Prediction of Broadband and Highly-Efficient Electromagnetic Wave-Absorbing SiC@SiO2 Nanowire Aerogel by Genetic Algorithm.

Searching for lightweight and high-temperature stable electromagnetic wave-absorbing materials with broad absorbing bandwidth and high efficiency is of significance for applications in daily life and industry. Optimizing the dielectric properties of SiC nanowire aerogel by both compositional and structural designs is an efficient way to obtain simultaneous efficient wave-dissipation ability and good impendence matching and thus the desired properties. However, due to the complex effects of dielectric parameters on the wave-absorbing properties, rational design of high-performance electromagnetic wave-absorbing materials remains challenging. Herein, we propose a genetic algorithm-based approach to predict broadband and highly efficient electromagnetic wave-absorbing materials in a SiC@SiO2 nanowire aerogel-based system. The obtained SiC@SiO2 nanowire aerogels exhibit a gradient multilayered structure with a low dielectric outer layer, a medium layer with alternatively distributed electromagnetic wave transparent and attenuation layers, and an inner high attenuation layer, giving it a broadband electromagnetic wave-absorbing performance covering almost all the 2-18 GHz bandwidth and simultaneous high efficiency. The results show that the genetic algorithm-based approach is efficient in predicting high-performance electromagnetic wave-absorbing ceramic aerogels.

Absolutely Structural Disorder Boosting Bandwidth toward Full-Spectrum White Light from Single Occupancy of Activator.

Achieving single-phase full-spectrum white light (SFWL) phosphors is a central goal in the optical field because they simplify white-LEDs assembly and avoid long-term color instability. Despite many approaches are developed, current SFWL phosphors still suffer from chromaticity drift due to inconsistent thermal quenching of multiple emitting centers. Herein, an absolutely structural disorder strategy is established to develop a single-emitting center-based SFWL phosphor. Precisely controlling the flux added induces a structural translation from the absolutely ordered Y0.75Ta0.25O1.75:Bi3+ to the absolutely disordered Y0.785Ta0.215O1.715:Bi3+, as directly identified by STEM-HAADF analyses. Structural disorder enables Y0.785Ta0.215O1.715:Bi3+ to produce SFWL with the FWHM of 6194 cm-1 (175 nm) by employing a single activator site, a 1352 cm-1 increase compared to the cyan-emitting Y0.75Ta0.25O1.75:Bi3+ despite Bi3+ occupies two lattice positions. This single-emitting center-based SFWL, coupled with minimal thermal expansion of the unit cell and inapparent spectral overlap of excitation and emission bands, ensure zero-chromaticity shift with elevated temperature. A prototype white-LEDs using Y0.785Ta0.215O1.715:Bi3+ as a single luminescent layer generates warm white light without perceptible CIE coordinates shift under various currents or after extremely long-term continuous operation. This work highlights the potential of structural disorder in designing SFWL phosphors with exceptional color stability.

Implantable small ultra-wideband circularly polarized antenna design for continuous blood pressure monitoring.

This paper presents a miniaturized circularly polarized (CP) implantable antenna Ultra-wide bandwidth for continuous blood pressure monitoring. The miniature and CP of the antenna are gained by using a new slot method. The symmetry slots in the radiation patch, two T-shape slots in the GND, coupled with the use of a short pin make the designed antenna with good physical and radiation properties. In simulation, the fractional effective axial ratio bandwidth is 23.6% (2.36-2.94 GHz), and the peak gain is - 28.9 dBi. Its total size is only 17.78 mm3 (0.056 × 0.04 × 0.004 λ03), which size is smaller compared to other antennas with similar performance. A prototype is fabricated and measured. The experimental results are in good agreement with the simulation results. And, the radiation patterns have good symmetry both in the simulation and measurement. In addition, the maximum SAR value is in accordance with the IEEE standard safety guidelines (IEEE C95.1-2019).

A low-complexity and high-frequency ASIC transceiver for an ultrasound imaging system.

This article presents a high-frequency application-specific integrated circuit (ASIC) transceiver for an ultrasound imaging system designed with a focus on low complexity. To simplify the design, it employs a conventional Class-D power amplifier structure for the transmitter (TX) and a resistive feedback transimpedance amplifier (TIA), which consists of a common-source amplifier followed by a source follower for the receiver (RX). Through careful optimization, the RX achieves a measured transimpedance gain of 90 dBΩ and an input-referred noise of 5.6 pA/√Hz at 30 MHz while maintaining a wide bandwidth of up to 30 MHz for both the TX and RX. The power consumption of the TX and RX is measured to be 7.767 mW and 2.5 mW, respectively. Further acoustic performance, assessed using an annular capacitive micromachined ultrasonic transducer (CMUT), showed a 1.78 kPa peak pressure from a 20 V pulser and confirmed the full bandwidth compatibility of the CMUT's bandwidth. The ASIC transceiver has been fabricated using a 0.18 µm HV bipolar-CMOS-DMOS (BCD) process.

