With the increasing use of radar technology across various fields, electromagnetic pollution has become a growing concern, posing significant risks to human health. Consequently, there is a rising interest in developing wearable, flexible fabric-based absorbers that can efficiently absorb electromagnetic waves. However, the low dielectric constant of fabrics makes it challenging to achieve high absorption rates and broad bandwidth at low frequencies. To address this issue, in this study, we introduce a fabric-based broadband metamaterial absorber using felt as the dielectric substrate. The absorber features a centrosymmetric square block array design, incorporating a PU conductive film as the surface resonant material. By fine-tuning the parameters of each component in the absorber's equivalent circuit and optimizing structural parameters, the absorber achieves an extended bandwidth from 3.92 to 15.25 GHz, with a relative absorption bandwidth of 118.21%. Impressively, in the lower frequency C-band, the absorber maintains an efficiency of over 95%. The absorber was fabricated using the ``cut-transfer-paste patterning method.'' Testing results demonstrate that it is insensitive to incident angle and polarization and retains excellent absorption performance even when being bent.

RF rectifier circuits are critical to powering IOT sensors through energy harvesting process, allowing devices to operate without conventional batteries. This paper presents an efficient and dual-band RF rectifier circuit working at 0.915 GHz and 2.45 GHz frequencies which could be used in IOT power sensor devices. The design of a dual-band matching circuit, which is a key element of the RF rectifier, is discussed, and closed-form expressions are derived to extract the most significant parameters. In order to simplify the matching circuit, only three microstrip line sections are required in this design. The first line makes the structure independent of frequency, and the second and third lines are used to transfer the desired impedance to 50 Ohm of the source. For validation, a dual-band RF rectifier circuit using SMS7621-079LF Schottky diode is fabricated. The measured results show that the fabricated rectifier can achieve power conversion efficiency (PCE) around 65.7% and 62.4% (with a load resistance of 2500 Ohm and 5 dBm input power) at 0.915 GHz and 2.45 GHz, respectively. The dual-band and high-efficiency features of the proposed rectifier make it suitable for energy harvesting (EH) systems to power IOT sensor devices.

The article presents a method that allows for the high gain of a stacked microstrip antenna on an air substrate in an ultrawide frequency range. The method uses an active exciter in the form of a modified E-shaped patch, as well as four single-sided bowtie passive elements placed in the corners above the active one. The active element can match an antenna in an ultra-wide frequency range (up to 100%) with an impedance bandwidth matching of 10 dB or better, whereas passive elements are able to produce unidirectional radiation in the range of approximately 70-80% with a gain of more than 10 dBi. Based on the method under study, an ultrawideband antenna design was made which operates in a frequency band of 3,915 to 11,046 MHz (95.3%) with an impedance bandwidth matching of 10 dB and a bandwidth about 83% with |S₁₁| ≤ -15 dB; the usable bandwidth with a gain of more than 10 dBi in the normal direction to the antenna plane with a cross-polar discrimination more than 55 dB is 77% (3,925-8,837 MHz). At frequencies below 4 GHz and above 9 GHz, the phase center shifts, and accordingly, the main lobe of the radiation pattern (radiation maximum) deflects. All antenna elements (one active and four passives) are made of sheet metal (e.g., stainless steel) and are connected to the conductive screen by steel or dielectric racks. The antenna dimensions are 1.05λ_max × 1.2λ_max × 0.1λ_max (1.7λ₀ × 1.9λ₀ × 0.2λ₀). Owing to its high performance, the antenna may be used as a measuring device in radio monitoring systems or in laboratories.

