Response Bandwidth Research Articles

Minority Resampling Boosted Unsupervised Learning With Hyperdimensional Computing for Threat Detection at the Edge of Internet of Things

The Internet of Things (IoT) has rapidly transformed digital environments across a multitude of domains with increased connectivity and pervasive virtualization. The distributed computing paradigm of Edge Computing has been postulated to overcome the concerns of response time, bandwidth, energy consumption, and cybersecurity. In comparison to the other concerns, limited studies have focused on cybersecurity, mainly due to the inherent complexity of threat detection at the Edge. However, the widespread adoption of IoT applications in economic, social, and political contexts is a stringent indication of the significant impact from cyber-attacks. This paper aims to address this challenge by presenting an effective and efficient machine learning approach for threat detection at the Edge of IoT. The novel contributions of this approach are, a new Enhanced Geometric Synthetic Minority Oversampling Technique (EG-SMOTE) algorithm to resolve the imbalanced distribution of data streams at the IoT Edge, an extension to the Growing Self Organizing Map (GSOM) algorithm based on Hyperdimensional Computing for energy efficient machine learning from unlabeled data streams. The proposed EG-SMOTE + GSOM approach has been tested using four open access datasets; three benchmark, KDD99 (F-Score = 0.9360), NSL-KDD (F-Score = 0.9647), CICIDS2017 (F-Score = 0.9999), and one industry-focused botnet IoT traffic dataset, BoT-IoT (F-Score = 0.9445). The EG-SMOTE approach has outperformed SMOTE and G-SMOTE approaches in a vast number of experiments that are tried with different classifiers. The results of these experiments confirm the novelty, efficiency and effectiveness of this approach for cybersecurity at the IoT Edge.

A Transparent Proximity-Coupled-Fed Patch Antenna With Enhanced Bandwidth and Filtering Response

This paper introduces a novel transparent proximity-coupled-fed patch antenna with enhanced impedance bandwidth and good filtering response. The proposed antenna consists of a ground plane, a specific feeding structure and a slotted patch. All the conducting surfaces are realized with metal meshes printed on glass substrates. Optical transparency of the antenna depends on the mesh density. The feed line of a traditional proximity-coupled-fed patch antenna is terminated with a driven stub etched with a half-wavelength U-shaped slot. This modification introduces an additional resonant mode but also a radiating null. By further etching a pair of quarter-wavelength open slots on the radiating patch, another resonant mode accompanied with an extra radiation null is generated. Finally, three resonant modes within the operating band along with two radiation nulls near the two edges of the passband are achieved. The proposed antenna is implemented to demonstrate an impedance bandwidth of 7.6% from 3.41 to 3.68 GHz and a maximum gain of 4.6 dBi.

A Travelling-Wave-Fed Slot Spiral Antenna With Wide Axial-Ratio Bandwidth and Beamwidth for GNSS Applications

A travelling-wave-fed slot spiral antenna with wide axial-ratio (AR) bandwidth and beamwidth for GNSS applications is proposed in this paper. The evolution procedure of the proposed antenna can be classified into three steps. Firstly, 12 identical spiral slots are arranged concentrically in a compact area, and AR roundness in low elevation plane is improved by virtue of good rotational symmetry of slot radiators. Secondly, a two-turn travelling-wave feed line is sequentially coupled to the slots, and wideband response of desired magnitude ratio and phase difference of $E_{\theta }$ and $E_{\varphi }$ is obtained by optimizing the number and growth rate of microstrip turns. Thirdly, by supporting the antenna with a modified metallic cavity, the CP radiation performance in low elevation plane is well improved, and thus a widened AR beamwidth is obtained. Finally, the proposed antenna with satisfactory performance is realized in a diameter of $0.56\lambda _{0}$ and height of $0.12\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength at center frequency 1.4 GHz. Measured bandwidth of $|S_{11}|$ fully covers the entire GNSS bands, and the 3-dB AR bandwidth ranges from 1.14 to 1.67 GHz (37.7%). Moreover, the 3-dB AR beamwidth exceeds 140° at 1.4 GHz.

