In order to improve the stability of sensorless high-speed operation of permanent magnet synchronous motors and effectively expand the speed range, a voltage closed-loop flux weakening sensorless algorithm based on the active flux model is proposed. Firstly, the mathematical model of sensorless control of the PMSM is designed based on the active flux model, and the state of the PMSM flux weakening operation is analyzed. Then, based on the voltage closed-loop flux weakening control method, the corresponding flux weakening control algorithm is analyzed and designed. Meanwhile, based on the active flux model, the speed and rotor position of the motor are observed by sliding mode observer and phase-locked loop method. After that, the flux weakening control method and the sensorless control method are combined to realize the sensorless flux weakening control method to improve the stability of the control system. Finally, the proposed algorithm is validated on the experimental platform. The experimental results show that the proposed method can prevent the system from losing control during flux weakening processes, effectively improve system stability, and have smaller angle errors. The speed convergence time is shortened by 80% compared to the non flux weakening control.

With combining the advantages of the hybrid excited machine and field modulation machine, hybrid excitation field modulation machine (HEFMM) exhibits obvious merits of controllable flux operation and independent flux distributon paths. A total copper loss minimization model is established to determine the optimal ratios of field current, d-axis and q-axis currents in low speed region. In high speed operating region, one flux weakening fuzzy control strategy combining with particle swarm optimization (PSO) algorithm for HEFMM was proposed, which improves the dynamic characteristic and decrease the harmful influence of parameters variation during the operation region of HEFMM. The correctness and effectiveness of the proposed flux weakening fuzzy control strategy were verified by the simulation data and experimental results, which demonstrated that the this current optimization method based on PSO algorithm can effectively reduce the total copper loss of the machine by 22%, the range of speed regulation with higher efficiency are ontained.

In this paper, a hexa-slot wheel shaped fractal antenna is proposed for UWB applications. Fractal structure (wheel shaped hexa slots) is developed by inscribing hexagons and circles inside a circular patch monopole antenna. Then orthogonal MIMO antenna with polarization diversity is proposed that operates from 1.39-15.18 GHz with an impedance bandwidth of 13.79 GHz. Its performance is analyzed at three resonant frequencies 5.8 GHz, 8.3 GHz and 10 GHz. It exhibits good diversity performance with ECC < 0.035, DG very close to 10, isolation > 35 dB, CCL < 0.35 bits/s/Hz values. The proposed MIMO fractal antenna achieved an average radiation efficiency of 83.11% with 3.26 dB maximum peak gain. TARC characteristics and time domain behavior using group delay are also examined. Simulated and measured results are in good agreement and hence the proposed MIMO antenna with polarization diversity is well suitable for UWB applications.

In this paper, we develop two new algorithms for snow water equivalent (SWE) retrieval based on the volume scattering snow at X (9.6 GHz) and Ku (17.2 GHz). Significantly, neither algorithm requires a prior on grain size or on scattering albedo. The two algorithms are based on modifications of the previous algorithm published in our previous two papers (Zhu et al. 2018, 2021). The physical model is the bi-continuous DMRT model, and a parametrization is carried out over a look-up table of DMRT results. The parameterized model gives the X and Ku band co-polarization backscatter as a pair of equations in terms of two parameters SWE and scattering albedo at X band (ω_X). By directly inverting the pair of equations for, σ^X (SWE, ω_X) and σ^Ku (SWE, ω_X), we show that there are at most a pair of solutions which have SWE values that are far apart in most cases, facilitating identification of the correct solution. The first algorithm described in this paper, labelled an algebraic algorithm, uses inversion alone and does not employ a cost function. The proposed algebraic algorithm is validated with multiple airborne data sets and three years of tower-based snow observations. The robustness of the no-prior approach was validated with the airborne observations, by using a prior SWE value that is intentionally far (75% different) from the true SWE. For the validation using tower-based data, three years of observations from the NoSREx experiment in Sodankyla, Finland were used in which the previous SWE result helps to correctly choose between the two solutions. The second cost function-based algorithm finds the SWE and ω_X pair which minimizes the difference between the observed volume scattering σ^X,obs and σ^Ku,obs and the model-predicted volume scattering σ^X,mod and σ^Ku,mod. The cost function uses prior information on SWE, also based on a time series starting with zero/low SWE. NoSREx data is used to show results from this approach. The new algorithm combined with time series eliminates needs of ancillary information of SWE and grain sizes, making the algorithm useful for level-2 products of a satellite mission.

