The use of transverse circular representation in circular cylinder coordinate system provides an alternative approach to the solution for vector Helmholtz partial differential equations (VH-PDE) of electromagnetics. After separation, VH-PDE for electric (magnetic) field splits into a set of three ordinary differential (Bessel) equations for two opposite transverse circular polarizations (TCP) and the axial component. The approach is suitable for solving the problem of cylindrical waveguides and cavities starting from the transverse fields. The coupling between TCP fields via the axial component affects nonreciprocal propagation in waveguides. The procedure is illustrated on a dielectric waveguide. It may be extended to the media with circular eigen polarizations including those displaying magnetooptical Faraday effect or optical activity.

This paper presents a dynamic modelling of a series of induction motors (IM) squirrel cage with different shapes of rotor deep bars taking into account the skin effect. The approach is divided into two parts. The first part consists in modelling the skin effect in a rectangular rotor deep-bar with three methods (conventional analytical method, nite element method and analysis method of circuit). These are compared (estimate of the relative error), and subsequently, generalized to more complex forms (trapezoidal, inverted, direct trapezoidal and double cage), done by using the two last methods which take into account the geometrical non-linearity of the slots. The second part consists in a dynamic modelling with variable parameters that take into account the skin effect, simulated for a series of motors with the same power (with different geometric shapes of rotor bars), to see their influence on the starting characteristics of these IM, and the results are compared and discussed.

This paper presents dosimetry of a high resonance wireless power transfer (HR-WPT) system when the transmitter and receiver are aligned and misaligned. An HR-WPT system with two resonant coils and two feeding loops, operating at 13.56 MHz is designed. The power transfer efficiency of the system, and the electric and magnetic fields are investigated using the method of moments. The power transfer efficiency in misalignment situations can be increased by matching the HR-WPT system. Dosimetry of the HR-WPT system is conducted at the optimum matching condition for alignment and misalignment, to achieve the best power transfer efficiency. The specific absorption rate (SAR) is computed using a two-step approach. In the first step, the magnetic fields generated by the HR-WPT system in the absence of a whole-body voxel human model are calculated using the method of moments. In the second step, the SAR in the human model is calculated using the impedance method, with the magnetic fields computed in the previous step regarded as the magnetic fields incident to the human body. Five exposure scenarios are set: one alignment condition and four misalignment conditions. The SAR computed for the alignment and misalignment cases in the matching condition are compared to each other. The compliance of the system is also investigated using the international safety guidelines. Finally, the maximum allowable powers to comply with the guideline are investigated for the five cases considered. The results show that the SARs observed in the misalignment case are higher than those in the alignment case. These results suggest that the misalignment situation should be considered in addition to alignment, when conducting dosimetry of the HR-WPT system.

In this paper, a novel monopole printed fork-shaped antenna for ultra-wideband (UWB) applications with triple band-notched characteristics is presented. The proposed antenna, with compact size of 42×24×1.6 mm³, yields an impedance bandwidth of 3.1-11 GHz for S11 < -10dB, except on the notched bands which are obtained by introducing three different types of slots. A U-shaped and two extended U-shaped defected ground structure (DGS) slots give respectively two notched bands， 3.3 to 3.7 GHz for WiMAX and 7.1 to 7.76 GHz for downlink X-band satellite communication systems. Therefore, a semi arc-shaped slot is etched on the radiating patch to notch the band from 5.15 to 5.825 GHz for WLAN applications. The proposed antenna is fabricated and measured.

We present an angular stable dual-band frequency selective surface (FSS) in this paper. By placing anchor-shaped elements with different structural parameters along x-axis alternately within hexagonal wire grid, the proposed FSS can provide two closely spaced passbands. And the resonant frequency ratios are only 1.16 and 1.19 for TE and TM polarizations, respectively. In addition, the proposed FSS has stable frequency response under oblique incidence, and resonant frequency deviation is below 0.5% within 60° incident angle. An FSS prototype is fabricated and measured for further verification, and good agreements between the simulated and measured results can be observed.

We proposed an efficient method to radiate the spoof surface plasmon polaritons (sspps) to the endfire direction, which added two parasitic strips as directors in front of the dipole antenna fed by the sspps structure. The directors were used to enhance the endfire radiation due to its beam modified function. Both simulated and measured results suggest good performance of the proposed antenna in a narrow band from 6.5 to 6.9 GHz with about 7.5 dBi realized gain and a 5 dBi increase in the endfire direction at the center frequency of 6.8GHz reference to the unloaded structure. Also, the surface electric field distributions of the unloaded and loaded sspps antenna were studied to verify the gain enhancement in the endfire direction in physical perspective. Our work tends to have better performance than other related work, such as broader bandwidth and higher realized gain with even greatly simplified design process. The proposed sspps antenna has potential applications in planer integrated circuits and communication systems.

