The current distribution and AC resistance of a microstripstructure

The AC resistance of the strip in a microstrip structure is compared with that of an isolated strip for better understanding of the conductor loss mechanism. An analysis is presented of the AC resistance in a microstrip structure for any metallization thickness by deriving the current distribution over the strip cross section. The analysis uses the separation of variables technique and the Green's function method. It shows that the skin current of the strip is concentrated toward the ground plane in a microstrip structure. In the extreme case, the AC resistance of the strip can be twice as high as the AC resistance of the same isolated strip. The imperfect ground plane also adds to the total conductor loss of a microstrip line. For a wide strip over a lossy ground plane at high frequency, the ground plane surface current distribution is concentrated directly under the strip, and the ground plane AC resistance can be as large as the strip AC resistance. Therefore, the total AC resistance at the microstrip line can be four times as high as that of an isolated strip conductor     

A miniaturised monopole antenna for ultra-wide band applications with band-notch filter

This study presents a new miniaturised printed monopole antenna. The size of the antenna is 18 x 18 mm². First simple design rules are given to arrive at an initial design for the antenna, then the antenna parameters are optimised for utilisation in ultra wide band (UWB) applications. The performance parameters like voltage standing wave ratio (VSWR) of the single antenna as well as transmission function, group delay and the fidelity factor of a two-antenna system are calculated and measured. It is shown that the band-notched performance can be obtained from the designed antenna by introducing simple p-shape or V-shape slots in its radiating element. Good agreements between simulated and measured results are observed.     

Nonuniform Arrayed Waveguide Gratings for Flat-Top Passband Transfer Function

The passband frequency response of an arrayed waveguide grating (AWG) is improved for better performance in wavelength-division multiplexing applications. Using the lengths of array arms as optimization variables, an optimization method is employed to obtain an ideal flat-top transfer function. Two different definitions of the desired transfer function to achieve the ideal flat-top response are given, and their results are compared. Rigorous mathematical derivation of the transfer function and definition of suitable objective functions generate closed-form expressions for the gradient vector of the objective function with respect to the optimization variables, thus enabling the implementation of a robust quasi-Newton optimization algorithm. This, in turn, provides accurate results and fast convergence, despite a large number of optimizing variables. It is shown that the optimized nonuniform AWG will have a flat passband with a broad bandwidth that is 2.3 times larger than that of an ordinary uniform AWG.     

Miniaturized integrated antennas for far-field wireless powering

This paper describes a series of high-efficiency miniaturized antennas of different sizes that can be integrated with the same wireless-powered RFID chip. Since this RFID chip has power scavenging capability in different ISM bands, several integrated on-chip and off-chip antennas in the three ISM bands of 900 MHz, 2.4 GHz and 5.8 GHz are designed, including one antenna integrated on chip. All proposed antennas are derived from a new planar antenna structure which can be designed toward arbitrary input impedance within a given area constraint. The measurement results for the presented antennas show a different read range. The resulting read range versus antenna size diagram specifies the best operating frequency band for a given read range and occupied area. Though this diagram depends on the chip's specifications like the power-on sensitivity and input impedance, it can be generated for any chip. In addition, the measurement results concerning read range and radiation patterns for the proposed antennas are presented and compared with simulation results, showing very good agreement.     

Integral equation analysis and optimization of 2D layered nanolithography masks by complex images Green's function technique in TM polarization

Analysis and optimization of diffraction effects in nanolithography through multilayered media with a fast and accurate field-theoretical approach is presented. The scattered field through an arbitrary two-dimensional (2D) mask pattern in multilayered media illuminated by a TM-polarized incident wave is determined by using an electric field integral equation formulation. In this formulation the electric field is represented in terms of complex images Green's functions. The method of moments is then employed to solve the resulting integral equation. In this way an accurate and computationally efficient approximate method is achieved. The accuracy of the proposed method is vindicated through comparison with direct numerical integration results. Moreover, the comparison is made between the results obtained by the proposed method and those obtained by the full-wave finite-element method. The ray tracing method is combined with the proposed method to describe the imaging process in the lithography. The simulated annealing algorithm is then employed to solve the inverse problem, i.e., to design an optimized mask pattern to improve the resolution. Two binary mask patterns under normal incident coherent illumination are designed by this method, where it is shown that the subresolution features improve the critical dimension significantly.     