In this paper, we propose a new sparse linear array (SLA) that enjoys a hole-free difference co-array (DCA) and closed-form expressions for its sensor positions. The proposed configuration is valid for arrays containing seven or more sensors (N≥7). Exact expressions for the array aperture and achievable degrees of freedom (DOFs) have been derived. Numerical simulations were performed using MATLAB to reinforce the theoretical understanding. The main aim of this study is not to claim superiority over any existing SLA design, but to report that we have found a new number sequence that can act as an SLA. Except for being highly susceptible to mutual coupling, the proposed array has all the desirable features of a good SLA. We observed that the proposed array is on par with other SLAs for N<20. However, for 20 or more sensors, the array aperture does not scale rapidly in proportion to the added sensors and fails to match the resolution and/or DOFs offered by other sparse arrays. Nevertheless, the proposed sparse array is based on a unique and previously unknown number sequence.

Wave propagation in forests at L-band has essential applications in satellite communication system design, foliage penetration (FOPEN), and remote sensing of forest canopy and soil using passive, active, and reflectometry techniques. In this work, we propose applying the fast hybrid method (FHM) for full wave simulations of forests. The FHM significantly improves CPU time and memory efficiency for full-wave electromagnetic solutions. In this paper, we present simulations of forests of up to 72 trees with heights up to 13 m with FHM. Spatial distributions of electric fields at the bottom plane of the trees are illustrated, showing constructive and destructive interferences. The electric field distributions show that the amplitudes of the electric fields can be as large as twice that of incident waves. The transmissivities are computed and averaged over realizations based on the electric fields underneath the forest. The simulations were performed on a desktop and required a CPU time of only 1346 seconds and the memory of 16.5 GB for the case of 72 13-m tall trees, demonstrating that the FHM method is substantially more efficient than the available commercial software. The results show that the L-band signals can penetrate forests to sense the soil moisture and detect targets hidden within forests, as evidenced by significant electric field intensities under forest canopies. Also, we illustrate that GPS signals can penetrate forests and be successfully received by GPS receivers. In the study on clustering effects, we present two distinct solutions for transmissivities, each corresponding to different spatial distributions of trees while maintaining the same average tree density.

Magnetic nanoparticles (MNPs) have been widely investigated as effective drug carriers for targeted tumor therapy. However, the successful application of this technology in the human body requires reliable imaging support. Magnetoacoustic Concentration Tomography of Magnetic Nanoparticles with Magnetic Induction (MACT-MI) is an electromagnetic-ultrasonic coupling imaging technique that holds great promise in improving imaging resolution and providing unique advantages for tumor monitoring and treatment. To evaluate the imaging feasibility of MACT-MI technology for targeted therapy of breast tumors, this study establishes a realistic breast model and takes into account the distribution of magnetic particles within the actual breast tissue environment. A concentration gradient model is introduced, and the finite element method is employed to solve the electromagnetic and sound fields. In addressing the research objective, the forward problem is investigated by analyzing the magnetic force and sound pressure distribution for various tumor sizes and locations, different breast tissues, and both benign and malignant tumors. The results obtained indicate that the magnetoacoustic signal emitted by magnetic particles facilitates accurate mapping of the size and location information of magnetic particles enveloping breast tumors, as well as distinguishing between benign and malignant tumors.

Wireless technology, a longstanding focus for researchers, has evolved into an exciting telecommunications topic over several decades. The most recent iteration, Fifth Generation (5G), has been introduced at high frequencies, commonly called millimeter waves. An integral component supporting wireless communication is the antenna. This report details the design of a microstrip antenna operating at a frequency of 26 GHz. The antenna is configured as a rectangular patch microstrip, utilizing coupled slot feeding, organized as an array, and implementing a ring as the gain enhancement technique. The designed antenna undergoes observation for both single-element and 1x2 arrays, both with and without rings. A thorough analysis encompasses gain, bandwidth, return loss, and radiation pattern. The antenna design, developed at a frequency of 26 GHz, demonstrates a substantial gain increase of up to 10 dB and 14 dB in the single-element and 1×2 array configurations achieved by adding a ring. The designed antenna surpasses the previous works' gain of about 3 dB more.

In this research work, a flexible polymer-based compact wearable antenna has been designed, fabricated, and analysed for Wireless Body Area Network (WBAN) IoT enabled applications. The antenna is fabricated on a Polyethylene Terephthalate (PET) with λ_L as the lowest operating free-space wavelength resonating for sub-6-GHz band at 2.4 GHz, 3.3 GHz, 4.1 GHz and 5.8 GHz. Periodic Frequency Selective Surface (FSS) reflector is used which reduces Electromagnetic Interference (EMI) antenna and enhances the gain of the antenna. The simulation results prove that this flexible wearable antenna radiates an increased gain of approximately 10 dB and returns loss of -36 dB at lowest frequency with FSS as a reflector. The simulation results are validated by experimental results which offer a good agreement. An average SAR value of l.5 watts/gm is measured within the specific safety limit which makes it feasible for practical implementation. This antenna provides better isolation against on-body losses and reduces SAR value with improved radiation efficiency for WBAN IoT enabled applications.