A broadband right-hand circularly polarized (RHCP) cross-type traveling wave antenna array is proposed for High-Rate Close Proximity (HRCP) point-to-point (P2P) wireless communication system at 60 GHz. Instead of low temperature co-fired ceramic (LTCC) technology, a single-layer structure of the proposed 2x1 element antenna array is fabricated with a conventional printed circuit board (PCB) process, to provide low manufacturing cost and low profile (0.05 λ0 at 60 GHz). A wide impedance bandwidth (57-64 GHz, VSWR < 2) and broad RHCP bandwidth (57-64 GHz, axial ratio (AR) < 3 dB) are achieved. The RHCP gain is higher than 6 dBic in the entire operating frequency band (57-64 GHz).

In this paper, the inverse scattering of a conducting cylinder is given by modified fireworks algorithm. Initially, the direct scattering is formulated as an integral equation, which contains the target shape function. The scattering integral equation is then solved by the moment method. To achieve image reconstruction, the target shape function is expanded as a Fourier series. The inverse scattering is transformed into a nonlinear optimization problem. The variables are Fourier series coefficients of the target shape function. The objective function is defined by comparing the scattered electric fields of guessed and true shapes. This nonlinear optimization problem is then optimized by our modified fireworks algorithm. The fireworks algorithm is a novel swarm intelligence algorithm for global optimization. It is inspired by practical fireworks explosion. In this paper, it is suitably modified so that it can treat the inverse scattering problem with fast convergence. Numerical results show that the inverse scattering based on our modified fireworks algorithm can accurately reconstruct the target shape with fast convergence.

In this paper, a new flower-shaped microstrip line feed reconfigurable band-notched UWB monopole antenna using single varactor diode is introduced and fabricated. Different notch frequencies can be obtained using different capacitor values. The effect of changing the varactor position is also examined. The flower shape is first optimized to obtain UWB characteristics. Then, a slot is made in the microstrip line to be loaded later with a single varactor diode. A wide range of notch frequencies can be obtained using this simple configuration which cover most of the narrow band coexistence systems. The notch frequency can be lower by increasing the capacitance value. The notch frequency covers the WLAN band when C=0.8 PF and covers the WIMAX band when the capacitance is changed to 0.7 PF for the same antenna configuration and varactor position. Two prototypes of the proposed antenna using two different single capacitor elements with capacitances 0.6 PF and 1.5 PF are fabricated, and their reflection characteristics are measured and compared with the simulated ones. Notch frequencies at 6.1 GHz and 4.3 GHz are obtained respectively in both simulated and measured antenna structures. The proposed antenna a directive radiation pattern in E-plane and omnidirectional pattern in H-plane. Also the gain is suppressed in the notched frequencies. The group delay is nearly stable in the UWB frequency range with very little variations, but it is distorted sharply at the notch frequencies. So, the proposed antenna is a good candidate for the modern UWB systems.

In this paper, a compact ultra-wideband bandpass filter using a back to back Coplanar Waveguide (CPW)-to-microstrip transition structure is proposed. Compared with traditional ultra-wideband bandpass filters using hybrid structures, the proposed filter has a sharper selectivity because of two transmission zeros located at the lower and upper edges of the passband, respectively, generated by a modified T-shaped stub. Moreover, to further improve its out-of-band performance open stubs are introduced to produce extra transmission zeros at high frequency. A prototype of the proposed filter is fabricated and measured. The results show that the proposed filter achieves a bandwidth of 133% from 2.4 to 11.9 GHz, and the selectivity (skirt factor) is optimized from 50% to 92% compared to a former ultra-wideband (UWB) bandpass filter (BPF) with a similar structure. Besides, the proposed filter can offer some other advantages such as good return loss, low insertion loss, stable group delay, and compact size (16×7.55mm²). This filter can be a good candidate for UWB applications.

