A transient finite-element model has been presented to simulate extracellular potential stimulating in a neural tissue by a nonplanar microelectrode array (MEA). This model allows simulating the extracellular potential and transmembrane voltage by means of a single transient computation performed within single finite element (FE) software. The differential effects of the configuration and position of MEA in electrical extracellular stimulation are analyzed theoretically. 3-D models of single nerve fiber and different MEA are used for the computation of the stimulation induced field potential, whereas a cable model of a nerve fibre is used for the calculation of the transmembrane voltage of the nerve fiber. The position of MEA and the spacing of the microelectrodes are varied while mono-, bi-, tri-, and penta-polar MEAs are applied. The model predicts that the lowest stimulation voltage threshold is obtained in the stimulation with penta-polar MEA. Moreover, the relationships, which exist between the thresholds of the electrical extracellular stimulation and the parameters including position of the electrode array and the spacing of the microelectrodes in array, are studied and obtained.
A high-efficiency rigorous approach for the solution of the two-dimensional Laplace equation with Dirichlet's boundary conditions is developed to tackle electrostatic problems involving metallic cylinders of arbitrary cross-sections. In this paper we demonstrate how this novel algorithm can be used to address the problems arising in the capacitance microscopy to provide a higher resolution in studies of micro-cavities and whiskers on the surface of metallic samples. The precise capacitance images of the probe/sample systems are presented.
In this paper, the synthesis of sparse time-modulated linear arrays with minimum number of elements and controlled harmonic radiations is investigated. The proposed iterative approach based on a particle swarm optimization is aimed at finding the array configuration with the minimum number of elements and the optimal pulse sequence that affords a beam pattern with the same features of a reference one also limiting the amount of sideband radiations under a specific threshold. A set of representative numerical examples are discussed to assess the effectiveness and the reliability of the proposed approach.
Applications of copper (Cu) nanorod arrays, produced by glancing angle deposition (GLAD) technique, which extends the function of conventional microstrip antennas to encompass passive wireless gas sensors at microwave frequencies are presented. The proposed microstrip antenna consists of Cu nanorod arrays grown on silicon wafers which were coated with thin films of Cu of 50 nm in thickness. To study the effect of the length of Cu nanorods on antenna performance, Cu nanorods of different lengths (400, 700, and 1000 nm) were fabricated. The effects of Cu nanorods morphologies (Cu thin film, closely-spaced Cu nanorods, and well-separated Cu nanorods), were investigated too. Conventional microstrip antennas based on sputtered Cu thin film were prepared for comparison. It was found that as the length of Cu nanorods increases, the antennas exhibit a wider bandwidth and lower frequency resonance than those of the conventional antennas based on Cu thin film. Furthermore, moving from flat surface to well-separated nanorods results in a decrease in the resonant frequency, while there was no observable effect on the bandwidth. These enhancements are attributed to the mutual coupling occurring among Cu nanorods. Based on the antenna characterization, the 1000 nm long Cu nanorods sample was selected for gas detection measurements due to its observed sharp resonance and narrow bandwidth. The detection mechanism is based on the change of in the magnitude of the reflection coefficient as well as the resonant frequency due to the introductions of different gases. The proposed sensor based on Cu nanorods shows a significant response in response to the introduction of different gases such as oxygen, nitrogen, and nitrogen, while the conventional antenna shows no measurable response. It is believed that the proposed sensor is applicable to the other gases based on the suggested sensing mechanism.
