This paper presents a Ku-band filter based on groove gap waveguide (GGW) technology which is composed of a filter with two transitions GGW and WR-62. The filter is operated from 13.8 GHz to 14.2 GHz. Actually, a fractional bandwidth of about 2.85% is obtained for maximum return loss of 20 dB and the maximum insertion loss of 0.05 dB over the bandwidth. The validity of the design results is confirmed both numerically and experimentally. Measurement results show that the performance of filter agrees well with simulation. This filter could be used as part of a gap waveguide based structure.

A novel flexible frequency and pattern reconfigurable antenna for wireless system is proposed. The antenna is composed of two completely symmetrical radiating elements, a feedline and ground. By controlling the on and off of 8 PIN diodes loaded on the symmetric hexagonal split ring and monopole branches to select the radiation element, the antenna achieves frequency reconfiguration in 1.9G band and 2.4G band, and is capable of steering the beam in two directions in each band. Meanwhile, the antenna works at four states with omnidirectional radiation patterns. Finally, the bending characteristics of the antenna at different bending degrees are analyzed. Measured results are in good agreement with simulations, which denotes that it is suitable for wireless systems.

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 fifth generation (5G) wireless communication systems are projected to work at millimeter wave (mm-wave) frequency bands that would bring new challenges with the implementation of antennas and safety level of electromagnetic field exposures. In this paper, a new design of 5G mmwave antenna for multi-frequency bands has been introduced. The antenna is small enough and has a form factor that can be easily fit into the current available mobile handset devices. The proposed antenna covers all the nominated frequency bands by the FCC for 5G communications and has good radiation performances at 28 GHz, 37 GHz, 39 GHz, and 64-71 GHz. The electromagnetic field exposure to the human head model has been studied by means of numerical simulation for all above frequency bands. The feature of our proposed antenna is that all the frequency bands for the 5th generation mobile handset will be available in a single and simple antenna structure; hence, analysis of EMF exposure in a wide range of frequency can be done on a single antenna design.

Recent years have witnessed an increasing interest in topological states of condensed matter systems, whose concepts have been also extended to wave phenomena. Especially at optical frequencies, several studies have reported applications of structured light exploiting topological transitions and exceptional points or lines, over which a field property of choice is undefined. Interesting properties of light beams with phase singularities (such as the creation, annihilation or motion of these topological points) have been observed in composite vortices

In the last decades, microwave imaging has been a new area of research due to its many advantages over current imaging systems. Microwave imaging system is used for in-depth inspection of biological tissues. The test provides the identification of morphological changes in these biological tissues, as well as their locations. The emerging Ultra-Wideband (UWB) microwave imaging gives better result with the main advantage of using non-ionizing radiation. In these systems, antennas play a very important role, and as such, their optimization has become a very important topic because of the device is placed close to the human body. Thus, many aspects are of great importance in the design of the antennas starting from the material with which it is constructed, its dimensions, operation bandwidth, human body influence on the antenna parameters, short-pulse propagation, etc. Recent research has shown several efforts in improving the electromagnetic sensors used in these systems, either as individual or array elements. In this paper, we provide an overview of the most relevant developments in the field of UWB high directivity sensors used in microwave imaging systems.

This article presents a new method for studying the near-field electromagnetic interaction between a dielectric filled open ended circular waveguide (OECW) and a layered dielectric structure. The proposed model is based on plane wave spectrum theory using a novel and computationally efficient two step integration method. The first integral, involving multiple singularities in the integration path, is efficiently solved using a deformed elliptical integration path which encircles the singularities of the integral. The infinite domain tail integral involving the slowly converging integrand is further solved using an efficient trigonometric transformation. The proposed OECW based method is capable of determining the unknown material properties of any layered dielectric medium, and hence finds application in nondestructive evaluation of materials.

