This paper proposes a fast coupled iterative algorithm for calculating the complex three-dimensional scattering of rough dielectric surfaces and conductive targets. The algorithm is designed for practical composite electromagnetic scattering models and establishes a coupled iterative integral equation system for the rough surface and target. Iterative calculations are performed until the specified accuracy is achieved. To improve computational speed, Physics Based Two Grid-Sparse Matrix Canonical Grid (PB-SM) acceleration algorithm and a hybrid domain basis function based on quadratic surface modeling are applied using the fast Method of Moments (MoM) for fast computation. The effectiveness of the fast coupled iterative algorithm is verified by comparing the results with those of high-precision MoM calculations. During the calculation process, error iteration curves are plotted to show that the error can be reduced to 10^-6 after 10 iterations, and the convergence rate meets the requirements of practical calculations. Based on the algorithm proposed in this paper, several examples are calculated, and the scattering variation of targets in different environments is mainly studied, and suggestions are given to improve the accuracy of target detection and identification in complex environments. The results of the study have some significance for ultra-low altitude target detection, precision strike, stealth and anti-stealth.

A low profile and high selectivity filtering slot antenna based on circular substrate integrated waveguide (SIW) cavity is presented. The proposed antenna is originated from a circular SIW cavity operating at its TM₀₁₀ mode. A cruciform slot is integrated on the top surface of the cavity, and the cavity is then split into four quarter-mode cavity resonators. In this aspect, the four similar quarter-TM₀₁₀ modes will be generated by the compact structure. By amalgamating four similar modes into a single-band, the bandwidth of antenna is widened. Based on the structure, a filtering slot antenna with central frequency of 8 GHz and bandwidth of 5.6% is designed and fabricated. Measured results agree well with the simulated ones. In addition, two radiation nulls are produced at the edges of the passband, and the selectivity in the transition band is enhanced greatly.

This paper presents a flexible wearable multiple-input multiple-output (MIMO) antenna with low specific absorption rate (SAR) and high isolation based on artificial magnetic conductor (AMC), which is applied to wireless body area network (WBAN). The antenna consists of two orthogonal antenna elements, which are connected to the ground, and the size is 45 mm×22 mm×0.1 mm. By integrating a 4×5 square artificial magnetic conductor array on the back of the antenna, the gain of the antenna is improved, and the backward radiation of the antenna to the human body is reduced. Both antenna and AMC array are printed on 0.1 mm flexible substrate liquid crystal polymer (LCP). The results of measurement illustrate that the integrated antenna operates at 5.55 GHz-6.4 GHz (14.6%), and the port isolation is better than 20 dB. At 5.8 GHz, the measured antenna gain is 7.92 dBi, and the front-to-back ratio (FBR) is 17.5 dB. The analysis results of integrated antenna placement at different parts of the human body and bending measurement show that the SAR value is reduced by 99.4%, and the measured performance is good. The proposed MIMO antenna integrated with AMC can be safely applied in wearable applications.

A miniaturized modulated scattering technique (MST) tag able to operate at millimetric frequency bands is proposed in this work. In particular, the proposed tag operates like an RFID tag, but thanks to the MST technique it does not require a radio frequency front end. The information is carried on by modulating an interrogating electromagnetic wave with a suitable change of load impedance of the tag antenna obtained by means of an electronic switch. With respect to standard RFID tags, characterized by limited operative range, MST tags can theoretically reach any distance up to kilometres. In this work, all the components of the MST tag are directly designed on-chip leading to a very compact design. In particular, the tag has been designed to operate at millimetric frequency bands up to 70 GHz. The preliminary experimental results are quite promising, and they demonstrated the capabilities and potentialities of this technique.

The purpose of this study is to design a multiband antenna using metamaterial for efficient satellite communication. The majority of the antennae described in the available research suffer from a variety of limitations, including intricate designs, great footprints, and erratic radiation patterns. Therefore, there is a significant demand for antennae that are of a smaller size but nevertheless perform well. This paper proposes a quad-band stub-incorporated split octagonal ring antenna for satellite communication-dependent wireless applications. The suggested antenna is built on an FR4 substrate that measures 22×39×1.6 mm³. CST EM studio software is used for the entire simulation. The proposed antenna resonates at four different bands, with operating frequencies ranging from 2.15 GHz to 2.30 GHz, 2.86 GHz to 3.76 GHz (due to stub 1), 4.47 GHz to 5.24 GHz (due to stub 2), and 5.67 GHz to 6.35 GHz (due to stub 3). (due to gap between the stub). The proposed antenna has resonant frequencies of 2.23 GHz, 3.28 GHz, 4.77 GHz, and 5.89 GHz, and bandwidths of 153 MHz, 9011 MHz, 7692 MHz, and 6813 MHz. Parametric analysis is used to select the best values. The designed antenna is built and tested. The measured and simulated values for return loss, gain, E-plane, and H-plane are compared, and they agree. Its dual-band operation, compact size, steady radiation pattern, and gain above 1 dBi across the whole resonating band make it suited for ISM, WIFI, WLAN, WIMAX, 5G, and C band satellite applications.

