This paper focuses on the decomposition of different modes of Loran-C resultant waves, including ground waves and one-hop/two-hop sky waves, propagating in the Earth-ionosphere waveguide obtained from direct finite-difference time-domain (FDTD) modeling in the presence of the natural magnetic field. After providing the FDTD iterative formulas for the ionosphere affected by the natural magnetic field, the Loran-C resultant waves propagating in the anisotropic Earth-ionosphere waveguide are estimated using the FDTD algorithm. In both the daytime and nighttime ionosphere models, different orientations of the natural magnetic field are taken into account. The arrival times of the different propagation modes for the resultant waves were then determined using a multipath time-delay estimation method. With the above delays, the amplitudes of the different modes are acquired by solving overdetermined equations. Finally, the decomposition results are compared with those obtained in the absence of the natural magnetic field. The numerical experimental results indicate that, with a radiation power of 1 kW and a natural magnetic field of 0.5 Gs, the influence of the direction of the natural magnetic field on the field strength of one-hop sky waves is significant when the propagation distance of LF radio waves is less than 1000 km. Radio waves have multipath effects such as convergence, divergence, and diffraction due to the curvature of the Earth and the ionosphere. This results in significant interference phenomena when the propagation distance of two-hop sky waves is greater than 500 km.

A model prediction based leading angle flux weakening control method is proposed to improve the dynamic and steady-state performance of permanent magnet synchronous motors during the flux weakening process. First, the mathematical model of a permanent magnet synchronous motor is used to construct the prediction model in this method, and then a thorough analysis of the permanent magnet synchronous motor's flux weakening control procedure is carried out. Secondly, based on the principle of model predictive control and the existing delay problems, the corresponding delay compensation method is proposed, and the leading angle flux weakening control method is applied to the proposed model predictive control algorithm, so as to achieve flux weakening speed-up control. Finally, the prototype is used to confirm the effectiveness and precision of the proposed technique. The experimental results show that the leading angle flux weakening control method based on model prediction has faster dynamic response to speed and current than the traditional vector flux weakening control method. At the same time, the steady-state current amplitude is smaller, which has superior current control.

Aiming at the problem of slow response speed and poor anti-interference ability using the traditional PI control in the direct torque control strategy of brushless DC motor (BLDCM), the direct torque control (DTC) of the BLDCM based on the sliding mode change (SMC) structure is proposed. In the BLDCM DTC system under the new flux linkage set mode, the traditional PI control is replaced by the improved SMC control to realize the new torque given mode and realize the DTC of the BLDCM. Firstly, the integral sliding mode surface is used instead of the traditional linear sliding mode surface to optimize the continuity of the SMC structure and reduce the high-frequency perturbation caused by the differential phase, thus reducing the smooth torque and system steady-state error. Secondly, the system is simulated by MATLAB/SIMULINK; the given torque of the improved SMC is the most stable; and the speed response curve is smoother. Finally, the construction of the BLDCM test platform is completed. The experimental results show that in the BLDCM DTC control system of the new flux linkage set mode, based on the improved SMC, the system has faster response speed and stronger anti-interference, and shows stronger dynamic and static performance.

Solid dielectric horn antennas have a directional radiation pattern and high gain. However, even when a solid dielectric horn antenna is excited with the fundamental mode metallic waveguide, there is a possibility that higher order modes in the guided region will be generated. Also, the energy can leak from the normal direction to the dielectric horn generating a leaky mode. It is one of the reasons that higher-order guided modes and leaky modes analysis of horn becomes important. In this paper, propagation characteristics for solid dielectric horns are derived and computed for fundamental and higher-order guided and also leaky modes in a solid dielectric horn antenna. We have also analyzed the radiation characteristics of the leaky mode and guided mode of a solid dielectric horn. Finally, radiation equations for a solid dielectric horn antenna that were deduced earlier by some of the authors, but omitted for brevity are given and compared with numerical and measured results. These results have been further verified by comparing them with the already reported literature on guided mode radiation characteristics of the solid dielectric horn. From the plotted graphs given in the paper, we can infer that the proposed propagation constant equations and radiation equations predict dispersion characteristics and the radiation pattern of guided and leaky modes well, respectively.

