To shield undesirable microwave radiation to protect electronic systems and human health, microwave perfect absorbers have attracted increasing interests in recent years. However, the opaque or semitransparent nature of most implemented microwave absorbers limit their applications in optics. Here, we demonstrate a high-performance microwave absorber based on an impedance-assisted Fabry-Pérot resonant cavity with an ITO-dielectric-ITO structure without complex nanofabrication. The device features near-unity absorption (99.5% at 14.4 GHz with a 4.5 GHz effective bandwidth), excellent electromagnetic interference shielding performance (24 dB) in the Ku-band, and high optical transparency (89.0% from 400 nm to 800 nm). The peak absorption frequency of the device can be tuned by changing the thickness of glass slab and sheet resistance of ITO films. Our work provides a low-cost and feasible solution for highperformance optically transparent microwave shielding and stealth, paving the way towards applications in areas of microwave and optics.

Energetic ion or electron beams cause plasma instabilities. Depending on plasma and the beam parameters, an ion beam leads to change in the dispersion relation of Alfven waves on interacting with magnetoplasmas as it can efficiently transfer its energy to the plasma. We have derived dispersion relation and the growth rates for oblique shear Alfven wave in hydrogen plasma. The particles of the beam interact with the Shear Alfven waves only when they counter-propagate each other and destabilize left-hand polarized mode for parallel waves and left-hand as well as right-hand polarized modes for oblique waves, via fast cyclotron interaction. The collisions between beam ions and plasma components affect the growth rate and the frequency of generated Alfven waves, differently for right-hand (RH) and left-hand (LH) polarized oblique Alfven modes. For (ω + k_zv_bo > ω_bc), the most unstable mode is the LH polarized oblique Alfven mode, and it is the RH polarized oblique Alfven mode for (ω + k_zv_bo < ω_bc), which shows a polarization reversal after resonance condition. Numerical results indicate that the growth rates increase with increase in angle of propagation. The maximum growth rate values in the presence or absence of beam increase due to obliquity of wave.

Inspired by neural networks based on traditional electronic circuits, optical neural networks (ONNs) show great potential in terms of computing speed and power consumption. Though some progress has been made in devices and schemes, ONNs are still a long way from replacing electronic neural networks in terms of generalizability. Here, we present a complex optical neural network (cONN) for holographic image recognition, within which a high-speed parallel operating unit for complex matrices is proposed, targeting the real-imaginary-splitting and column splitting. Based on the proposed cONN, we have numerically demonstrated the training-recognition process on our cONN for holographic images converted from handwritten digit datasets, achieving an accuracy of 90% based on the back-propagation algorithm. Our training verification integrated architecture will enrich the further development and applications of on-chip photonic matrix computing.

Chirp sequence has been adopted in automotive applications for its simple generation and flexible integration within radar-centric systems. Besides, recent studies have shown its ability to carry data between communicating vehicles in the surroundings. Since the parameters adopted from current automotive radar sensors can differ at the transmitter side dependent on the automotive supplier, the carrier alignment of the communication receiver of one of the communicated nodes might not concur with the one in the transmitter. This paper presents a novel two-stage synchronization method for communication-assisted chirp sequence (CaCS) signals. The proposed synchronization method applies a sequence of up- and down-chirp as a preamble to estimate frequency and time offsets during the transmission. The suggested synchronization scheme supports partial chirp modulation systems and can be adapted for similar radar-centric systems that employ chirp modulation. The former stage performs a coarse synchronization, reallocates the receive carrier frequency, and corrects eventual time offsets between the communication receiver from one CaCS-node and the transmitter of another node. The carrier allocation at the communication receiver side is based on a combination of spectrum sensing via short-time Fourier transforms and image processing to estimate the transmitting signal pattern (slope, frequency offset, and delay). The latter stage, in its turn, relies on range-Doppler estimation to perform a fine correction of time and frequency offsets and compensates residual offsets of the coarse synchronization stage. Furthermore, the paper analyzes the case of a multi-user scenario with mutual interference between the signals that affects the synchronization and communication data detection. Besides, measurements are provided based on two completely unsynchronized software-defined radios to validate the proposed method. The study also illustrates the influence of the signal-to-noise ratio on the proposed method and verifies it with simulations in MATLAB. As a result, the offsets at the investigated CaCS-node are returned to recover the transmitted data correctly.