The article presents a research of the effect of different types of short circuits (SC) on the performance of the gas turbine and ultra-high-speed microgenerator (MG) in a wide frequency range (from 200 000 rpm to 1,000,000 rpm) at a power from 10 W to 1 kW. The studies are carried out on a specific two-pole 100 W, 500,000 rpm microgenerator with permanent magnets with a toroidal winding. The research is carried out by finite element method using Ansys Maxwell software. Numerical study by the finite element method is performed at the rated operation mode and various types of short circuits: single-phase, two-phase, three-phase circuits coil inside MG. By the results of these studies, we estimate a negative impact of different types of faults on the parameters of MG and the mechanical characteristics of the gas turbine. Also we consider various options MG with SC for various types of bearings. Then, using the full-sized 100 W sample we carried out experimental studies of the MG operation in nominal operation mode at the 500,000 rpm. That allows to verify the developed computer model and confirm the results of our practice research. The obtained results can be used in the aerospace industry for design the high reliability complexes such as new energy systems for satellite power supply, unmanned aerial vehicles and microturbines. In addition, it can be used to design the ultra-high-voltage electric machines with a high fault tolerance for the compressor plants, air supply systems of hydrogen fuel cells, new medical tools and machine tools.

Objective: As well known, using a single body worn sensor exposimeter introduces systematic errors on the measurement of the incident free space electric field strength. This is because the body creates around it high, intermediate and low level field zones, which depend on the direction of arrival of the incident field. The goal of this work is to propose an efficient method for the reduction of these errors. Methods: After classifying the perturbations induced by the body on the measured electric and magnetic fields thanks to realistic numerical simulations, we then propose a two-sensor setup in conjunction with simple semi-empirical correction formulas, in order to compensate these perturbations. Results: At 942 MHz, when the two sensors are placed in any opposite sides of the body at chest height, the worst case, maximum and average errors respectively decrease to 12% and 3% compared to 83% and 22% for measurement techniques using a single sensor, or 32% and 11% when using the average value of the measurements. Conclusion: The error related to the measurement in the presence of the body was significantly reduced by the proposed method making use of two opposite sensors, E-field and H-field at the chest. Significance: The conformity of exposure to EMF in terms of reference values according to the ICNIRP is given in the abscence of the human body. The interest of this work lies in the reduction of the errors made when measuring the field in the presence of the body.

Two novel compact 2.6/5.2 GHz diplexers with high common-mode suppression were designed and fabricated on the FR4 substrate. The diplexers were designed based on two open loop rectangle ring (OLRR) resonators and the two different resonant frequencies could be easily obtained by tuning the lengths of OLRRs. In the past, the traditional balun diplexer needed matching circuit to transfer signal to radio frequency (RF) transceiver with low loss because of the existence of unmatched impendences between the balun diplexer and RF transceiver. In order to improve their efficiency and low down the cost of the fabricated circuits, we would propose a method to tune the output impendence of the balun diplexer and the diplexer could have matching output impendence with the RF transceiver. The proposed balun diplexer had the structure of two stub-loaded microstrip lines, and the needed output impendence could be changed by tuning the widths of microstrip lines and stubs and by changing the length and position of stubs. For that, if the output impendence is well tuned, the designed balun diplexer will have the higher efficiency and low cost because the matching circuit is not necessary.

In stomach tumor imaging, traditional time domain algorithm, i.e., back projection (BP) algorithm, and traditional frequency domain algorithm, i.e., frequency wave number migration (F-K) algorithm, can locate tumor target accurately. However, BP and F-K algorithms perform poorly in identifying tumor sizes and shapes. The algorithms must consider the influence of various tissues in the human body: the attenuation of the signal strength of electromagnetic waves, the decrease in speed and the refraction due to the different permittivities between different organs of the body. These factors will eventually lead to image offset and even generate a virtual image. It is effective to refrain the displacement of image with modifying the time element of the imaging algorithm by iteration. This paper proposes a method based on combination of support vector machine (SVM) with BP and F-K algorithms to solve problems in recognizing tumor shape. The method uses field strength obtained by BP and F-K algorithms as input in SVM to establish the SVM model. Based on BP algorithm, recognition method for SVM includes the following characteristics: short prediction time of SVM and good virtual elimination effect. However, the algorithm requires long periods and possibly misses tumor targets. Except the same characteristics as BP algorithm: short prediction time of SVM and good virtual elimination effect, F-K algorithm also works more efficiently, does not miss any tumor targets, and conforms more with requirements of real-time imaging. When the data are contaminated by noises, the tumor shape in the stomach can still be suitably predicted, which demonstrates the robustness of the method.

In this article, a compact ultra-wideband (UWB) band-pass filter (BPF) with wide upper stopband is presented. The filter is designed with a UWB response from 3.2 GHz to 10.8 GHz with low insertion loss of 0.9 dB and less than 0.19 dB at the center frequency (6.67 GHz). The filter is also designed with a broad upper stopband with high rejection level of 20 dB. The group delay is flat with maximum of 0.4 ns. The proposed UWB filter is constructed by using a pair of parallel coupled lines and two ring resonators. In this design, the ring resonators provide two new excited modes to widen the desired UWB passband and also create two tunable transmission zeros to achieve a wide stopband. Good agreement is observed between simulated and measured performances of the UWB filter.