The wideband gap-coupled configuration of an E-shape microstrip antenna, with two C-shape microstrip patches and loaded with a parasitic printed rectangular loop element, is proposed. In 1200 MHz frequency range and on a substrate thickness of 0.11λ_g, with an optimum inter-spacing between the frequencies of TM₁₀ and TM₀₂ resonant modes of the rectangular patch along with TM₂₀ resonant mode frequencies on the parasitic C-shape and printed rectangular loop element, the maximum reflection coefficient bandwidth of 945 MHz (68.11%) is achieved. The gap-coupled antenna offers broadside radiation characteristics across the complete bandwidth with a peak broadside gain of 9 dBi. Design methodology to realize wideband gap-coupled configuration in different frequency ranges is presented which yields similar result. The antenna response is experimentally verified, which yields close agreement against the simulated result.

Wireless communication is an essential part of future smart mines. However, the complex structure of mines, especially curved mine tunnels, makes the coverage of wireless signals drastically reduced compared to the ground, which increases the difficulty of wireless communication inside the mine. In order to improve the transmission characteristics of wireless signals in the underground non line of sight (NLOS) region, a new passive reconfigurable intelligent metasurface (PRIS) is proposed, which realises the reconfigurable characteristics of the PRIS beam through the principles of passive coding and splicing, and can be applied to different turning angle tunnels. Finally, the PRIS with different radiation directions is designed and simulated in the simulation software, and loaded into different turning angle tunnels for the simulation of tunnel power distribution. By comparing with the simulation results of unloaded PRIS, the PRIS is the most effective when the turning angle is 50˚. The overall power intensity of the tunnel is improved by 25 dBm, and the overall power intensity of the tunnel is improved by 14~17 dBm at other turning angles, which proves the effectiveness of passive splicing metasurface in the application of underground wireless communication blindness mending scenarios.

A non-standard rectangular waveguide-to-coaxial converter designed for the X-band (9.3-9.5 GHz) is presented. This converter builds upon traditional coaxial probe coupling and stepped contact feeds by integrating a Chebyshev impedance transformer and stepped impedance matching technique. The proposed improved converter features a coupling probe combined with a stepped contact, enabling a vertical feed configuration from the bottom. This design offers an effective option for optimizing array antenna layouts. Simulation results indicate that within the operational frequency range, the rectangular waveguide-to-coaxial converter achieves |S₁₁| less than -27 dB and |S₂₁| greater than -0.04 dB. Practical measurements for non-standard rectangular waveguides show a VSWR below 1.1 across the working frequency band.

This article presents millimeter wavelength measurements of the mass normalized extinction cross section (extinction efficiency) of thin copper circular discs at broadside incidence. The extinction efficiencies of the discs were measured as a function of diameter and thickness at a fixed frequency of 35 GHz. The measurements cover a wide range of diameters and thicknesses and were compared with the approximate numerical solution of the problem provided by the CWW code. A good agreement between the measurements and CWW code was achieved after applying the extinction paradox for small particles with high index of refraction to the CWW code calculations.

In this article, a fractal slotted metamaterial inspired multiband antenna for wireless communication applications is presented. The proposed structure incorporates the fractal formation of a radiating patch attached with metamaterial SRR cell and rectangular slotted partial ground plane to cover multiple wireless standards. The antenna is printed on FR4 epoxy substrate material having the thickness of 1.6 mm and relative permittivity of 4.4. The antenna has compactness in size as 37×22×1.6 mm³ and achieves five wireless communication modes, including S band (2.4 GHz; WLAN: IEEE 802.11g), S band (3.65 GHz; WiMAX: IEEE 802.16e), C band (5.0/5.8 GHz; WLAN: IEEE 802.11a/j), X-Band (Satellite communication, radar, terrestrial broadband, space communication), 5G NR bands (n41: 2.496-2.690 GHz, n46: 5.15-5.925 GHz, n47: 5.855-5.925 GHz, n53: 2.483-2.495 GHz, n102: 5.925-6.425), and Lower Ku band (Molecular rational spectroscopy). The antenna also showcases consistent radiation characteristics, gain, and efficiency across resonant bands crucial for obtained resonant bands regarding multi-standard wireless applications. It attains an optimized peak gain of 4.38 dBi and a radiation efficiency of 86.23%.