A novel approach for designing planar dual-mode bandpass filters using symmetrical T-shaped stub-loaded stepped-impedance resonators (TSLSIRs) with high frequencies selectivity is presented. The proposed symmetrical TSLSIR structure is mainly composed of three elements, i.e. a stepped-impedance resonator (SIR), and two T-shaped stubs which symmetrically loaded at the middle sections of the SIR. Then, two dual-mode bandpass filters based on TSLSIRs with high frequencies selectivity are proposed for experimental verification. Firstly, a dual-mode single passband filter with two transmission zeros located at the both sides of passband is presented, whose passband is centered at 5.23 GHz with the fractional bandwidth of 10.1%, and a wide upper-stopband with harmonic suppression better than 20 dB in range of 5.9 GHz to 12.9 GHz is achieved. Secondly, a dual-mode dual-band bandpass filter with four transmission zeros located at the both sides of the two passbands is presented, whose two passbands are centered at 3.4 GHz and 4.54 GHz with the corresponding fractional bandwidth of 8.4% and 7.5% respectively, and the spurious frequencies from 4.9 GHz to 8.45 GHz are successfully suppressed to the level lower than -20 dB. Both filters have been designed, fabricated and measured. The measured results show good agreements with those of the simulation.
Depending on the aperture extension (AE), a high performance three-dimensional (3D) near-field (NF) source localization algorithm is proposed with the nonuniform linear array (NLA). The proposed algorithm first generates some fictitious sensors to extend the array aperture by constructing a new Toeplitz matrix, and then obtains a two-dimensional (2D) covariance matrix which only contains the elevation angle and range parameters, and another 3D covariance matrix which contains the elevation/azimuth angle and range parameters. Then based on the 2D covariance matrix, both the elevation angle and range parameters are estimated by using the NLA along the Z axis. With the estimates of both the elevation angle and range parameters and combining the 3D covariance matrix, the estimates of the azimuth angle parameters are obtained using the NLA along the Y axis. The proposed algorithm has four main merits: i) unlike some classical NF source localization algorithms, the quarter-wavelength sensor spacing constraint is not required and more sources can be located simultaneously by the proposed algorithm; ii) the 3D parameters of the proposed algorithm are paired automatically; iii) the 3D search required in conventional 3D multiple signal classification (MUSIC) algorithm is replaced with only one-dimensional (1D) search, and thus the computational burden is reduced; iv) the proposed algorithm gains superior parameter estimation accuracy and resolution.
In through-the-wall radar imaging (TWRI), wall returns are often stronger than target returns, which make the targets behind walls invisible in the radar image. Spatial filtering that relies on the removal of the spatial zero-frequency components is a useful way for wall-clutter mitigation. Unfortunately, it applies to through-the-wall radar (TWR) with synthetic aperture array only. In this paper, a method based on spatial signature is proposed to suppress the wall-clutter in multi-input and multi-output (MIMO) TWRI. Firstly, the traditional spatial filtering method is discussed, as well as the reasons for the inapplicability for MIMO TWR. Secondly, the wall and target spatial signatures based on MIMO array are analyzed, respectively. The results indicate that the former has stability and symmetry, whereas the latter not. Thirdly, according to the above differences, a new method, symmetry subtraction, is applied to describe the wall-clutter suppression procedure. Finally, simulation results demonstrate that the proposed method is efficient in mitigating the wall returns and highlighting the targets.
This paper presents the technique to solve inhomogeneous profiles in the cross section of the helical rectangular waveguide. We present the technique to solve inhomogeneous dielectric profiles and the relation to the method of the propagation of electromagnetic fields along a helical waveguide with a rectangular cross section. The inhomogeneous examples will introduce for a dielectric slab, for a rectangular dielectric profile, and for a circular dielectric profile, in a rectangular metallic waveguide, in the cross section of the helical waveguide. This model is useful to improve the output results of the output power transmission in the cases of space helical waveguides, by increasing the step's angle or the radius of the cylinder. The application is useful for space helical waveguides in the microwave and the millimeter-wave regimes.
We study the electrodynamic characteristics of a strip loop antenna located on the surface of a circular column filled with a resonant magnetoplasma and surrounded by a homogeneous isotropic background medium. The antenna current is excited by a time-harmonic voltage creating an electric field with the azimuthal component in a narrow gap on the strip surface. It is shown that the current distribution and input impedance of such an antenna are strongly influenced by the presence of an infinite number of propagating quasielectrostatic modes that are guided by a column containing a resonant magnetoplasma.