New generation wireless communications are expected to provide new services over the existing variety of wireless applications in the coming years. In this perspective, advances in utilization of computational electromagnetics (EM) and millimeter-waves (mmW) frequency bands make them as candidates for ultra-high-resolution and ultra-high-speed wireless communications. With the deployment of mmW wireless technologies, brinks of potential mmW induced biological and health effects should be evaluated carefully. The EM exposure is usually measured in terms of absorbed power from any user operating wireless devices. The exposure varies with the part of the body and location of the source that is exposed to the radio frequency waves. The purpose of this study is to observe EM exposure in terms of Specific Absorption Rate (SAR) and temperature elevations at mmWs from the designed Antipodal Linear Tapered Slot Antenna (ALTSA) at 60 GHz on different body parts utilizing EM computations and experiments with Infrared Thermal Camera.

In this paper, a microstrip lowpass filter with -3 dB cutoff frequency of 1.8 GHz composed of two resonators with different polygon patches and six symmetric suppressing cells is presented. To design the proposed filter, the impact of each microstrip transmission line on the scattering parameters of the employed resonators is separately determined by extracting the equations of the insertion loss (S21) and return loss (S11) on the basis of their equivalent LC circuit. The designed filter is fabricated and measured, and a good agreement between the results of simulation and measurement is obtained. In the whole stopband region, a return loss better than -0.35 dB and an acceptable suppression level of -22 dB from 1.87 to 19.75 GHz are achieved. Furthermore, a flat insertion loss in the passband and an acceptable return loss (-19.32 dB) in this band can verify desired in-band performance. The designed lowpass filter has a high figure of merit about 36969.34.

A varactor-tuned microstrip bandpass filter (BPF) with independently tunable center frequency and bandwidth is proposed in this paper. The proposed BPF with a simple configuration is composed of a half-wavelength transmission line with both ends short-ended and a T-shaped transmission line. Meanwhile, two varactors are inserted symmetrically in the middle section of the half-wavelength transmission line to adjust the resonant frequency. The T-shaped transmission line is connected to the half-wavelength transmission line by a lumped capacitor. In addition, two inductors loaded symmetrically in the feed line are employed to control the coupling coefficient. It is convenient to adjust the frequency and bandwidth of the filter independently by using only three varactors, which simplifies the circuit structure greatly. The predicted results on S parameters are compared with the measured ones, and a reasonable agreement is achieved.

This paper presents a new hybrid switching technique for enhanced pulse mode solid-state power amplifiers (SSPAs). In the proposed technique, pulse timing for bias stabilization is effectively decoupled from pulse amplification. The decoupling allows fast pulse switching by reducing the pulse width and increasing the pulse repetition frequency (PRF). The new switching method is applied to an X-band SSPA using GaN HEMT. The advantage of the proposed method is demonstrated by its excellent pulse characteristic. The proposed technique achieves a fast PRF of 100 kHz and a narrow pulse width of 1 μsec. The measured rise/fall time (RFT) is 12.5/11.1 nsec, which is more than four times less than that of previous works. In addition, an excellent pulse droop of 0.43 dB is achieved with an output power of 51.3 dBm at 9.9 GHz. The fabricated SSPA shows a maximum output power of 135 W, a small-signal gain of 47 dB, and power added efficiency (PAE) of 28.2% at 9.9 GHz. These results show that the proposed pulse switching technique provides a promising solution for SSPAs using a high-power GaN HEMT.

The Weibel instability of intense and collimated MeV fast electron beams in multi-layer structure is investigated. It is found that the electromagnetic instability of fast electron beams can be significantly suppressed by this structure. A strong magnetic field will be created at the interfaces between materials with different resistivities as these fast electrons are injected into this structure. It obstructs the transverse movement of the fast electrons and confines them to propagate along the interfaces. In consequence, the positive feedback loop between magnetic field perturbation and electrons density perturbation is broken, and the Weibel instability is thus weakened. Furthermore, the calculated results for Au/Si multi-layer structure by a hybrid Particle in Cell code have proven this weakening effect on the Weibel instability of intense fast electron beams. Because of the high energy-density delivered by the MeV electrons, these results indicate applications in high-energy physics, such as radiography, fast electron beam focusing, and perhaps fast ignition.