Reconfigurable Compact Wideband Circularly Polarised Dielectric Resonator Antenna for Wireless Applications

In this work, a novel compact wideband reconfigurable circularly polarised (CP) dielectric resonator antenna (DRA) is presented. The L-shaped Dielectric resonator antenna is excited by an inverted question mark shaped feed. This arrangement of feed-line helps to generate two orthogonal modes inside the DR, which makes the design circularly polarised. A thin micro-strip line placed on the defected ground plane not only helps to generate a wideband response but also assist in the positioning of the two diode switches. These switches located at the left and right of the micro-strip line helps in performing two switching operations. The novel compact design offers the reconfigurability between 2.9–3.8 GHz which can be used for different important wireless applications. For the switching operation I, the achieved impedance bandwidth is 24% while axial ratio bandwidth (ARBW) is 42%. For this switching state, the design has 100% CP performance. Similarly, the switching operation II achieves 60% impedance bandwidth and 58.88% ARBW with 76.36% CP performance. The proposed design has a maximum measured gain of 3.4 dBi and 93% radiation efficiency. The proposed design is novel in terms of compactness and performance parameters. The prototype is fabricated for the performance analysis which shows that the simulated and measured results are in close agreement.

Bandwidth Enhancement Technique of a Dual-Band Circularly Polarized Dielectric Resonator Antenna

This paper presents the rectangular aperture coupled dielectric resonator antenna with dual-band circularly polarized response. The antenna geometry have stair case shaped rectangular dielectric resonator in the form of main radiating element. The specific geometry provides increment of aspect ratio of the dielectric resonator. This allows merging of various resonant frequencies having higher order modes that result in the bandwidth enhancement. This antenna provides 18.63% and 7.68% of -10 dB S11-parameter bandwidth response in operating passbands, respectively. The specific geometry and the introduction of circular slots in ground plane results in the orthogonal modes excitation at the nearby resonant frequencies. Due to this, the circular polarization response at 7.76 and 8.33 GHz frequencies is achieved. The peak gain of 5.8 and 4.6 dBic is obtained in the respective lower and upper operating passbands. Through parametric analysis, tuning of antenna responseis also achieved. The proposed antenna with the optimized parameters may have potential applications in the microwave C- and X-band setups.

MIMO Antenna Design and Optimization with Enhanced Bandwidth for Wireless Applications

This paper demonstrates a compact MIMO (Multi Input Multi Output) fractal type antenna for ultra-wide band applications. The proposed antenna is manufactured on a lowcost substrate material and the design is analyzed for various iterations in terms of reflection coefficient, gain, and bandwidth. The 50 Ω transmission line feed is used for both fractal patches and a metamaterial structure is used as the ground plane. The proposed design achieved a wide-band frequency response between 5.8 and 15 GHz, with the reflection coefficient of less than –10 dB. Reduced mutual coupling, positive gain and stable radiation patterns were observed throughout the operating band as well. The bandwidth of 9.2 GHz is achieved with the use of a metamaterial structure on the ground plane. The ECC and diversity gain obtained prove the excellent diversity performance of the antenna. The design was simulated using HFSS software and was tested in a lab.

On-chip Ge, InGaAs, and colloidal quantum dot photodetectors: comparisons for application in silicon photonics

The past twenty years have seen explosive growth in silicon photonics technology. It has revolutionized numerous fields such high-speed optical interconnects in data centers. A photodetector (PD) is one of the key building blocks in silicon photonics, enabling on-chip light detection. Here a comprehensive study has been demonstrated in which three materials, germanium (Ge), indium gallium arsenide (InGaAs), and colloidal quantum dots (CQD), are compared for a PD integrated with a waveguide in silicon photonics. Comparisons are conducted by assuming InGaAs and CQD PDs have the same interface quality as mature Ge PD technology. With this premise, we intend to predict future InGaAs and CQD PD performances. Figures of merit such as dark current, responsivity, and RF bandwidth are compared using simulations. With the premise that epitaxial InGaAs on silicon is as of high quality as epi-Ge, results found that the InGaAs PD is advantageous over the Ge PD with higher-efficiency bandwidth product and lower dark current. CQD PD, on the other hand, is slow but has the lowest dark current, which is suitable for medium-speed applications where ultralow noise is required.

Ultra-wideband underwater acoustic transducer with a gradient impedance matching layer

In complex marine environments, high-efficiency, wideband and high-frequency transducers can improve the imaging resolution of sonar systems and there is an urgent need for the detection and identification of seafloor landforms. The bandwidth expansion of the traditional transducer is usually achieved by using a single or multiple uniformly matching layers, but it cannot meet the ultra-wideband performance requirement of the transducer in water because it fails to achieve an optimal acoustic impedance transition. Based on theoretical analysis of sound transmission, analytical calculation, and finite element simulation, an acoustic gradient impedance matching layer transducer is studied. We propose an acoustic gradient impedance matching layer material that largely compensates for this shortcoming. This gradient matching layer material has the characteristic that the acoustic impedance decreases in the direction of thickness according to an exponential law z(x)=z1e2αx. It is implemented by filling the specific binary mixture into the conical cavities structure produced by 3D accurately printing. Experimental testing results show that the transducer's transmitting voltage response bandwidth (−3dB) reaches 110%.

