Vol. 69

Magnetic resonant wireless power transfer (WPT) is an emerging technology that may create new applications for wireless power charging. However, the output voltage fluctuations resulting from lateral misalignments are main obstructing factors for promoting this technology. In this paper, an asymmetric two-coil WPT system is presented. The mathematical model of the proposed topology with lateral misalignments is built based on equivalent circuit method. The expression of the output voltage is then derived by solving the system equivalent equations. In addition, a method of optimization parameters is proposed. The mutual inductance between the receiving coil and transmission coil is nearly constant by the proposed method with lateral misalignments. Therefore, the output voltage can be kept nearly constant. The asymmetric two-coil WPT system via magnetic resonance coupling is designed. Simulated and experimental results validating the proposed method are given.

This study presents a polarization reconfigurable antenna with frequency diversity function. The antenna incorporates a novel positive and negative perturbation technique to achieve different polarization sense. A square shape slot is loaded on the ground plane to excite circular polarization by creating a negative perturbation. An L-shape segment is integrated to the patch using a switching diode. This segment creates a positive perturbation to eliminate the negative perturbation created by the defected ground slot, and the antenna excites linear polarization. Frequency diversity is achieved by exciting different polarization senses at different frequencies. A 3-dB axial ratio bandwidth of 1.41% is obtained for circular polarization radiation while the 10-dB impedance bandwidth during linear polarization is 1.8%. The antenna shows good radiation performances with high gain at both polarization states, and the performances are confirmed experimentally.

A novel dual-band and dual-sense circularly polarized coplanar waveguide (CPW) fed planar antenna with an asymmetric rectangular slot is presented. An F-shaped feed line is protruded from the signal line into the slot. Circular polarization is obtained due to the F-shaped feed line and asymmetry in the slot. Axial ratio bandwidth is significantly enhanced by placing parasitic elements adjacent to the feedline. The antenna has a size of 63.5×55 mm². The measured results agree well with simulation. The measured impedance bandwidths are 26.04% (1.57 GHz-2.04 GHz) for the lower band and 18.93% (2.87 GHz-3.47 GHz) for the upper band. The measured 3 dB axial ratio bandwidths of lower band and upper bands are 22.22% (1.6 GHz-2 GHz) and 10.53% (3.15 GHz-3.5 GHz), with respect to 1.8 GHz (RHCP) and 3.325 GHz (LHCP), respectively.

This paper presents a combinatorial triangle type artificial magnetic conductor checkerboard surface for wideband radar cross section reduction. The structure consists of a combination of a single band and dual band AMC unit cells with 180±370 phase difference from 4.06 GHZ to 11.2 GHz. 10 dB RCS reduction compared to PEC surface is realized from 4.4 GHz to 11.68 GHz (91%) for the proposed structure. The performance of the structure is compared with the conventional checkerboard surface. The distribution of scattered fields from both the structures are analyzed using array theory. The angular stability of the structures are also studied for TE and TM polarized wave incidences. A prototype of the proposed structure is fabricated, and the measured data are in good agreement with simulated results.

This paper presents a compact and novel coupling structure for diplexers and power dividers based exclusively on coupled resonators. It consists of two cross-coupled structures joined together by two common resonators with a cluster of only four resonators. For a diplexer, it represents one of the most compact topologies that produces two 2nd-order channel filters with two fully controllable transmission zeros. This can be used to increase the rejection and isolations between channels without increasing the number of resonators. The same topology can also be used to realise a 3rd-order filtering power divider (FPD), with its embedded cascade trisection (CT) structure generating an asymmetric transmission zero. The coupling matrices of several diplexers and power dividers have been synthesized. Two microstrip diplexers with different positions of the transmission zeros have been demonstrated to verify the device concept. A 1.8 GHz FPD with a fractional bandwidth of 5% has also been prototyped, showing an improved out-of-band rejection from 15 dB to 25 dB below 1.71 GHz. The isolation performance of the divider has been investigated and improved from 7 dB to 18 dB across the band by adding only one resistor.