This article presents a novel numerical approach to reduce scattering echoes in the front region of dielectric objects with the method of auxiliary sources. The method involves using a Gaussian radio pulse covering the 6-12 GHz frequency range. The approach involves optimizing the dimensions and dielectric permittivity of an elliptical cylinder in order to make it invisible, thus eliminating the need for metamaterial cloaking. The proposed approach has been validated by comparing the results of numerical experiments obtained during pulse echo observations with the FDTD and MoM numerical methods. The proposed method is a highly efficient and practical approach for scattering problems, such as scattering echo reduction, offering comparable results to FDTD and MoM methods with significantly reduced computational requirements.

The purpose of this paper is to study the RF/microwave constant phase shift (CPS) designed as an integrated circuit (IC) in 130-nm Bi-CMOS technology. The CPS understudy is constituted by a bandpass (BP) negative group delay (NGD) passive cell combined in cascade with a positive group delay (PGD) circuit. The CPS real circuit is represented by a CLC-network associated in cascade with a BP-NGD passive cell. The CPS characterization is based on the S-parameter modelling. The CPS is analytically modeled by the frequency independent transmission phase modelling by the mathematical relation φ(f)=a*exp(-j*φ₀) = constant around working frequency [f_n-Δf/2, f_n+Δf/2] by denoting center frequency f_n and frequency band Δf. The analytical principle of the constant PS is explored by means of the RLC-network based NGD cell. The design formula of the NGD and CLC passive circuit parameters in function of desired operation frequency is established. The validity of the developed theory is verified with a proof-of-concept (POC). A CPS miniature IC having physical size 1.15 mm × 0.7 mm is designed and implemented as POC in 130-nm Bi-CMOS technology. The ADS® and layout versus schematic of Cadence® simulation results from 130-nm Bi-CMOS CPS POC confirms the theoretical investigation feasibility. The simulated results of the obtained CPS IC POC layout show φ₀=-67°+/-1° phase shift around f_n=0.85 GHz within the frequency band delimited by f₁=0.73 GHz to f₂=0.984 GHz or Δf=f₂-f₁=254 GHz. The CPS robustness designed in 130-nm Bi-CMOS IC technology is stated by Monte Carlo statistical analysis from 1000 trials with respect to the component geometrical parameters. It was reported that the phase shift and insertion loss flatness's of the CPS IC is guaranteed lower than 5% in Δf/f_n=30% relative frequency band around f_n.

To tackle the slow response and insufficient interference resistance exhibited by permanent magnet synchronous motors (PMSMs) under traditional field-oriented control (FOC). This paper proposes an integral sliding mode controller (SMC) to improve the speed loop, and adaptive law is also developed using a nonlinear smooth function to eliminate the chattering phenomenon of the sliding mode control. Meanwhile, an extended state observer is designed to estimate and compensate for the disturbances caused by wind speed uncertainty and the system's internal disturbances. Then, model predictive control (MPC) is employed for the current loop to eliminate the overshoot and achieve fast tracking. Finally, a step-by-step model reference adaptive scheme (MRAS) is proposed to identify the parameters and eliminate the internal disturbances in addressing parameter perturbation in the motor during operation. The simulation results demonstrate that the enhanced system exhibits almost no overshoot, superior steady-state performance, quick dynamic response, and resistance to both internal and external disturbances, ultimately validating the efficacy of the approach.

Wireless power transfer (WPT) with dynamic charging capabilities is a promising technology that can charge moving objects in real-time. However, maintaining high-efficiency power transfer during vehicle movement continues to be a significant challenge. To address this challenge, this study proposes a dynamic WPT system that utilizes orthogonal transmitter and receiver coils, offering the advantages of stable output power and efficiency, even when the vehicle is in motion. Unlike other systems, the proposed topology eliminates the need for a complicated feedback control system, thereby reducing hardware costs. To verify the effectiveness of the proposed topology, a dynamic WPT system was implemented in this study. Measurement results demonstrate that even when the vehicle moves a distance of 400 mm (four times the length of the receiving coil), the output voltage and power variations are only 4.9% and 9.6%, respectively.