Ferroelectret Ultrasonic Transducers for Pulse-Echo Water Immersion

Ferroelectrets are thin and porous polymeric films with a cellular microstructure, high porosity, permanent polarization and piezoelectric response. They have been used for different applications, where one of the most interesting ones is for the fabrication of air-coupled ultrasonic transducers. More recently they have been tested as water immersion transducers, showing a promising wide bandwidth but limited sensitivity along with other technical problems. This paper investigates ultrasonic transducers for water immersion and pulse-echo operation based on ferroelectret films. Two different ferroelectret foams with different resonant frequencies, acoustic impedances and cellular structures were tried. Flat and spherically focused prototypes (radius of curvature of 22 and 35 mm) were produced and tested. Finally, different materials and methods were tried to provide a protective surface coating. Acoustic field measurements for the focused transducers confirm the possibility to efficiently focus the ultrasonic beam by the proposed fabrication method, with focal spot size of 1.86 mm at −6 dB. Results show that in spite of the reduced sensitivity (about −115 dB), some of the tried ferroelectret films provide a very wide band response (−6 dB band from 0.29 to 2.7 MHz) and short pulse duration (2–3 us) that can be of interest for different applications.

Quasi-distributed acoustic sensing with interleaved identical chirped pulses for multiplying the measurement slew-rate.

Quasi-distributed acoustic sensing (Q-DAS) based on ultra-weak fiber Bragg grating (UWFBG) is currently attracting great attention, due to its high sensitivity and excellent multiplexing capability. Phase-sensitive optical time-domain reflectometry (Φ-OTDR) based on phase demodulation is one of the most promising interrogation schemes for Q-DAS. In this article, a novel interleaved identical chirped pulse (IICP) approach is proposed on the basis of pulse compression Φ-OTDR with coherent detection. Different from the frequency-division-multiplexing (FDM) method, the identical pulses are used for multiplexing in the IICP scheme, and the mixed reflection signals can be demodulated directly, so the inconsistent phase offsets in FDM can be avoided. As a result, this scheme can enlarge the measurement slew-rate (SR) of Q-DAS by times compared with traditional single pulse scheme. In the proof-of-principle experiment, the SR of 28.9 mɛ/s has been achieved with an 860 m sensing range, which is 5 times as that of the traditional single pulse scheme; meanwhile, the response bandwidth has been enlarged by 5 times. The 277 kHz response bandwidth has been achieved, with 5 m spatial resolution and 2.8 pε/Hz strain sensitivity.

Hierarchical data replication strategy to improve performance in cloud computing

Cloud computing environment is getting more interesting as a new trend of data management. Data replication has been widely applied to improve data access in distributed systems such as Grid and Cloud. However, due to the finite storage capacity of each site, copies that are useful for future jobs can be wastefully deleted and replaced with less valuable ones. Therefore, it is considerable to have appropriate replication strategy that can dynamically store the replicas while satisfying quality of service (QoS) requirements and storage capacity constraints. In this paper, we present a dynamic replication algorithm, named hierarchical data replication strategy (HDRS). HDRS consists of the replica creation that can adaptively increase replicas based on exponential growth or decay rate, the replica placement according to the access load and labeling technique, and finally the replica replacement based on the value of file in the future. We evaluate different dynamic data replication methods using CloudSim simulation. Experiments demonstrate that HDRS can reduce response time and bandwidth usage compared with other algorithms. It means that the HDRS can determine a popular file and replicates it to the best site. This method avoids useless replications and decreases access latency by balancing the load of sites.

Simetrik Olarak Yerleştirilmiş Dairesel Boşluklara Dayalı 24-28 GHz bant 5G Anten Tasarımı

