We characterize the pulse propagation on a traveling-wave field-effect transistor (TWFET) with the drain line periodically loaded with Schottky varactors for short pulse amplification. Owing to the coupling between the gate and drain lines, two propagation modes are developed on a TWFET. It is expected that the pulses carried by one of the two modes are uniquely amplified, whereas those carried by the other mode are attenuated. By properly introducing nonlinearity via the loaded varactors, the proposed TWFET succeeds in the amplification of short pulses by compensating for dispersive distortions. This study verifies the design criteria for the amplification of short pulses in TWFETs through the experimental observation of the properties of the linear and nonlinear pulses on a TWFET.
This paper presents the application of unconditionally stable fundamental finite-difference time-domain (FADI-FDTD) method in modeling the interaction of terahertz pulse with healthy skin and basal cell carcinoma (BCC). The healthy skin and BCC are modeled as Debye dispersive media and the model is incorporated into the FADI-FDTD method. Numerical experiments on delineating the BCC margin from healthy skin are demonstrated using the FADI-FDTD method based on reflected terahertz pulse. Hence, the FADI-FDTD method provides further insight on the different response shown by healthy skin and BCC under terahertz pulse radiation. Such understanding of the interaction of terahert pulse radiation with biological tissue such as human skin is an important step towards the advancement of future terahertz technology on biomedical applications.
In this work, approximate formulas are presented for computing the magnetic field intensity near electric power transmission lines. Original expressions are given for single circuit lines of any type of arrangement and double circuit lines in both super-bundle and low-reactance conductor phasing. These expressions can be used for assessing directly the Right-of-Way width of power lines related to maximum magnetic field exposure levels which may be efficiently used in environmental impact assessment. The accuracy of approximate formulas is demonstrated by comparison with exact formulas for computing the rms field distribution.
The design of filter antennas with reconfigurable band stops is proposed. They are meant for employment in ultrawideband cognitive radio (UWB-CR) systems, where unlicensed users communicate using adaptive pulses that have nulls in the bands used by licensed users. Neural networks or circuits implementing the Parks-McClellan algorithm can generate such pulses. With filter antennas, reconfigurable bandstop filters are first designed, to induce adaptive nulls in UWB pulses, and are then integrated in the feed line of a UWB antenna. The advantages of this combination are discussed. The filters are based on split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs). The relationship between the SRR and CSRR parameters and the stop band is also studied.
This paper deals with adaptive array beamforming in the presence of errors due to steering vector mismatch and finite sample effect. Diagonal loading (DL) is one of the widely used techniques for dealing with these errors. However, the main drawback of DL techniques is that there is not an easy and reliable manner to determine the required loading factor. Recently, serval DL approaches proposed the so-called automatic scheme on computing the required loading factor. In this paper, we propose a fully data-dependent loading to overcome the difficulties. The novelty is that the proposed method does not require any additional sophisticated scheme to choose the required loading. The loading factor can be completely obtained from the received array data. Analytical formulas for evaluating the performance of the proposed method under random steering vector error are further derived. Simulation results are provided to confirm the validity of the proposed method and make comparison with the existing DL methods.
A proximity-fed annular slot antenna for UWB applications with a band rejection using different techniques is presented. The proposed antenna provides an UWB performance in the frequency range of ≈2.84 to ≈8.2 GHz with relatively stable radiation parameters. Three different techniques to construct a resonant circuit for the proposed antenna are investigated to achieve the band-notch property in the band ≈5.11 to ≈5.69 GHz band which include the WLAN and HIPERLAN/2 services without degrading the UWB performance of the antenna. Three resonators are considered; a single complementary split ring resonator (CSRR), a complementary spiral loop resonator (CSLR) and a spurline slot. Furthermore, the band-notched resonance frequency and the bandwidth can be easily controlled by adjusting the dimensions of the resonator. The proposed antenna is simulated, fabricated and measured. The measured data show very good agreements with the simulated results. The proposed antenna provides almost omnidirectional patterns, relatively flat gain and high radiation efficiency over the entire UWB frequency excluding the rejected band.