This paper addresses the bandwidth limitations inherent in microstrip patch antennas, which are commonly employed in radar applications owing to their compact size and integration convenience. To overcome these limitations, this study explores the application of Prosopis Africana conductive ink-based thick film, an innovative and environmentally friendly material. Originating from the African mesquite tree, this ink exhibits high conductivity owing to its elevated carbon content, presenting a compelling solution for enhancing microstrip patch antenna bandwidth. The research entails thoroughly examining microstrip antenna design principles and associated challenges, followed by exploring the unique properties of Prosopis Africana conductive ink. A detailed methodology outlines the fabrication process of the ink-based thick layer or film on the substrate, with simulation and measurements employed to evaluate its impact on impedance matching and radiation characteristics. Emphasizing the eco-friendliness of Prosopis Africana conductive ink aligning with green electronics trends, the study showcases its potential for advancing wireless communication systems while reducing ecological footprints. Results demonstrate a substantial bandwidth improvement exceeding 1.85 GHz, a simulation |S₁₁| return loss value of -16.19 dB, and achieved 84.5% radiation efficiency of the operating frequency at 9.5 GHz and a peak realized gain of 7.10 dB. Hence, integrating Prosopis Africana conductive ink-based thick film is a viable strategy for augmenting microstrip patch antenna bandwidth, rendering them more adept for radar applications.

Rotor segment skew pole can effectively weaken the cogging torque, but the traditional rotor segment skew pole can also cause the unbalanced axial electromagnetic force, then add load to the bearing thus affecting the performance and decreasing the service life of the motor. It is complicated to study the effect of segment skew pole by the energy method. According to the generating mechanism of cogging torque, this paper presents an easy method. The relationship between segment number and cogging torque harmonics weakening is analysed through the application of geometrical relation and Fourier series, and a simple method for determining segment number is obtained. By analysing the main source of axial force in rotor segment, a new type of rotor arrangement is proposed, which can avoid excessive axial force while retaining the effect of traditional oblique pole mode on cogging torque weakening. The correctness of the conclusion is verified by finite element simulation and prototype experiment.

Targeting the problems of traditional particle swarm algorithm easily falling into local optimum and low recognition accuracy, an adaptive learning co-evolutionary variational particle swarm optimization algorithm (ALCEVPSO) is proposed in this paper to identify the parameters of permanent magnet synchronous wind generator (PMSWG). At first, an adaptive learning strategy is adopted for the inertia weights of the PSO, and the global optimization seeking ability of the PSO is improved. After that, multiple swarm co-evolution strategies are introduced to share the best positions within sub-populations, and by this method, the algorithm's falling into local optimality is avoided. Finally, Cauchy Gaussian mixed variants are introduced, and the population diversity is enriched. The proposed method has the advantages of strong optimization ability and high search accuracy compared with the traditional particle swarm algorithm, which is shown by simulated and experimental results. By this method, the motor parameters of the permanent magnet synchronous motor can be accurately identified.

Finite-control-set model predictive control (FCS-MPC) for permanent magnet synchronous motors (PMSMs) has attracted attention due to its better theoretical performance. However, as motor operating conditions change, motor parameter mismatch can lead to intolerable prediction errors which significantly deteriorate stator current harmonics and torque ripples. To solve this issue, a finite-control-set model predictive current closed-loop control strategy is proposed. First, based on the analysis of the prediction equations, the voltage-independent and voltage-dependent parts of the prediction errors are separated. Secondly, according to the different features of prediction errors caused by zero and non-zero vectors, the decoupling of the two parts of prediction error is realized. And the PI controllers are introduced to observe the two different types of DC components respectively to make the observation more stable and accurate. Thirdly, feedback compensation is performed to modify the prediction equations. With the design of model predictive current closed-loop control, the prediction error quickly converges to the minimum. Finally, the experimental outcomes prove the effectiveness of this strategy.

In this paper, a compact quad-port Rhombus-Shaped MIMO Patch (RSMP) antenna with a complete ground structure has been designed for dual-band wireless applications. The RSMP antenna has a common patch configuration and resonates at 12.9 GHz and 16.5 GHz with the reflection coefficients of -17 dB and -25.7 dB, respectively. A rhombus-shaped slot is etched from the patch to generate dual-band frequencies. Microstrip feed lines are connected to the common patch and are used to improve the overall performance of the RSMP antenna. The RSMP antenna has gains of 9.62 dBi and 9.98 dBi at resonating frequencies. The bandwidths of the proposed MIMO antenna model are 300 MHz and 350 MHz, respectively. The proposed RSMP antenna model was fabricated and tested with the vector network analyzer Keysight N9917A for validation. The simulated and measured results for the gain, reflection coefficients, surface current distribution, radiation pattern, envelope correlation coefficient (ECC), diversity gain (DG), total active reflection coefficient (TARC), and channel capacity loss (CCL) are compared, and they are agreed well for wireless applications at Ku-band for broadcasting communications.

