We derive van der Waals-London and Casimir forces by calculating the eigenmodes of the electromagnetic field interacting with two semi-infinite bodies (two halves of space) with parallel surfaces separated by distance d. We adopt simple models for metals and dielectrics, well-known in the elementary theory of dispersion. In the non-retarded (Coulomb) limit we get a d^-3-force (van der Waals-London force), arising from the zero-point energy (vacuum fluctuations) of the surface plasmon modes. When retardation is included we obtain a d^-4-(Casimir) force, arising from the zero-point energy of the surface plasmon-polariton modes (evanescent modes) for metals, and from propagating (polaritonic) modes for identical dielectrics. The same Casimir force is also obtained for "fixed surfaces" boundary conditions, irrespective of the pair of bodies. The approach is based on the equation of motion of the polarization and the electromagnetic potentials, which lead to coupled integral equations. These equations are solved, and their relevant eigenfrequencies branches are identified.

Ultra-Wide Band (UWB) technology is a new, useful and safe technology in the field of wireless body networks. This paper focuses on the feasibility of estimating vital signs --- specifically breathing rate and heartbeat frequency --- from the spectrum of recorded waveforms, using an impulse-radio (IR) UWB radar. To this end, an analytical model is developed to perform and interpret the spectral analysis. Both the harmonics and the intermodulation between respiration and heart signals are addressed. Simulations have been performed to demonstrate how they affect the detection of vital signs and also to analyze the influence of the pulse waveform. A filter to cancel out breathing harmonics is also proposed to improve heart rate detection. The results of the experiments are presented under different scenarios which demonstrate the accuracy of the proposed technique for determining respiration and heartbeat rates. It has been shown that an IR-UWB radar can meet the requirements of typical biomedical applications such as non-invasive heart and respiration rate monitoring.

An improved finite-difference time-domain (FDTD) method has been extended to analyze the antennas with complicated lumped/active networks in this paper. The improved FDTD method is based on a novel integral transform and the matrix theory. Combing the novel integral transform with Kirchhoff's circuit laws, the hybrid networks comprised of high order linear and nonlinear elements with arbitrary connection can be modeled by a stable matrix equation. An effective model is built for the linear lumped networks including the internal independent sources. A wire antenna loaded with wideband match network and a two-element active patch antenna loaded with Gunn diodes are analyzed by the developed techniques. The analysis results indicate that the improved matrix-type FDTD method is not only stable and accurate, but also time-saving in simulating the complicated hybrid networks.

A new efficient technique for the analysis of complex antenna around a scatterer is proposed in this paper, termed the iterative vector fields with uniform geometrical theory of diffraction (UTD) technique. The complex field vector components on the closed surface enclosing the antenna without platform are computed by higher order Method of Moments (MOM), and the scattered fields from the platform are calculated by UTD method. The process of iteration is implemented according to the equivalence theorem. Based on this approach, an approximation method is outlined, in which the computational time is saved largely, while the accuracy is not reduced. The relative patterns obtained from the present method and the approximation method both show good agreements with that obtained from MOM.

In this paper, some important concepts about the defected microstrip structure (DMS) and defected ground structure (DGS) interconnections are introduced. In concept number one, three different types of interconnections are analyzed for determining the unit length and frequency dependent characteristics, based on the perturbed direct and return current paths and electromagnetic (EM) simulations. Therefore, the proposed interconnections with nonuniform circuit and ground planes (DMS and DGS) can be modeled using the uniform circuit and ground planes with frequency dependent unit length parameters. This concept can be used for designing the microwave circuits loaded with DMS or DGS. Results show that the unit length parameters are the same at high frequencies but different at low frequencies due to the different current distributions and consequently different geometry shapes. In concept number two, the level of radiation in these interconnections due to the area of defects is determined and compared. The very large radiation, due to large etched area on ground plane, is a deficiency of DGS interconnections. Using the DMS version, the harmful radiation can be decreased effectively. In concept number three, the level of transition from passband to stopband is calculated and compared. Sharper transition can better suppress the band spurious signals. Finally, all performances are tabulated and compared.

In this paper, we present a new class of miniaturized microstrip bandpass filters with low-insertion loss, sharp-rejection and narrow-band performance. The proposed filters are composed of two spiral-shaped resonators and rectangle window feed structures. Both back-to-back and interdigital combinations of the resonators are adopted to obtain the miniaturized filter size. Compared to the traditional square loop bandpass filter, the sizes are reduced by 82% and 80%. It is also found that there is a pair of transmission zeros located on each side of the passbands, resulting in high selectivity. To validate the proposed idea, two demonstration filters with back-to-back and interdigital spiral-shaped resonators are implemented. The measured results exhibit good agreement with the full-wave simulation results.