5G (fifth generation) cellular system is expected to work in a wide frequency range to meet the demand for mobile services and applications. Antennas will be addressed to the future 5G applications should pose superior characteristics, such as high gain and ultra-large bandwidth response by considering atmospheric absorption/free-space path loss on planned millimeter-wave frequency range of 5G communications. Therefore, antenna design for the future 5G applications is a challenging process. In this article we present a high-gain, broadband mm-Wave antenna based on a circular patch structure with a ground plane and resonator gaps. The designed antenna is analyzed using a widely used full-wave electromagnetic solver. The major antenna figure-of-merits including reflection coefficient, VSWR (voltage-standing wave ratio), antenna patterns in E- and H-planes, surface current distribution, antenna directivity and maximum gain, are obtained. The simulation results show that the gapped circular patch based design has the S11 response less than −10 dB in the frequency range of 21.6-28.8 GHz, which includes 24-28 GHz band of 5G cellular systems. Moreover, it is observed that the symmetrically located circular gaps on both top and bottom layers decrease the side lobe level under −10 dB value, and enhance the gain. We attribute the improvement in the antenna performance to the created current regions due to gaps hosting large vortex current distributions. With 10 mm × 13mm surface area, the proposed antenna demonstrates the peak gain of 9.44 dBi and the radiation efficiency of over 85%. High gain and compact size make this antenna suitable for coming 5G devices.

Paralleling of LLC Resonant Converters

The LLC resonant converter is a popular, variable switching frequency dc--dc converter that may be controlled using two methods: charge and frequency control. In this article, the application of LLC resonant converters to input-parallel, output-parallel system is studied. In this respect, the models of output-port I-V characteristics and small-signal output impedance of the charge controlled LLC converter are proposed. In addition, a mathematical framework is developed for droop-based paralleled dc--dc systems. It distinctly identifies the output dc voltage and circulating current modes of stability, even in systems comprising of nonidentical converters. The developed model and the analytical framework are utilized to study the two modes of stability in droop-based parallel-connected LLC converters. It finds the circulating current mode instability for both the charge and frequency control methods, despite a stable output dc bus voltage. The instability inhibits fast response and high closed-loop bandwidth, eroding the reported advantages of the charge control method over frequency control. Further investigation into the output port I-V characteristics reveals the superiority of charge-controlled LLC converters in paralleled systems than the conventional frequency-controlled converters. A novel application of “common inner reference” based “automatic load sharing” strategy is developed and uniquely applied to the charge controlled system. In addition, the effects of component tolerance and communication delay on this strategy are also briefly explored. The theoretical output-port models and the stability analyses of parallel-connected LLC resonant converters are validated through experiments on a hardware prototype. Further, the supplementary video files illustrate the advantage of the charge control method over frequency control in such system. Finally, the proposed automatic load sharing strategy is validated in steady-state and through a step-change in load.

Structural optimization of optoelectronic components in millimeter-wave radio-transmitting modules

The paper analyzes the effect of structure inherent to optoelectronic radio-transmitting modules of a phased array antenna (PAA) on the noise characteristics in the millimeter range (MMR) of waves. Considered are promising structures of MMR modules for generating radiation with a phased array for communication systems based on optoelectronic technologies. The promising types of photodiodes that are used to form MMR radio signals as well as the distance and physical limitations for photodetectors associated with a limited bandwidth and nonlinear response characteristics have been analyzed. Mathematical modeling of the oscillation of the output current after the optoelectronic conversion of the signal and noise characteristics of the radio-transmitting modules capable to form MMR radiation in PAA has been carried out. The analysis of the nonlinearity of the sensitivity of photodiodes in the high-frequency regions of formation of radio signals has been carried out. The necessity to structurally optimize optoelectronic components in the MMR transmission module has been shown depending on the noise characteristics of the output signal. It has been shown that fundamental studies of nonlinear characteristics and factors limiting the band of photodetectors are important tasks for further developing MMR telecommunications of the next generations.

A wideband graphene coated dielectric resonator antenna with circular polarization generation technique for THz applications

A circular polarization generation technique is implemented in the rectangular dielectric resonator antenna (DRA) using graphene material. A partial coating of graphene material on the faces of DR is being used instead of the conventional metallic coating for obtaining the circularly polarized response. This coating acts like the electric wall is arranged in orthogonal fashion on the faces of DR. It generates the orthogonal degenerate modes inside the DR which is amenable for the generation of circular polarization. The proposed antenna provides a wide 10-dB impedance bandwidth of 48.86% and 7.06% of overlapped 3-dB axial-ratio (AR) bandwidth. The wideband response is obtained due to the merging of higher-order modes inside the rectangular DR. Furthermore, the AR bandwidth can be tuned at different frequencies within the operating passband by varying the arrangement of orthogonal coating.

Aluminum Plasmonics Enriched Ultraviolet GaN Photodetector with Ultrahigh Responsivity, Detectivity, and Broad Bandwidth.