This article proposes an 8-port MIMO antenna based on double-negative metamaterial Split Ring Resonators (SRRs) for three-dimensional (3D) non-planar applications, such as hotspots. The antenna features eight radiators arranged orthogonally to each other, placed in two perpendicular planes, operating at 3.5 GHz. Each resonator incorporates six embedded SRRs to enhance the metamaterial behavior, achieving a 40% size reduction compared to a conventional disc monopole at the same frequency. Simulated and measured results demonstrate excellent performance for MIMO applications, with Envelope Correlation Coefficient (ECC) values below 0.001 and Diversity Gain (DG) around 20 dB. The Total Active Reflection Coefficient (TARC) bandwidth is approximately 930 MHz at the -10 dB threshold. The S-parameters indicate excellent electromagnetic isolation between radiators exceeding 20 dB, and a very low cross-polarization level below -30 dB. However, the main limitation of this design is a reduction in gain, an expected result.

This paper presents a multifunctional antenna with high isolation for interweave and underlay cognitive radio (CR) applications. The proposed antenna consist of an ultra-wideband (UWB) antenna (ANT1) for sensing and communication in UWB spectrum range and a frequency reconfigurable antenna (ANT2) for communication over frequency ranges from 3 to 3.7 GHz and 3.8 to 5.6 GHz. The proposed antenna is designed on an FR-4 substrate 50 × 65 × 1.6 mm³ with a shared ground plane. A square slot and a rectangular stub is introduced in the ground plane to achieve -10 dB wide impedance bandwidth and good isolation over the frequency range of 1.8 to 12 GHz. An underlay CR operation is attained with a UWB ANT1 with reconfigurable band notch of 2.76 to 3.7 GHz by introducing a U-shaped slot. The interweave operation is obtained by incorporating ANT1 and ANT2 in a same substrate. ANT1 without notch band is used for sensing spectrum and ANT2 with reconfigurable frequency is used for communication. The proposed antenna attains both interweave and underlay operations with inter-port isolation greater than 17 dB all over the proposed UWB and communication band.

To solve the problem of poor control performance of internal permanent magnet synchronous motors (IPMSM) due to parameter perturbations and external perturbations when adopting mode-free sliding mode control (MFSMC) algorithm, a double-closed-loop model-free super-twisting terminal sliding mode control (MFSTTSMC) algorithm of IPMSM based on third-order super-twisting observer (TOSTO) is proposed. Firstly, according to the new model-free control (MFC) algorithm, an ultra-local expansion model of IPMSM speed-current double closed-loop is established. Secondly, based on the ultra-local expansion model, a double closed-loop MFSTTSMC is designed to achieve global rapid convergence of system state errors. At the same time, a TOSTO is designed to estimate the disturbance in real time and carry out feedforward compensation, which enhances system robustness. Finally, the viability and superiority of the proposed control algorithm is demonstrated through simulation and experiments.

Through the analysis of experimental data, it is found that the optimal communication frequencies of mine tunnels with different cross-sections are different. These optimal operating frequency bands (580-600 MHz, 806-826 MHz, 1427.9-1447.9 MHz, 2401.5-2481.5 MHz, 5150-5600 MHz) are not only numerous, but also wide-ranging. Meanwhile, because the wireless repeater in the mine tunnel has great restrictions on the antenna size, the antenna has to be designed in a very small range of transverse size. In this paper, an ultra-narrow sized multi-frequency dipole (0.41λ × 0.04λ) is proposed to cover the optimal communication bands of underground mine tunnels with different cross-sections. This multibranch dipole consists of three main parts: lateral long branch, middle short branch, and end-loaded reverse branch. By adjusting the length of the two lateral long branches and utilizing the high harmonics, the antenna covers the lowest and highest operating bands that differ by a factor of seven. The middle short branch is one of the contributors to 1.4 GHz band. Meanwhile, the performance of the antenna at high frequencies is optimized by adjusting the distance between branches. The bandwidth of 1.4 GHz band is expanded by the loaded reverse branches. The test results are in good agreement with the simulation data, and the antenna covers all the optimal communication frequencies of underground mine tunnels with different cross-sections. Its peak gain at the resonance point is greater than 0 dBi, and the structure is simple.

