independent control of amplitude and phase with a single resonance. Therein, the frequency and phase decoupling can be achieved by precise dispersion control between two frequency states, while the amplitude distribution of each meta-atom can be controlled by properly allocating the energy of copolarized and cross-polarized waves. As a proof of concept, a bi-functional meta-mirror shaping multifocal points at two different frequencies have been experimentally demonstrated. The measured results are in good agreement with simulated results, showing the diffraction efficiencies (DEs) of 38% and 45%, and a signal-to-noise ratio (SNR) of 8.36 and 10.35 at $f_{1}$ and $f_{2}$ , respectively. In addition, another three meta-mirrors with tailorable amplitudes at dual frequencies are designed to further verify our strategy. This method offers an alternative platform for designing high-performance devices with dual-frequency wavefront manipulations, which may find potential applications in microwave integrated systems and wireless communication systems. [ABSTRACT FROM AUTHOR]

We have proposed a dispersive formulation of scalar-based meshless method for time-domain analysis of electromagnetic wave propagation through left-handed materials (LHMs). Moreover, we have incorporated Berenger’s perfectly matched layer (PML) absorbing boundary condition (ABC) into the dispersive formulation to truncate open-domain structures. In general, the dispersive formulations of conventional numerical methods are proper tools for analysis of left-handed (LH) media, whenever the LH media can be characterized by considering spatial or frequency dispersion effect for the constitutive parameters. In comparison to the grid-based numerical methods, it is proven that meshless methods not only are strong tools for accurate approximation of derivatives in Maxwell’s equations but also can provide more flexibility in modeling the spatial domain of problems. However, we have not seen any reports on using dispersive forms of meshless methods for simulation of wave propagation in metamaterials and applying any PML ABCs to dispersive formulation of meshless method. The proposed formulation enables us to take advantage of meshless methods in analysis of LH media with frequency-dependent parameters. For modeling the frequency behavior of the medium, we have used auxiliary differential equation (ADE) method based on the relations between electromagnetic fields intensities and current densities. Effectiveness of the proposed formulation is verified by analysis of 2-D and 3-D numerical examples; also, some basic factors which affect the accuracy, stability, and computational cost of the simulations are studied. [ABSTRACT FROM AUTHOR]