In this paper, a WiFi-UWB multiband monopole antenna is designed, fabricated, and tested based on the characteristic mode theory, which mainly consists of an L-shaped metal, an ``ok''-shaped metal radiator, and a T-shaped metal patch. The substrate dimensions are 40×43×1.6 mm<sup>3</sup>, featuring a rectangular ground plate at the substrate's bottom. The ``ok''-shaped metal on the upper surface is composed of a metal ring and a curved finger-shaped metal. To improve impedance matching and broaden the bandwidth, strategic modifications are implemented. Specifically, a rectangular slot is introduced at the top of the L-shaped metal, and the T-shaped metal is rotated 90° counterclockwise and positioned beneath the ``ok''-shaped metal. The microstrip feed line, constructed from metal, incorporates a feed point. Simulation results indicate that the antenna effectively covers the frequency ranges of 2.30-2.50 GHz and 3.65-9.77 GHz. At the resonance point, the maximum return loss is below -40 dB, signifying superior directional radiation characteristics. The antenna design is characterized by a wide frequency band, simple structure, and holds significant practical value for multi-frequency communication.

A tiny electromagnetic band gap (EBG) based microwave sensor with dual-band operation for dielectric characterization of Liquids is presented in this work. The suggested design uses a suspended microstrip line placed over the stack dual-band type EBG (SD-EBG) unit cell at 2.40 GHz and 2.98 GHz. To achieve the dual band characteristics, the stack type of EBG with different patch sizes and offset vias is used. To validate the sensor performance, absolute solution of butan-l-o1, methonal, and water are considered as liquid under test (LUT) and loaded in transparent polypropylene (PP) material, and the maximum sensitivity of 1.14% from the first resonance with maximum Q-factor of 137.5 from the second resonance is achieved with frequency detection resolution of 27.4 MHz. The size of proposed SD-EBG based sensor is 54.95% and 39.02% of that of planar EBG based sensor and cesaro fractals EBG based sensor.

The paper details the development of an innovative Ultra-Wideband (UWB) Circularly Polarized (CP) Multi-Input Multi-Output (MIMO) antenna. Drawing inspiration from an Electromagnetic Band-Gap Structure, the antenna incorporates two compact electromagnetic bandgap cells strategically positioned near the feedline. The result is a sophisticated triple-band notched planar antenna configuration. To enhance its performance, a slot and a stub are strategically added to the ground plane, effectively broadening the Axial Ratio Bandwidth (ARBW). This carefully designed setup achieves a wide ARBW while simultaneously rejecting interference at 3.5, 5.5, and 8.2 GHz. Notably, the MIMO antenna demonstrates an axial ratio spanning from 3 to 10.4 GHz, coupled with an impedance bandwidth ranging from 3.1 to 10.6 GHz. Diversity features of the proposed structure are quantified through three key parameters: ECC (Envelope Correlation Coefficient) greater than 0, TARC (Total Active Reflection Coefficient) surpassing 10, and DG (Diversity Gain) exceeding 9.7. These parameters collectively indicate robust diversity characteristics, underscoring the antenna's efficacy in challenging communication scenarios. Practical implementation involves the use of FR4 dielectric substrates, with precise measurements of 42.7×55×1.6 mm³. This meticulous construction ensures the realization of the proposed structure's theoretical framework, highlighting the antenna's potential applicability in advanced UWB communication systems.

A novel multiband microstrip patch antenna (Antenna-1) is introduced in this paper to target the frequencies of interest required for RF energy harvesting applications, including mobile DCS (Digital Cellular System), mobile LTE (Long Term Evolution), mobile 5G, WLAN (Wireless Local Area Network), and WIMAX (Worldwide Interoperability for Microwave Access) services. The simulated results for the proposed antenna showed outstanding performance. The antenna supports a high number of total (11) eleven operating frequencies and covers all of the frequencies of the 2.4 GHz (IEEE 802.11) band, as well as the downlink frequencies of mobile DCS 1800 and the downlink frequencies for mobile LTE/5G (Band 68). The proposed antenna has achieved a high gain for most of its resonating frequencies, with a high gain of (4.49 dBi) at the frequency of (2.4527 GHz), and a peak gain of (6.349 dBi) at the frequency of (3.95 GHz). Furthermore, the proposed antenna achieved a high bandwidth capacity of (677 MHz) at the resonating frequency of (5.2 GHz), which covers a lot of frequencies utilized by WLAN, WIMAX, and mobile LTE services, making it a suitable antenna for radio frequency energy harvesting applications. Good agreement between the measured and simulation results was observed.

