Linear Frequency Modulation (LFM) signals are widely used in radar and sonar technology. Many applications are interested in determining the source of an LFM signal. In recent years, the rapid development of machine learning has facilitated research in various fields, including signal recognition. The neural networks can extract the implicit features of the signals, which can help the system to sort and recognize the signal sources quickly and accurately. High performance of neural networks requires large amounts of high-quality labeled data. However, it is difficult and expensive to obtain a large amount of high-quality labeled data. Simultaneously, some features will be lost during data preprocessing, and feature extraction and classification tasks will be inefficient. The self supervised network is proposed in this paper for pre-training the signal waveform and fine-tuning the classification with a small amount of labeled data. The proposed method can extract more signal waveform features, save labeling costs, and has higher precision. This method can provide up to 99.7% recognition accuracy at 20 dB.

Generalized Mie theory provides a theoretical solution to the extinction cross-section curve of an electromagnetic scattering event with a multiparticle aggregate, given the configurational information of the constituent particles. However, deducing the configuration of the aggregate from the extinction cross-section curve is a non-trivial inverse problem that can be cast as a global optimization problem. To address this challenge, we propose a computational scheme that combines global optimization search algorithms with a calculator known as the Generalized Multiparticle Mie-solution The scheme is tested using mock scattering cross-section curves based on randomly generated aggregate configurations. The scheme successfully reproduces the scattering curve by minimizing the discrepancy between the two scattering curves. However, the ground-truth configuration is not reproduced, as initially expected. This is due to the inability of the global optimization algorithm scheme used in the present work to correctly locate the global minimum in the high-dimensional parameter space.Nonetheless, the partial success of the proposed scheme to reconstruct the mock curves provides an instructive experience for future attempts to solve the inverse electromagnetic scattering problem by fine-tuning the present approach.

In order to reduce the cogging torque and improve the back electromotive force (EMF) performance of the motor, a three-phase permanent magnet (PM) synchronous motor with magnetic pole eccentricity and slotting design is proposed in this paper. Firstly, the analytical expression for the cogging torque of the motor is derived based on the energy method, and the factors influencing cogging torque are analyzed. Subsequently, taking the cogging torque and the amplitude of the back EMF as the optimization objectives, the response surface method (RSM) and multi-objective genetic algorithm (MOGA) are combined to obtain the optimal values for the eccentricity distance of the PMs, slotting radius, and slot position. Finally, a finite element model is established for simulation comparison. The results show that compared with the traditional model, the optimized model effectively reduces the cogging torque while slightly sacrificing the back-EMF amplitude, and improves the sine degree of the no-load back-EMF.

This paper presents the design and implementation of a C-Band Frequency Generator developed for Space-borne Synthetic Aperture Radar. This Frequency Generator subsystem generates stable and coherent reference signals for all the sub-systems of C-Band Synthetic Aperture Radar payload. Frequency Generator based on frequency multiplication technique generates various coherent signals namely 500 MHz signal for digital clock, local oscillator (LO) signals of 900 MHz and 4500 MHz needed for receivers and chirp signal of 5400±37.5 MHz. This chirp signal is generated by direct modulation of the full bandwidth baseband signal of DC-37.5 MHz at 4500 MHz and subsequently mixing with 900 MHz signal. Frequency generator unit is realized in a compact two-tier architecture, using novel concept of full chirp modulation, resulting in 6° rmsphase error in the transmit chirp signal along with in-band spurious rejection better than 20 dBc, whereas other coherent frequencies resulting in out of band spurious rejection better than 53 dBc against the specification of 40 dBc.

The core structure of transformers and reactors is subject to stress and high-frequency excitation during operation. The core structure is made of laminated silicon steel sheets, which are subject to magnetostrictive strain under alternating magnetic fields. To investigate the comprehensive magnetic properties of oriented silicon steel sheets under the influence of harmonics and stress, this paper builds a magnetic property measurement system for electrical steel and investigates the magnetization and magnetostriction characteristics of oriented silicon steel sheets of type 30SQGD105 under working frequency, harmonic and applied stress conditions. The results show that the effects of harmonics and stress on the hysteresis characteristics of the silicon steel sheet are small, and the effects on the magnetostriction characteristics are large.