A novel microstrip balun bandpass filter (BPF) is designed by using open loop resonators having interdigital capacitors. The interdigital capacitors are employed to control the center frequency easily. Opposite phase difference between the balanced outputs can be provided according to the suitable coupling topologies based on parallel and anti-parallel coupled lines. By this way, minimized magnitude imbalances between the balanced ports can also be obtained. In order to obtain two poles inside the passband, two identical resonators are coupled to each other. The designed balun BPF was fabricated and measured to validate the proposed methodology. Phase and magnitude imbalances inside the passband were measured within 180±5˚ and 0.5 dB, respectively. The simulated and measured results are in good agreement.

Widely applied in confined areas communication, leaky coaxial cable (LCX) is used as an antenna to provide communication services for mobile devices. In order to improve the quality of mobile communication in narrow and long spaces such as subway or tunnel, the method of designing LCX with circular polarization radiation property is proposed, which consists of aperture's design, circular polarization simulation verification and coupling loss test. Firstly, the regular circumferential asymmetry apertures are designed and slotted in the outer conductor of the LCX to achieve radiating φ component of the electric field, and the optimized size of the aperture for achieving circular polarization is obtained by the simulation results from Ansoft HFSS. Then, the circular polarization characteristics in the maximum radiation direction are obtained. Further, the relation between it and the gain of the optimized aperture is analyzed. Finally, the coupling loss is calculated for evaluating the performance of the LCX. The simulation results show that the two designed LCXs have the circumferential circular polarization range of 30~70 deg in the maximum radiation direction at 900MHz, and the range is twice of the conventional LCX. The coupling loss indicator also meets the requirements.

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.

Partially coherent Lorentz beams have been introduced to describe the output of the diode laser, which have been investigated due to the special spreading properties. The analytical expressions of partially coherent Lorentz beam propagating in oceanic turbulence are derived. Using the derived equations, the average intensity distributions of partially coherent Lorentz beam are analyzed and discussed. It is shown that the partially coherent Lorentz beam with smaller coherence length will evolve into the Gaussian-like beam faster, and the beam propagation in oceanic turbulence will spread faster with increasing strength of oceanic turbulence. The results have potential application in underwater optical communications and sensing.

In this paper, a four switchable beam antenna dedicated to Wireless Sensor Network (WSN) nodes in the 2.4 ISM band (2.4-2.485 GHz) is presented. It consists of two fed monopoles and two loaded parasitic ones. The nature and value of the load are obtained using the Uzkov equations, allowing to determine current weighting coefficients in the case of two separately fed antennas, in order to maximize the gain and the directivity in a given direction. Reconfigurability is achieved using reflector and director elements activated by PIN diodes to reduce the back radiation and pointing in the desired direction. Thus, a first system is obtained which consists of two elements, one fed and the other loaded with an inductor, with a maximum gain of 5.2 dBi in simulation and 4.7 dBi measured at 2.4 GHz in azimuthal directions of 90˚ and 270˚. Then, the system is compared with another, composed of two antennas fed separately. Finally, the same methodology is applied to an array of four antennas, in which two antennas are fed, and two are loaded. This last structure is capable of steering its radiation pattern in the azimuth plane, covering a 360˚ angle with four beams (0˚, 90˚, 180˚ and 270˚). The total gain achieved is 4 dBi for each beam in the azimuth plane.

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.

Graphene, a one-atom thick layer of carbon atoms arranged to form a honeycomb lattice exhibits intriguing mechanical, thermal and electrical properties, which make it attractive for bio- and chemical sensors as well as flexible electronics applications. In this paper, graphene films with different amounts of graphene loading (weight fraction 12.5% and 25%) deposited by screen printing technique are characterized in the microwave frequency range. By fitting the measured scattering parameters of graphene-loaded microstrip lines with Advanced Design System (ADS) circuit simulations, a simple equivalent lumped circuit model of the film is obtained. The proposed equivalent lumped circuit model presented in this paper proves suitable as an initial step towards the full-wave electromagnetic modeling and analysis of graphene loaded microwave structures intended for sensing and tuning applications.