The electromagnetic force between two misaligned coils (coils with parallel axes) with uniform current density distribution and rectangular cross section based on the derived semi-analytical expressions was presented. Using the semi-analytical expressions for magnetic force between filamentary misalignment circular coils we calculate the propulsive and the transverse magnetic force. In order to verify the validity of the expressions, we use the filament method with Grover's formula to calculate the magnetic force for two coils with parallel axes. The results obtained by two methods are in a very good agreement. In this paper, the derivation of the semi-analytical expressions and the calculation results of the magnetic force are introduced.
Target localization is one challenge in passive coherent location (PCL) radar system, and the time delay is the most important parameter in the location. The difficulty of time delay estimate (TDE) in PCL system is that the target signal is completely buried in direct path signal, multipath and clutter (DMC). The conventional clutter cancellation algorithms in matched filter (MF) are time consuming. In this paper, we propose a time delay estimate method based on blind source extraction (BSE) which directly extract the target signal from the mixed signals, thus a new passive coherent location system is built. In this model, the reference antenna is not needed any more. For low signal to interference plus noise ratio (SINR) and frequency overlapped signals in passive coherent location, we introduce the cyclostationarity to enhance the target signal. The experiments on FM broadcast signals show that the computational burden of the proposed algorithm is extremely small and the improved SNR satisfies the location requirements of PCL system.
The problem of excitation of electromagnetic fields by a material body of finite dimensions in presence of coupling hole between two arbitrary electrodynamic volumes is formulated. The problem is reduced to two-dimensional integral equations for the surface electric current on a material body and the equivalent magnetic current on a coupling hole. A physically correct transition from the initial integral equations to one-dimensional equations for the currents in a thin impedance vibrator which, in general case, may have irregular geometric parameters, and a narrow slot is justified. A solution of resulting equations system for the transverse slot in the broad wall of rectangular waveguide and a vibrator with variable surface impedance in it was found by a generalized method of induced electro-magneto-motive forces. The calculated and experimental plots of electrodynamic characteristics of a vibrator-slot structure in a rectangular waveguide are presented.
The paper gives an analytical transition from the Maxwell Garnett model of a biphasic mixture (dielectric host and dielectric or conducting inclusions) to the parameters of a single- or double-term Debye representation of the material frequency response. The paper is focused on modeling biphasic mixtures containing cylindrical inclusions. This is practically important for engineering electromagnetic absorbing composite materials, for example, containing carbon fibers. The causal Debye representation is important for incorporation of a composite material in numerical electromagnetic codes, especially time-domain techniques, such as the finite-difference time-domain (FDTD) technique. The equations derived in this paper are different for different types of host and inclusion materials. The corresponding cases for the typical combinations of host and inclusion materials are considered, and examples are provided. The difference between the original Maxwell Garnett model and the derived Debye model is quantified for validating the proposed analytical derivation. It is demonstrated that in some cases the derived equivalent Debye model well approximates the frequency characteristics of the homogeneous model based on the MGA, and in some cases there is an exact match between Debye and Maxwell Garnett models.