A metamaterial-inspired antenna is proposed that utilizes an artificial mu-negative (MNG) transmission line (TL) to incorporate the zeroth-order resonance (ZOR) into Wi-Fi 7 operation in the 2.4/5/6 GHz wireless local area network (WLAN) bands. The antenna comprises a meta-structured loop with periodically loaded series interdigital capacitors and a parasitic shorted strip, all formed on the same substrate layer in a coplanar structure. The 2.4 and 6 GHz bands are produced by the parasitic strip and the close-form loop strip, respectively, which are of typical right-handed antennas. The 5 GHz band caused by the ZOR mode, where the permeability is zero, can be adjusted by the series capacitance in the unit cell. The total antenna size is 5.4 mm × 19.6 mm only. In this work, the design applied to notebook computers for the upcoming Wi-Fi 7 operation is also demonstrated. Both numerical and experimental results validate our proof-of-concept design.

Pulmonary edema assessment is a key factor in monitoring and guiding the treatment of critically ill patients. To date, the methods available at the bedside to estimate the physiological correlation of pulmonary edema and extravascular pulmonary fluid are often unreliable or require invasive measurements. The aim of this article is to develop an imaging method of reliably assessing pulmonary edema by utilizing functional electrical impedance tomography. In this article, the Split-Bregman algorithm is used to solve the Total Variation (TV) minimization problem in EIT image reconstruction. A thorax model is constructed according to CT images of rats. Through simulation and experiment, the proposed method improves the quality of reconstructed image significantly compared with existing methods. A pulmonary edema experiment in rats is also carried out. The development of pulmonary edema is analyzed numerically through EIT images.

The rapid advancement of communication technology has led to an increase in electromagnetic interference (EMI), or electromagnetic (EM) pollution. This is a cause for concern, as EMI can disrupt communication services, damage electronic equipment, and pose health risks. Regulatory bodies are working to develop standards for the safe use of wireless devices, but the problem of EMI is likely to continue to grow as the number of Internet of Thing (IoT) devices continues to increase. To address this issue, this study investigated the effectiveness of carbon-coated cobalt ferrite nanoparticles as a potential material for electromagnetic shielding. The synthesis of cobalt ferrite (CoFe₂O₄) nanoparticles was successfully achieved using the co-precipitation method. Subsequently, a carbon coating was applied to the nanoparticles through a hydrothermal process using a 200 mL autoclave made of teflon-lined stainless steel. This process was carried out at a temperature of 180˚C for a duration of 12 hours, with a heating rate of 8˚C per minute. This study examined both uncoated and carbon-coated CoFe₂O₄ nanoparticles at various ratios of glucose to CoFe₂O₄ (1:1, 2:1, and 3:1) using techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and higher resolution transmission electron microscopy (HRTEM) analysis. The XRD analysis revealed distinct and well-defined peaks corresponding to CoFe₂O₄, indicating the successful synthesis of the nanoparticles. The crystallite size of the uncoated CoFe₂O₄ nanoparticles was measured to be 11.47 nm, while for the carbon-coated CoFe₂O₄, the average crystallite size was determined to be 14.15 nm through XRD analysis. The results obtained from the FTIR analysis were consistent with previous reports and confirmed the formation of spinel CoFe₂O₄ nanoparticles, as suggested by published data. The morphological and structural properties of the prepared samples were further characterized using FESEM and HRTEM analysis, which demonstrated uniformity in both particle size distribution and morphology. Overall, the research findings indicated that the structure and properties of CoFe2O4 nanoparticles were significantly influenced by the carbon coating process. Notably, the optimum ratio of carbon to CoFe₂O₄ was found to be 2:1, which resulted in the highest carbon thickness. The electromagnetic properties of the samples were evaluated using a vector network analyzer (VNA) and measured S-parameters in the frequency range of 8.2 to 12.4 GHz, known as the x-band region, suitable for radar applications. The sample with a carbon ratio of 2:1 exhibited the highest total shielding effectiveness (SE) of -17 dB at approximately 10 GHz. As a conclusion, the carbon-coated CoFe₂O₄ nanoparticles showed promising potential as an effective material for shielding against electromagnetic wave pollution, particularly when the carbon coating and filler composition reached an optimal point. Additionally, the shielding effectiveness performance of the sample could be further enhanced by incorporating a conductive polymer as an auxiliary material.