Electrical Capacitance Tomography (ECT) is a non-invasive and non-destructive imaging technique that uses electrical capacitance measurements at the periphery of an object to generate map of dielectric permittivity of the object. This visualization method is a relatively mature industrial process tomography technique, especially in 2D imaging mode. Volumetric ECT is a new method that poses major computational challenges in image reconstruction and new challenges in sensor design. This paper shows a nonlinear image reconstruction method for 3D ECT based on a validated forward model. The method is based on the finite element approximation for the complete sensor model and the solution of the inverse problem with nonlinear iterative reconstruction. The nonlinear algorithm has been tested against some complicated experimental test cases, and it has been demonstrated that by using an improved forward model and nonlinear inversion method, very complex shaped samples can be reconstructed. The reconstruction of very complex geometry with objects in the shape of letters H, A, L and T is extremely promising for the applications of 3D ECT.

In this paper, the design of Log Periodic Fractal Koch Antennas (LPFKA) is proposed for Ultra High Frequency (UHF) band applications. The procedure to design the LPFKA with three different numbers of iterations in order to reduce the antenna size is discussed. The Computer Simulation Technology (CST) software has been used to analyze the performances of the designed antennas such as return loss, radiation patterns, current distribution and gain. The antennas have been fabricated using FR4 laminate board with wet etching technique. Using fractal Koch technique, the size of the antenna can be reduced up to 27% when the series iteration is applied to the antennas without degrading the overall performances. Both simulated and measured results are compared, analyzed and presented in this paper.

The problem about the electrical current distribution along thin radial impedance monopole, located on the perfectly conducting sphere, has been solved in a rigorous electrodynamic formulation in the paper. The problem formulation strictness is provided by the use of the Green's function for the Hertz's vector potential for unbounded space outside the perfectly conducting sphere at formulation of the initial integral equation concerning the current in monopole. The approximate analytical solution of the integral equation has been obtained by the method of iterations both for the case of excitation of the monopole by the δ-generator of voltage, located on the finite distance over the spherical scatterer, and at the excitation of the monopole at its basis.

With deregulation of telecom sector (law 24/96) in our country (Morocco), many operators of cellular network appear. Among the operators technology that operate, we find GSM9800 and CDMA900 that are used by two different operators. It turns out from the measurements of indicator of quality of service that the performance of GSM900 is degraded, and the major cause is the interference created by CDM800 which cannot be neglected. In this paper, we adopt a new approach in order to make GSM900 and CDMA800 operate in harmony. This method is based on a physical optimization of antenna systems and could be understood as a physical symmetry rotation in the space of parameters such that tilt and Azmit control the system. It independently reduces the interference effects on the distance between the base stations. Moreover, it allows us to improve client service without using hard installations and inexpensive technologies.

In this paper, a dual-loop gate antenna is designed to generate the magnetic field distribution in various directions. It is applied to Radio Frequency Identification (RFID) systems for animal identification operating at the low frequency (LF) band of 125 kHz and 134.2 kHz. The percentage of volume of magnetic field intensity is introduced and used as a figure of merit in the design. The optimum antenna parameters are also designed by the genetic algorithm (GA) in conjunction with the Numerical Electromagnetic Code (NEC). The prototype antenna was fabricated and tested to confirm the antenna performance in the LF-RFID system for animal identification. It is found that the dual-loop gate antenna can be efficiently used in the LF-RFID system.

A novel complementary split ring resonators (CSRR) is applied to realize a compact Ultra-Wide Band (UWB) bandpass filter based on half-mode substrate integrated waveguide (HMSIW) in this paper. Sharpened rejection skirts and widened upper stopband are achieved due to the two resonant frequencies of the proposed CSRR. Very good agreement is observed between measurement and simulation results.

Numerical results are presented for single-mode guidance, which is based on photonic band gap (PBG) effect, in one-dimensional planar all-dielectric light-guiding systems. In such systems there may be two kinds of light-speed point (the intersection of a mode-dispersion curve and the light line of guiding region ambient medium): One is the intrinsic light-speed point that is independent of the guiding region width, and the other is the movable light-speed point that varies with the guiding region width. It is found that the intrinsic light-speed point plays an important role to form the single-mode regime by destroying the coexistence of the lowest guided TM and TE modes that are born with a degeneration point. A mode-lost phenomenon is exposed and this phenomenon suggests a way of how to identify PBG-guided fundamental modes. Quasi-cutofffree index-guided modes in the PBG guiding structures are examined, which appear when the higher-index layers are adjacent to the guiding region and the guiding region width is small. The transverse resonance condition is derived in the Maxwell optics frame, and it is shown that there is a significant revision to the traditional one in the ray optics model. A sufficient and necessary condition for intrinsic light-speed points is given, which provides strong support to the numerical results.