To filter out the high harmonic content of the back electromotive force (EMF) in the conventional sliding mode observer (SMO), a novel flux SMO (FSMO) is designed in this paper. The feedback matrix is designed to replace the external filter or other modules, and its higher-order feedback characteristics further enhance the convergence of the FSMO. The Lyapunov function is used to assess the stability of the FSMO. Importantly, a compensated phase-locked loop (CPLL) with an angular compensation strategy is used to extract both position and speed information, resulting in less speed fluctuation and lower position estimation error. Furthermore, the simulation model and experimental platform are developed to evaluate the reliability of the proposed method. Both simulated and experimental results confirm that the proposed hybrid control algorithm performs well in both steady state and dynamic one, high or low speed of the system, with suppressed harmonics of 50.1% and 7.3%, respectively, and an improved response time of 54.1%, providing a concrete program for sensorless control of permanent magnet synchronous motors (PMSMs).

The time-varying amplitude error and phase error in the multi-channel will affect the system performance of Range Digital Beam Forming-Synthetic Aperture Radar (RDBF-SAR), which will lead to the elevation of the side lobes amplitude of the echo signal, thus affecting the quality of space-borne synthetic aperture radar (SAR) images. A multi-channel error compensation method for space-borne RDBF-SAR is proposed in this paper. The echo signals of each channel are aligned in the frequency domain. For the amplitude error, the amplitude error compensation factor is obtained by comparing the amplitude of each channel signal with the amplitude of the reference channel signal. For the phase error, the phase error compensation factor is obtained by conjugate multiplication of the phase of each channel signal and the phase of the reference channel signal. Reduce the amount of calculation by averaging. This method can well compensate the amplitude error and phase error, suppress the elevation of the echo side lobe, and make the synthetic aperture radar image more focused and accurate. Finally, the effectiveness of the method is verified by simulation experiments. Under the simulation conditions in this paper, the amplitude compensation reduces the side lobes pulse compression amplitude by 2~10 dB, and the phase compensation reduces it by -1~9 dB.

An innovative nonlinear (NL) modelling of K-band power amplifier (KPA) designed and fabricated in Gallium Nitride (GaN) technology operating at frequency f0=24 GHz is investigated in this paper. Two KPA prototypes are characterized by single- and double-frequency tests (SFT and DFT). Then, fitting memory NL model from SFT established for input-output power (Pin-Pout) characteristic @ f0 enables to the confirmation of KPA performance. Accordingly, the KPA presents 27.8 dB gain when Pin increases from -5 dBm to 20 dBm, 40.8 dBm saturation output power, and 38.6% saturation power added efficiency (PAE). Moreover, the DFT with f1=23.995 GHz and f2=24.005 GHz enables the assess to the third-order intermodulation distortion (IMD3) which is assessed from 10.4 dBc to 35 dBc. The KPA critical IMD3 is identified with the Pout variation range from 16.35 dBm to 36.35 dBm. The developed NL model is useful in the future for the electromagnetic interference prediction of multi-carried front-end transceiver communication system due to NL distortion signal.

This study presents a comparative analysis of Direct Torque Control with Space Vector Modulation (DTC-SVM) and Finite Control Set Model Predictive Control (FCS-MPC) applied to five-phase induction motors. Five-phase induction motors offer enhanced performance, reliability, and efficiency over traditional three-phase motors, making them suitable for high-reliability applications. The performance of DTC-SVM and FCS-MPC is evaluated through experimental implementation on a 3.5 kW five-phase induction motor, focusing on both dynamic response during speed reference changes and load variations, and static response, under steady-state conditions, as well as energy quality, specifically stator voltage and current. Experimental results show that FCS-MPC provides superior dynamic response, effectively managing speed changes and load variations, while DTC-SVM, owing to its fixed switching frequency, excels at reducing torque ripple and minimizing stator current harmonics. The choice between DTC-SVM and FCS-MPC depends on the application's needs, weighing dynamic performance, torque stability, and harmonic content. This study provides valuable insights for optimizing five-phase induction motor control and encourages future research to refine these methods or develop hybrid approaches that combine their strengths.

