An electromagnetic analysis is presented for experiments with strong permanent disc magnets. The analysis is based on the well known experiment that demonstrates the effect of circulating eddy currents by dropping a strong magnet through a vertically placed metal cylinder and observing how the magnet is slowly falling through the cylinder with a constant velocity. This experiment is quite spectacular with a super strong neodymium magnet and a thick metal cylinder made of copper or aluminum. A rigorous theory for this experiment is provided based on the quasi-static approximation of the Maxwell equations, an infinitely long cylinder (no edge effects) and a homogeneous magnetization of the disc magnet. The results are useful for teachers and students in electromagnetics who wish to obtain a deeper insight into the analysis and experiments regarding this phenomenon, or with industrial applications such as the grading and calibration of strong permanent magnets or with measurements of the conductivity of various metals, etc. Several experiments and numerical computations are included to validate and to illustrate the theory.

The split-step Fourier (SSF) algorithm is applied to simulate the propagation of radio waves in an atmospheric duct. The refractive-index fluctuation in the ducts is assumed to follow a two-dimensional Kolmogorov power spectrum, which is derived from its three-dimensional counterpart via the Wiener-Khinchin theorem. The measured profiles of temperature, humidity and wind speed in the Gulf area on April 28, 1996, are used to derive the average refractive index and the scaling parameters in order to estimate the outer scale and the structure constant of turbulence in the atmospheric boundary layer (ABL). Simulation results show significant turbulence effects above sea in daytime, under stable conditions, which are attributed to the presence of atmospheric ducts. Weak turbulence effects are observed over lands in daytime, under unstable conditions, in which the high surface temperature prevents the formation of ducts.

A three-stage recursive approach is proposed to improve the recovered distribution of electric parameters in a well-logging environment. The first stage is executed using the conventional linear sampling method (LSM) and the contrast source inversion (CSI) method. In the second stage, the background distribution is updated to better identify the target shape, using the recovered results in the first stage. In the third stage, the background distribution is made closer to the results in stage two, which improves the recovered distribution near the target boundary. The effect of noise is also simulated.

In this paper, a vehicular antenna design scheme considering the vehicular body effects is proposed. A wire antenna for GPS and LTE is implemented on the plastic plate, then it is mounted on the front glass. The outputs are commonly used to share the feed. It is necessary for GPS to increase the right hand circularly polarization (RHCP) gain near the zenith and to reduce the axis ratio while for LTE to increase the horizontal and vertical polarization (HP and VP) gain in the horizontal plane. Also for LTE, multiband characteristics are required. In order to achieve the specified performance, the antenna shape is optimized by Parato genetic algorithm (PGA). When the antenna is mounted on the body, the performance is seriously changed. To evaluate performance of the antenna mounted on the body with a complex shape, a commercial electromagnetic simulator (Ansoft HFSS) is used. To apply electromagnetic results output by HFSS to PGA algorithm operating on the MATLAB, MATLAB to HFSS linking program via Visual BASIC (VB) script was used. It is difficult to carry out the electromagnetic analysis with the whole body because of limitations of the calculating load and memory size. To overcome the limitation, we consider only a predominant part where it has an influence on the performance. It is presented that degradations caused by the body are improved through a series of optimization stages. The simulation results obtained clearly show that it is well optimized at 1.575 for GPS and 766.5 MHz and 2.135 GHz for LTE, respectively.

In this paper we present a detailed theoretical analysis of lateral and angular misalignment effects in RF coils. Radio-frequency (RF) coils are used extensively in the design of implantable devices for transdermal power and data transmission. A design procedure is established to maximize coil coupling for a given configuration to reduce the effects of misalignment on transmission efficiency. Formulas are derived for the mutual inductance between all possible coil configurations including the coils of cross section, thin solenoids, pancakes and filamentary circular coils whose axes are laterally and angularly displaced. Coils are in air. In this approach we used the filament method and the mutual inductance between filamentary circular coils placed in any desired position. We completely describe all mathematical procedures to define coil positions that lead to relatively easy method for calculating the mutual inductance between previously mentioned coils. The practical coils in implantable devices fall into two categories: disk coils (pancakes) and solenoid coils. From the general approach for calculating the mutual inductance between coils of rectangular cross section with lateral and angular misalignments the mutual inductance between misalignment solenoids and disks will be calculated easily and accurately.

In this paper, we present a full-wave semi-analytical solution to calculate the self and mutual impedances of two coupled spiral inductors with rectangular cross sections. In low-frequency electromagnetism, the self and mutual impedance of planar spiral inductors can be obtained based on the eddy current approximation, where the displacement current is disregarded. As the frequency increases, the size of the system can be designed to be smaller. However, the displacement current becomes more important in inductively-coupled systems. By directly deriving the Maxwell's equations without the eddy current assumption, the obtained full-wave model could be applied to both homogeneous and planarly layered media for wireless power transfer systems. Compared to the traditional methods, the newly derived impedances show a considerable discrepancy at GHz frequencies for millimeter-sized inductors, indicating the significance of the displacement current if the operating frequency of wireless power transmission reaches the GHz-range.