In this paper, an SM-PB (Sparse Matrix Canonical Grid method-Physics Based Two Grid) acceleration algorithm is proposed which can be used to calculate electromagnetic scattering from two-dimensional rough surfaces with large dielectric constants. Firstly, a two-dimensional rough surface model is established based on the Monte Carlo method and Gaussian spectral function, and a conical incident wave with Gaussian characteristics is introduced to eliminate the error caused by artificial truncation of the rough surface. In the scattering calculation, the integral equation of the rough surface is processed by the SMCG algorithm, and then the matrix equation is further processed by applying the PBTG algorithm to decompose the matrix equation into the very near-field matrix, near-field matrix and far-field matrix. The FFT method is then used to calculate the matrix vector product during the iteration for fast computation. The proposed algorithm and the MOM algorithm were compared from the perspectives of computational accuracy and efficiency. Through comparison, it was found that the two algorithms produced highly consistent results, validating the effectiveness of the proposed algorithm. The proposed algorithm demonstrated a significant advantage in computational efficiency, with considerable efficiency also observed for large-scale rough surfaces. The electromagnetic scattering from rough surfaces with large dielectric constants was calculated, and the influence of the correlation distance r_d and dielectric constant on the electromagnetic scattering characteristics was investigated. It was found that it is important to set a reasonable value of r_d in order to balance calculation accuracy and calculation efficiency.

Magneto-acousto-electrical tomography (MAET) is an imaging method generating a source current under excitation of both static magnetic field and acoustic field, and electrodes are used to detect the electrical signal to further reconstruct conductivity image. Previous studies ignored the non-uniformity of magnetic field. However, the reconstructed image will introduce artifacts due to magnetic field inhomogeneity, which is small but cannot be neglected. We analyzed the characteristics of magneto-acousto-electrical signal under uniform and inhomogeneous magnetic fields in simulation. This paper deduces the relation of magneto-acoustic signal generated by inhomogeneous static magnetic field, and reconstructed conductivity image under non-uniform static magnetic field through synthetic aperture imaging. Furthermore, to verify the validity of the theory, an experimental platform was built to reconstruct the conductivity of phantom. In clinical applications, non-uniform static magnetic field can achieve a fully open magnetic field structure, which is much more friendly for inspection of patients with autism and even children. Permanent magnets that generate non-uniform static magnetic fields have the advantages of smaller size, lighter weight, and lower cost than magnets that generate uniform static magnetic field, which can effectively optimize equipment space.

The positive-definite stability analysis (PDSA) is presented as a technique complementary to the companion-matrix stability analysis (CMSA). The PDSA is used to analyze the stability of marching-on-in-time (MOT) schemes. The heart of the PDSA is formed by the analysis on particular linear combinations of interaction matrices from an MOT scheme, which are assumed to be real-valued. If these are all positive definite, then the PDSA guarantees the stability of the scheme. The PDSA can be of a lower complexity than the full CMSA. The construction of the PDSA is shown and applied to two numerical examples.

