Small Bandwidth Research Articles

Decentralized Learning of Quantile Regression: a Smoothing Approach

Distributed estimation has attracted a significant amount of attention recently due to its advantages in computational efficiency and data privacy preservation. In this article, we focus on quantile regression over a decentralized network. Without a coordinating central node, a decentralized network improves system stability and increases efficiency by communicating with fewer nodes per round. However, existing related works on decentralized quantile regression have slow (sub-linear) convergence speed. We propose a novel method for decentralized quantile regression which is built upon the smoothed quantile loss. However, we argue that the smoothed loss proposed in the existing literature using a single smoothing bandwidth parameter fails to achieve fast convergence and statistical efficiency simultaneously in the decentralized setting. We propose a novel quadratic approximation of the quantile loss using a big bandwidth for the Hessian and a small bandwidth for the gradient. Our method enjoys a linear convergence rate and has optimal statistical efficiency. Numerical experiments and real data analysis are conducted to demonstrate the effectiveness of our method.

Anomalous Hall Crystals in Rhombohedral Multilayer Graphene. I. Interaction-Driven Chern Bands and Fractional Quantum Hall States at Zero Magnetic Field.

Recent experiments on rhombohedral pentalayer graphene with a substrate-induced moiré potential have identified both Chern insulators and fractional quantum Hall states at zero magnetic field. Surprisingly, these states are observed in strong displacement fields where the effects of the moiré lattice are weak, and seem to be readily accessed without fine-tuning. To address these experimental puzzles, we study a model of interacting electrons in this geometry. Within self-consistent Hartree-Fock (SCHF) calculations, we find an isolated Chern band with small bandwidth and good quantum geometry. Exact diagonalization and density-matrix renormalization group calculations both confirm the band hosts fractional quantum Hall states without a magnetic field. Remarkably, the Chern band is stable at a wide range of angles, at four through six rhombohedral layers, at varying rhombohedral hopping parameters, and-most strikingly-survives in SCHF calculations when the moiré potential vanishes. In this limit, the state spontaneously breaks time-reversal and translation symmetry simultaneously, giving a topological crystalline state that we term the "anomalous Hall crystal." We argue this is a general mechanism to create stable Chern bands in rhombohedral multilayer graphene, opening the door to studying the interplay between electronic topology, fractionalization, and spontaneous translation symmetry breaking.

Ultrabroadband and >93% Microwave Absorption Enabled by "Doped" Water Meta-Atom Lattice with Subwavelength Thickness.

Perfect microwave absorbers, which absorb electromagnetic waves completely, play pivotal roles in electromagnetic shielding, and stealth technologies. Existing microwave absorber technologies rely on either electromagnetic properties of absorptive materials, the resonance behavior of meta-atoms, or a combination of both. So far, achieving simultaneous broadband absorption, high efficiency, and compact sizes remains a great challenge. Inspired by atomic doping techniques employed in conventional optical materials to broaden spectral bandwidths, a single-layer microfluidic metasurface microwave absorber is proposed with the assembly of two distinct types of water meta-atoms. By manipulating electromagnetic resonances of these water meta-atoms, the metasurface maintains impedance matching over a broad working range. A microwave absorber design with a thickness equivalent to 0.2 times the central wavelength is showcased, measuring over 93% absorption across both K and Ka bands (17.5-40.0GHz). The results highlight unprecedented superiorities of microwave absorbers based on a 2D doped water meta-atom lattice when compared to previously reported metasurface absorbers utilizing identical meta-atoms. This absorber has advantages including small thickness, broad bandwidth, and cost-effectiveness, making it promising for applications in electromagnetic shielding, camouflage, and multi-spectral stealth.

Design and Implementation of Long Range Wide Area Networks for Future Industrial IoT Applications

Background: The evolution of Long Range Wide Area Networks (LoRaWAN) is a potential candidate for next generation networks for managing the massive number of devices in the Industrial Internet of Things (IIoT). LoRaWAN is more suitable for transmitting smaller intermittent data but using smaller bandwidth over a long distance. Objective: This research paper proposes to design a Low Power Wide Area Network (LPWAN) to provide long-range data transfer for Industrial IoT applications, especially for industrial sensor data. Methods: This research work deploys the experimental setup of LoRaWAN devices using LoRa gateways and Internet of Things network server to evaluate its performance for IIOT applications. Results: The deployment of this LoRaWAN has demonstrated its long range, low power, stability and low deployment cost through extensive performance evaluation carried out. LoRaWAN has been analyzed for its coverage and throughput performance. Conclusion: Through performance analysis, potential enhancements have been identified to overcome its shortcomings. This paper concludes the feasibility of deploying LoRaWAN technology for the future generation IIOT applications.