Tailoring the Microstructure and Porosity of Porous Piezoelectric Ceramics for Ultrasonic Transducer Application.

Porous piezoelectric ceramics and composites are advantageous for ultrasonic transducers due to their capability to decouple longitudinal and transverse modes, their improved voltage sensitivity, and their enhanced acoustic matching. However, the design and fabrication of porous piezoelectric ultrasonic transducers with excellent electromechanical properties are still challenging. In this work, porous lead zirconate titanate (PZT) ceramics with an aligned pore structure were prepared using the freeze-cast technique, and the effect of porous structure and porosity on the electromechanical parameters was investigated. The introduction of an aligned pore structure is beneficial to enhance the electromechanical properties and reduce the acoustic impedance. A high d33 (∼530 pC/N), a higher kt (∼0.676), and a lower acoustic impedance (∼10.4 MRalys) were achieved in the porous PZT ceramic with the porosity of 44 vol %. The effect of porosity and pore structure on the decoupling degree of vibration modes and ferroelectric polarization was considered to correct the homogeneous medium model, which can quantify the relationship between the kt and porosity of the porous structure. A demonstration of a piezoelectric ultrasonic transducer based on freeze-cast porous PZT ceramics was presented, which exhibits a -6 dB bandwidth of 52% and a theoretical axial resolution of 520 µm. This work therefore provides a potential alternative of piezoelectric ultrasonic transducers for nondestructive testing and imaging applications.

Solvent mediated synthesis of multicolor narrow bandwidth emissive carbon quantum dots and their potential in white light emitting diodes.

The development of efficient and environmentally sustainable materials for white light-emitting diodes (WLEDs) is of paramount importance in the field of lighting technology. In this study, we present a solvent-modulated synthesis approach for the fabrication of multicolor narrow-bandwidth emissive carbon quantum dots (CQDs) as a promising solution for constructing WLEDs. The synthesis method involves the controlled reaction of organic precursors in different solvent environments, leading to the formation of CQDs with distinct emission wavelengths with a relatively small full width at half maximum, ranging from 28 to 42 nm. Moreover, these synthesized multicolor CQDs demonstrate a remarkably high fluorescence quantum yield of up to 65%, indicating their potential for constructing efficient WLED when incorporated in polymer matrix and coated on the surface of blue light-emitting diode (LED).

A V-Band Wideband Power Amplifier with High Gain in a 130 nm SiGe BiCMOS Process.

This paper introduces a high-gain wideband power amplifier (PA) designed for V-band applications, operating across 52 to 65 GHz. The proposed PA design employs a combination of techniques, including pole-gain distribution, base-capacitive peaking, and the parallel configuration of multiple small-sized transistors. These strategies enable significant bandwidth extension while maintaining high gain, substantial output power, and a compact footprint. A two-stage PA using the combination technique was developed and fabricated in a 130 nm SiGe BiCMOS process. The PA prototype achieved a peak gain of 27.3 dB at 64 GHz, with a 3 dB bandwidth exceeding 13 GHz and a fractional bandwidth greater than 22.2%. It delivered a maximum saturated output power of 19.7 dBm and an output 1 dB compression point of 18 dBm. Moreover, the PA chip occupied a total silicon area of 0.57 mm2, including all testing pads with a compact core size of 0.198 mm2.

Textile Bandwidth-Enhanced Half-Mode Substrate-Integrated Cavity Antenna Based on Embroidered Shorting Vias.

A textile bandwidth-enhanced half-mode substrate-integrated cavity (HMSIC) antenna based on embroidered shorting vias is designed. Based on the simulated results of the basic HMSIC antenna, two embroidered hollow posts with square cross-sections are added as shorting vias at the intersections of the zero-E traces of the TM210HM and TM020HM modes to shift the TM010HM-mode band to merge with the bands of the higher-order modes for bandwidth enhancement. A prototype is practically fabricated based on computerized embroidery techniques. Measurement results show that the prototype is of an expanded -10 dB impedance band of 4.87~6.17 GHz (23.5% fractional bandwidth), which fully covers the 5 GHz wireless local area network (WLAN) band. The simulated radiation efficiency and maximum gain of the proposed antenna are above 97% and 7.6 dBi, respectively. Furthermore, simulations and measurements prove its robust frequency response characteristic in the proximity of the human tissues or in bending conditions, and the simulations of the specific absorption rate (SAR) prove its electromagnetic safety on the human body.