This paper discusses the challenges faced by existing power amplifier configurations in meeting the bandwidth requirements of modern communication technology while maintaining high efficiency due to the overlap of fundamental and harmonic frequencies. To address this issue, the paper proposes a matching method based on mode combination theory that utilizes the overlap of harmonic and fundamental impedance to simplify the design of broadband amplifiers. In this paper, a Chebyshev low-pass filter is used to control the higher harmonics instead of the conventional quarter-wavelength harmonic control network with a combination of harmonic impedances. The proposed method combines three modes of Resistive-Reactive class F^-1, class J, and class F power amplifiers, which can achieve high efficiency and octave frequency at the same time. The paper verifies the proposed method by designing and fabricating a multi-multiplier power amplifier with a drain efficiency of 61.8-73.9%, an operating bandwidth of 1.4-2.9 GHz, and a saturation output of 41.1-42.3 dBm. The amplifier also has a gain greater than 11.1-12.3 dBm, and at an output power of 36 dBm, the ACPR value is -32 to -33.1 dBc across the band.

Exact analytic solutions for the electromagnetic field due to a thin, uniform circular loop current are presented. The solutions are provided in the form of a power series with respect to wavenumber. The coefficients of the series are real functions of the spatial coordinates and loop radius and involve recursions of complete elliptic integrals or finite sums of elementary functions. Explicit expressions for the magnetic vector potential and electric and magnetic fields are provided for both cylindrical and spherical coordinate systems. The expressions are adapted for computing the electric field and axial magnetic field on the interface of two half spaces generated by a current loop lying on the half-space interface. Expressions for the self and mutual loop impedances are provided for both the free-space and interface case. Computed examples are given for specific frequency and half-space parameters and are compared to known solutions based on spherical Hankel functions or direct integration. The solutions are shown to be particularly efficient in the near field. Their derivation is motivated by recent developments of large sensors used in magnetic resonance sensing of minerals.

Flux-switching permanent magnet (FSPM) machine has wide application prospects in aerospace and automotive fields. To enhance the machine's electromagnetic performance, a novel multi-tooth flux-switching permanent magnet (MT-FSPM) machine with high-temperature superconducting (HTS) bulks is proposed. The HTS bulks are arranged in the middle of the stator teeth, aimed at diminishing flux leakage and amplifying torque output. The method of stator tooth chamfering and rotor flange is adopted to effectively suppress the torque ripple. Then based on the comprehensive sensitivity analysis, the key design parameters of the machine are layered, and the high sensitivity parameters are optimized by response surface method (RSM) and multi-objective genetic algorithm (MOGA) to obtain the optimal value. Finally, a 6/19 MT-FSPM machine model is established in 2D finite element method (FEM). Comparative analysis with the conventional model indicates a 16.4% increase in output torque and an impressive 79.6% reduction in torque ripple for the proposed model.

The armature and rail sizes of electromagnetic rail launcher vary greatly, and the refined 3D finite element computation occupies a large amount of physical memory. In order to enhance the economy of dynamic computation, this paper proposes an adaptive hexahedral mesh method based on mesh expansion, compression and translation. In addition, split nodes are used on both sides of the contact surface, and interface conditions and frictional heat sources are constrained through point penalty function method to solve non-ideal sliding electrical contact problems. Comparative calculations with the same type of software and the same model are carried out, and the results calculated in this paper are consistent with the relevant results of MEAP3D. This paper also compares the EMRL calculation results of adaptive mesh model and constant mesh model to verify the reliability of the method. In addition, the C-type EMRLs are compared and analyzed. The results show that due to the influence of velocity skin effect, the dynamic inductance gradient of the rail gradually increases over time and is greater than the static value. The maximum difference between the two is 5.65% of the dynamic inductance gradient. The steel shell generates eddy currents, causing a decrease in armature velocity of 4.7 m/s under the small caliber launcher. The maximum eddy current density waveform of the shell exhibits two peaks. In the frictionless heat, the temperature of the armature is underestimated, and under the action of frictional heat, the trailing edge of the armature is ablated and melted.