Microwave-assisted extraction (MAE) is an effective method for extracting tea polyphenols. However, research on MAE mainly focuses on experimental methods, which not only leads to a large amount of experimental work but also generates a lot of material waste. In addition, due to the lack of mechanism research, it is difficult to find a more effective method. In this study, based on electromagnetic field theory, the heat and mass transfer model of tea polyphenol extraction is established based on measuring the dielectric properties of the extract. The distribution of temperature, diffusion coefficient, and flow rate of microwave-assisted extraction of tea polyphenols are all analyzed in detail. The results show that the temperature distribution in the extraction system is uneven. The middle temperature of the extraction solution is high and the edge is low. Moreover, with the increase of microwave power and extraction temperature, the diffusion coefficient is gradually increased, and the flow rate increases, which is more conducive to the extraction process as time goes by. This study provides a theoretical basis for the microwave-assisted extraction of tea polyphenols, reducing experimental workload and material waste.

A new circularly polarized (CP) array using the filtering phase shifting theory is designed. First, it is displayed that a phase designable filter can be obtained by controlling the position of the transmission zero (TZ) of the doublet topology. Next, by mapping the topology into a stub-loaded resonator (SLR) and using the patch as the last resonating mode, a phase designable 3rd-order filtering antenna element is designed. Then, two filtering antenna elements with 90° phase difference are obtained. Finally, by using the slot-coupled feed structure, four elements with phases of 0°, 90°, 180°, 270° are rotated sequentially to form a circularly polarized array. The measured results show that the impedance bandwidth is 8.1% (5.07-5.5 GHz); the axial ratio (AR) bandwidth is 6.7% (5.05-5.4 GHz); the maximum CP realized gain is 10.5 dBic; and the good filtering function is implanted.

In this paper, a microstrip filtering antenna is proposed with gain-filtering response. The antenna consists of an E-shaped radiator and a slotted U-shaped coupling structure. Three radiation nulls are obtained by the radiator, the U-shaped coupling structure and the two slots. The filtering antenna has no extra circuits, which indicates that it is easy to design. A 4-element filtering OAM antenna array is also designed to validate its applicability in OAM antennas. Measured results show excellent performance of the array, which also make it a potential candidate for 5G wireless communication devices.

This paper presents an on-chip integrated sensing circuit for real-time detection of phase currents in three-phase brushless direct current (BLDC) motors. The three-phase sinusoidal currents generated in the motor winding are detected by an innovative Sense FET technology, which can accurately measure the currents of high-side P-type power transistors and low-side N-type power transistors simultaneously. A dynamic matching elimination method is proposed for the detection current mismatch problem due to the large difference in aspect ratio. Using a 90 nm dual-polarized cmos-DMOS (BCD) process for design and verification, the detection circuit of the high and low sides can well follow the change of sine wave phase current of the three-phase motor, and the accuracy is above 96%. The best accuracy can reach 99.219%. The elimination effect of circuit current mismatch is obvious, and the error of the sense current can be reduced by 38.9%.

In this paper, the power handling of a slot loop frequency selective surface based on approximate analytical method is proposed. The physical nature of the slot array periodic moment method is derived in detail. It is found that the left and right sides of periodic scatter matrix respectively represent the total tangential magnetic field acting on the left and right magnetic dipole arrays and moving in the direction of the reference array. According to the principle of equivalence, a slot array can be modeled by an array of magnetic currents on each side of the perfect electronic conductor. As a result, the total tangential magnetic field is zero in the sense of physical concept. Furthermore, a simple sinusoidal function is then used to approximate the magnetic current distribution along the slot loop which is similar to that of dipole antenna. By studying the corresponding zero points and extreme point of the magnetic current for the slot loop frequency selective surface element, the transmission coefficients and maximum electronic field are calculated. Examples of rectangle and triangle slot ring frequency selective surface have verified the efficiency and accuracy of the proposed method.

In this study, we investigate electromagnetically induced transparency (EIT) and Fano resonances, focusing on the propagation of electromagnetic waves in a system of parallel waveguides associated with asymmetric resonators. Our design includes five waveguides and two resonators, generating discrete modes influenced by their respective lengths. The EIT resonance is characterized by a prominent transmission peak flanked by two transmission zeros, while the Fano resonance is characterized by a pronounced transmission peak adjacent to a transmission zero. Using the transfer matrix method (TMM), we calculate transmission and reflection rates. Our results indicate that the EIT resonance appears when the resonator lengths show slight differences, whereas the Fano resonance appears when the resonator lengths are identical. Both resonances are sensitive to resonator lengths and permittivity indices. Consequently, the geometrical parameters of the system must be carefully selected according to the application in question, whether waveguiding or multi-channel electromagnetic filtering.