This paper presents a novel microstrip three-mode filtering power divider (FPD) with high frequency selectivity and high isolation, which integrates only a single resonator and a resistor to realize the dual functions of the power division and filtering. In order to further improve its frequency selectivity and obtain wide upper stop band, three open stubs are loaded into the input and output ports of the filter power divider. The measured and simulated results show that the range of S₁₁ < -10 dB is 1.86~2.1 GHz; the relative bandwidth of 3 dB is 17.9%; the in-band isolation is higher than 26 dB; and it has a relatively simple topology.

This paper presents an analytical method for the optimal estimation of time constants of synchronous machine from Standstill Frequency Response Testing (SSFR). We show that the analytical method is advantageous over the conventional one since the latter is based on curve fitting representing the variation of the operational inductance as a function of the frequency and provides in accurate and non-unique solutions. In fact, the analytical method applies the standard theory of linear systems to locate the values of poles and zeros in the frequency response and determines the optimal order of the equivalent circuit that can model the machine accurately. The proposed method is simple, practicable and effective. However, it needs an optimisation process based on parameter differentiation, to improve the values of time constants. Based on the measured data, realistic tests are given to show the advantages of the method.

A novel Variable Inclination Continuous Transverse Stub (VICTS) antenna element and array model is proposed in this paper. The bandwidth and gain of the element are increased by adopting a linear-gradient stub, matching structure and rectangular grating slow-wave structure (SWS). A circular array can be obtained by arranging antenna units of different lengths linearly. The array antenna uses a bow-parabolic box antenna as the line source generator (LSG) and utilizes a double-layer transition waveguide structure to realize the propagation of planar wave. Finally, a wide range of beam scanning in the elevation plane was achieved. The results of the simulation and antenna prototype test are in good agreement. Showing the impedance matching characteristics of the antenna unit and array meets the engineering requirements in the range of 12~16 GHz. The maximum gain of the antenna array is 34.3 dBi, and the maximum 3 dB beamwidth is less than 10°. It is confirmed that the designed antenna has the characteristics of high gain, narrow beam, and low profile, and realizes two-dimensional beam scanning in the range of 6~79° in the elevation plane, which meets the requirements of the Satellite Communications On-the-Move system (SOTM).

This paper theoretically describes a new concept of passive contactless concentric magnetic gear, which, unlike the existing ones, does not use any separate modulator structure, and instead, a set of strength modulated permanent magnet pole pieces are introduced on the outer permanent magnet rotor structure. Mathematical analysis shows that stable operation in this proposed system is possible with any specific gear ratio, dependent on the number of pole pieces and on the choice of modulation constant of the pole strength variation. The system described is simpler because of the absence of separate modulator structure. The concept is new, leads to less parts count, and hence deserves consideration due to its simplicity. A simple simulation study result is also included at the end, which confirms the presented theory. The main contribution of the paper is the introduction of a new concept for designing magnetic gears using fewer physical components and showing that it is a viable design and able to produce a tangible toque at a particular gear ratio. In addition, the mathematical theory in the paper leads to interesting new results indicated in the design section of the paper, which have not been seen in the literature known to the author.

An innovative methodology for the design of dual-band microstrip monopole antennas is presented in this work. It leverages on the unconventional modeling of the radiator shape based on the perturbed Minkowski fractal in order to fit arbitrarily-defined resonances. A System-by-Design (SbD) technique is exploited to solve the arising global optimization problem with high computational efficiency. Representative benchmarks are reported to assess the effectiveness, reliability, and efficiency of the proposed synthesis approach.

The computation of the fields scattered by a dielectric sphere illuminated by a plane wave and the evaluation of the resultant optical forces is a classical problem that can be analytically solved using Mie theory. Whereas extending said formulation to arbitrary incident fields does not pose any conceptual difficulty, the actual computation of the scattering coefficients and force components substantially grows in complexity as soon as interactions beyond the electric dipole arise. By formulating an equivalent electromagnetic problem, we derive a set of computationally efficient formulas for the evaluation of scattering and optical forces exerted by arbitrary incident fields upon dielectric spheres in the Mie regime. As opposed to force calculations by direct integration of the Maxwell’s Stress Tensor, the present formulation relies on a set of universal interaction coefficients that do not require any problem-specific integration and can therefore be all precomputed and tabulated. The proposed methods can be easily integrated with the T-Matrix method to calculate forces on non-spherical dielectric objects.