This paper proposes the configuration of a novel dual-polarized wide-band patch antenna system suitable for indoor mobile communication applications. This configuration consists of two compact patch antennas, which have different feed structures from classical patch antenna configuration. These antennas, which are separated by a thin absorber to have a good isolation, are fed independently to obtain dual polarization. The antenna structure is designed, simulated, manufactured and measured. The operation bandwidth spans 1900-2700 MHz covering Bluetooth, Wireless Local Area Networks (WLAN) and Universal Mobile Telecommunications System (UMTS) bands. The simulations show good agreement with the measurement results that the antennas have return losses higher 15 dB, and the coupling between two antennas is below -20 dB within the operation band.

In this paper, an innovative technique for the determination of the dielectric properties of planar substrates is presented. Starting from a set of impedance measurements performed on a section of a microstrip transmission line built on the planar dielectric substrate under test, the proposed technique formulates the reconstruction problem in terms of an optimization one successively solved by means of an effective stochastic algorithm. Such a method allows one the reconstruction of the permittivity values at multiple frequencies by simply using a vector network analyzer and a standard calibration procedure for the impedance measurement. The results of some representative experimental tests are shown for a preliminary assessment of the effectiveness of the proposed approach.

A novel circularly polarized microstrip rectenna operating on C-band with low profile is proposed. The input and output match networks of the rectifying circuit are realized by λ/4 microstrip lines and open stubs with the harmonics being inhibited. The circularly polarized receiving antenna is a truncated-corner square patch fed by microstrip line with DGS (Defect Ground Structure) for suppressing high order harmonics further. The voltage of 4.34V on the load of 298 Ω is measured and the overall RF-DC conversion efficiency of 68.4% is obtained. This kind of rectenna can be extended to large arrays for wireless power transmission applications.

A novel design of multiband microstrip antenna array with dumbbell shape defected ground structure (DGS) is presented. The DGS is inserted into the ground plane between the two elements of the antenna array in order to suppress mutual coupling. Both simulation and measurement results verified that the DGS had improved the radiation properties of the antenna array. Measurement results of the DGS antenna showed mutual coupling reduction of maximum 5 dB and gain enhancement to 3 dB.

In this paper, a broadband quadrature hybrid is presented. The hybrid comprises a Wilkinson divider, followed by an improved Schiffman phase shifter. An improved wideband Schiffman phase shifter on a single layer printed circuit board is accompanied by a lumped capacitor between two coupled lines. Lumped capacitor is in parallel with the odd-mode capacitance of the two coupled lines, hence, the odd-mode capacitance is increased and consequently the odd-mode impedance is decreased. Therefore, by this method we can control the ratio of the even mode impedance to the odd mode impedance which is critical in Schiffman phase shifter design. Compared with the cascading Microstrip multi-section coupled lines, our proposed single layer phase shifter is smaller in size. Also, the proposed phase shifter has the greater bandwidth compared to the patterned ground plane Schiffman phase shifter and its realization is simpler because of its single layer structure. As an example, a Schiffman phase shifter at frequency f₀ =650 MHz is designed and simulated. With the proposed phase shifter a 90°hybrid is designed, simulated, fabricated and measured. Exprimental results show that the amplitude and phase imbalance between two paths at worth case are within 0.75 dB and 5°, respectively, over the frequency band from 362 MHz to 891 MHz, or around 84% bandwidth. The measured return loss is better than -10.8 dB over the operating frequency band.

A modified two-element Yagi-Uda antenna with tunable beams in the H-plane (including four significant beams: forward, backward, omni-directional, and bi-directional beams) is presented. These tunable beams are achieved by simply adjusting the short-circuit position of the transmission line connected to the parasitic element. The principle of operation is investigated by examining the current relations between the driven and parasitic elements. Measured results of a fabricated prototype are presented and discussed.

In this paper, the design of compact and high performance parallel coupled line wideband bandpass filter using image parameter method are proposed. The filter mainly comprising one-stage parallel coupled line and two open stubs are designed and implemented on commercial RT/Duroid 5880 substrate. The equivalent circuit of the proposed structure is initially derived by using the image parameter method. It is found that, the normalized bandwidth (NBW) of image impedance for the one-stage parallel coupled line has a relation to the electromagnetic (EM) simulated bandwidth. To further improve the selectivity, two open stubs are connected near the input/output (I/O) ports. The design procedures and their limitations are discussed in detail. The proposed filters are fabricated, measured and showing good characteristics of 87% fractional bandwidth as well as good insertion/return loss, flat group delay varies between 0.3-1.5 ns. High passband selectivity and wide stopband from 8-14 GHz are obseved. The measured results are also having a good agreement with the simulated results.