A substrate-integrated waveguide (SIW) miniaturization filter is proposed, which features high attenuation characteristics, effectively reduces filter loss and size, and improves frequency selectivity. The filter is miniaturized using the evanescent-mode theory and embeds a nested U-shaped resonator in the upper metal surface of the SIW. The proposed filter's equivalent circuit structure incorporates two LC parallel resonant loops with resistance characteristics that can, in turn, create two transmission zeros in the filter's stopband to enhance its selectivity. The filter has an effective size of only 0.39λ_g×0.23λ_g with a center frequency of 2.5 GHz. The -3 dB bandwidth measures 120 MHz, while the relative bandwidth is 4.8%. The insertion loss is -0.6 dB in the passband, and the return loss is more than 25 dB. Out-of-band rejection exceeds 40 dB in the range of 2.9~4.4 GHz. The measured and simulated results agree well. The filter offers benefits in terms of high rejection, miniaturization, and low insertion loss. It can be implemented in 5G (sub-6 GHz) wireless communication systems.

This paper presents a dual-band implantable antenna with coaxial probe feeding for wireless biotelemetry applications. The antenna features spiral patches, resulting in a compact size of 27 × 14 × 1.6 mm³. It can operate in two different frequency bands, 241-641 MHz and 1.17-2.06 GHz, providing coverage for the medical implant communication service (MICS) band and the industrial, scientific, and medical (ISM) band. This simple design offers improved return loss and higher bandwidths that are achieved by incorporating patch slots and shortening pins in spiral patches, representing a significant contribution to the field of dual-band antenna design for wireless biotelemetry systems. The SAR values of 48.9 mW/kg and 1.19 W/kg are achieved, which satisfy the IEEE standard safety constraints. An experimental prototype of the proposed antenna is fabricated which demonstrates acceptable return loss and VSWR.

In this exploration, our focus lies on unveiling a novel Mixed Multi-Elliptical Shaped (MMES) microstrip patch antenna, notably compact in design. Using the co-planar waveguide (CPW) port technique on an FR-4 substrate, we introduce an antenna showcasing a dual fractional bandwidth, and it spans 76.95% from 2.87 to 6.5 GHz and 53.85% from 8.06 to 14 GHz. To enhance both Gain and Directivity, our design integrates a Hexagon Cell with an Octagon Slot array reflector. This addition results in a peak gain of 8.759 dBi and a maximum directivity of 9.537 dBi at 6 GHz. Achieving optimal Gain and Directivity involved precise adjustments to the gap between the antenna and the reflector plane. The overall dimensions of our proposed antenna measure 59×59×11.67 mm³. Rigorous simulations and empirical validation strongly support the potential of this antenna for applications in BT, WLAN, and WiMAX.

Antennas are significant passive components in Microwave Imaging (MWI) system. The proposed work focuses on the design and analysis of a Vivaldi antenna of size 45×40×1.6 mm³ for breast cancer diagnosis. The proposed antenna utilizes an FR4 substrate and offers a wideband response. The suggested antenna design is based on a tapered slot antenna. The design utilizes microstrip slot line transition feed as it provides good impedance matching and wide bandwidth. The proposed antenna's design attributes like the radius of the slot and tapering rate are optimized through parametric analysis to achieve desired ultra-wideband (UWB) performance. The UWB offered by the designed antenna is 13.87 GHz (2.79 GHz-16.66 GHz). A Voltage Standing Wave Ratio (VSWR) of less than 2 is obtained for the entire resonating frequency range. The proposed antenna exhibits 60% size reduction compared to the conventional Vivaldi antenna with a peak gain and directivity of 4.77 dBi and 5.84 dBi, respectively. A breast phantom has been designed and simulated for Specific Absorption Rate (SAR) calculation. The designed structure exhibits an average SAR of 0.997\,W/kg. Further, the proposed antenna is fabricated and tested. The measured results agree with simulation findings. Hence, the compactness and radiation performance of the proposed antenna makes it suitable for breast cancer diagnosis.