A Wide-Bandwidth Inexpensive Current Sensor Based on the Signal Fusion of Tunneling Magnetoresistance and a Current Transformer.

In technology and industrial production, many applications require wide-bandwidth current measurements. In this paper, a signal fusion scheme for a current sensor comprising tunneling magnetoresistance and a current transformer is proposed, achieving a flat frequency response in the DC to MHz range. The measurement principles in different cases of the scheme are introduced, and the total transfer function of the entire scheme is derived by analyzing each section separately. Furthermore, the feasibility and selected parameters of the scheme are verified through a systematic simulation utilizing the MATLAB software. Based on the proposed scheme, a group of principal prototypes are built to experimentally evaluate the bandwidth, amplitude and phase flatness, accuracy, sensitivity, and impulse response. The relative amplitude variation in the passband of the fusion sensor is less than 4%, and the estimated bandwidth of the fusion sensor is close to 17 MHz. The accuracy is better than 0.6%, even when measuring the current at 1 MHz, and the relative standard deviation is 5% when measuring the impulse signal. The sensors developed using this scheme, with a low financial cost, have advantages in many wide-bandwidth current measuring scenarios.

Design implementation analysis of multi-band antenna for terrestrial applications.

A multi-band antenna is proposed for terrestrial applications above 5 GHz. The design includes one director element, three split ring resonators (SRR), and a printed patch antenna on a FR4 substrate to make the miniature structure. The novelty is the addition of "C" split rings and one identical stub linked to the partial ground into the radiating element, which improves impedance matching and radiation characteristics across the target bands. The prototype is designed with five distinct resonance frequencies and radiation patterns compared to those produced by the patch, the director and resonators are added. Return loss simulation results and measured radiation pattern findings are validated and analyzed. The antenna produces a gain of 7.84 dB, overall efficiency of 84.76 %, and a VSWR of 1.8 at 7 GHz frequency, which is achieved due to the peculiar features of the FR4 and it is highly suitable for traditional communication. VSWR, gain, and radiation efficiency are all higher on this antenna than they are on a typical multiband antenna. At 20 GHz, the designed antenna band is efficient to operate with five dissimilar resonant frequency bands, pinpointed at 7.224 GHz, 10.723 GHz, 13.808 GHz, 17.014 GHz and 19.549 GHz through different impedance bandwidths.

Detection of sleep arousal from STFT-based instantaneous features of single channel EEG signal.

OBJECTIVE: Sleep arousal, a frequent interruption in sleep with complete or partial wakefulness from sleep, may indicate a breathing disorder, neurological disorder, or sleep-related disorders. These phenomena necessitate the detection of sleep arousals. Uses of deep learning methods to detect features inhibits the scope to understand the specific distinctive nature of the signals and reduces the interpretability of the model. To evade these inconsistencies and to improve the classification performance of the sleep arousal detection model, a model has been proposed in this study on the prospect of understandable features that are useful in detecting sleep arousals. Approach: Time-frequency analysis of the electroencephalogram (EEG) signals was performed using Short-Time Fourier Transform (STFT). From the STFT coefficients, the spectrogram and instantaneous properties (frequency, bandwidth, power spectrum, band energy, local maxima, and band energy ratios) were investigated. From these properties, instantaneous features were generated by statistical analysis. Additive feature sets and reduced feature sets, formed by adding features successively and reducing features using the analysis of variance test respectively, were subjected to a tri-layered neural network classifier to evaluate the capability of the features to detect sleep arousal and normal sleep segments. Main results: The reduced feature set (Set 6) has proved to be efficacious in facilitating superior classification performance metrics (accuracy, sensitivity, specificity, and AUC of 89.14%, 83.52%, 89.49%, and 93.84% respectively). Significance: This efficient model can be incorporated with an automatic sleep apnea detection system where the estimation of hypopnea requires the detection of sleep arousal. .

Broad bandwidth and excellent thermal stability in BiScO3-PbTiO3 high-temperature ultrasonic transducer for non-destructive testing.

High-temperature ultrasonic transducer (HTUT) is essential for non-destructive testing (NDT) in harsh environments. In this paper, a HTUT based on BiScO3-PbTiO3 (BS-PT) piezoelectric ceramics was developed, and the effect of different backing layers on its bandwidth were analyzed. The HTUT demonstrates a broad bandwidth and excellent thermal stability with operation temperature up to 400 °C. By using a 10 mm thick porous alumina backing layer, the HTUT achieves a broad -6 dB bandwidth of 100 %, which is about 4 times superior to the transducer with an air backing layer. The center frequency (fc) of the HTUT remains stable with fluctuations of less than 10 % across the temperature range from room temperature to 400 °C. The HTUT successfully detected simulated defects in pulse-echo mode for NDT over 200 °C. This research not only advances high-temperature ultrasonic transducer technology but also expands the NDT applications in harsh environmental conditions.