A microstrip patch antenna of red cross bag shape is designed, simulated, and fabricated. The antenna is designed to work at 5.8 GHz for on-body applications. Small size, low specific absorption rate, and high front to back ratio with a low-profile design are achieved. The measured frequency is 5.878 GHz with 25 mm as the largest dimension used, and the matching impedance is -47.06 dB. Other parameters are recorded from the simulator, such as front-to-back ratio which is 37.37 dB and a specific absorption rate of 0.0984 W/kg in 10 gm. Finally, this work is compared with a compact dual-band antenna with paired L-shape slots, a watchstrap integrated wideband antenna, and a dual-band AMC-based MIMO. The proposed red cross bag antenna overcomes the mentioned works in terms of small size, high front-to-back ratio, and low specific absorption rate.

This article presents a novel compact ultra-wideband (UWB) planar monopole antenna printed on an FR4 substrate. The antenna consists of a pentagonal radiating element and incorporates loading metamaterial complementary split ring resonator (CSRR) on the ground plane to optimize impedance matching for UWB operation. The overall dimensions of the designed antenna are 17.75×20 mm². The proposed compact UWB antenna exhibits an operating bandwidth from 3.01 to 12.41 GHz with a -10 dB return loss, and a fractional bandwidth (FBW) of approximately 123%. Additionally, the proposed antenna exhibits a stable radiation pattern with a peak gain of 6.3 dB and a peak radiation efficiency of 98.3%. To validate the simulation results, a prototype has been fabricated and measured, which shows good coherence with the simulation results. In addition, the proposed design is compared with leading antennas for similar applications to demonstrate the suitability of its concept. Moreover, an equivalent circuit model of the CSRR metamaterial cell is developed and validated using ADS software.

Turbulence is a longstanding problem in fluid mechanics for which experimentation remains unavoidable. In contrast to conventional experimental techniques that inevitably require the introduction of probes into the flow, a very convenient technique would be one in which there is no contact between the measuring sensors and the flow. The laser-based diagnostic technique reported in this work is described as an estimation of a large number of parameters defining the diffusion coefficient profile in the heated turbulent wind tunnel jet, which is required in the formula of the Karman turbulence spectrum for the jet under study. For this purpose, some required experiments in the jet are carried out. A laser beam is then sent perpendicular to the jet exhaust, and measurements of the probabilities of the position of the laser beam's impact on a photocell placed outside the jet are performed. Using the Markovian model, the same probabilities are calculated numerically. For these numerical results to agree with the experimental results, a numerical optimal-control strategy is applied. Due to the large number of unknown parameters searched, a genetic algorithm (GA) computation is performed. A good agreement observed between the GA results and those derived from the previously published cold-wire-anemometer data, combined with the use of the Dale-Gladstone law, proves the validity and accuracy of the laser-based genetic measurement technique.

In this manuscript, we propose a conformable and flexible meander dipole rectenna array for omnidirectionally harvesting ambient RF power for application in Internet of Things (IoT) water meters. The array unit consists of an antenna for RF power harvesting and a Schottky diode for converting the harvested RF power into DC power. The impedance between the antenna and diode is directly conjugated and matched using a meander structure and coupling loop. Traditional matching networks introduce additional losses, while direct conjugate matching maximizes power transmission efficiency and reduces energy losses. The elimination of the matching network simplifies the design of the rectenna, reducing the number of components and the overall size and weight. The rectenna unit is suitable for low-power ambient energy harvesting and operates at 2.45 GHz. The measured RF to DC conversion efficiency of the rectenna unit reaches 50% at 0 dBm. The rectenna array is formed by connecting eight antenna units in parallel, and units are affixed to the four surfaces of the water meter case to achieve omnidirectional RF environmental power harvesting. The output DC power of the array can be up to 1.3 mW at 100 μW/cm² received power density. An energy management circuit (BQ25504) is designed to efficiently store, distribute, and manage the harvesting of RF power for powering the IoT water meter. Measured results demonstrated that the proposed rectenna array exhibited excellent adaptability and application potential in IoT scenarios.

A novel corrugated subreflector is developed to achieve sufficient side lobe level suppression for antenna systems used in meteorological applications. The subreflector operates at 9.41 GHz, with a 60 MHz bandwidth and an efficiency of more than 70%. Its structure is rotational symmetric and is suitable for parabolic antenna applications. It can be utilized in single-polarized or polarimetric radar systems. The pattern-forming property of the subreflector is achieved with corrugations of different depths. Analytical design formulas have been deduced by solving the aperture integral. The analytical formulas provide the initial geometrical configuration and the reference illumination pattern in the objective function to which full-wave electromagnetic optimizations are performed to obtain the final corrugation depths. The subreflector has been manufactured with CNC machining. The radiation characteristics are measured, and for both polarizations, suppression of -28 dB side lobe level has been achieved with a 1.2 m diameter main reflector.