In animal production, behavioral selection is becoming increasingly important to improve the docility of livestock. Several behavioral traits, including motion, are experimentally recorded in order to characterize the reactivity of animals and investigate its genetic determinism. Behavioral analyses are often time consuming because large numbers of animals have to be compared. For this reason, automatization is needed to develop high throughput data recording and efficient phenotyping. Here we introduce a new method to monitor the position and motion of an individual sheep using a 24 GHz frequency-modulated continuous-wave radar in a classical experimental paradigm called the arena test. The measurement method is non-invasive, does not require equipping animals with electronic tags, and offers a depth measurement resolution less than 10 cm. Parasitic echoes (or ``clutters'') that could alter the sheep backscattered signal are removed by using the singular value decomposition analysis. In order to enhance the clutters mitigation, the direction-of-arrivals of electromagnetic backscattered signals are derived from applying the MUltiple Signals Classification algorithm. We discuss how the proposed automatized monitoring of individual sheep could be applied to a wider range of species and experimental contexts for animal behavior research.

A frequency-domain-based electromagnetic model of the lightning protection system of buildings is presented in this paper. Numerical model can accurately take into account all conductors of the lightning protection system, i.e. air-termination system, down-conductor system and earth-termination system. Using the presented electromagnetic model, attenuation effects of a grid-like spatial shield - sometimes used in lightning protection of buildings - will be analyzed for both the electric field and the magnetic field caused by a lightning strike. Three-dimensional distributions of the fields inside the shield are provided in the paper.

In this paper, a planar simplified dual composite right/left-handed (SD-CRLH) transmission line (TL) structure is proposed and applied to the design of branch-line coupler. The SD-CRLH TL is obtained by a microstrip line with an open-ended stub in spiral form. Since this structure has unusual phase shift characteristics with a transmission zero out of the passband, the branch-line coupler with the planar SD-CRLH TL can achieve both size reduction and harmonic suppression. Such a branch-line coupler operating at 0.915 GHz is investigated and fabricated. The equivalent circuit simulation, full-wave simulation and measurement results agree well with each other. From the results, it is shown that the area of the proposed branch line coupler is reduced by 74% compared to the conventional one while maintaining similar performance, and the second harmonic suppression can be lower than -45 dB.

A novel hexagonal ring-based reactive impedance surface (RIS) has been proposed and comprehensively employed as a ground plane of a circular polarized patch antenna (CPPA) for enhancing impedance bandwidth (IBW) and axial ratio bandwidth (ARBW), simultaneously. Furthermore, a simple analytical model analysis has been developed to estimate the resonance frequency and to predict the surface characteristics of the RIS structure. Two slits over the patch render the antenna to radiate circular polarized (CP) wave. The RIS has improved the CP antenna performance in terms of compactness, improved gain and increased efficiency. The proposed loaded structure has been numerically and experimentally studied with a layout of 40×40×3.2 mm³ at 3.7 GHz. The measured results indicate that the prototype antenna has produced a relatively wider IBW and ARBW of 9.32% and 2.1%, respectively with peak gain about 2.98 dBiC. Both gain and efficiency of the loaded structure have been improved owing to the low conductive loss of the ring-shaped RIS. The proposed CP antenna might be suitable for radar application used in S-band.

The article analyzes a nine-channel Wavelength Division Demultiplexer based on a two-dimensional photonic crystal lattice. In the design of the device, defects and air holes are shifted in the resonant cavities: by changing characteristics such as radii of defects, distance between them and position of defects, a compact optical filter circuit is designed with a 1 nm channel spacing. The properties of these devices are investigated using finite-difference time-domain method. The resonant wavelengths of nine channel demultiplexers are 1481.4, 1503.7, 1526.6, 1538.4 ,1550.3, 1562.3, 1574.7, 1587.2 and 1612.9 nm. The value of transmission efficiency for channels was obtained in 79-96% range. In addition, the maximum value of crosstalk and average quality factor for channels were calculated -11.3 dB and 2000, respectively. The overall size of the structure is small (11.3 μm × 15.3 μm) which is suitable for photonic integrated circuits and optical communication network applications.