Metamaterial Broadband Absorber Induced by Synergistic Regulation of Temperature and Electric Field and Its Optical Switching Application.

Nowadays, metamaterial absorbers still suffer from limited bandwidth, poor bandwidth scalability, and insufficient modulation depth. In order to solve this series of problems, we propose a metamaterial absorber based on graphene, VO2, gallium silver sulfide, and gold-silver alloy composites with dual-control modulation of temperature and electric field. Then we further investigate the optical switching performance of this absorber in this work. Our proposed metamaterial absorber has the advantages of broad absorption bandwidth, sufficient modulation depth, and good bandwidth scalability all together. Unlike the single inspired layer of previous designs, we innovatively adopted a multi-layer excitation structure, which can realize the purpose of absorption and bandwidth width regulation by a variety of means. Combined with the finite element analysis method, our proposed metamaterial absorber has excellent bandwidth scalability, which can be tuned from 2.7 THz bandwidth to 12.1 THz bandwidth by external electrothermal excitation. Meanwhile, the metamaterial absorber can also dynamically modulate the absorption from 3.8% to 99.8% at a wide incidence angle over the entire range of polarization angles, suggesting important potential applications in the field of optical switching in the terahertz range.

Dynamic Bandwidth Slicing in Passive Optical Networks to Empower Federated Learning.

Federated Learning (FL) is a decentralized machine learning method in which individual devices compute local models based on their data. In FL, devices periodically share newly trained updates with the central server, rather than submitting their raw data. The key characteristics of FL, including on-device training and aggregation, make it interesting for many communication domains. Moreover, the potential of new systems facilitating FL in sixth generation (6G) enabled Passive Optical Networks (PON), presents a promising opportunity for integration within this domain. This article focuses on the interaction between FL and PON, exploring approaches for effective bandwidth management, particularly in addressing the complexity introduced by FL traffic. In the PON standard, advanced bandwidth management is proposed by allocating multiple upstream grants utilizing the Dynamic Bandwidth Allocation (DBA) algorithm to be allocated for an Optical Network Unit (ONU). However, there is a lack of research on studying the utilization of multiple grant allocation. In this paper, we address this limitation by introducing a novel DBA approach that efficiently allocates PON bandwidth for FL traffic generation and demonstrates how multiple grants can benefit from the enhanced capacity of implementing PON in carrying out FL flows. Simulations conducted in this study show that the proposed solution outperforms state-of-the-art solutions in several network performance metrics, particularly in reducing upstream delay. This improvement holds great promise for enabling real-time data-intensive services that will be key components of 6G environments. Furthermore, our discussion outlines the potential for the integration of FL and PON as an operational reality capable of supporting 6G networking.

Supporting Differentiated Streaming Services in Heterogeneous Vehicle-to-Everything Networks.

Advancements in assisted driving technologies are expected to enable future passengers to use a wide range of multimedia applications in electric vehicles (EVs). To address the bandwidth demands for high-resolution and immersive videos during peak traffic, this study introduces a bandwidth-management algorithm to support differentiated streaming services in heterogeneous vehicle-to-everything (V2X) networks. By leveraging cellular 6G base stations, along with Cell-Free (CF) Massive Multi-Input Multi-Output (mMIMO) Wi-Fi 7 access points, the algorithm aims to provide a high-coverage, high-speed, and low-interference V2X network environment. Additionally, Li-Fi technology is employed to supply extra bandwidth to vehicles with limited connectivity via V2V communication. Importantly, the study addresses the urgency and prioritization of different applications to ensure the smooth execution of emergency applications and introduces a pre-downloading mechanism specifically for non-real-time applications. Through simulations, the algorithm's effectiveness in meeting EV users' bandwidth needs for various multimedia streaming applications is demonstrated. During peak-bandwidth-demand periods, users experienced an average increase in bandwidth of 47%. Furthermore, bandwidth utilization across the V2X landscape is significantly improved.

Leveraging Edge Computing for Video Data Streaming in UAV-Based Emergency Response Systems.