A novel compact wideband differential bandpass filter with wideband common mode suppression using a Marchand balun is presented in this paper. Open/shorted coupled lines and stubs are used to improve the selectivity for the differential mode and common mode suppression. The demonstrated filter with a compact size of 50 mm × 30 mm exhibits a fractional bandwidth of 53% centered at 3.0 GHz and 13 dB common-mode suppression from 0 to 9 GHz. The theoretical and measured results agree well with each other and show good in-band performances.

This paper presents a compact tri-band bandpass filter (BPF) with high selectivity. The proposed filter utilizes novel stub-loaded quarter-wavelength resonators and conventional uniform quarter-wavelength resonators. The latter is embedded in the former, and they are separated by a feed line. Due to these quarter-wavelength resonators, the total size is greatly reduced. Moreover, the passband frequencies can be controlled individually. To enhance its selectivity, source-load coupling is employed. For demonstration, an experimental filter is implemented. High skirt selectivity and suppression levels are observed in the measured results. The circuit area of the filter is 0.17λ_g×0.19λ_g, featuring compact size.

In this paper, a compact band-stop filter with a wideband and high-selectivity performance is proposed and analyzed. This band-stop filter includes two parallel-coupled lines of different electrical lengths and two open-circuit stubs. A lossless transmission line model is used to obtain the filter design parameters. In order to verify this new filter circuit structure and its corresponding design theory, five groups of numerical examples are demonstrated. Finally, a practical band-stop filter with a 3-dB cutoff frequency bandwidth of 58.2% centered at 0.94 GHz has been designed, simulated and measured. The measured results show a good agreement with the simulated responses.

A Fabry-Perot interferometer sensor based on a fiber-tip bubble-structure micro-cavity is proposed, fabricated, and demonstrated for transverse load sensing. The micro-cavity is fabricated by using arc discharge at the end of a multimode fiber which has been processed with chemical etching. A transverse load sensitivity of 3.64 nm/N and a relative low temperature sensitivity of about 2 pm/°C are experimentally demonstrated for the proposed fiber-tip bubble-structure micro-cavity sensor. The sensor has the advantages of low-cost, ease of fabrication and compact size, which make it a promising candidate for transverse load sensing in harsh environments.

A new out-of-phase power divider (PD) without phase shifter at the output ports is proposed. Based on admittance matrix, a new topology of uniplanar power divider with symmetrical outputs is designed. Under conditions of good matching, perfect isolation, and 180° phase difference between two output ports, the corresponding design equations and synthesis procedures are derived and given with admittance matrix. To verify the design approach, an out-of-phase power divider operating at 2 GHz with equal power division ratio is designed, fabricated, and measured. Experimental results demonstrate that the input return loss is better than 32 dB, the insertion loss is less than 0.29 dB and the isolation is better than 33 dB. The amplitude imbalance between the output ports is 0.03 dB and the phase difference between the two output ports is 181.6 °at the operation frequency. Further more, 49.9% relative bandwidth of 15 dB return loss and 39.4% relative bandwidth of 20 dB port isolation are achieved.

The accuracy of scattering measurements in near-field millimeter-wave cylindrical scanning imaging system is often degraded by the contamination from additive noise and clutter. Thus, efficient noise removal technique is necessary to achieve accuracy improvement. This paper proposes an independent component analysis denoising algorithm, which relies on the assumption of statistical independence of the sources, where high order statistical properties are used. In the algorithm, the virtual noise components are incorporated into the independent component analysis model, which expands original one-dimensional observation to virtual multi-dimensional observations. The computationally efficient sources estimation technique is presented, based of joint diagonalization of fourth order cumulant matrix. The high speed millimeter-wave near-field cylinder scanning imaging system is set up to verify the denoising results of range profiles, three-dimensional scatter intensity and two-dimensional projection images. The results indicate both the feasibility and validity of the proposed denoising algorithm to be applied in the near-field millimeter-wave cylindrical scanning imaging system.

During the last two-three decades the importance of computer simulations based on numerical full-wave solutions of Maxwell's has continuously increased in electrical engineering. Software products based on integral equation methods have an unquestionable importance in the frequency domain electromagnetic analysis and design of open-region problems. This paper deals with the surface and volume integral equation methods for finding time-harmonic solutions of Maxwell's equations. First a review of classical integral equation representations and formulations is given. Thereafter we briefly overview the mathematical background of integral operators and equations and their discretization with the method of moments. The main focus is on advanced techniques that would enable accurate, stable, and scalable solutions on a wide range of material parameters, frequencies and applications. Finally, future perspectives of the integral equation methods for solving Maxwell's equations are discussed.