Three scenarios of high gain bow-tie based antenna array systems are introduced and investigated in this paper. The proposed designs are intended for integration as Tx/Rx antennas in C-band communication systems. Wide operating bandwidth and consistent radiation characteristics over the frequency range from 4 GHz to 5 GHz are defined for the three configurations. A two-stage Wilkinson power divider provides the feed mechanism for the proposed array. The initial structure has four radiating elements, each incorporating seven bow-tie dipoles arranged in a printed Log-Periodic Directional Array (PLPDA) configuration. The gain of the second and third designs is improved by adding resonators in front of the array elements. Furthermore, the second design features triangular-shaped resonators, while the third design employs H-shaped resonators. The designs are simulated and optimized using HFSS and CSTMWS software, and subsequently, they are fabricated using the photolithography technique. The initial design demonstrates an experimental bandwidth from 3.7 GHz to 5.1 GHz and achieves a measured gain of 13.8 dBi at 4.7 GHz. The second and third configurations operate in the frequency bands of 4.3 GHz to 5.3 GHz and 3.7 GHz to 5 GHz, respectively, exhibiting measured gains of 14.1 dBi and 15 dBi. The overall dimensions of the proposed arrays are kept within reasonable limits, with the first array being 2.51λ × 2.74λ, the second being 2.09λ × 2.82λ, and the third being 2.51λ × 2.97λ. The three array designs can be considered as good candidates for C-band communication applications.

Electromagnetic thermal performance is critical during electromagnetic launch. However, due to the harsh in-bore environment, it is difficult to obtain multi-parameter information by means of experimental measurement, which further limits our understanding of the field distribution of electromagnetic launcher. In this paper, considering the temperature dependence of material conductivity and armature solid-liquid isothermal phase transition, a bidirectional coupling model of electro-magnetic-thermal field of multi-turn electromagnetic rail launcher is established. The reliability of this model is verified by comparing the calculation results of the same model and input conditions with the numerical tool EMAP3D, as well as the related experimental comparison. In addition, the multi-turn and traditional EMRLs are compared and analyzed. The results show that compared to single-turn EMRL, the armatures have greater driving force in two multi-turn configurations, and the impulse lifting rates are about 1/2. In the multi-turn configurations, the lateral resultant forces of the two armatures are not zero, while the lateral force difference in the integrated negative rail configuration is relatively small. The ablation of the armature in the integrated negative rail configuration is less severe.

To reduce the coupling resulting from structural asymmetry and enhance the load-bearing capacity per unit area, a six-pole axial-radial active magnetic bearing (AR-AMB) has been suggested. To refine the precision of the mathematical model derived from the conventional equivalent magnetic circuit model, a modeling technique that employs the flux density and magnetic field segmentation has been proposed. Firstly, the structure and operational principle of the six-pole AR-AMB are introduced. Subsequently, an improved model based on the flux density is established by considering the internal relationship between the iron core and air gap magnetic field in a magnetic bearing with pole shoes. The model addresses issues related to the accurate calculation of fringing magnetic flux and magnetic saturation of core materials while accounting for eddy current effects on suspension force. Finally, the accuracy of the theoretical analysis results has been validated through finite element simulation and experiment, and demonstrated that the rotor based on this model exhibits robust anti-interference capabilities.

In this paper, a broadband bowtie-based log-periodic array antenna is proposed and investigated for 5G millimeter wave (mm-wave) applications. Using a Glass Integrated Passive Device (GIPD) process, the proposed antenna is implemented on a high dielectric constant glass substrate. To address the directional radiation issues associated with the traditional straight connection, the proposed antenna uses a crisscross connection effect with carefully spaced three dipole elements. Furthermore, the use of bowtie-based dipole offers a wide bandwidth advantage. The study also examines the effects of changes in key parameters on critical antenna features. The feeding structure uses a combination of coplanar waveguide (CPW) and microstrip line to strip line. For demonstration, a prototype antenna is optimized, fabricated and measured. The measurement results show that the 10 dB impedance bandwidth of the proposed antenna is from 21.5 to 36.1 GHz, and the gain is higher than 5.63 dBi.