Enhancement of gain and bandwidth of cylindrical dielectric resonator antenna excited by cavity-backed slot

Dielectric resonator antennas have been demonstrated to be an efficient radiator, especially with the possibility of fabricating it at low cost based on 3-D printing technologies. However, they have two main limitations which are: their relatively small gain (about 5dBi) and narrow bandwidth. To enhance the gain of DRA, higher-order mode excitation can be utilized; however, typically this has a limit of a few dB increments besides its negative effects on the bandwidth. This study employs a cavity-backed slot to provide an appropriate feeding method for a cylindrical dielectric resonator antenna (CDRA). This design effectively facilitates the excitation of higher-order modes, resulting in a significant gain of up to 15 dBi, which is essential for many wireless systems that are unable to support larger aperture sizes through the standard use of arrays. Additionally, two modes are excited to keep a relatively broadband of about 15 %. The proposed design consists of a cylindrical dielectric placed on top of a cavity-backed slot that is excited by a coaxial probe soldered to the top patch of the cavity. With this feeding, a good matching is achieved for different dielectric resonator heights, hence, the gain can be adjusted easily without the need of reoptimizing the antenna or the feed structures. The design process is explained in addition to performing a sensitivity analysis of fabrication tolerances which confirms that the 3-D printer provides enough accuracy with a negligible effect on the antenna’s performance. Then a prototype with a medium length is fabricated and measured to provide high realized gain and impedance bandwidth of 11 dBi and 14.5 %, respectively. The measured data demonstrate the good performance of the antenna with great matching compared to the simulated ones. Furthermore, the antenna presents a good performance in terms of sidelobes and polarization. This proposed design outperforms other DRA designs based on higher-order modes.

Optimized multi-frequency nonlinear broadband piezoelectric energy harvester designs

Many electrical devices can be powered and operated by harvesting the wasted energy of the surroundings. This research aims to overcome the challenges of output power with a sharp peak, small bandwidth, and the huge dimensions of the piezoelectric energy harvesters relative to the output power. The aforementioned challenges motivated us to investigate the effect of nonlinearity in the shape (tapered and straight cross-section area) as well as the fixation method (the number of fastened ends) to determine the optimal design with high output power and wide working frequency. This research proposes a novel piezoelectric energy harvester array, where each beam is made up of three fixed beams that are joined together by a center mass. The proposed design produces an output power of 35 mW between 25 and 40 Hz. The output power of the proposed design is 3.24 times more than the conventional designs. The recommended approach is simulated utilizing finite element analysis FEA. Analytical and experimental methods validate the proposed FEA, which exhibits excellent agreement.

Graph-based minimum error entropy Kalman filtering

When the Gaussian kernel function is chosen with a small kernel bandwidths, the minimum error entropy Kalman filter (MEEKF) exhibits excellent performance. However, further narrowing the kernel bandwidths leads to a degradation in performance. To address this issue, this paper proposed a Graph-based MEEKF (G-MEEKF) algorithm based on Graph Signal Processing (GSP) theory. The G-MEEKF algorithm addresses the problem by smoothing the errors using graph filtering and incorporating graph topology into the cost function. The convergence of the algorithm is theoretically analyzed and simulations demonstrate that G-MEEKF improves the performance of MEEKF under small kernel bandwidths. Furthermore, it is emphasized that the topology of the graph abstracted from the minimum error entropy (MEE) definition also influences the performance of the algorithm.

A Small Power Margin and Bandwidth Expansion Allow Data Transmission during Rainfall despite Large Attenuation: Application to GeoSurf Satellite Constellations at mm–Waves

The traditional approach of considering the probability distribution of rain attenuation leads to provide very large power margin (overdesign) in data channels. We have extended a method which, with a small power margin, bandwidth expansion and variable symbol rate, avoids overdesign and can transfer the same data volume as if the link were in clear–sky conditions. It is characterized only by the link mean efficiency, suitably defined. It is useful only if: (a) data must be up– and downloaded when it is raining; (b) real–time communication is not required. We have applied it to the links of GeoSurf satellite constellations (in which, at any latitude of ground stations, propagation paths are at the local zenith) by simulating rain attenuation time series at 80 GHz (mm–wave)–the new frontier of satellite frequencies–with the Synthetic Storm Technique, from rain–rate time series recorded on–site, at sites located in different climatic regions. The power margin to be implemented at 80 GHz ranges from 2.0 dB to 7.4 dB–well within the current technology–regardless the instantaneous rain attenuation. The clear–sky bandwidth is expanded 1.75 to 2.80 times, a factor not large per se, but it may challenge current technology if the clear–sky bandwidth is already large.