Synchronous reluctance motor (SynRM) has been a hot research topic in recent years. In this paper, a composite speed controller based on the concept of super-twisting sliding mode (STSM) control is designed and innovatively applied to SynRM. For current control, the maximum torque per ampere (MTPA) strategy is used. For torque control, a design method based on an STSM controller is given. In order to solve the chattering phenomenon existing in STSM, a simple structure disturbance observer (DOB) is further introduced as a feed-forward compensation to offset the disturbances. A novel composite sliding mode speed controller is formed based on DOB and STSM. By using Matlab/Simulink, a composite sliding mode speed control system was built. The characteristics of the motor such as current, speed, and torque were researched. Compared to the STSM controller, the speed overshoot of the new controller is reduced by up to 50% (for no-load start). The speed drop is reduced by up to 75% (for sudden load), and the recovery time is shortened by up to 50%. The results show that the designed composite speed control system has better dynamic performance.

This paper proposes a novel knowledge-based neural network approach that, in the absence of specific device SPICE models, can utilize the measured data of actual diode devices to map the existing diode coarse model to a more accurate package model through neural network mapping techniques, thereby achieving precise and efficient modeling of the small-signal characteristics of diode devices. A knowledge-based neural network model for packaged diodes is proposed, which enhances modeling accuracy by learning the discrepancies between the diode coarse model and the actual device data. A training method for rapid parameter adjustment is suggested, where the neural networks within the input and output packaging modules automatically learn and adjust, continuously optimizing their internal parameters to enhance modeling efficiency. Modeling experiments conducted on the measurement data of the MA4AGFCP910 diode show that the proposed packaged diode model can effectively and accurately match the small-signal characteristic data of the diode device.

This study presents a technique to enhance the bandwidth of substrate-integrated dielectric rod antennas. The technique involves adding a tapered grating at the antenna input, which improves impedance matching. The tapered grating converts some of the guided mode fields into leaky mode fields, leading to improved matching and broader bandwidth. The effectiveness of this approach is demonstrated through simulations and measurements, showing significant bandwidth enhancement in both X-band and Ku-band designs. The design parameters and optimization process are detailed, and the scalability of the technique is confirmed by its successful application to different frequency bands. A design for X-band demonstrates the effectiveness of this technique, yielding a bandwidth of 40%. Additionally, the technique is applied to a previously reported Ku-band design, resulting in an improved bandwidth of 52%, up from 36%. The paper concludes that the proposed tapered grating is an effective approach to enhance the bandwidth of substrate-integrated dielectric rod antennas, particularly for medium or high-gain applications.

The finite set model predictive control (FCS-MPC) method for quasi-Z-source inverter-permanent magnet synchronous motor (QZSI-PMSM) system suffers from the problems of unclear linkage between control objectives, complex control system, and poor control performance. A three-phase duty cycle modulation-based model predictive control (TDCM-MPC) strategy without cost function is proposed. In this strategy, the control objectives are converted firstly to make a connection between the control variables of inverter-side and motor-side, and based on it construct a system of nonhomogeneous linear equations to calculate the three-phase duty cycle. In addition, the three-phase duty cycles may have a secondary correction according to the size of the capacitor voltage error to realize the overall control of the four control variables. Finally, the driving pulse is generated based on space vector modulation (SVM) to obtain smaller steady-state ripples. The experimental results show that, compared with the conventional FCS-MPC, the proposed TDCM-MPC strategy reduces the computation of the control system and can obtain better control performance.