This manuscript proposes a hybrid energy harvest and management system to manage harvested ambient thermal and radio frequency (RF) energy and provide constant voltage for an electronic water meter. It mainly includes an antenna, a rectifier, thermoelectric generators (TEGs), and an energy management circuit. The antenna harvests the ambient RF power, and the rectifier converts it to DC power. The harvested RF and thermal powers are stored in a capacitor and managed by an FEH710 energy management circuit to power an electronic water meter. Eight thermoelectric generators convert thermal energy into DC power. The proposed hybrid energy harvesting and management system has been evaluated by simulation and measurement. The antenna's reflection coefficient and peak gain at 2.45 GHz are -30 dB and 3.6 dBi, respectively. The rectifier's measured RF-DC power conversion efficiency (PCE) is 66.7% at 0 dBm. As a demonstration, a commercial electronic water meter worksstably by the harvested ambient RF and thermal energy. The proposed hybrid energy harvesting system is expected to find potential practical applications for the Internet of Things (IoT) in environments with RF radiation coverage and temperature gradients.

The internal structural details of unknown structures are very helpful to our personnel in carrying out activities during anti-terrorism operations and emergency disaster relief operations in urban environments. According to multipath identification and propagation mechanism separation technology, a building structure perspective imaging algorithm based on the ray-tracing model is proposed in this paper by making full use of the rich multipath delay power spectrum information and gradually filtering the multipath. Based on the imaging results taking overall consideration of all the propagation factors involved, the presented study is used to obtain the intricate geometric structure of indoor buildings. The original approach is then verified by using measured data, and the proposed algorithm is further optimized by extracting the internal wall structure of the building scene based on the Hough transform algorithm. In comparison with the real wall of the building, the average error of the inverse building wall position using simulated data is 0.071 m, and the average error of the inverse building wall position using the measured data is 0.355 m.

The electromagnetic characteristics analysis of the scattering signals from targets, which usually exist or are hidden in the surrounding environment, is one of the necessary prerequisites for the reliable reception of echo signals. Utilizing the GNSS signals as an opportunistic illumination source for detecting maritime targets has vast development prospect and scientific application value. GNSS signals, including GPS signals, are the right-hand circular polarization waves at L-band. Therefore, in this study, a comprehensive electromagnetic composite scattering model is established under circular polarization, which encompasses sea surface scattering, target single scattering, target multiple scattering, and coupled scattering between the target and sea surface. Then, the research investigates the variation characteristics of different scattering components (including the scattering of sea surface, the first, second, and third-order scattering of target, the total scattering of target, the coupled scattering of target induced by the reflection waves from sea surface, and the coupled scattering of sea surface induced by the reflection waves from target) in the composite scene under different polarizations, incident angles, wind speeds, and headings. The results indicate that the scattering of sea surface under LR polarization (which means that the polarization states of scattering and incident wave are left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP), respectively) is significantly greater than that under RR polarization, while the opposite trend is observed for the target. Therefore, in the applications such as the detection and identification of ship targets on sea surface, it is better to choose the right-hand circular polarization channel to receive the scattering echo signal from target, which could effectively suppress the scattering echo of sea surface. These findings are of crucial significance in enhancing the effectiveness and accuracy of maritime target detection.

Wearable textile antennas have obtained remarkable attention in various medical fields due to their ease of integration and flexibility. This paper puts forward an Ultra Wide Band (UWB) Compact Textile Wearable Antenna (CTWA) for Wireless Body Area Network (WBAN) applications. The proposed antenna is a semicircular slotted elliptical antenna with an L shaped stub and a partial defected ground plane. The antenna is fabricated on denim jeans (ε_r = 1.77) and has an overall dimension of 27 × 28 × 0.7 mm with an operating frequency range 3.01-15.98 GHz, radiation efficiency of 83.5-90.11% and maximum gain of 5.81 dBi. Structural deformation studies including human body loading of the antenna are carried out, and the performance of the antenna is found to be stable. The proposed antenna has a low profile and high fractional bandwidth (137%) compared to the UWB wearable antennas reported in the literature. The calculated Specific Absorption Rate (SAR) of the antenna at the frequencies 4,7 and 10 GHz are 1.2, 1.06, and 1.58 W/Kg, respectively, which lies within the FCC (Federal Communications Commission) standard. The proposed CTWA is compact, flexible, wearable, and robust, which makes it suitable for on-body WBAN applications.

In this paper, a high gain antenna using Frequency selective Surface (FSS) is proposed. The compact structure is designed from a circular Ultra-wide band (UWB) monopole. Higher order modes of UWB antenna are suppressed by decreasing the thickness of the monopole, ground plane dimensions and increasing the gap between the ground plane and the monopole. Symmetrical portion of circular monopole is etched to form a semicircular monopole, and an off-set feed is employed. Dual band characteristics and miniaturization are achieved by etching horizontal and vertical slots and reducing ground plane dimensions. An FSS reflector is designed for gain enhancement. This miniaturized antenna offers less blockage and therefore, higher gain improvement when an FSS is used as a reflector.

In this paper, analytical formulas for tensor holographic impedance metasurface (THIMS) are presented to generate circularly polarized (CP) circular Airy orbital angular momentum (OAM) multibeams with flexibly independent control of the beam direction, polarization and OAM mode. As an example, a millimeter-wave THIMS is designed to generate CP circular Airy OAM dual beams: Beam-I: (θ1 = 0, φ1 = 0, LHCP, l = +1, 36 GHz), Beam-II: (θ2 = 0, φ2 = 0, RHCP, l = 0, 30 GHz). To the knowledge of the authors, for the first time, the THIMS generates circular Airy beams. Compared with the published metasurface on Airy beam, the created THIMS has the following advantages simultaneously: dual frequencies, dual CP, small size 30λ₀ at 30 GHz, high conversion efficiency (CE) (above 40%), long nondiffractive distance (ND) (up to 134.4λ₀), high OAM purity (above 89%), co-modulation for polarization, beam direction and OAM mode. The generated circular Airy OAM beams can be used in near-field scenarios such as high-efficiency wireless power transmission (WPT), high-capacity communication systems, and high-resolution imaging.

The THz spectrum (0.1-10 THz) is a region between optics and electronics, and it is still not fully explored and is unlicensed. Recent studies show that it will bring a revolution in technology, especially in the field of communication. Future communication technologies such as 6G and Terabit DSL will utilize this THz band as it has the capability to support high data rates in Tbps. For designing an efficient system that propagates these THz waves with low loss, it is required to understand the propagation channel properly. THz channel modeling is at its infancy stage, and a detailed investigation of channel behavior is required to study the efficient propagation of THz waves. In this study, the methods applied to the modeling of the THz channel are discussed in detail. Although channel modeling is a broad topic here only the methods and techniques are discussed along with their advantages and limitations. Lastly, the challenges and the future direction in the field of THz channel modeling are also discussed.

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.