An improved Mini Antenna Designed at 60GHZ for a New Generation Mobile Phone

Five-generation (5G) communication systems are being required to meet the needs of small, high-speed, and big bandwidth systems [2]. This paper simulates and designs a 60GHZ rectangular micro strip patch antenna. The proposed antenna resonates at 60GHZ with a return loss of -32.126 dB, efficiency of 87.7119%, and gain of 6.96485 dBi. The patch is 2.726 x 2.364 x 0.125 mm. The radiating patch and the 50Ω micro strip feed line are matched using an iset feed transmission line approach. A Roger RT Duroid 5880 substrate, with a height of 0.125mm and a dielectric constant of 2.20 and a loss tangent of 0.0009, was selected in the design. The Advanced Design System (ADS) was used to compute the antenna's parameters and evaluate the results of simulations.

Plasmonic tuning of nano-antennas for super-gain light amplification

Nanoscale conductive materials are often used for inducing localized free electron oscillations known as plasmons. This is due to their high electronic excitability under optical irradiation owing to their super-small volume. Recently, plasmons have been of interest for enhancing the gain-bandwidth product of optical amplifiers. There are currently two well-established mechanisms for light amplification. The first one is via stimulated emission of radiation (lasers) using a given energy source and often an optical feedback mechanism. The second one is based on the nonlinear coupling of a low-intensity input wave and a high-intensity pump wave for energy exchange (parametric amplifiers). Both techniques have shortcomings. Lasers have a small operation bandwidth and offer a limited gain, but require moderate energy pumping to operate. Whereas optical parametric amplifiers (OPAs) offer a high operation bandwidth along with a much higher optical gain, with the drawback of requiring intense pumping to be functional. The aim of this paper is to introduce a technique that combines the advantages and eliminates the drawbacks of both techniques in the nanoscale to allow for a better amplification performance in integrated optical devices. This is achieved by inducing a plasmonic chirp in conductive nanomaterials a.k.a nano-antennas, which enables the confinement of an enormous electric energy density that can be coupled to an input beam for amplification. Using the Finite Difference Time Domain numerical-method with the material parameters of well-known semiconductors, intramaterial condensation of electric energy density is observed in semiconductor nano-antennas for certain plasmonic chirp-frequencies which enables broadband high-gain optical amplification based on free-electron oscillations that is promising for small-scale optical devices requiring a high gain-bandwidth product. The results are in good agreement with semiempirical data.

Ultra-broadband tunable terahertz metasurface absorber with multi-mode regulation based on artificial neural network

The multi-window tunable absorption of terahertz (THz) waves faces challenges such as a small tunable bandwidth, discontinuous tuning windows, and a complex design process. This study addresses these issues by employing inverse design based on artificial neural networks (ANN) to achieve an ultra-broadband tunable THz metasurface absorber (UTTMA). Leveraging the electrically tunable property of graphene and the phase transition property of vanadium dioxide (VO2), the UTTMA achieves multi-domain dynamic operation across a large frequency band. The design allows for arbitrary switching between multiple windows by transforming between graphene surface-localized plasmon resonance (LSPR), fundamental order surface plasmon polaritons (SPP) resonance, and graphene surface plasmon resonance (SPR), and second order SPP resonance. The tunable windows cover the range between 1.90 and 10.00 THz, encompassing four-fifths of the entire THz band, surpassing previously reported absorbers. The accuracy of the ANN inverse design is verified, and a systematic analysis of the optical performance of the UTTMA is conducted. These findings offer a viable and effective method for expanding the tunable bandwidth and simplifying the design process for THz metasurfaces.

Towards 21-cm intensity mapping at z = 2.28 with uGMRT using the tapered gridded estimator – IV. Wide-band analysis