We detail the optimization of a nanobeam design and show how the fabrication imperfections can affect the optical performance of the device. Then we propose the design of a novel configuration of a photonic crystal nanobeam cavity consisting of a membrane structure obtained by sandwiching a layer of Flowable Oxide (FOx) between two layers of Silicon-Nitride (SiN). Finally, we demonstrate that the presence of a low refractive index layer does not impair the performance of the nanobeam cavity that still exhibits a Q factor and mode volume V of the order of 10^{5} and 0.02 (λ/n)^{3<\sup>, respectively. }
This paper proposes a simple semi-analytical method for designing coil-systems for homogeneous magnetostatic field generation. The homogeneity of the magnetic field and the average magnitude of the magnetic flux density inside of the volume of interest are the objective functions chosen for the selection of the coil-system geometry (size and location), number of coils and the number of turns of each winding. The spatial distribution of the magnetostatic field is estimated superposing the magnetic induction numerically computed from the analytical expression of the magnetic field generated by each coil, obtained using the Biot-Savart's law and the current filament method. The homogeneous magnetic field is synthesized using an iterative algorithm based on TABU search with geometric constraints, which varies the design parameters of the windings to meet the requirements. The number of turns of each coil and gauge of wire used for the windings is adjusted automatically in order to achieve the target average magnitude of the magnetic induction under the constraints imposed by power consumption. This method was used to design a coil arrangement that can generate up to 10 mT within a volume (0.5 × 0.5 × 1) m with 99% of spatial homogeneity, with square loops of length less than or equal to 1.5 m, and with a power dissipated by Joule effect less than or equal to 1 W per coil. The synthesized magnetic field distribution was validated using Finite Element Method simulation, showing a good correspondence between the objective values and the simulated fields. This method is an alternative to design magnetic field exposure systems over large volumes such as those used in bioelectromagnetics applications.
A modeling of the metallic wires susceptibility facing to the disturbances caused by electromagnetic (EM) near-field (NF) radiated by electronic structures in radio frequencies (RF) is introduced by using a hybrid method. This latter is based on the use of the given EM-data calculated or determined from the standard computation tools associated with basic analytical methods expressing the coupling voltages at the victim wire extremities and the EM-NF radiations. In difference to the classical methods based on the far-field radiations, the main benefit of this method lies on the possibility to take into account the evanescent waves from the disturbing elements. The basic principle illustrating the hybrid method principle is explained. To verify the relevance of the method proposed, we consider a metallic wire having cm-length above the ground plane disturbed by the EM-near-waves from the electronic circuits in proximity. For that, we model the EM radiation of the disturbing electronic circuits and then, apply the hybrid method to evaluate the coupling voltages induced through the wires. By considering the radiations around hundreds MHz, we demonstrate that the hybrid method proposed enables us to generate voltages in good agreement with the simulations performed with the commercial tools. Two types of realistic configurations are studied. First, with a microstrip loop circuit radiating at about 0.7 GHz, we calculated induced voltages at the extremities of the structures. Then, the same analysis was made with a 3D-model coil self for the large band from 0.1 GHz to 0.5 GHz. The results are in good accordance between the terminal voltages of the wire. The relative error in the second configuration falls less than 10%. This investigation is important for the EM compatibility (EMC) analysis of the radiating coupling between wires and complex electrical and electronic systems disturbed by RF harmonics.
We investigate the characterization of defect modes in one-dimensional ternary symmetric metallo-dielectric photonic crystal (1DTSMDPC) band-gap structures. We consider the defect modes for symmetric model with respect to the defect layer. We demonstrate reflectance with respect to the wavelength and its dependence on different thicknesses and indices of refraction of dielectric defect layer, angle of incidence and number of periods for both transverse electric (TE) and transverse magnetic (TM) waves. Also, we investigate properties of the defect modes for different metals. Our findings show that the photonic crystal (PC) with defect layer, made of two dielectrics and one metallic material, leads to different band-gap structures with respect to one dielectric and one metallic layer. There is at least one defect mode when we use dielectric or metallic defect layer in symmetric structure. And, the number of defect modes will be increased by the enhancement of refractive index and thickness of dielectric defect layer.
The scattering properties of dielectric waveguides connected in cascade can be obtained by using the generalized scattering matrix concept, together with the generalized telegraphist equations formulism and the modal matching technique. This review aims to show the potential of periodic structures in dielectric waveguides in order to gain control of light in the design of microwave and photonic devices. The new inverted Π dielectric waveguide is presented. Numerical and experimental results of the complex scattering coefficients were obtained at microwave frequencies. At optical frequencies, results for planar waveguide photonic crystals are included and compared with the numerical values from commercial software. In all cases the agreement was excellent. Electromagnetic and photonic band gaps, photonic windows, optical switching, optical resonant microcavities as well as refractive index optical sensors can be achieved by means of dielectric waveguides in cascade.