The diffraction by a finite sinusoidal grating is analyzed for the H-polarized plane wave incidence using the Wiener-Hopf technique combined with the perturbation method. Assuming the depth of the grating to be small compared with the wavelength and approximating the boundary condition on the grating surface, the problem is reduced to the diffraction problem involving a flat strip with a certain mixed boundary condition. Introducing the Fourier transform for the unknown scattered field and applying an approximate boundary condition together with a perturbation series expansion for the scattered field, the problem is formulated in terms of the zero-order and first-order Wiener-Hopf equations. The Wiener-Hopf equations are solved via the factorization and decomposition procedure leading to the exact and asymptotic solutions. Taking the inverse Fourier transform and applying the saddle point method, the scattered field expression is explicitly derived. Scattering characteristics of the grating are discussed in detail via numerical examples of the far field intensity.

Theory, numerical simulation, and experiment on the interaction of electromagnetic wave with suddenly created periodic plasma layers are presented. In the experiment, frequency-downshifted signals of considerably large spectral width and enhanced spectral intensity were detected. Numerical simulation of the experiment, that the plasma has a finite periodic structure and is created much faster than its decay, shows that the frequency downshifted waves have a broad power spectrum and are trapped in this plasma crystal until the plasma frequency drops to become less than the wave frequency. The spectral power increases exponentially with the frequency of the frequency downshifted wave, consistent with the experiment. The simulation reveals that wave trapping results in accumulating the frequency-downshifted waves generated in the finite transition period of plasma creation and decay. Though frequency-upshifted signals were missing in the experimental measurement, it might be attributed to the collision damping of the plasma.

The method of a T-shaped antenna loading T-shaped slots for multiple band operation is presented in this paper. Inspired by the fractal antenna, the proposed method is intended to be used for designing multiple band antennas. Through loading T-shaped slots in the terminals of a T-shaped antenna, dual or triple operating bands can be achieved. In order to validate the feasibility of this method, this type of antenna is designed and simulated. The antennas are respectively fed by two different feeding transmission lines (microstrip transmission line and coplanar waveguide (CPW) transmission line) for the purpose of identifying the method that can be commonly used. The parametric analysis in detail has been given to explain the effects of the key parameter variations. For WLAN and WiMAX applications, the antennas are fabricated and measured. Both simulated and measured results are presented to demonstrate the feasibility of these designs.

This paper presents a general method to isolate the compact dual-element antenna for mobile radio communications. The basic concept to cancel the coupling current is proposed, and two individual implemental solutions, connecting the transmission lines and the antenna elements, are illustrated respectively. Two examples targeted at 2.4 GHz ISM band have been implemented for the practical cellular phone environment. The antennas are well designed followed by the proposed principle. The result shows that the magnitude of S₂₁ between two ports can be no higher than -10 dB in the interested bandwidth after applying the proposed methods. Good agreements are observed between measurements and simulations. It is suitable for application to mobile terminals due to its relatively low profile and good MIMO performance.

The traditional coplanar electromagnetic bandgap (EBG) structure is analyzed. The method is studied to lower the center frequency and broaden the bandwidth in this paper. A novel structure of U-bridged EBG power plane is proposed. The simulation and test results show that the bandwidth of the new structure is 4.32 GHz, and the lower side cutoff frequency is at 380 MHz with stopband depth at -40 dB. The elimination of simultaneous switching noise (SSN) as this kind of U-bridged coplanar EBG structure is more effective below 1 GHz. In addition, the eye diagram of the structure is analyzed. The degradation of the maximum eye open and the maximum eye width on the structure is about 1.2% and 5.7% respectively. Finally, the IR-drop and dc resistance is accurately investigated through 3-D simulations.

The analytic expressions for the absorption coefficient (ACF) of a weak electromagnetic wave (EMW) by confined electrons in rectangular quantum wires (RQWs) in the presence of laser radiation modulated by amplitude are calculated by using the quantum kinetic equation for electrons with the electron-optical phonon scattering mechanism. Then, the analytic results are numerically calculated and discussed for GaAs/GaAsAl RQWs. The numerical results show that the ACF of a weak EMW in a RQW can have negative values, which means that in the presence of laser radiation (non-modulated or modulated by amplitude), under proper conditions, the weak EMW is increased. This is different from the similar problem in bulk semiconductors and from the case of the absence of laser radiation. The results also show that in some conditions, when laser radiation is modulated by amplitude, ability to increase a weak EMW can be enhanced in comparison with the use of non-modulated laser radiation.

In a real airborne synthetic aperture radar (SAR), its major phase errors are usually composed of two categories, such as slow-time varying phase errors (less than several cycles of change in phase during synthetic aperture time) and fast-time varying phase errors (otherwise, including wide band random) according to the motion of aircraft. If the fast errors are no more negligible compared to the slow errors, they should be estimated and then compensated accurately to obtain a well focused image. However, it is not proper to estimate all phase errors at the same time like conventional autofocus techniques because the estimation of the fast-time varying phase errors are seriously affected by blurring in image due to the slow-time varying phase errors. In this paper, we presents an accurate hybrid phase estimation technique using two independent estimation stages of sub-aperture and an iterative golden section search method, which has advantages over several existing methods, because of its better estimation accuracy and less sensitive to the quality of extracted range bins as well as requiring less computation time. The performance of our method is illustrated by simulations of point targets and an experiment with real SAR data.