In this paper a multifunctional patch antenna loaded with near zero index refraction metamaterial (NZIM) is presented. This multifunctional antenna operates at 5.8 GHz and provides high gain and beam steering capability. The proposed configuration comprises a patch antenna placed below an NZIM superstrate. The rectangular microstrip antenna is used as a radiation source to demonstrate the performance of this design. The NZIM superstrate, which behaves as an NZIM, based on 9×9 resonating unit cells of split ring resonators (SRRs), allows gathering radiated waves from the antenna and collimating them toward the superstrate's normal direction, which results in gain enhancement. The beam-steering in the E-plane is obtained by slowly tilting the NZIM over the patch antenna. The main characteristics of the antenna placed near the NZIM superstrate are studied numerically and experimentally to successfully demonstrate this dual function feature. It is found experimentally that the gain enhancement of 8 dB with improved directivity and radiation efficiency are obtained in comparison with the antenna without the NZIM metasurface. In addition, we were also able to steer the direction of the main beam just by tilting the NZIM superstrate from -20° to 20° with a gain variation of 5 dB and without changing the whole dimension of the structure.

The study investigates the mathematical background of the method of auxiliary sources (MAS) employed in electromagnetic diffraction. Here, the mathematical formulation is developed for E-polarized plane wave diffraction by perfectly conducting two-dimensional objects of arbitrary smooth shape, and the comparison with an analytical and a numerical approach is provided in the numerical part. The results reveal a quite high accuracy among all methods. The importance of the study is to develop the complete mathematical background of MAS for two-dimensional TM-polarized electromagnetic scattering problems by conducting objects. Different from the method of moments (MoM) and other integral equation approaches in electromagnetic scattering problems, here the integral equation resulting from the boundary condition on the scatterer is solved by expanding the current density as orthonormalized Hankel's function with the argument of the distance between the scatterer actual and auxiliary surfaces. The approach can be summarized by that first the sources are shifted inside the scatterer and second, the boundary condition is employed as the total tangential electric field is zero on the surface and inside the object. Then, such expansion leads to eliminating the singularity problems by shifting the sources from the actual surface.

A bidirectional, coplanar waveguide (CPW) fed dumbbell-shaped slot antenna with partially reflecting surface (PRS) with parasitic patches for gain, bandwidth, and radiation pattern improvement is investigated. A dumbbell-shaped CPW-fed slot antenna has a dimension of 0.71λ_g x 0.71λ_g x 0.0571λ_g. The proposed antenna is simple in design and has low profile structure. To achieve improvement in bandwidth, gain, and bidirectional radiation pattern, PRS with parasitic patches are placed on top and bottom of antenna at a distance of 0.25λ_g. The proposed design yields wide bandwidth of 4.11 GHz (4.48-8.59 GHz) with percentage bandwidth of 62.89%, S₁₁ ≤ -10 dB, and peak gain of 5.61 dBi. The variation in the gain over desired bandwidth is less than 3 dB. The antenna is fabricated using an FR4 substrate with relative permittivity of 4.4. The measured results corroborate the design and stipulate the proposed structure to be suitable for applications in C Band.

In this paper, the effect caused by the suspension force windings on the torque windings in a bearingless synchronous reluctance slice motor (BsynRSM) is analyzed, and a new slide model observer is proposed to reduce the speed estimation vibration caused by this effect. Firstly, the effect of suspension force windings is analyzed in a Maxwell model. The suspension force windings will generate an asynchronous torque and current, which are similar to superimposing an asynchronous motor on the original motor. And a special Matlab/Simulink model is built. Secondly, the effect of current and torque generated by suspension force windings on speed sensorless is analyzed. The sliding mode observer (SMO) is studied considering the effect of suspension force windings. Simulation result shows that the current generated by suspension force windings of the BsynRSM will cause the estimate speed vibrating with the rotor vibration, and the frequency of speed estimation vibration is much higher than the additional current and torque generated by the suspension force windings. Thirdly, an improved SMO is proposed. By using the improved SMO, the amplitude and frequency of the speed estimation are obviously reduced. Finally, the improved SMO is verified on the experimental platform, which proves the feasibility of the method.