ABSTRACT We present a Wide-band tapered gridded estimator (TGE), which incorporates baseline migration and variation of the primary beam pattern for neutral hydrogen ($H\, {\small I}$) 21-cm intensity mapping (IM) with large frequency bandwidth radio-interferometric observations. Here we have analysed $394-494 \, {\rm MHz}$ (z = 1.9–2.6) uGMRT data to estimate the Multifrequency Angular Power Spectrum (MAPS) Cℓ(Δν) from which we have removed the foregrounds using the polynomial fitting (PF) and Gaussian Process Regression (GPR) methods developed in our earlier work. Using the residual Cℓ(Δν) to estimate the mean-squared 21-cm brightness temperature fluctuation Δ2(k), we find that this is consistent with 0 ± 2σ in several k bins. The resulting 2σ upper limit $\Delta ^2(k) \lt (4.68)^2 \, \rm {mK^2}$ at $k=0.219\, \rm {Mpc^{-1}}$ is nearly 15 times tighter than earlier limits obtained from a smaller bandwidth ($24.4 \, {\rm MHz}$) of the same data. The 2σ upper limit $[\Omega _{H\, {\small I}} b_{H\, {\small I}}] \lt 1.01 \times 10^{-2}$ is within an order of magnitude of the value expected from independent estimates of the $H\, {\small I}$ mass density $\Omega _{H\, {\small I}}$ and the $H\, {\small I}$ bias $b_{H\, {\small I}}$. The techniques used here can be applied to other telescopes and frequencies, including $\sim 150 \, {\rm MHz}$ Epoch of Reionization observations.

Correlation-Induced Symmetry-Broken States in Large-Angle Twisted Bilayer Graphene on MoS2.

Strongly correlated states commonly emerge in twisted bilayer graphene (TBG) with "magic-angle" (1.1°), where the electron-electron (e-e) interaction U becomes prominent relative to the small bandwidth W of the nearly flat band. However, the stringent requirement of this magic angle makes the sample preparation and the further application facing great challenges. Here, using scanning tunneling microscopy (STM) and spectroscopy (STS), we demonstrate that the correlation-induced symmetry-broken states can also be achieved in a 3.45° TBG, via engineering this nonmagic-angle TBG into regimes of U/W > 1. We enhance the e-e interaction through controlling the microscopic dielectric environment by using a MoS2 substrate. Simultaneously, the width of the low-energy van Hove singularity (VHS) peak is reduced by enhancing the interlayer coupling via STM tip modulation. When partially filled, the VHS peak exhibits a giant splitting into two states flanked by the Fermi level and shows a symmetry-broken LDOS distribution with a stripy charge order, which confirms the existence of strong correlation effect in our 3.45° TBG. Our result demonstrates the feasibility of the study and application of the correlation physics in TBGs with a wider range of twist angle.

A graphene-based THz selective absorber with absorptivity 95 % and wide-range electrical tunability

A growing adoption of Terahertz (THz) frequency across various applications is witnessed in the recent years. This specific frequency range is said to yield a breakthrough in high-speed electronics and communications, besides its significant role in the medical field regarding scanning and treatment. As frequency absorbers are one of the common blocks in the mentioned applications, they were the focus of many research work. In this paper, we present a theoretical model for a selective THz frequency absorber that has more than 90 % absorptivity and can reach 95 % and near unity absorptivity at some frequencies. The structure is based on monolayers of nanoribbons of graphene, MoS2, and phosphorene. The utilization of the surface plasmon oscillations of these two-dimensional (2D) materials, in addition to the impedance matching, is employed to achieve maximum absorptivity. The structure has an electrically tunable selective frequency from 1.3 THz to 10 THz that nearly covers the whole THz range, and a bandwidth ranging from 0.9 THz to 1.3 THz. Electrical tunability is done through varying the applied voltage on the MoS2/graphene heterostructure (0.2 V ∼ 5 V) based on the tunable conductivity of graphene. In addition to the voltage tunability of the design, the absorption frequency is also swept by varying the nanoribbons widths (20 nm ∼ 160 nm). The proposed design surpasses previous ones by its simple structure and high absorption through the entire THz range, besides its low cost of fabrication. The structure is ultrathin (∼10 nm) that it can fit in ultrathin electronics. It has a relatively small bandwidth compared to previous work, that represents the basis for narrowband absorbers. The structure is simulated using the finite element method (FEM) and verified using the transmission line circuit theory which demonstrated the validity of the structure for higher frequency ranges. The possibility of future synthesis is also discussed.

Modelling and analysis of a novel E-shape piezoelectric vibration energy harvester with dynamic magnifier

An important issue in conventional harvesters is that the output performance is limited to small strains and narrow bandwidth. To address these issues, a novel E-shape harvester with dynamic magnifier is devised to magnify the base vibration and enhance electric energy in low-frequency complicated environment. In this study, a novel electromechanical coupling dynamic model is established by considering the characteristics of the E-shape structure. Meanwhile, the analytical expressions of the eigenfunction and resonance frequency of the developed model are presented. The effect of system parameters on the power output are investigated and discussed. Results indicate that the electric energy can be significantly enhanced and the vibration amplitude can be magnified using properly design structural parameters. The proposed harvester with dynamic magnifier is a simple and effective approach for enhancing energy harvesting near a target operating frequency.