The rapid advancement of technology has greatly expanded the capabilities of unmanned aerial vehicles (UAVs) in wireless communication and edge computing domains. The primary objective of UAVs is the seamless transfer of video data streams to emergency responders. However, live video data streaming is inherently latency dependent, wherein the value of the video frames diminishes with any delay in the stream. This becomes particularly critical during emergencies, where live video streaming provides vital information about the current conditions. Edge computing seeks to address this latency issue in live video streaming by bringing computing resources closer to users. Nonetheless, the mobile nature of UAVs necessitates additional trajectory supervision alongside the management of computation and networking resources. Consequently, efficient system optimization is required to maximize the overall effectiveness of the collaborative system with limited UAV resources. This study explores a scenario where multiple UAVs collaborate with end users and edge servers to establish an emergency response system. The proposed idea takes a comprehensive approach by considering the entire emergency response system from the incident site to video distribution at the user level. It includes an adaptive resource management strategy, leveraging deep reinforcement learning by simultaneously addressing video streaming latency, UAV and user mobility factors, and varied bandwidth resources.

Smoothing level selection for density estimators based on the moments.

This paper introduces an approach to select the bandwidth or smoothing parameter in multiresolution (MR) density estimation and nonparametric density estimation. It is based on the evolution of the second, third and fourth central moments and the shape of the estimated densities for different bandwidths and resolution levels. The proposed method has been applied to density estimation by means of multiresolution densities as well as kernel density estimation (MRDE and KDE respectively). The results of the simulations and the empirical application demonstrate that the level of resolution resulting from the moments method performs better with multimodal densities than the Bayesian Information Criterion (BIC) for multiresolution densities estimation and the plug-in for kernel densities estimation.

Estimation of time-varying kernel densities and chronology of the impact of COVID-19 on financial markets.

The time-varying kernel density estimation relies on two free parameters: the bandwidth and the discount factor. We propose to select these parameters so as to minimize a criterion consistent with the traditional requirements of the validation of a probability density forecast. These requirements are both the uniformity and the independence of the so-called probability integral transforms, which are the forecast time-varying cumulated distributions applied to the observations. We thus build a new numerical criterion incorporating both the uniformity and independence properties by the mean of an adapted Kolmogorov-Smirnov statistic. We apply this method to financial markets during the onset of the COVID-19 crisis. We determine the time-varying density of daily price returns of several stock indices and, using various divergence statistics, we are able to describe the chronology of the crisis as well as regional disparities. For instance, we observe a more limited impact of COVID-19 on financial markets in China, a strong impact in the US, and a slow recovery in Europe.

A Metamaterials-Based Absorber Used for Switch Applications with Dynamically Variable Bandwidth in Terahertz Regime.

A broadband absorber based on metamaterials of graphene and vanadium dioxide (VO2) is proposed and investigated in the terahertz (THz) regime, which can be used for switch applications with a dynamically variable bandwidth by electrically and thermally controlling the Fermi energy level of graphene and the conductivity of VO2, respectively. The proposed absorber turns 'on' from 1.5 to 5.4 THz, with the modulation depth reaching 97.1% and the absorptance exceeding 90% when the Fermi energy levels of graphene are set as 0.7 eV, and VO2 is in the metallic phase. On the contrary, the absorptance is close to zero and the absorber turns 'off' with the Fermi energy level setting at 0 eV and VO2 in the insulating phase. Furthermore, other four broadband absorption modes can be achieved utilizing the active materials graphene and VO2. The proposed terahertz absorber may benefit the areas of broadband switch, cloaking objects, THz communications and other applications.

Structural Optimization Design of Magnetoelectric Thin-Film Antenna for Bandwidth and Radiation Enhancement.

The acoustically actuated nanomechanical magnetoelectric (ME) antennas represent a promising new technology that can significantly reduce antenna size by 1-2 orders of magnitude compared to traditional antennas. However, current ME antennas face challenges such as low antenna gain and narrow operating bandwidth, limiting their engineering applications. In this paper, we enhance the bandwidth and radiation performance of ME antennas through structural optimization, leveraging theoretical analysis and numerical simulations. Our findings indicate that optimizing the inner diameter of the ring-shaped ME antenna can elevate the average stress of the magnetic layer, leading to improved radiation performance and bandwidth compared to circular ME antennas. We establish an optimization model for the radiation performance of the ME antenna and conduct shape optimization simulations using COMSOL Multiphysics. The results of the Multiphysics field optimization align with the stress concentration theory, demonstrating a strong correlation between the radiation performance and bandwidth of the ME antenna with the average stress of the magnetic film. The resonant frequency in the thickness vibration mode is determined to be 170 MHz. Furthermore, shape optimization can enhance the bandwidth by up to 104% compared to circular ME antenna structures of the same size.