This paper presents an efficient algorithm to calculate the primary basis functions (PBFs) of the characteristic basis function method (CBFM) for the scattering from a dielectric object. The use of the Poggio-Miller-Chang-Harrington-Wu (PMCHW) integral equation discretized by the Galerkin method of moments (MoM) with Rao-Wilton-Glisson basis functions leads to solving a linear system. For a collection of incident waves and for a given block, the CBFM needs to invert the whole PMCHW self-impedance matrix to calculate the PBFs. By decomposing the PMCHW impedance matrix into four sub-matrices of halved sizes, related to the electric and magnetic surface currents and their coupling, the computation of the PBFs is accelerated by using the impedance matrix derived from the electric field integral equation (EFIE) combined with the physical optics (named POZ) approximation. In addition, the PO developed by Jakobus and Landstorfer [35], named POJ and valid for a perfectly-conducting scatterer, is extended to a dielectric surface. Recently, the MECA (modified equivalent current approximation, Li and Mittra [29]) based on the tangent plane or Kirchhoff approximation, has also been applied to expedite the PBF calculation. The presented method, HCBFM-POZ (H means halved), accelerated by the adaptive cross approximation (ACA), is tested and compared with CBFM-MECA and HCBFM-POJ on a cube and on a sphere. The numerical results show that HCBFM-POZ is valid for both the shapes, whereas the CBFM-MECA and HCBFM-POJ are not valid on a sphere.

Compelling evidence suggests that the interaction between electromagnetic metasurfaces and deep learning gives rise to the proliferation of intelligent metasurfaces in the past decade. In general, deep learning offers a transformative force to reform the design and working style of metasurfaces. A majority of the inverse-design literature announce that, given a user-defined input, the pre-trained deep learning models can quickly output the metasurface candidates with high fidelity. However, they largely ignore an important fact, that is, the practical input is always semi-known. In this work, we introduce a generation-elimination network that is robust to semi-known input and information pollution. The network is composed of a generative network to generate a number of possible answers and then a discriminative network to eliminate suboptimal answers. We benchmark the feasibility via two scenes, the on-demand metasurface design of the reflection spectra and the far-field pattern. In the microwave experiment, we fabricated and measured the reconfigurable metasurfaces to automatically meet the semi-known beam steering requirement that widely exist in wireless communication. Our work for the first time answers the question of how to cope with semi-known input, which is ubiquitous in a panoply of real-world applications, such as imaging, sensing, and communication across noisy environment.

Phased array radar (PAR) systems are critical for modern defense and surveillance applications, but their reliability and availability are affected by various factors, including physical and performance degradation. Furthermore, implementing prognostics and health management (PHM) framework for the whole radar system is challenging. To address these issues, this paper proposes an efficient solution by hierarchically implementing PHM frameworks in an active PAR (APAR) system. The proposed framework subsumes device-level, subsystem-level, and system-level health prediction models to enable comprehensive health monitoring and maintenance decision-making. This approach addresses the unique challenges involved in implementing PHM for the APAR system and facilitates the transition from traditional reactive maintenance practices to a predictive maintenance approach, thereby improving the overall system. Mathematical models that relate the radar's physical degradation to its performance deterioration are formulated, analyzed and presented. Subsequently, a Bayesian long short-term memory (BayesLSTM) architecture is developed and integrated into the proposed framework for estimating the remaining useful life (RUL) of critical devices/subsystems. The effectiveness of the proposed deep learning-based prognostic framework is evaluated through simulations and experimental studies. The proposed hierarchical framework has the potential to be applied to other radar systems that require effective health monitoring strategy.

The outage probability performance of a hybrid free space optical (FSO)/radio frequency (RF) system with a reconfigurable intelligent surface (RIS) assisted full-duplex relay is presented in this paper. The FSO link follows the Gamma-Gamma distribution over pointing error and atmospheric turbulence with random foggy impairments. The RF link between the relay and the destination is subject to Nakagami-m distributions, while the RIS links and the relay self-interference (SI) link follow Rayleigh fading. As a result, the RIS-to-relay link's cumulative distribution function (CDF) of the signal to interference plus noise ratio (SINR) is obtained. On the basis of this, the system's outage probability is determined according to the decode and forward relay protocol. Thus, Monte-Carlo simulations are utilized to verify the obtained expression's accuracy. Our findings show how atmospheric turbulence, pointing errors, fog conditions, and the number of RIS reflecting elements affect the system performance. Furthermore, it is concluded that, under the identical channel conditions, heterodyne detection performs better than intensity modulation/direct detection (IM/DD).