Traditionally, the direction of arrival (DOA) estimation usually employs homogeneous antenna arrays consisting of many identical antennas. This paper proposes a new technique of DOA estimation by using a heterogeneous array which has many elements with each element pointing to a different direction from others. A general expression of the manifold for planar heterogeneous array is derived. Then, a polarized MUSIC (Pol-MUSIC) method for unknown polarizations is proposed. One advantage of this Pol-MUSIC method is that it can obtain the DOA of signals with any unknown polarizations while no search of the polarizations is required. The proposed method is verified by simulation, and its performance is analyzed. The heterogeneous array is a polarization-sensitive array though it has one channel at each point of spatial sampling. This provides favorable conditions for simplifying the systems.

In order to effectively improve the communication quality in the extremely-low frequency (ELF) communication, an integrated model of the analog circuit combined with the multi-channel array algorithm is constructed, and a highly sensitive magnetic sensor is designed. An array algorithm based on generalized singular value decomposition is proposed to find the optimal filter coefficient, and then to achieve the purpose of suppressing interference in ELF communication. In the manufacture of magnetic antenna, the method of partitioned windings divided by acrylic effectively reduces the distributed capacitance of the magnetic antenna, and the rational design of the amplification filter circuit lays the foundation for the interference suppression in the next step. Specific process of the proposed algorithm is deduced. The corresponding evaluation indices are given, and the correlation among evaluation indice is expounded. The simulated and experimental results are discussed respectively. The experimental setups are designed and presented. The results show that no matter which the simulated signal or the experimental data is, the proposed algorithm can effectively suppress the interference, and the output signal to interference ratio is increased by 30 dB.

The electromagnetic characteristics of a high speed IC power distribution network (PDN) are of vital important with the rapid increasing of operation speed and scale down CMOS manufacturing size, in particular, the fundamental electromagnetic theory including impedance and loop inductance of various designed IC power-plane structures. In addition, the area occupancy ratio of slot (AOROS) of irregular parallel-plane structures with multi-slots plays a key role in PDN impedance and loop inductance, where the influence of AOROS on impedance and loop inductance is investigated for various structures. Moreover, experimental work is carried out to validate the influence of AOROS on impedance and loop inductance of the PDN. The simulation and measurement of impedance are performed up to 10 GHz, and a good agreement is obtained between the simulation and experiment.

The Meissner effect is studied by using an approach based on Newton and Maxwell's equations. The objective is to assess the relevance of London's equation and shed light on the connection between the Meissner and skin effects. The properties of a superconducting cylinder, cooled in a magnetic field, are accounted for within the same framework. The radial Hall effect is predicted. The energy, associated with the Meissner effect, is calculated and compared with the binding energy of the superconducting phase with respect to the normal one.

The joint direction-of-arrival (DOA) and frequency estimation problem has received significant attention recently in some applications, including pulsed Doppler radar, multipath parameter estimation, etc. This paper presents a novel virtual space-frequency matrix method to estimate the DOA and frequency jointly. Via the temporal smoothing technique, a virtual space-frequency matrix is defined, which includes the information of the incident DOAs and the frequencies. Making using of the proposed method, both the frequencies and DOAs can be estimated by eigenvalues and the corresponding eigenvectors of the new defined virtual space-frequency matrix, respectively. Therefore, the pairing of the estimated DOAs and frequencies is automatically determined. Compared with related works, the proposed method can provide superior performance, such as higher estimation accuracy, without the procedure of parameter search or parameter matching. Simulation results are presented to demonstrate the efficacy of the proposed approach.

This paper aims to study the plasma discharge process of a 5 kW hall thruster developed by Lanzhou Institute of Physics and to provide the knowledge for implementing an improved thruster design. A 2D Particle-In-Cell (PIC) model is built, in which the electron-electron and electron-ion Coulomb collisions are included, in addition to the elastic, excitation, and ionization collisions between electrons and neutral atoms, and the elastic and charge-collisions between ions and neutral atoms. Different Bohm diffusion coefficients are applied in different regions to simulate the Bohm diffusion. The deviation between the simulated and experimental results of the thruster performance is within 15%, validating the accuracy of the model indirectly. The discharge process including the transient and steady-state oscillations is well reproduced. The character of the plasma during different phase of the discharge process including the plasma density and ionization rate is simulated and analyzed. Finally, the probable factor causing the anode erosion is determined.