Wireless communications need antennas of different sizes, shapes, frequency-bands, bandwidths, and radiation patterns due to technical requirements, physical constraints, and FCC (Federal Communication Commission) regulations. For example, S-band antennas (2 GHz~4 GHz) are used in navigation, C-band antennas (4 GHz~8 GHz) used in Air-borne RADAR, X (8~12) band antennas used in Satellite communications, and millimeter wave (40 GHz and above) antennas used in autonomous vehicles. Ultrawide Band (UWB) antennas of different frequency bands have also applications in different fields such as medical imaging, radar imaging, software defined radios, surveillance, and health monitoring of different equipment. Microstrip patch antennas of different gains, bandwidths, shapes, and radiation patterns will play a vital role in different wireless applications of future 6G systems. In this paper, we have discussed different novel designs of patch antennas at different frequency bands: V-shaped patch antenna at 2.4 GHz, and hexagonal slotted half-circular patch antenna at 4.29 GHz. We have designed antennas of different shapes for different frequencies since some applications require UWB; some applications require narrow band but higher gain; and some applications require different gain/radiation patterns at the same frequency. We have designed a patch antenna at 2.4 GHz that can be used in Wi-Fi, and UWB patch at 4.29 GHz with omnidirectional radiation pattern that can be used in energy harvesting or biomedical applications. In this paper, we have also discussed the prototype development and testing results of the novel hexagonal slotted half-circular patch antenna at 4.29 GHz.

A wide band circularly polarized planar antenna of high radiation efficiency is proposed in the present work for future generations of wireless communications requiring circular polarization in the X-band of the microwave spectrum. The main radiating part of the antenna is a rectangular turn-shaped strip that is capacitively loaded by two corner-shaped parasitic elements. The antenna is fed through coplanar waveguide (CPW) region whose ground structure is defected by etching two rectangular annular slots. The purposes of both the corner-shaped parasitic elements and the rectangular annular slots of the CPW ground plane are to increase the impedance matching and the 3 dB axial ratio (AR) bandwidth, and to enhance the antenna efficiency. The design is achieved through complete parametric study to find the optimum dimensions of the antenna. A prototype of the proposed antenna is fabricated for experimental assessment of its performance. The results obtained by both simulation and experimental measurements show that the impedance matching bandwidth is about 5.3 GHz (8-13.3 GHz); the 3 dB AR bandwidth is about 3.1 GHz (8-11.1 GHz); the maximum gain ranges from 4.5 to 5.5 dBi; and the radiation efficiency is higher than 98% over the operational frequency band.

An optimization method utilizing a multistage genetic algorithm (MS-GA) and considering parameter variations has been proposed to obtain optimal design of one-dimensional dielectric bandgap(1D D-EBG) structures with a few periods in small packaging power distribution networks. One-dimensional finite method (1D FEM) is used to improve computational efficiency and iteration speed. MS-GA consists of 3 stages: In stage 1, the population was initialized by Hamming distance, and the fitness was calculated to determine the number of EBG period. In stage 2, genetic manipulation and sensitivity analysis were used to improve local search ability and obtain preliminary results. In stage 3, cubic spline interpolation and local integral were used to reconstruct the fitness evaluation function considering parameter deviation, adjust the results and obtain the optimal parameters. Three optimized target frequency bands with center frequencies of 2.4 GHz, 3.5 GHz and 28 GHz were optimized, and Pearson coefficient was used to analyze the correlation between the parameters to better understand the influence of parameter deviation on the optimization results. The achieved results meet the optimization object within the allowable range of parameter errors, and the parameter constraints were successfully met for all three designs, with their final dimensions below 20 mm. Three-dimensional full-wave simulation software was used to simulate and analyze the stopband bands, and the simulation results were consistent with the calculation results.

