Michael E. Baginski

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.

A Capacitive Fringing Field Sensor Design for Moisture Measurement Based on Printed Circuit Board Technology

Interdigitated electrode capacitive fringing field sensors have been utilized in numerous applications. Although various technologies are used to realize these types of sensors, printed circuit board technology is particularly advantageous for realizing this type of sensor through fabricating the interdigitated electrode structures in the patterned Cu foil. Additionally, the solder mask coating can insulate the electrodes to prevent shorting in the presence of water. Using this approach, prototype sensors were designed, simulated, fabricated, and successfully evaluated. Applications include water detection and quantity measurement and soil moisture content measurement.

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.

High heat flux cooling for silicon hybrid multichip packaging

Recent projections have suggested that heat fluxes will reach or exceed 100 W/cm/sup 2/ in future integrated circuit chips. Research on the application of both liquid-jet impingement with boiling and direct liquid immersion to the cooling of silicon substrates used in hybrid multichip packaging is described. The authors report the first data on cooling of silicon substrates using direct immersion cooling in Freon-12 and compare the results to those of liquid-jet impingement cooling of the same substrates. Heater fluxes of 200 W/cm/sup 2/ at a maximum temperature rise of 50 K have been achieved using 16 jets impinging with a nozzle velocity of 1 m/s. Immersion cooling experiments have reached heater fluxes of 100 W/cm/sup 2/ with a 45-K temperature rise. Results from two-dimensional numerical simulations of the test wafer are in excellent agreement with the immersion cooling data. These results indicate that both modes of cooling will be highly useful in the cooling and packaging technology for the next generation of high-performance computer systems. >

Electromagnetic Scattering From Electrically Large Arbitrarily-Shaped Conductors Using the Method of Moments and a New Null-Field Generation Technique

In this work, a new numerical procedure is developed to apply the well-known method of moments (MoM) formulation to electrically large conducting bodies of arbitrary shape. The numerical procedure involves developing a combination of subdomain-entire domain basis functions which result in a sparse moment matrix as opposed to a full matrix in the traditional method. Moreover, the zeros in the MoM matrix are precisely at the same locations where one would have encountered the most significant values. The solution of the new matrix may be obtained using the simple Gauss-Seidel iterative procedure with only two or three iterations. All the traditional advantages of the MoM procedure are retained including the solution for multiple incident fields. Several numerical results are presented to illustrate the validity of the new approach.

Electromagnetic Scattering From Arbitrarily Shaped Dielectric Bodies Using Paired Pulse Vector Basis Functions and Method of Moments

A pair of orthogonal pulse vector basis functions is demonstrated for the calculation of electromagnetic scattering from arbitrarily-shaped material bodies. The basis functions are intended for use with triangular surface patch modeling applied to a method of moments (MoM) solution. For modeling the behavior of dielectric materials, several authors have used the same set of basis functions to represent equivalent electric and magnetic surface currents. This practice can result in zero-valued or very small diagonal terms in the moment matrix and an unstable numerical solution. To provide a more stable solution, we have developed orthogonally placed, pulse basis vectors: one for the electric surface current and one for the magnetic surface current. This combination ensures strongly diagonal moment matrices. The basis functions are suitable for electric field integral equation (EFIE), magnetic field integral equation (HFIE), and combined field formulations. In this work, we describe the implementations for EFIE and HFIE formulations and show example results for canonical figures.

Three-Dimensional FDTD Simulation of Nonlinear Ferroelectric Materials in Rectangular Waveguide

Nonlinear transmission lines have numerous applications in the communications and defense industries due to their ability to form and propagate short-duration ultrawideband pulses. This paper simulates a short-duration Gaussian transient exciting low-order TEm,0 modes in a nonlinear ferroelectric-filled conducting waveguide. A 3-D finite-difference time-domain simulation is employed in the analysis, and the ferroelectric-filled waveguide model is based on a nonlinear polarization relationship extrapolated from measurements. A small portion of the frequency band operates in the nonlinear polarization region. These components will propagate at higher velocity than lower amplitude components, and this effect counteracts dispersion and results in compression of the pulses into solitons as they propagate.

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

Finite-element analysis of microstrip systems in the vicinity of a substrate edge and approximate formulas for capacitance

The TEM electrical characteristics of a microstrip system in the vicinity of a dielectric edge are investigated via a series of numerical simulations and empirical formulas based on the simulations derived. A finite-element routine is used as the basis for the simulations that solve the Maxwell equations (/spl nabla//spl middot/D=/spl rho//sub f/) subject to the appropriate electromagnetic boundary conditions. The geometric and electrical parameters used in the simulation are selected to be representative of those found typically in printed circuit board fabrications (microstrip features /spl sim/10-30 mils). An empirical formulation for the capacitance of the microstrip is developed and shown to be in good agreement with the simulations (maximum difference of 1070). The formulation is also compared to measurements. Several plots of the vector electric-field intensity are presented. These plots identify the general structure of the electric-field intensity near the edge of the dielectric; thereby providing the design engineer with insight into the typical field fringing expected. >

Experimental and numerical characterization of the radio-frequency drying of textile materials (II)

The experimental and numerical characterization of radio frequency drying of textile materials is investigated here. The study focuses on modeling, via a numerical simulation of the electromagnetic phenomenology, the experimentally determined thermal and electrical behavior of a 1110 scaled version of a prototype industrial drying system. A wet dyedfabric (50% water by weight)is placedparallel to a21-element drying system, contained within an approximately rectangular metal structure. Internal dielectric drying of the material is induced by molecular motion which produces heat, caused by rapid electric field reversals. The experimental system is designed to facilitate efficient power transfer, using a 10 Kw 22 MHz power generator. The variance in the material’s drying rate is inferred from the post processing coloration (wicking effect). It is described and contrasted to that implied by a series of computer simulations. A finite element routine serves as the basis of the computer modeling. Preliminary res...