The design of Interleaver/Deinterleavers using Fibonacci-class quasistructures is proposed. We introduce an optical passive configuration composed of Fibonacci quasistructures and circulators which acts as interleaver and deinterleaver. Odd and even channels are interleaved/deinterleaved with dense wavelength-division multiplexing (DWDM) multichannel filter based on Fibonacci quasi-periodic structures. We use Fibonacci based DWDM filters in order to separate the odd and even wavelength channels. These quasi-periodic structures, with different geometrical and physical parameters, act as DWDM filters that reflect even and odd wavelengths. A modified numerical approach is presented to design the Fibonacci based DWDM filter. We demonstrate that it is possible to optimize DWDM filter response by varying the parameters of the Fibonacci structure, such as generation number, Fibonacci order and optical lengths of the layers. The proposed filter structures can separate 32 DWDM channels with 0.8 nm spacing into two 16 DWDM channels with 1.6 nm spacing. In order to eliminate the crosstalk between the adjacent channels, we apply the refractive index profile apodization. These structures are useful for multiplexing/demultiplexing of a high numbers of the channels.
This paper proposes a new imaging algorithm based on a novel accurate range model to process the data acquired by Geosynchronous-Earth-orbital Synthetic Aperture Radar (Geo-SAR). The new range model, called DRM-5, is obtained from the 1-5^{th} order Doppler parameters of spaceborne SAR. It is employed to describe the slant range of Geo-SAR during the super-long integration time. Furthermore, the two-dimensional frequency spectrum of point targets based on the new range model is derived and analyzed. An advanced Frequency Domain Algorithm (FDA) based on DRM-5 is proposed to process the data of stripmap mode Geo-SAR. The varied Doppler parameters in the cross-azimuth direction are considered in the new imaging algorithm, and the space-varied range-azimuth coupling phase term is compensated through data blocking. A simulation experiment is performed to verify the efficiency and superiority of the new algorithm, and the results show that it has a good effect on an L-band stripmap mode Geo-SAR system with azimuth resolution around 5m and 300km range swath.
We present a theory to describe the transient and steady state behaviors of the active modes of a photonic crystal with active constituents (active photonic crystal). Using a couple mode model, we showed that the full vectorial Maxwell-Bloch equations describing the physics of light matter interaction in the active photonic crystal can be written as system of integro-differential equations. Using the method of moments and the mean value theorem, we showed that the system of integro-differential equations can be transformed to a set of differential equations in slow time and slow spatial scales. The slow time (spatial) scale refers to a duration (distance) that is much longer than the optical time period (lattice constant of the photonic crystal). In the steady state, the slow scale equations reduce to a nonlinear matrix eigenvalue problem, from which the nonlinear Bloch modes can be obtained by an iterative method. For cases, where the coupling between the modes are negligible, we describe the transient behavior as an onedimensional problem in the spatial coordinate, and the steady behaviors are expressed using simple analytical expressions.
Stacked concentric circular antenna arrays (SCCAA's) supporting both the scanning mode and the tracking mode are optimized in both the azimuth and elevation planes. The gbest-guided artificial bee colony algorithm (GABCA) is adopted to optimize the dual-mode field patterns of thinned SCCAA's. Performance comparison of the GABCA with conventional ABCA and particle swarm optimization (PSO) algorithms is also presented.
An underground coal mine medium frequency (MF) communication system generally couples its electromagnetic signals to a long conductor in a tunnel, which acts as a transmission line, and exchanges signals with transceivers along the line. The propagation characteristics of the transmission line, which is usually the longest signal path for an MF communication system, play a major role in determining the system performance. To measure the MF propagation characteristics of transmission lines in coal mine tunnels, a method was developed based on a basic transmission line model. The method will be presented in this paper along with the propagation measurements on a transmission line system in a coal mine using the method. The measurements confirmed a low MF signal power loss rate, and showed the influence of the electrical properties of surrounding coal and rock on the MF propagation characteristics of the line.
In this work we examine several sources of measurement uncertainty that can hinder the use of time-domain microwave techniques for breast imaging. The effects that are investigated include those due to clock and trigger jitter, antenna movements, discrepancies in antenna fabrication, and random measurement noise. We explore the significance of the noise contribution of each effect, and present methods to mitigate them when possible and necessary. We demonstrate that, after applying the aforementioned methods, the noise is minimized to the noise floor of the system, thereby enabling successful tumor detection.