Investigation of ambient vibration sources for direct energy harvesting by optimizing resonant frequency using proof mass

Ambient mechanical sources typically vibrate below the frequency of 200 Hz, posing challenges for thin film piezoelectric sensors, including low power, high resonant frequency, and small bandwidth. To optimize the electrical energy harvesting from the ambient sources, it is crucial to reduce the resonant frequency of the energy harvester to match that of the ambient sources. In this study, the energy harvester’s resonant frequency dependency on proof mass is thoroughly investigated using the finite element method (FEM). Further, the FEM results are experimentally validated through a custom-designed vibration set-up. Different ambient vibration energy sources, their vibrating frequencies, and accelerations are examined to harness direct mechanical energy and convert it into electric energy using the piezoelectric sensor. Further, the effective proof mass and position are determined to achieve the targeted frequency obtained from ambient sources. Consequently, the harvester is utilized for direct energy harvesting from the ambient sources. The addition of proof mass can lower the resonant frequency of the harvester from 160 Hz to 40 Hz allowing the harvester to vibrate at maximum amplitude to obtain maximum output voltage. Significant enhancement of output power is observed after the tuning of harvester resonant frequency, harvesting a maximum output power of 19.29 μW when mechanically sourced from the bike mirror, measured at an acceleration of 4.50 g at 43 Hz.

Signal processing scheme for broadband heterodyne gigahertz interferometry with a broadband and a second low-noise photodetector with limited bandwidth

There is a need for highly accurate vibration measurements in the gigahertz range. To measure these vibrations with heterodyne interferometers, methods in the state of the art require both high photodetector bandwidths and high carrier frequencies. However, conventional methods such as acousto-optic modulators rarely achieve frequency shifts above 500 MHz and are inefficient at higher frequencies. Additionally, detector bandwidths are limited, or the noise level of high bandwidth detectors is insufficient. In this paper, we propose a solution to these limitations by using a setup with two phase-locked lasers to create a beat frequency in combination with a signal processing scheme that utilizes a broadband and a second low-noise photodetector with a much smaller bandwidth and low noise. Our method could enable gigahertz heterodyne vibration measurements with high resolution. The novelty of our concept is that we only detect the lower sidebands and are still insensitive to AM. This is achieved by two consecutive measurements with frequency shifting of the lasers, effectively swapping the upper and lower sidebands.

Evaluating the Impact of OFDM Parameters on the Operation of the LTE System in Different Conditions

These days we find an enormous growth in wireless communication technologies. The use of OFDM in wireless systems has created a way to provide high data rates, less intercarrier interference(ICI), and less intersymbol interference(ISI). OFDM has become the core of most 4G communication systems, a Long Term Evolution (LTE) system. OFDM system divides the available signal spectrum into smaller bandwidths and transmits them to the receiver without interference with each other by inserting the cyclic prefix in between the signals. LTE uses OFDM for downlink, SC-FDMA for uplink and MIMO for enhanced throughput. The OFDM uses inverse fast fourier transform(IFFT) and fast fourier transform(FFT) for conversion of data. The system performance is measured by correlating the signal to noise ratio to bit error rate. The system performance is evaluated to study the effect of various LTE design parameters by simulating in MATLAB

Microwave absorption properties of oriented Sm2Fe14BHx/polyurethane with planar anisotropy

Realization of microwave-absorbing materials with “small thickness, light weight, broad bandwidth, and low reflectivity” is an invariable topic. In this paper, Sm2Fe14BHx/polyurethane (SFBH/PU) composites with planar anisotropy were prepared by reduction–diffusion (R/D) and water bath hydrogenation (WBH) process. A minimum reflection loss (RL) value reaches −59.7 dB at the perfect matching frequency of 13.79 GHz with a thickness of only 1.035 mm. Compared with unhydrogenated SFB, the bandwidth and reflectivity are significantly improved. It is mainly attributed to the fact that introduction of hydrogen atoms effectively modulates the electromagnetic parameters and increases the Snoek limit ((μi−1)fr), which leads to the improvement of the high-frequency microwave absorption performance. In addition, the bandwidth equation is derived and simplified from the perspective of the reflected wave at the interface, which is in good agreement with the measured results.

Vector Locally Repairable Codes With Small Repair Bandwidth and Small Sub-packetization Levels

Vector Locally Repairable Codes With Small Repair Bandwidth and Small Sub-packetization Levels