Time-domain MoM for the analysis of thin-wire structures above half-space media using complex-time Green's functions and band-limited quadratic B-spline temporal basis functions

The transient response of a thin wire in the presence of a half-space is calculated with a new formulation of the Method of Moments (MoM) in time domain, based on a novel Time-Domain Mixed Potential Integral Equation (TD-MPIE), using complex-time Green's functions. The excitation is a Gaussian voltage source and the solution is obtained by using a Marching-On-in-Time (MOT) procedure. Band-Limited Quadratic B-spline (BL-QB) functions are used as Temporal Basis Functions (TBFs). They are compared with Band-Limited Linear B-spline (BL-LB) interpolation functions. Numerical results show that the solution using BL-QB TBFs is stable and accurate, without late-time instabilities, and efficient in terms of memory usage and computation time.     

Design and optimisation of a high-frequency EMC wideband horn antenna

A new approach for the design of high-frequency electromagnetic compatibility (EMC) broadband double-ridged horn (DRH) antennas is presented. In this approach, first a conventional DRH antenna at 1-18 GHz frequency band is considered. Using a thorough sensitivity analysis of different structural parameters of the 1-18 GHz DRH antenna, several modifications are applied to this antenna to overcome its deficiencies especially in its radiation pattern at higher frequencies. The final achieved design is then scaled up in the frequency to arrive at a design suitable for higher frequency ranges. A wideband DRH antenna for 18-40 GHz frequency band is then designed using this approach. The lower frequency ratio of 1:2.2 in the new antenna as opposed to the 1:18 ratio in the conventional antenna permits us to choose the best frequency window for the scaling up process. Besides, an optimisation technique is employed to further improve the antenna performance to meet the design goals over the entire new frequency band, that is, to have a single main lobe directed along the horn axis without any deterioration, and to have acceptable broadband gain with the minimum of 10 dB, and voltage standing wave ratio (VSWR) of less than 1.5. The final design which is more compact compared with the other commercial antennas has been used to make a prototype antenna. Measurements show that the built prototype meets the design goals very well     

A New Open-Source Toolbox for Estimating the Electrical Properties of Biological Tissues in the Terahertz Frequency band

The dielectric properties of biological tissues and their substructures at terahertz frequencies are needed for computational dosimetry, radiation safety regulation, and medical imaging, but experimental tissue data are only scarcely available for the terahertz band. Tissue properties can be theoretically predicted at terahertz frequencies if the tissue microstructure and composition, and the dielectric properties of several basic biological materials are known. This paper introduces a new open-source toolbox where a material database and many of the relevant formulas are implemented to facilitate related research. Several examples have been analyzed and successfully verified with experimental data from the literature.     

Comments on `Analysis of superconducting microwave structures:application to microstrip lines' [and reply]

For the original article see ibid., vol.40, no.3, p.499-508 (1992). The commenters present experimental and theoretical evidence that purports to show that in the above-titled paper by S.M. El-Ghazaly et al. and an earlier paper by the same authors, the distribution of longitudinal current component J in the transverse plane is related to the surface charge density ρ_S and the distribution of J_z in the transverse plane varies with the dielectric constant of the substrate. El-Ghazaly replies that the commenters failed to understand some salient features of his papers. Also, he argues that they overestimate the application of Wheeler's approximation, namely the inductance per unit length is independent of the dielectric constant in transmission lines, and he provides clarification     

Estimating Brain Deformation During Surgery Using Finite Element Method: Optimization and Comparison of Two Linear Models

This paper addresses estimation of brain deformation during craniotomy using finite element modeling. Two mechanical models are optimized and compared for this purpose: linear solid-mechanic model and linear elastic model. Both models assume the realistic finite deformation of the brain after opening the skull. In this study, we use pre-operative and intra-operative magnetic resonance images (MRI) of five patients undergoing brain tumor surgery. Anatomical landmarks are identified by an expert radiologist on MRI and used for the method development and comparison studies. We use tetrahedral finite element meshes and optimize model parameters by minimizing the mean distance between the predicted locations of the anatomical landmarks using the pre-operative images and their actual locations on the intra-operative images. Evaluation of the objective function using a second set of landmarks not used in the optimization process suggests that accuracy of the solid mechanic model is higher than that of the elastic model for our application. Visual inspection of the results confirms this conclusion. The proposed method along with the location information of the surface landmarks measured in the operating room and marked on the pre-operative images can be used to estimate the brain deformations without needing intra-operative images. In this case, since the parameters of the brain tissue are not the same for different patients, the proposed optimization process is crucial for obtaining accurate results.