Daniel L. Faircloth

Comparison of two optimization techniques for the estimation of complex permittivities of multilayered structures using waveguide measurements

In this paper, two separate techniques, i.e., sequential quadratic programming (SQP) and a genetic algorithm (GA), were used to estimate the complex permittivity of each layer in a multilayer composite structure. The relative performance of the algorithms was characterized by applying each algorithm to one of three different error functions. Computer generated S-parameter data sets were initially used in order to establish the achievable accuracy of each algorithm. Based on these data sets and S-parameter measurements of single and multilayer samples obtained using a standard X-band waveguide procedure, the GA was determined to be the more robust algorithm in terms of minimizing rms error of measured/generated and formulated S-parameters. The GA was found to perform exceptionally well for all cases considered, whereas SQP, although a more computationally efficient method, was somewhat limited for two error function choices due to local minima trapping.

Complex permittivity and permeability extraction for multilayered samples using S-parameter waveguide measurements

In this paper, a novel technique is presented for accurately extracting the complex constitutive parameters (/spl epsiv//spl circ/, /spl mu//spl circ/) for individual layers of a multilayer sample using S-parameter waveguide measurements. The technique is based on a modified sequential quadratic programming algorithm, which utilizes a large number of initial guess points, thereby alleviating the possibility of local minima trapping. The algorithm was found to be significantly faster and more accurate than traditional global optimization methods such as the genetic algorithm. Computer-generated S-parameter data sets were initially used to establish the achievable accuracy of the algorithm for one-, two-, and three-layer cases. Sensitivity of the S-parameters to changes in the constitutive parameters and layer thicknesses was also investigated. Two-port S-parameter measurements (8.2-10 GHz) were conducted on three material samples in single and multilayer arrangements. The algorithm accurately extracted the complex constitutive parameters for each layer. These values were then compared with values extracted using a modified short-circuit line (SCL) method (single-layer cases only). S-parameters were also generated using the extracted values and compared with the measured data. In all cases, results were found to be in good overall agreement with both the SCL method values and the measured data.

Calculating Effective Skin Depth for Thin Conductive Sheets

In this presentation the conventional skin depth is compared with a modified skin depth that considers a finite thickness conductor, and with an effective skin depth that also considers wave reflection at the backside of the conductor. The comparison yields recommended thickness ranges over which each version of skin depth is accurate

Biaxial Permittivity Determination for Electrically Small Material Specimens of Complex Shape Using Shorted Rectangular Waveguide Measurements

A method for determining the complex anisotropic permittivity for electrically small material specimens of complex shape with biaxial dielectric anisotropy is described and representative measured results are presented. The method extracts the anisotropic tensor elements from specimen reflection measurements made with a shorted rectangular waveguide. A number of independent reflection measurements, using different specimen orientations in the waveguide equal to the number of unknown permittivity terms, are required. The specimens need not fill either dimension of the waveguide cross section and are permitted to be electrically short in the propagation direction. Measurements using WR1500 and WR1150 waveguide were made for a known isotropic low-loss dielectric specimen of complex shape. Additional measurements in WR1500 were made on two engineered anisotropic artificial dielectric specimens. Tensor permittivity elements were extracted from the measurements and were used to validate and demonstrate the accuracy and capability of the method by comparison with known values for the dielectric specimen or with explicit inclusion-binder simulation results for the engineered specimens.

Microwave Permittivity Determination for Materials With Out-of-Plane and Off-Diagonal Dielectric Anisotropy

A general and fast procedure for determining the complex anisotropic and dispersive permittivity for materials with anisotropy along the permittivity tensor diagonal and in-plane off-diagonal is presented. The procedure extracts the anisotropic tensor elements from co- and cross-polarized free-space transmission measurements of a material slab of arbitrary thickness. Numerical studies involving simulated transmission data are presented to demonstrate the validity and accuracy of the approach. Measurements of a known isotropic dielectric and two engineered anisotropic specimens were used to further validate and demonstrate the accuracy and capability of the procedure.

Complex Constitutive Parameter Extraction for Multilayered Samples using S-Parameter Waveguide Measurements

In this paper, a method was presented for accurately determining the complex CP from individual layers within a multilayer sample using S-parameter waveguide measurements. MPSQP, a modification of SQP, provided a simple mechanism to avoid local minima trapping while still obtaining the global minimum in a short amount of time. Comparison of the extracted CP to those of the SCL method showed that the MPSQP algorithm was successful in accurately estimating the CP for three single layer materials (one nonmagnetic and two radar absorbing). Results were also shown for a three layer material. Based on RMS error comparisons, the CP were found to be accurate to within the tolerance of the available measurements

Finite element modeling of the vertical and horizontal electric field signatures in the presence of a sprite

Recently Pasko Barrington-Leigh, and Inan have discussed models explaining the electromagnetic and optical behavior of sprites. Research presented herein extends Baginskis lightning transient model by including Paskos self-consistent conductivity model for parameters consistent with sprite observations. Equations are solved simultaneously in differential form (Maxwells equations and electron ionization). Cylindrical symmetry is assumed and fields simulated at radius /spl sim/ 0-50 km, and altitude /spl sim/ 40-80 km. Vertical and horizontal field signatures are presented and anomalous behavior discussed. The research differs from earlier models by including the low altitude conductivity in the solutions and over the entire region simulated.

Multi-GPU accelerated fast ACA direct solve for moment method solution of composite bodies

A fast moment method solution of composite body problems is presented based on a combination of a modified Adaptive Cross Approximation (ACA) algorithm for matrix fill and LU decomposition. The ACA LU algorithm is optionally accelerated by multiple GPUs and comparisons are presented for various problems simulated on Intel Xeon processors and NVIDIA GPU cards.

Modified genetic algorithm to design arbitrary response filters for rectangular waveguides: Research Articles

The new generation of System-on-Chip (SoC) incorporates digital, analogue, RF/microwave and mixed-signal components. Such circuits impose to reconsider the traditional design methods. Mixed-signal designers need novel design methodologies which will have to include accurate behavioral libraries of devices and processes into hierarchical design flows. Thus, this paper describes a behavioral modeling approach which generates neuro-fuzzy-based models for RF/microwave devices. The models, so obtained, can be easily integrated into a VHDL-AMS simulator. This modeling approach is applied to a microwave tunable phase shifter and it is illustrated by the development of a VHDL-AMS model library for RF/microwave applications.

A novel constitutive parameter extraction technique using a single short circuit waveguide measurement

In this paper, a method was presented for accurately determining the complex CP of a material sample using a single SCL waveguide measurement. An analytic expression for the complex reflection coefficient at the reference plane of the waveguide serves as the forward problem in the novel MPSQP algorithm. The MPSQP is a very robust optimization technique which exploits the speed and accuracy of SQP while avoiding local minima trapping. This technique proves beneficial for several application areas including high temperature material characterization. At high temperatures, a considerable amount of time is devoted to changing terminations, and this process usually requires some amount of cooling and reheating of the sample. During this time, the sample may shift inside the waveguide which, in turn, may introduce errors into the measured data