We report a novel characteristic of the phenomenon of Fano resonance obtained by the interaction of incident electromagnetic waves and waveguides system formed of loop and resonators. The Green Function Method (GFM) is employed to calculate the transmittance of the incoming electromagnetic waves. Our proposed system achieve a selecting and filtering device either by total transmission or by total reflection with a very high performance. The proposed structure contains four segments of the same lengths, and asymmetric resonators (N and N' resonators) are moving in the structure. Through parameters optimization, we show that the system creates Fano resonances, which are sensitive to the variations of the segment lengths, the resonator lengths, the positions of the resonators and the physical properties of the system components. Then, the proposed system is able to filter at least two resonance modes with different frequencies. This system has potential applications in the field of microwave communication antennas.

This paper proposes a sparse array consisting of two separated generalized nested arrays. The unit element-spacing of each generalized nested array can be adjusted to multiple half-wavelengths of the incident signal. By adjusting the element-spacing, the mutual coupling effect can be greatly reduced. For this array, a direction of arrival (DOA) estimation method of quasi-stationary signals has also been proposed. By using the received signals of the separated generalized nested array, a signal subspace is obtained. Then, this subspace is filled into a higher-order signal subspace to avoid angle ambiguity. Using the higher-order signal subspace, DOAs of all signals can be estimated by spectral peak search. Simulation results show that the proposed separated generalized nested array has better than the conventional nested array performance in DOA estimation.

This paper presents some opportunities in the development of antennas when using Distilled Water (DW) as a dielectric with high relative electrical permittivity (ε_r(DW) = 80). By embedding an antenna in DW, the electrical growth of the antenna is achieved without significantly increasing its physical size. In other words, the antenna will resonate at frequencies lower than those to whom it originally resonated. It was also found that the antennas developed through this technique are usually multiband antennas, offering various resonance frequencies at frequencies lower than the original ones. Finally, the change in radiation patterns was also verified through the use of this technique that allows beamforming to be carried out by varying the size and shape of the DW block. The development of more efficient antennas has a direct impact on the energy consumption of wireless systems, which represents an effective contribution to climate change mitigation, the reason that the improvement of antennas is a very important research area.

Since the performance of the spectral moment estimation algorithm commonly used in engineering degrades under the conditions of low SNR, this paper introduces the Extreme Learning Machine (ELM) to the spectral moment estimation of weather signals based on the correlation of the signals of adjacent range cells. To solve the problem that the hidden layer nodes of ELM algorithm are difficult to be determined, the Bidirectional Extreme Learning Machine (B-ELM) algorithm is applied to achieve the high resolution of spectral moments. Firstly, to improve the SNR of the training samples, time-domain pulse signals are converted into weather power spectrum by Welch method. Then, the parameters of the B-ELM hidden layer nodes are directly calculated by backpropagation of network residuals. The model parameters are optimized according to the least-squares solution, where the optimal number of hidden layer nodes is determined adaptively. Finally, the optimized B-ELM model is employed for the spectral moment estimation of weather signals. The algorithm is validated to be fast and accurate for spectral moment estimation using the measured IDRA weather radar data and is easy to implement in engineering.

To enhance the reaction speed, suspension performance, and anti-interference ability of a Bearingless Induction Motor (BIM) operation control system, an improved Active Disturbance Rejection Control (ADRC) technique is proposed. Firstly, the ADRC in the suspension system and the ADRC in the torque system are designed, respectively, using the BIM's mathematical model as the basis. Furthermore, the error integral signal is incorporated into the nonlinear state error feedback control law of the standard ADRC controller. Subsequently, a novel optimal control function is formulated using the fitting method, which is based on the original fal function. This approach effectively mitigates the impact of output signal fluctuations at the inflection point of the fal function. Simultaneously, the RBF neural network technique is employed to autonomously adjust the control parameters of the extended state observer, therefore enhancing the system's observation capability. Ultimately, the classic ADRC control strategy and the IADRC strategy are compared through simulation and experimentation. Simulations and experimental findings demonstrate that the suggested control method enhances the BIM control system's response time and resilience to external disturbance. Additionally, it enhances the levitation performance of the BIM system.

The characteristics of nonlinear and strong coupling of a bearingless permanent magnet synchronous motor (BPMSM) greatly affect the improvement of its control performance. In the traditional decoupling control of least squares support vector machine (LSSVM) inverse system, the kernel function parameter σ and regularization parameter c are determined according to the empirical value, but not the nonoptimal value, so large error exist in the decoupling control. Therefore, this paper proposes a decoupling control method of LSSVM inverse system based on improved grey wolf optimization algorithm (IGWO). Firstly, the working principle of the BPMSM is described, and the mathematical model is derived. Secondly, the reversibility of the BPMSM is analyzed, and the σ and c of LSSVM are optimized by IGWO, before establishing a generalized inverse system for decoupling control. Thirdly, the simulation tests of the speed regulation and anti-interference are carried out, which show that the decoupling performance of the proposed method is better than the traditional LSSVM inverse system method. Finally, the dynamic experiments, static experiments and anti-interference experiments are carried out. The feasibility and superiority of the proposed method are verified according to the built experimental platform.