A 26 × 25 mm² arbitrary-shaped antenna is constructed in this article, and it was expanded to 2 x 2 Multiple Input Multiple Output (MIMO) antenna. It has a range of 3.1 to 8.2 GHz. A T-shaped stub is employed in this instance to reduce the mutual coupling between the two ports. The effectiveness of the MIMO aerial is demonstrated using envelope correlation coefficient and radiation pattern. Additionally, it has been shown that simulated and measured results generally agree.

In this paper, a novel magnetic gear motor (MGM) with nonuniform air gap Halbach array magnetization is proposed to study the influence of temperature change on its electromagnetic performance. The inner PM adopts the Halbach array magnetization structure, which makes the inner rotor air gap have an uneven air gap structure, thereby improving the air gap flux density. In addition, the air gap magnetic field of MGM is analyzed by the finite element method (FEM), and the 3D model of the motor is established. The main losses of the motor, including copper loss, eddy current loss, and hysteresis loss are coupled to each component as a thermal source and studied by magneto-thermal coupling. The transient variation characteristics of loss distribution during MGM operation are comprehensively considered. The temperature variation of each component of the MGM with time during load operation is studied in detail. The results show that the temperature of the PM of the MGM is close to 91.8˚C when the rated load is running, and the PM of the motor does not undergo irreversible demagnetization.

Multi-vector model predictive control (MPC) of permanent magnet synchronous motors (PMSM) has two issues: selecting the optimal voltage vector (VV) combination is very complicated, and multiple prediction calculations to minimize the cost function result in a heavy computational burden; applying a VV with a short duration may generate narrow pulses, while the effect of reducing torque ripples and stator current harmonics is not obvious. The hybrid-vector model prediction flux control (HV-MPFC) strategy considering narrow pulse suppression is proposed in this paper. First, the optimal VV combination is quickly identified by the sector where the stator flux error vector is located, which lowers the control complexity and computational burden. Secondly, by the relationship between the action time of three VVs and the set time threshold, the hybrid-vector strategy to switch among three VVs, two VVs, and a single VV is employed to prevent the generation of narrow pulses. Finally, experimental results show that, compared with the existing three-vector MPC strategy, the HV-MPFC strategy effectively suppresses the generation of narrow pulses and achieves smaller torque ripples and stator current harmonics at the same switching frequency.

In order to support 5G communication, this article suggests a small, four-port MIMO antenna with a G slot. This antenna has an electromagnetic band gap (EBG) in the shape of an S that is engraved on the substrate in the space between consecutive pairs of radiating patches. The recommended MIMO antenna is constructed from an FR4 substrate and measures 48x48x1.6 mm³. Between antenna elements 1 and 2, the integrated EBG structure of the MIMO antenna can reduce mutual coupling by 10.5 dB. The suggested four port G slot MIMO antenna with an S-shaped EBG structure displays the performance in terms of ECC less than 0.0002 and diversity gain larger than 9.99 with consistent frequency band extending from 3.3 GHz to 3.7 GHz. The proposed four port MIMO antenna is designed using HFSS software, and its simulation results are measured using anritsu combinational analyzer MS2037C vector network analyzer.