Cellular UHF (Ultra High Frequency) transceiver networks and base transceiver station antenna systems comprise high power phase shifters for changing and adjusting the phases or delays of high-power transmitting signals delivered to antenna elements. In this work, theoretical and practical adjustment method of amplitudes and phases for electronic steering of a phased array antenna pattern are illustrated. In otherwords, a high power phase shifter with an asymmetric power divideris designed. The phases are changed and adjusted progressively, and thus the beam direction changes from -60° to 60°. The UHF phase shifter has been simulated in Advanced Design System (ADS) and CST STUDIO SUITE SPARK3D and measured. The simulations show that the designed and manufactured UHF phase shifter can also handle more than 20 KW and can be redesigned to reach up to more than 100 KW RF (Radio Frequency) power (microstrip/stripline structures) and can control/change phases of transmitting/receiving antennas. The phase shifter can be designed on any low loss substrate. By using this method in planar high power phased array antenna systems, 360° planar beam tilting is also achievable.zzz

We study two array antennas to expand a 3 dB axial ratio bandwidth. Each array is located at a quarter wavelength above the ground plane and analyzed using the moment method. First, we use paired spiral elements fed by balanced parallel lines to avoid unwanted radiation from the feedline. It is found that the antenna shows an axial ratio bandwidth of 30%. Next, the elements are separated and fed by a single feedline to simplify the feed system. It is revealed that the antenna can radiate a circularly polarized wave under a feedline radiation of less than -16 dB. The frequency responses show that an axial ratio < 3 dB and VSWR < 2 are obtained in a bandwidth of 21%, where the gain is more than 13.3 dBi. The simulated results are verified with experimental ones.

Wave probing systems are used to obtain 2D or 3D images of objects. According to the nature of the waves used (acoustic-microwave and others), these waves can penetrate the fabrics or barriers that are in their way, so it is possible to photograph hidden objects. A system for ultrasonic wideband probing in air with multiple transmitters and multiple receivers with parallel digitization of signals from the receiving array using undersampling is proposed. Probing at frequencies from 38 kHz to 43 kHz is considered when receiving array signals are digitized at a frequency of 18 kHz. Transmitter and receiver placements have been optimized to minimize artifacts and noise. the transmitting and receiving arrays are located at the same plane. The presented results of the experimental study confirm that the processing of measured signals based on spatially matched filtering makes it possible to visualize scattering objects in the environment, including those hidden behind sound-permeable barriers.

Aiming at the problem of poor identification accuracy in traditional particle swarm optimization algorithms, an adaptive search particle swarm optimization algorithm (ASMDRPSO) method for permanent magnet synchronous wind generator (PMSWG) parameter identification is proposed. Firstly, in order to solve the issue of the under-rank equation, a full-rank state equation and fitness function are established. Then, in ASMDRPSO, a dynamic adjustment strategy is adopted in the inertia weight update process to enrich population diversity. In addition, the average best position strategy is designed to avoid getting stuck in a local optimum. Moreover, an adaptive learning radius is supplemented in ASMDRPSO, and the particle search range is enlarged when the ASMDRPSO evolution is stalled. Finally, the simulated and experimental results are presented to verify the stronger optimization ability, stronger robustness, and higher search accuracy of the proposed control strategy than the traditional PSO.

A study of the impact of mutual coupling effects in a co-located multiple input multiple output (MIMO) radar system is presented. Predicted and measured results corroborate that the active reflection coecient (ARC) and beampatterns are impacted by the excitation of each sub-array, the geometric configuration, and their polarization. A uniform linear array (ULA) and a uniform planar array (UPA) layouts are considered. The excitations used in the study are linear frequency modulation (LFM) and Doppler division multiple access (DDMA). A thorough analysis is presented to understand the effects these parameters have on the ARC and on the beampatterns of the radar system.

Partitioning large planar antenna arrays into smaller subarrays reduces the system costs and gives many other advantages. In this article, symmetrical T-shaped tetromino subarrays are suggested to perform the partition process of the large planar arrays. Different structures of T-shaped tetromino subarrays have been obtained by simply rotating its orientation by multiple angles of 90 degrees such that the entire planar array aperture can be filled. Two array architectures based on different T-shaped tetrominoes are constructed. The amplitude weights of the designed subarrays are optimized by means of the genetic algorithm such that the resulting array patterns have low sidelobe level. In the first architecture, all the elements in the original array are divided into several subarrays based on three T-shape structures, while in the second architecture all the elements are combined into eight different T-shapes. To control the sidelobe level in the proposed T-shaped tetromino subarrays, a surface mask boundary function is included in the optimization process to find the optimum weights of the T-shaped subarrays. Simulation results showed that the sidelobes can be reduced to less than -20 dB in the first architecture, and less than -25 dB in the second architecture, in addition to a significant reduction in the complexity of the feeding network for each one. Moreover, detailed connections of the feeding network circuitry of the used T-shaped tetromino subarray structures are given for practical implementation.