This paper presents a design methodology for realizing broadside-coupled microstrip bandpass filters on multilayer substrates to reduce the size of the filter. The new filter configuration consists of broadside coupled split-ring resonators on two layers backed by a ground plane. With the proposed new method, miniaturization to a greater extent can be achieved compared to the conventional method of realizing microstrip multilayer filters. In addition, coupling apertures in the ground plane used to achieve coupling among the resonators in conventional multilayer structures are eliminated. The proposed design is more flexible compared to traditional multilayer filters. Layers can be easily added to increase the filter order. To demonstrate the method, a miniaturized two-layered bandpass filter centered at 728 MHz with low insertion loss is implemented and investigated. Miniaturization of more than 25% is achieved compared to the conventional broadside coupled structure and more than 40% miniaturization compared to the edge coupled structure. The new microstrip filter discussed in this paper can be realized using simple fabrication techniques.
Noise reduction in PCB is a major concern in the present digital electronic systems with data rate beyond 10 Gbps. The noise, due to simultaneous switching noise, radiation from signal vias crossing the planes, etc. can propagate within parallel plane cavity at its resonant frequencies, thus allowing coupling between integrated circuits (ICs) far from each other. Electromagnetic band-gap (EBG) structures are largely employed as noise reduction technique. This paper presents a quick and efficient analytical approach for evaluating the EBG noise reduction performances in terms of band-gap limits. The study is based on the physics behavior of the planar EBG structures, focusing on its resonant properties. The resonant modes of the EBG cavity are affected by the additional inductance of the patterned plane respect to the case of the ideal solid plane cavity. The formulas provided, based on the quantification of such inductance, can be easily implemented and employed for a quick layout design of power planes in multilayer PCBs, as shown in a practical example of a partial EBG plane.
Two probe-compensated near-field-far-field transformations with spherical spiral scanning tailored for antennas having two of their dimensions very different from the third one are developed by properly applying the unified theory of spiral scans for nonspherical antennas. One is suitable for electrically long antennas, which are considered as enclosed in a cylinder ended in two half-spheres. The other adopts a surface formed by two circular ``bowls'' with the same aperture diameter but different lateral bends to shape a quasi-planar antenna. These flexible modelings fit very well many actual antennas by properly setting their geometric parameters. Great reduction of the number of data to be acquired is achieved, thus significantly reducing the required measurement time. Numerical tests validating the accuracy of the proposed techniques and their stability with respect to random errors affecting the data are shown.
In this paper, the interaction of a planar inverted-F antennas array, mounted on a mobile handset, with a human hand-head phantom is investigated in the 1.9 GHz band. The hybrid approach involving the particle swarm optimization (PSO) and Nelder-Mead (NM) algorithm is considered to optimize the complex excitations of the adaptive array elements in a mutual coupling environment for different beamforming synthesis. Firstly, the effect of the human hand-head on the handset radiation characteristics is studied. Then, the spatial-peak specific absorption rate (SAR) values of 2- and 4-element PIFA arrays for mobile handset in the vicinity of a human hand-head are evaluated numerically for different scenarios. The antenna is analyzed completely using finite difference time domain (FDTD) method while the interaction is performed using the CST Microwave Studio software.
We investigate analytically the asymptotic behavior of high-order spurious prolate spheroidal modes induced by a second-order local approximate DtN absorbing boundary condition (DtN2) when employed for solving high-frequency acoustic scattering problems. We prove that these reflected modes decay exponentially in the high frequency regime. This theoretical result demonstrates the great potential of the considered absorbing boundary condition for solving efficiently exterior high-frequency Helmholtz problems. In addition, this exponential decay proves the superiority of DtN2 over the widely used Bayliss-Gunsburger-Turkel absorbing boundary condition.