The folding antennas are anticipated to become mandatory because of integration necesity according to communication object shapes. The effect of folded antennas on the electromagnetic (EM) radiation is an open question for RF and microwave wireless engineers. An innovative approach to explore the flexible patch antenna (FPA) parameters through V-folding analysis is addressed for this problem. This paper is focused on the methodological approach of FPA study by considering an innovative V-folding behaviour compared to the classical flat condition. As proof-of-concept, FPA prototypes are designed on Kapton substrate, simulated, fabricated, and tested. A non-shifting operating frequency is achieved at 3.4 GHz for all percentage-wise folding with a flat (unfold) bandwidth of about 360.8 MHz with good acceptable performance. The FPA performance prediction as reflection coefficient, efficiency, gain, and directivity versus forward and back V-folding percentage and angle is examined. The obtained result can be exploited to predict the V-folding effect on the communication performances of transceiver systems like radar, satellite and multimedia applications.

To ensure normal operation of a control system for a bearingless induction motor (BIM) after current sensor failure, a virtual current sensor (VCS) fault-tolerant control strategy was proposed. First, on the basis of the coordinate transformation of the stator current of the torque winding, the fault detection marks were set to realize current sensor fault detection. Second, according to the mathematical models of BIM, the stator current differential equations included in the VCS were derived, and the solutions of the equations were used as the reconstruction current of the fault current sensor, achieving fault-tolerant operation control after the sensor fault. The simulated and experimental results show that the set fault detection marks can realize the quick and accurate identification of sensor faults, and the estimated current from the VCS output can replace the faulty current after the current sensor fails, and the stator current can be reconstructed effectively under no-load, load change, and speed change conditions, and also ensure a good suspension of the motor rotor under sudden addition of disturbance condition.

This manuscript introduces an innovative customizable dual pole bandpass filter using a substrate-integrated waveguide technology on a conventional Rogers RT/Duroid 5880 high-frequency laminate. This structure is bifurcated into two identical cavity resonators to get the band stop-band pass-band stop behavior. The structure comprises lumped capacitors to indicate each resonator's operating frequency. Additionally, altering the capacitors in the proposed design facilitates the generation of the tunable dual pole in passband frequency, adding to its versatility. Further, measured and simulated results indicate that the design attains large tuning bandwidth, excellent insertion loss (better than 0.4 dB) and return loss (>22 dB), high Q-factor (11.8 to 16.87) with fractional bandwidth of 4.8% to 8.9% throughout the tuning range, affirming its practicality and functionality in X-band. A total of 12.3% of tunability is achieved from the structure.

This paper presents a compact loop-shaped omnidirectional rectenna for RF energy harvesting at 2.45 GHz and 5.8 GHz. Firstly, a loop-shaped antenna with iterated circular concave and convex structures is proposed to operate at both frequencies. Then, a rectifier circuit uses a complex impedance correlation matching technique to achieve high conversion efficiency. By connecting a piece of microstrip, two uncorrelated input impedances are transformed into a pair of conjugate impedances. In addition, by using a π-shaped structure with the same equivalent characteristic impedance and complementary equivalent electrical lengths at both frequencies, the pair of conjugate impedances are simultaneously matched to 50 Ω. The rectifier circuit is integrated in the loop-shaped antenna to form a compact dual-band rectenna. The overall size of the rectenna is 67.5 mm x 71.5 mm x 1.016 mm. The test results show that the S₁₁ of the antenna is -13.5 dB and -18.7 dB, and the peak conversion efficiencies of the rectenna are 65.1% and 38.4% at 2.45 GHz and 5.8 GHz, respectively. The simulated and tested results are quite similar.

A dual-port pattern diversity antenna is proposed in this letter for omnidirectional coverage. Two end-fire radiating beams are realized based on a two-element magnetic currents array. A folded half-mode substrate integrated waveguide (FHMSIW) is introduced to ensure that the distance between the two equivalent magnetic current radiation sources is about λ₀/4 (λ₀ is the wavelength in free space). When the two elements are driven by signals with a 90˚ or -90˚ phase difference, two end-fire radiation patterns with opposite directions can be realized. A prototype working at 2.425 GHz is fabricated and tested, achieving two independent end-fire radiation beams with a maximum gain of 4.3 dBi. Compared with conventional omnidirectional antennas, this work can effectively improve the gain of omnidirectional coverage based on a very compact structure.