Due to the increasing complexity of metamaterial geometric structures, direct optimisation of these designs using conventional approaches, such as Gradient-based and evolutionary algorithms, are often impractical and limited. This is in part due to the inherently high computational cost associated with running multiple expensive high-fidelity full-wave simulations, commonly required to optimise the constitutive parameters of a single metamaterial particle. In order to alleviate this issue, we propose an efficient optimisation approach which exploits the Co-Kriging methodology, such that we can successfully couple varying levels of discretisation and solver accuracy obtained from a 3d full wave numerical solver suite. In contrast to other optimisation strategies, we investigate the improvement in efficiency of optimisation through the use of the LOLA-Voronoi, in conjunction with Expected Improvement and the embedding of a trustregion framework within our optimisation algorithm, to accelerate the convergence of Co-Kriging. Finally, the effectiveness of the outlined algorithm will be demonstrated by a quantitative evaluation of the performance of optimised planar 2D negative index of refraction structures.
This paper presents a new analytical method for predicting magnetic field distribution and levitation force in three configurations of high temperature superconducting (HTSC) maglev vehicles. The permanent magnet guideways (PMG) are composed with ferromagnetic materials and NdFeB permanent magnets. The proposed analytical model is based on the resolution in each region of Laplace's and Poisson's equations by using the technique of separation of variables. For the study, we consider the HTSC as a perfect diamagnetic material. The boundary conditions and Fourier series expansion of interfaces conditions between each region are used to find the solution of magnetic field. The developed analytical method is extended to compute the magnetic field distribution generated by the three types of PMGs when removing the HTSC bulk. Magnetic field distribution and vertical force obtained analytically are compared with those issued from the finite element method (FEM).
Traditional contacting measurement has numerous disadvantages, including high cost, high damage rate, low mobility, etc. In this study, to resolve these serious problems, a simiple, broadband non-contacting loop has been disigned to transmit and receive a signal. An equivalent dual-port non-contacting measurement model and a theorem of vertical coupling capacitance and inductance have been proposed. From the results of the dual-port model simulation and the fabricated sample measurement, a theorem of singal reconstruction and novel non-contacting measurement presented.
This article focuses on the 2D hybrid technique between the Frequency Domain Transmission Line Matrix Method (FDTLM) and the Wave Concept Iterative Procedure (WCIP). 3D hybridization has already been studied, but results may be improved through a better knowledge of method order. Consequently, developing 2D hybridization aims at understanding the hybridization in simplest problems, especially because Transverse Electric (TE) and Transverse Magnetic (TM) are uncoupled. Our study dwells on accuracy and convergence order of the 2D hybrid method, which will help for 3D mesh use. In this perspective, the scattering nodes and electromagnetic elds expressions are established in the 2D general case with anisotropic materials. As a result, validation examples are presented to check the approach.
In this study, the impact of finite ground plane edge diffractions on the amplitude patterns of aperture antennas is examined. The Uniform Theory of Diffraction (UTD) and the Geometrical Optics (GO) methods are utilized to calculate the amplitude patterns of a conical horn, and rectangular and circular waveguide apertures mounted on square and circular finite ground planes. The electric field distribution over the antenna aperture is obtained by a modal method, and then it is employed to calculate the geometrical optics field using the aperture integration method. The UTD is then applied to evaluate the diffraction from the ground planes' edges. Far-zone amplitude patterns in the E and H planes are finally obtained by the vectorial summation of the GO and UTD fields. In this paper, to accurately predict the H-plane amplitude patterns of circular and rectangular apertures mounted on square ground plane, the E-plane edge diffractions need to be included because the E-plane edge diffractions are much more intensive than those of the H-plane edge regular and slope diffractions. Validity of the analysis is established by satisfactory agreement between the predicted and measured data and those simulated by Ansoft's High Frequency Structure Simulator (HFSS). Good agreement is observed for all cases considered.