Wideband phased arrays for Electronic Warfare (EW) applications utilize narrowband phase shifters in a switched configuration to cover a multi-octave bandwidth in split bands. Wideband True Time Delay (TTD) line circuits are the best candidates to replace narrowband phase shifters in such systems, covering the complete operating bandwidth in a single step. The Transmit Receive Module (TRM) is a critical component of any phased array system. A novel design of a TTD line-based Octal Transmit Receive Module (OTRM) for a 32-element EW phased array over a frequency range of 1-6 GHz is presented in this paper. The OTRM is designed on a single multi-layer PCB by integrating eight transmit-receive (TR) channels, associated controllers, and power conditioning circuitry in a compact size and weight of 800 grams. The paper addresses challenges associated in design of TR channels to fit within the inter-element spacing of 14 mm and to achieve isolation of ≥40 dB between channels. The designed OTRM tunes time delay up to 508 ps maximum with a step of 2 ps by using a single TTD line circuit for ±45° scan coverage. The OTRM has demonstrated its potential capability for use in wideband Radar, EW, and Communication system applications. Efficient thermal management of the OTRM is achieved by introducing Copper coins below the final power amplifiers and a liquid cold plate to dissipate a heat load of 32 watts per TR channel. The proposed OTRM delivers transmit power of 8 watts (CW), receive gain of 25 dB, and a noise figure of 6 dB per TR channel with an overall efficiency of 19% (min) over a 5 GHz bandwidth. RF path analysis of the TR channel in transmit and receive paths is carried out using the Systemvue software tool. To verify the design of the OTRM over different time delay and attenuator states, measurements are conducted using a Vector Network Analyzer (VNA).

The fast inverse Laplace transform (FILT) proposed by Hosono is recently applied to various transient response problems in electromagnetics. The frequency-domain methods have been the mainstream of electromagnetic simulation for many years, and a lot of knowledge has been accumulated. The FILT makes it possible to utilize frequency-domain techniques to transient analyses, and it is expected to provide reliable transient response analyses. Since the evaluation points of the image function in the conventional FILT depend on the observation time, the scope of application is sometimes limited when evaluation of the image function takes a relatively long computation time. This paper modifies the FILT so that the evaluation points are independent of the observation time, and the number of image function evaluations is reduced.

The reliability of DC-bus capacitors in six-phase drives is an important issue in multi-phase drive systems, and the influence of symmetrical and asymmetrical motor winding loads on the lifetime of DC-bus capacitors is essential. This article uses the SVPWM modulation algorithm to analyze the current and voltage ripple of DC-bus capacitors in a six phase voltage source inverter. Then, by optimizing the capacitance value when searching for the maximum stress point, the capacitance range of DC-bus capacitors is determined. At a power factor of 0.6 and modulation ratios of 0.4, 0.7, and 0.9, considering the changes in ESR, current, and voltage ripple in the capacitor, taking 80% of the rated lifespan as an example, it is found that the lifespan of the DC-bus capacitors in symmetrical configuration of the motor winding is increased by 0.20%, 1.80%, and 10.08% compared to that in asymmetric configuration, respectively. Finally, the analytical and experimental results were compared with existing methods, and the experimental results verified the effectiveness of the proposed method.

Focused arrays are attracting increased interest because of their wide range of applications. Focusing the antenna's radiation in the near field requires proper phase distribution of the array elements that must be fed through many phase shifters. This work presents a design idea for a focused circular array antenna, whose focal distance can be varied by only a single variable phase shifter. The idea is implemented on a dual-ring circular array having a six-wavelength diameter and focused at five wavelengths by using a single fixed phase shifter. Theoretical analysis and computer simulations of a sample design using MATLAB and CST Microwave Studio show that a phase change of 0.9π leads to a four-wavelength change in the focal distance. A formula for the estimation of the depth of field DOF is derived. The proposed array offers a simple method to vary the focal length continuously by a single variable phase shifter. This idea can be utilized in hyperthermia, RFID, and imaging applications, where the position of the focal spot needs to be moved along the normal to the array.