A compact and novel star shaped fractal microstrip patch conformal MIMO antenna suitable for WLAN, vehicular communications (5.855-5.925 GHz) and Fixed Satellite Services (FSS) applications is proposed in this paper. Analysis of planar and conformal single element and four element MIMO antennas is presented. Proposed star shaped fractal MIMO antenna is prototyped on Polyamide substrate of geometry 104 x 30 x 0.4 mm³. It achieved an impedance bandwidth (S₁₁ < -10 dB) of 3.7 GHz operating from 4.53-7.86 GHz. Radiation patterns and surface current distribution are investigated at 5.9 GHz and 7.3 GHz center frequencies. A peak gain of 5.42 dB and 4.86 dB are obtained at 5.9 GHz and 7.3 GHz respectively. Radiation efficiency is more than 98% and MIMO performance parameters are also analyzed. Proposed conformal MIMO antenna showsfine diversity performance for WLAN, vehicular and FSS communications.

A waveguide mode solver based on boundary integral equation (BIE) method and matrix compression is developed in this study. Using an accurate discretization based on a Nystrom method and a kernel-splitting technique, the BIE method gives rise to three different formulations of a nonlinear eigenvalue problem. H-matrices are used in order to accelerate and increase the precision of the subsequent computations. Results from these investigations on a canonical photonic crystal fiber (PCF) chosen as an example demonstrate that the data sparse representation of the BIE discretization reduces the memory storage, as well as the assembly and solution times.

In XLPE cables, partial discharge (PD) is often accompanied by the generation of ultrasonic waves, which can be used to estimate the location and size of PD. Studying the propagation law of ultrasound along the cable is of great significance for establishing the mathematical model of PD and the layout method of ultrasonic detection terminal. This article adopted simulation and experiment to study the propagation law of PD ultrasound in cables. The results indicated that the propagation process of ultrasonic waves can be divided into three stages when ultrasonic waves propagate along the cables: the diffusion process with the characteristics of spherical waves, the propagation process which is rather similar to plane waves, and the transition process of both. When propagating along the cable, the ultrasonic amplitude attenuates and exhibits multi-peak characteristics as the distance increases. By analyzing the signal strength of the experimental results, it was found that the ultrasonic amplitude decays exponentially with propagation distance due to viscous heat loss of materials and the air gaps between cable layers, which provided a reference to the placement of distributed ultrasonic terminal for insulation weakness and design of spatial localization algorithm for PD.

A Coplanar Waveguide (CPW) fed antenna with a T-type slot and Partially Reflecting Surface (PRS) for gain, bandwidth, and efficiency improvement is presented. The antenna is miniaturized to get size reduction of 46.50%. The miniaturized antenna covers frequencies in C band. The presented antenna structure is easy to design and has size of 0.682λ_g x 0.99λ_g x 0.053λ_g. The PRS with parasitic patches is placed on top of the antenna at a distance of 0.25λ_g. The presented antenna design has a bandwidth of 4.42 GHz (Antenna~1) and 3.87 GHz (Antenna~2) with a percentage bandwidth of 75.81% and 59.58% respectively having average radiation efficiency above 90%. The gains obtained are 7.03 dBi and 6.12 dBi for Antenna~1 and Antenna~2. The gain has < 3 dB variation over the complete band. The obtained results support the design and make the antenna suitable for C band applications.

A compact four-element multiple-input multiple-output (MIMO) antenna is proposed for 5G applications. The offset fed antenna structure is designed from a rectangular and semicircular monopole antenna. In this novel MIMO structure, the surface current and near fields of left element are mainly concentrated toward left and that of right element towards right, and thus high isolation is achieved between left and right elements even without using any isolation technique, whereas the little surface current at the nearby edges of top and bottom elements helps in achieving high isolation. The fabricated prototype has board dimensions of 0.374λ₀×0.275λ₀, where λ₀ is the free-space wavelength at 3.3 GHz. The structure offers isolation > 20 dB between the elements over 3.3-6.3 GHz. The envelope correlation coefficient (ECC), diversity gain (DG), and mean effective gain (MEG) confirm to MIMO antenna specifications. The antenna offers stable nearly omnidirectional radiation patterns.