The design of a terahertz short-slot coupler with curved waveguide is proposed. A traditional short-slot coupler uses a step-like structure in order to suppress higher order modes and improve bandwidth. It becomes difficult to control the fabrication of tiny steps with the incensement of frequency especially in terahertz band. The designed coupler is composed of two curved waveguides overlapping in the middle to realize a specific coupling coefficient. Then the step-like structure can be replaced with a curved structure which is much easier to fabricate. The coupling coefficient of the coupler is 3 dB, and the variation is less than 1dB around the center frequency. The phase difference between two output ports is 90°. The isolation is greater than 10 dB in the whole working band. Measured results show high agreement with simulation predictions. The designed coupler can be widely used as feed networks of horn antenna array.

In this paper, an enhanced characteristic basis function method (ECBFM) is proposed to calculate the monostatic radar cross section (RCS) of electrical large targets efficiently. The enhanced characteristic basis functions (ECBFs) are defined by combining improved primary-characteristic basis functions (IP-CBFs) with the first level improved secondary-characteristic basis functions (IS-CBFs) for each block. IS-CBFs are obtained by substituting IP-CBFs for PCBFs in Foldy-Lax multiple scattering equation in which mutual coupling effects among all blocks can be included systematically. As a result, a small number of incident plane waves (PWs) is sufficient when dealing withlarge scale targets. The numerical results demonstrate that the computational efficiency in this paper is much higher than that of the improved primary-characteristic basis function method (IP-CBFM) without losing any accuracy.

Bearingless brushless DC (BBLDC) motor in the flywheel energy storage system has advantages of low energy consumption, high critical speed and better speed adjustment performance. However, torque ripple exists inevitably due to the current commutation of the BBLDC motor and the wide range of speed changes when the flywheel energy storage system charges and discharges. In this frame, an approach of combining the direct torque control (DTC) with the current prediction control (CPC) is proposed to suppress torque ripple in wide speed regulation range. In this paper, the mathematical model of the BBLDC motor is given, and the principle of DTC scheme is introduced. On the basis of analyzing the causes of commutation torque ripple when using DTC scheme, CPC scheme is employed to minimize the commutation torque ripple by controlling the changes of phase current during commutation. During the non-commutation, the DTC is selected, and the CPC is selected during the commutation. Results show that the proposed approach is feasible, and torque ripple is effectively suppressed both in high speed and low speed. Moreover, this method has no effect on the suspension performance.

We performed an experiment to verify quadrupole model of the electric field of a rotating magnet. It is found that the rotating magnet insulated from the earth and enclosed in a conductive insulated screen induces the potential difference across an air capacitor arranged on the outside the screen. The field of an electric quadrupole cannot penetrate through the screen; therefore the electric field detected outside the screen has the source of another nature. The field observed in the experiment can be explained by arising of a fictitious electric charge upon rotating of the magnet in accordance with the transformations of the electromagnetic field in the theory of relativity.

This paper presents a planar, compact 8-element frequency-reconfigurable multiple-input-multiple-output (MIMO) antenna system. The proposed design can be utilized as a communication antenna for cognitive radio (CR) front-end applications. The proposed antenna design contains 8 elements on a single substrate board. Frequency reconfigurablility is achieved using varactor diode in the middle of each antenna element by varying the capacitive reactance of the slot. The proposed antenna system provides very wide frequency tunable characteristics from 1.6 to 2.48 GHz. The proposed design covers several well-known frequency bands like LTE, GSM-1800, PCS-1900, WLAN along with several others. Moreover, rectangular defected ground slots are used between vertically placed antenna elements to enhance the isolation. The complete antenna system is realized on single FR-4 substrate of dimensions 120×60×1.56 mm³. The performance of proposed design is demonstrated by presenting both the simulated and measured results with close agreement achieved between the two which validates the proposed design.