Sepsis is a life-threatening infectious disease. Mitochondrial dysfunction is widespread in severe sepsis. The myocardium contains a large number of mitochondria, and the survival rate of sepsis decreases sharply when cardiac dysfunction is involved. Vericiguat (BAY 1021189) is a novel drug for the prevention of heart failure. In this study, we evaluated the mitochondrial function of septic mice and drug-treated mice by resonance Raman spectroscopy (RRS). RRS can accurately identify the Raman characteristic peak at 750 cm^-1, 1128 cm^-1 and 1585 cm^-1 attributed to the reduced cytochrome in septic mice. We found that the intensity of the characteristic peak was significantly decreased in septic mice, indicating an imbalance of mitochondrial redox function, while the function was improved in the drug-treated group. It proves that BAY has the potential as a novel treatment for mitochondrial dysfunction in sepsis.

A coaxially pin-fed multiband fractal square antenna is proposed in this paper. The designed antenna resonates in five bands: 5 GHz, 10 GHz, 13.2 GHz, 16 GHz, and 20.5 GHz. This multibands are achieved by using a fractal square antenna. The fractal square is formed from an initial square patch and then optimized with increasing fractal iterations to resonate at these bands. The fractal property of the design also helps in the miniaturisation of the antenna. The proposed antenna has gain ranging from 4.9 dB to 9.7 dB and radiation efficiencies from 70% to 98%. The proposed antenna is simulated using the CST microwave studio. The antenna is then fabricated, and its performance parameters are measured. After finding a match between simulated and measured results, the same antenna and its array are tested in a MATLAB simulation environment for direction of arrival (DOA) and adaptive beam forming (AB) at all five bands. Using different DOA and AB algorithms, the performance of the antenna array is evaluated. The ability to accurately estimate the DOA of all signals delivered to the adaptive array antenna allows it to maximise its performance in terms of recovering the required transmitted signal and suppressing any interference signal. Then, the beam of the antenna is modified using the DOA algorithm to generate a beam in the desired direction and nulls in the unwanted direction for proposed satellite communications.

In this research work, a low-profile microstrip patch antenna has been designed with broad circularly polarized resonant bandwidth. The designed antenna consists of an equilateral triangular-shaped radiating patch with two triangular coplanar parasitic elements along with a square-shaped ground plane. The unique feature of this antenna design is a generation of circularly polarized radiation by only optimum corner truncation of the two parasitic elements along with a small portion of the driver patch. The designed antenna can be used for (5.725-5.850 GHz) WLAN and (5.85-5.925 GHz) dedicated short-range communication applications with circularly polarized radiation property. The overall resonant bandwidth for (S₁₁ ≤ -10 dB) is 1.52 GHz 24.75% with a frequency range (5.38-6.90 GHz), and the circularly polarized resonant bandwidth for (Axial ratio ≤ 3 dB) is 240 MHz 4.13% with a frequency range (5.69-5.93 GHz). The gain of the antenna is 4 dB at 5.81 GHz and almost remains the same for the entire resonant bandwidth. The complete design of the antenna has been done using theoretical calculation and HFSS ver13 simulation software. After that, it has been fabricated, and different parameters have been measured using Vector Network Analyser. It has been found that the measured results are very much similar to the simulated results.

This study investigates beamforming and optimization in Multiple-Input-Multiple-Output Orthogonal-Frequency-Division-Multiplexing (MIMO OFDM) radar systems. The objective of this research is to mitigate the range-angle coupling effect in MIMO OFDM radar systems by adopting range compensation and distance-angle decoupling methods, which is to ensure that the signal processing during radar waveform formation does not impact the aforementioned coupling effect. In distance compensation, the CVX toolbox is used to minimize peak sidelobe after distance compensation is performed in the angle dimension. A mathematical model is established, and an optimal set of transmission frequencies is achieved through the use of the Alternating-Direction-Method-of-Multipliers (ADMM) algorithm in the context of distance-angle decoupling. Both methods effectively eliminate distance-angle coupling and enhance detection and identification capabilities of MIMO OFDM radar systems.