In view of lower power density and being unable to produce big radial force, this paper presents a new design of the hybrid excitation double-stator bearingless switched reluctance motor, which combines conventional double-stator bearingless switched reluctance motor (DSBSRM) with rare-earth permanent magnetic materials of high performance. Firstly, the basic structure and principle of the hybrid excitation DSBSRM are introduced. Secondly, the electromagnetic analysis is performed on the motor by two-dimensional finite element analysis (2D FEA), and the comparison is made between the proposed motor and traditional DSBSRM. Thirdly, the magnetic equivalent circuit (MEC) is established to deduce the mathematical models of the radial suspension force, torque and inductance. The current stiffness coefficient and displacement stiffness coefficient are derived by linearizing the mathematical models. Finally, the mathematical models are proved to be correct by 2D FEA.

In 2016 a study reported observing a concentration of magnetite nanocrystals in human brains, with four orders of magnitude larger than previously thought. In the context of magnetite's role and function inside the human brain not being properly understood, this development prompts a question concerning the impact that a significant magnetic near-field component, in the hundreds of MHz range, might have on power loss in tissues having ferrimagnetic properties. This article highlights the importance of thorough research on possible thermal and non-thermal effects that could be caused by the magnetic field component to which one could be exposed while using certain communication devices near or in front of the head. Furthermore, this article provides preliminary estimations of magnetic contribution to the specific absorption rate (SAR) of energy deposition in tissues, using two approaches - one based on existing research concerning magnetic hyperthermia, and the other one based on a simulation model that takes into account the magnetic properties of tissues. By simulating the propagation of a 440 MHz wave in a ``magnetic'' (as opposed to pure dielectric) brain, we observed changes of the SAR values, and, more importantly, superficial hot spots appeared at the surface of small magnetite particles, distributed in the homogenous brain.

The eigen-mode technique of rigorous diffraction theory is employed for computation of spatial structure of electromagnetic field, arising under diffraction of a plane wave by a narrow slot of the width of the order of the wavelength or smaller in a perfectly conducting screen of finite thickness. The effects of little step change and of strong enhancement for relative averaged energy density are investigated in dependence of the slot width and depth. It is shown that the field in a space behind the slot represents the sum of a field, slowly and monotonically decreasing in the directions away from a slot, and a harmonic field with sinusoidal spatial inhomogeneities of the order of the wavelength. It is established that the comparative contributions of these two field constituents are unequal for various spatial components of the electric and magnetic fields, and also that the contribution of the first constituent decreases with increase of the slot width.

A compact printed multi-band frequency reconfigurable patch antenna for 4G LTE applications is presented in this paper (50 x 60 x 1.6 mm³). The antenna consists of W-shaped and Inverted-U shaped patch lines connected in a Tree-shape on the front side of the antenna. The back-side of the antenna contains a 90°-tilted T-shaped strip connected with an Inverted-L shaped strip which is shorted with a patch on the front side for increasing the electrical length to cover lower frequency bands. Frequency reconfigurability is achieved by inserting three switches i.e., PIN diodes. The most critical part of this work is the designing of RLC-based DC line circuits for providing the DC biasing to the PIN diodes used as switches and inserting them at optimum locations. This antenna is reconfigurable among eight different 4G LTE frequency bands including 0.9 GHz, 1.4 GHz, 1.5 GHz, 1.6 GHz, 1.7 GHz, 1.8 GHz, 2.6 GHz, 3.5 GHz and WLAN band 2.5 GHz. The antenna exhibits different radiation patterns having a different direction of peak gain at different frequencies and for different switching combinations. The antenna is simulated with CST, and a prototype is fabricated to compare the measured and simulated results with good accuracy.