Sourav Chakravarty

Application of a microgenetic algorithm (MGA) to the design of broadband microwave absorbers using multiple frequency selective surface screens buried in dielectrics

Over the years, frequency selective surfaces (FSSs) have found frequent use as radomes and spatial filters in both commercial and military applications. In the literature, the problem of synthesizing broadband microwave absorbers using multilayered dielectrics through the application of genetic algorithms (GAs) have been dealt with successfully. Spatial filters employing multiple, freestanding, FSS screens have been successfully designed by utilizing a domain-decomposed GA. We present a procedure for synthesizing broadband microwave absorbers by using multiple FSS screens buried in a dielectric composite. A binary coded microgenetic algorithm (MGA) is applied to optimize various parameters, viz., the thickness and relative permittivity of each dielectric layer; the FSS screen designs and materials; their x- and y-periodicities; and their placement within the dielectric composite. The result is a multilayer composite that provides maximum absorption of both transverse electric (TE) and transverse magnetic (TM) waves simultaneously for a prescribed range of frequencies and incident angles. This technique automatically places an upper bound on the total thickness of the composite. While a single FSS screen is analyzed using the electric field integral equation (EFIE), multiple FSS screens are analyzed using the scattering matrix technique.

On the application of the microgenetic algorithm to the design of broad-band microwave absorbers comprising frequency-selective surfaces embedded in multilayered dielectric media

In this paper, we present a procedure for synthesizing broad-band microwave absorbers incorporating frequency-selective surface (FSS) screens embedded in dielectric media using a binary coded genetic algorithm (GA). The GA simultaneously and optimally chooses the material in each layer, thickness of each layer, FSS screen periodicity in the z- and y-directions, its placement within the dielectric composite, and the FSS screen material. Additionally, the GA generates the cell structure of the FSS screen. The result is a multilayer composite that provides maximum absorption of both TE and TM waves for a prescribed range of frequencies and incident angles. This technique automatically places an upper bound on the total thickness of the composite.

Experimental validation of crosstalk simulations for on-chip interconnects using S-parameters

Since the design of advanced microprocessors is based on simulation tools, accurate assessments of the amount of crosstalk noise are of paramount importance to avoid logic failures and less-than-optimal designs. With increasing clock frequencies, inductive effects become more important, and the validity of assumptions commonly used in simulation tools and approaches is unclear. We compared accurate experimental S-parameters with results derived from both magneto-quasi-static and full-wave simulation tools for simple crosstalk structures with various capacitive and inductive couplings, in the presence of parallel and orthogonal conductors. Our validation approach made possible the identification of the strengths and weaknesses of both tools as a function of frequency, which provides useful guidance to designers who have to balance the tradeoffs between accuracy and computation expenses for a large variety of cases

A Layered Finite Element Method for Electromagnetic Analysis of Large-Scale High-Frequency Integrated Circuits

A high-capacity electromagnetic solution, layered finite element method, is proposed for high-frequency modeling of large-scale three-dimensional on-chip circuits. In this method, first, the matrix system of the original 3-D problem is reduced to that of 2-D layers. Second, the matrix system of 2-D layers is further reduced to that of a single layer. Third, an algorithm of logarithmic complexity is proposed to further speed up the analysis. In addition, an excitation and extraction technique is developed to limit the field unknowns needed for the final circuit extraction to a single layer only, as well as keep the right-hand side intact during the matrix reduction process. The entire procedure is numerically rigorous without making any theoretical approximation. The computational complexity only involves solving a single layer irrespective of the original problem size. Hence, the proposed method is equipped with a high capacity to solve large-scale IC problems. The proposed method was used to simulate a set of large-scale interconnect structures that were fabricated on a test chip using conventional Si processing techniques. Excellent agreement with the measured data has been observed from dc to 50 GHz

A novel technique for full-wave modeling of large-scale three-dimensional high-speed on/off-chip interconnect structures