Plasmonics have been well investigated on photodetectors, particularly in IR and visible regimes. However, for a wide range of ultraviolet (UV) applications, plasmonics remain unavailable mainly because of the constrained optical properties of applicable plasmonic materials in the UV regime. Therefore, an epitaxial single‐crystalline aluminum (Al) film, an abundant metal with high plasma frequency and low intrinsic loss is fabricated, on a wide bandgap semiconductive gallium nitride (GaN) to form a UV photodetector. By deliberately designing a periodic nanohole array in this Al film, localized surface plasmon resonance and extraordinary transmission are enabled; hence, the maximum responsivity (670 A W−1) and highest detectivity (1.48 × 1015 cm Hz1/2 W−1) is obtained at the resonance wavelength of 355 nm. In addition, owing to coupling among nanoholes, the bandwidth expands substantially, encompassing the entire UV range. Finally, a Schottky contact is formed between the single‐crystalline Al nanohole array and the GaN substrate, resulting in a fast temporal response with a rise time of 51 ms and a fall time of 197 ms. To the best knowledge, the presented detectivity is the highest compared with those of other reported GaN photodetectors.

Design, Fabrication and Non-destructive Microwave Measurement of a Quad Resonance, Mono-band Metamaterial Polarization Converter Realized by a Fractal Inspired Split-Ring Resonator

The development and measurement of a single layer, wideband, and angularly stable microwave polarization converter (PC), specifically at a low-frequency regime, is still a very challenging task. In this article, a quad resonance, mono-band metamaterial polarization converter is fabricated and measured using a non-destructive free-space microwave measurement setup. A comprehensive study of a single-layer metamaterial (MTM) structure using a miniaturized fractal element array reveals that four resonances can be achieved within its operating frequency band to realize a wide operating band. The proposed MTM-PC is inspired by the split-ring resonator (SRR) based fractal geometry to control the linearly polarized electromagnetic (EM) wave in the C-band. The result shows the average polarization conversion ratio over 87% in a single broad frequency band (i.e., 5.5 GHz to 8.0 GHz). A careful study reveals that wideband response at lower frequency is achieved by introducing four resonances due to fractal inspired SRR geometry. Moreover, the proposed structure is the oblique angle insensitive up to 45°. The results reflect the enormous potential of the proposed approach for various practical EM applications.

Numerical investigation of tunable multistacked metamaterial‐based graphene grating

AbstractWe present a tunable multistacked metamaterial‐based graphene grating structure for the lower THz frequency range. Circular gold wire is placed between graphene layers to obtain wideband response. Reflectance, transmittance, absorption, and refractive index parameters are analyzed for metamaterial‐based graphene grating structure. The results show wideband reflectance response ranging from 1 to 2.5 THz frequency. Reflectance in grating can be controlled by different chemical potentials of the graphene sheet. The design results are also analyzed for different incident angles ranging from 0° to 80°. The proposed grating structure has the wideband tunable reflectance response and is envisioned to become basic building blocks of several THz systems which is going to be applicable in circulator, sensor, and imaging applications.

Bandwidth-Enhanced Quasi-Distributed Acoustic Sensing With Interleaved Chirped Pulses

In this letter, to break through the response bandwidth limit of quasi-distributed acoustic sensing system, a novel interleaved chirped pulses (ICP) approach is proposed on the basis of pulse compression ${\Phi }$ -OTDR with coherent detection. As shown in the theoretical analysis, for ultra-weak fiber Bragg grating (UWFBG) array with fixed positions and intervals, the space between any two FBGs can be used to multiplex probing pulses, without occupying extra detection bandwidth. The cross-correlation peak of probe pulses can be separated from each other in the time domain with matched filtering. By injecting probe pulses which are evenly interleaved as positive-chirped and negative-chirped, crosstalk of the cross-correlation peaks can be suppressed. In the proof-of-principle experiment, the response bandwidth is 3 times as that of the traditional single pulse probing scheme, all with the same detection bandwidth; 860 m sensing range with 166.4 kHz response bandwidth has been achieved, with 5 m spatial resolution and 1.8 p ${\varepsilon /\sqrt {Hz}}$ strain sensitivity.

Fast speed switching response and high modulation signal processing bandwidth through LiNbO3 electro-optic modulators

Abstract This work outlined the fast speed response and high modulation bandwidth through LiNbO3 electro-optic modulators. The refractive index is analyzed to estimate the switching voltage and modulation bandwidth for these modulators. The modulation voltage and data transmission data rates are analyzed and discussed clearly through LiNbO3 electro-optic modulators. The modulator’s performance efficiency is upgraded with the optimum modulator length of 10 mm and its thickness of 2 mm. The proposed modulators are compared with GaAs electrooptic modulators under various electro-optic modulators dimensions at 1300 nm near-infrared region and room temperature.