This paper presents a novel, rigorous, and fast method for full-wave modeling of high-speed interconnect structures. In this method, the original wave propagation problem is represented into a generalized eigenvalue problem. The resulting eigenvalue representation can comprehend conductor and dielectric losses, arbitrary dielectric and conductor configurations, and arbitrary materials such as dispersive, and anisotropic media. The edge basis function is employed to accurately represent the unknown field, and the triangular element is adopted to flexibly model arbitrary geometry. A mode-matching technique applicable to lossy system is developed to solve large-scale 3D problems by using 2D-like CPU time and memory. A circuit-based extraction technique is developed to obtain S-parameters from the unknown fields. The proposed technique can generate S-parameters, full-wave RLGC, propagation constants, characteristic impedances, voltage, current, and field distributions, and hence yield a comprehensive representation of interconnect structures. Experimental and numerical results demonstrate its accuracy and efficiency.

Application of the micro-genetic algorithm to the design of spatial filters with frequency-selective surfaces embedded in dielectric media

We present an efficient method of optimizing spatial filters comprising of single and multiple frequency-selective surface (FSS) screens embedded in multilayered dielectric media. Two such filter designs are optimized via the micro-genetic algorithm (MGA) and their frequency responses are validated by alternate methods.

Design of a frequency selective surface (FSS) with very low cross-polarization discrimination via the parallel micro-genetic algorithm (PMGA)

We discuss the design of a frequency selective surface (FSS) with low cross-polarization discrimination. In the past, FSS screens have been employed to improve the cross-polarization performance. The objective of this paper is to synthesize an FSS subreflector with low cross-polarization via the application of a parallel binary coded micro-genetic algorithm (PMGA). The PMGA optimizes the metallization pattern and the periodicity of the FSS screen in both the x- and y-directions to maintain a low cross-polarization level for a wide band of frequencies and a range of incident angles.

Experimental validation of crosstalk simulations for on-chip interconnects at high frequencies using S-parameters

Since advanced microprocessors are designed based on simulation tools, accurate assessments of the amount of crosstalk noise are of paramount importance to avoid logic failures and less-than-optimal designs. With increasing clock frequencies, inductive effects become more important, and the validity of assumptions commonly used in simulation tools and approaches is unclear. We compared accurate experimental S-parameters with results derived from both magneto-quasi-static and fullwave simulation tools, for simple crosstalk structures with various capacitive and inductive couplings, in the presence of parallel and orthogonal conductors. Our validation approach made possible the identification of the strengths and weaknesses of both tools as a function of frequency, which provides useful guidance to designers who have to balance the trade-offs between accuracy and computation expenses for a large variety of cases.

Stability characteristics of absorbing boundary conditions in microwave circuit simulations

In this paper, we examine the stability properties of several absorbing boundary conditions in the finite-difference time-domain (FDTD) simulations of microwave circuits. The numerical experiments show that the stability characteristics of absorbing boundary conditions, e.g., Murs (1981) and perfectly matched layers (PML), can depend upon the discretization of the computational domain.

A silicon-validated methodology for power delivery modeling and simulation

Power integrity has become increasingly important for the designs in 32nm or below. This paper discusses a silicon-validated methodology for microprocessor power delivery modeling and simulation. There have been many prior works focusing on power delivery analysis and optimization. However, none of them provided a comprehensive modeling methodology with post-silicon data to validate the use of the models. In this paper, we present power delivery system models that are able to achieve less than 10% deviation from the supply noise measurements on a 32nm industrial microprocessor design. Our models are able to capture the unique impacts of on-die inductance, state dependent coupling capacitance and die-package interaction. Those impacts happen to be prominent for the designs in 32nm or below but were considered negligible or even not noted in earlier technology nodes. Comparisons were made to quantify the impacts of different modeling strategies on supply noise prediction accuracy. This specifically provides designers insights in selecting appropriate models for power delivery analysis. The impact of power delivery noise on timing margin was accurately estimated showing a good agreement to the worst-case jitter measurements.