Dongying Li

A High Gain Antenna With an Optimized Metamaterial Inspired Superstrate

A metamaterial unit cell with a low refractive index over a wide frequency band is proposed and designed. The effective material parameters of the unit cell are extracted, and the unit cell forms a planar three-layer metamaterial structure used as a superstrate for broadside gain enhancement of a patch antenna at 10 GHz. The proposed superstrate is optimized along with the antenna to enhance its beam-focusing ability, taking into account the oblique wave incidence from the radiation source. Both simulation and measurement of the antenna with the optimized superstrate show that this configuration is able to achieve a broadside gain 70%-80% of the maximum gain from the ideal effective radiation surface.

Efficient Finite-Difference Time-Domain Modeling of Driven Periodic Structures and Related Microwave Circuit Applications

The sine-cosine method for the finite-difference time-domain-based dispersion analysis of periodic structures is extended to incorporate the presence of nonperiodic wideband sources. A new formulation of this method is presented to clearly demonstrate that it can be employed for the characterization of periodic structures over a broad bandwidth. Moreover, its coupling with the array-scanning technique enables the incorporation of nonperiodic sources, thus enabling the fast characterization of driven periodic structures in the time domain via a small number of low-cost simulations. The convergence, accuracy, and efficiency of the proposed method is demonstrated with its application to the analysis of a negative-refractive-index transmission-line ldquoperfect lensrdquo and the successful comparison of simulated with experimental results. Finally, a modified version of this method is proposed for the accelerated simulation of microwave circuit geometries printed on periodic substrates.

Impedance calculation and equivalent circuits for metal–insulator–metal plasmonic waveguide geometries

This Letter presents an analytical expression for the equivalent impedance of the fundamental mode of both 2D and 3D metal-insulator-metal (MIM) plasmonic waveguides. It also presents circuit models for passive 2D MIM waveguide components represented by additional parasitic circuit elements. Moreover, a modeling library for various 2D MIM waveguide structures is developed. The proposed analytical results have been verified and show great accuracy compared to the full-wave characterizations.

Efficient finite-difference time-domain modeling of driven periodic structures

The paper proposes an efficient method to analyze the response of periodic structures to non-periodic excitations in the time domain, employing the finite-difference time-domain (FDTD) method. To that end, the array-scanning method, which has been previously associated with frequency-domain, integral formulations of periodic structure problems, is translated into the context of FDTD. Hence, the application of periodic FDTD techniques, based on the simulation of a single unit cell, to problems involving non-periodic source excitations is enabled. While a validation case study involves a microstrip line on an electromagnetic band-gap substrate, the utilization of this approach to metamaterial structure modeling is envisaged.

Time-Domain Modeling of Nonlinear Optical Structures With Extended Stability FDTD Schemes

Two numerical methodologies based on the finite-difference time-domain (FDTD) technique are formulated and applied to model optical structures with Raman and Kerr type nonlinearities. The first scheme is based on the alternating-direction implicit finite-difference time-domain (ADI-FDTD), while the second one is based on a recently introduced spatially filtered FDTD method. Both methods are able to extend FDTD time steps beyond the conventional Courant-Friedrichs-Lewy stability limit. It is demonstrated that both methods are significantly faster than the standard nonlinear FDTD, while maintaining its level of accuracy. Their potential as design and analysis tools for nonlinear periodic structures is demonstrated with the study of a 1-D problem involving a nonlinear Bragg reflector.

Integrated System-Level Electronic Design Automation (EDA) for Designing Plasmonic Nanocircuits

This paper proposes a system-level circuit simulation framework for nanoplasmonic devices, and presents an example of the simulation of a plasmonic nanocircuit. The electronic design automation environment provides an equivalent circuit model library for several plasmonic metal-insulator-metal-based devices. The accuracy of the equivalent models for the plasmonic nanocircuit library is verified by using full-wave simulations and analytical equations. These models are then used to design an ultracompact Mach-Zehnder plasmonic modulator. It is shown that the voltage required to achieve a π phase shift Vπ in the modulator can be predicted by the simulator with reasonable accuracy. The optimized design of the modulator is also presented that reduces the value of Vπ according to the required specification.

Time-domain modeling of nonlinear pulse propagation with an extended stability spatially filtered FDTD method

Nonlinear pulse propagation studies for microwave and photonics applications are known to present large computational load to conventional simulators, including commercial packages. Therefore, there is a need for innovating existing algorithms for nonlinear problems, especially the Finite-Difference Time-Domain (FDTD) method which is particularly suitable for nonlinear structure analysis. To this end, a numerical methodology based on a recently introduced spatially filtered FDTD technique is presented and applied to nonlinear pulse propagation studies. It is demonstrated that the method is significantly faster than the standard nonlinear FDTD, while maintaining its level of accuracy.

Accelerated time-domain modeling of microstrip based microwave circuit geometries on periodic substrates

Advances in the design of electromagnetic bandgap and meta-material structures have opened new possibilities for substrate engineering to optimize the performance of microstrip or coplanar waveguide based integrated microwave circuits. Periodic substrates alone can be fully characterized through their dispersion analysis. On the other hand, modeling the interaction between metallic guides and such substrates usually involves lengthy simulations, because the resulting geometry is non-periodic. We propose a Finite-Difference Time-Domain based solution to this problem, which leads to significant acceleration of the relevant modeling process over broad bandwidths, without compromising accuracy.

A New Approach for the FDTD Modeling of Antennas Over Periodic Structures

A new approach is proposed for the time-domain modeling of antennas over periodic substrates. This class of problems would typically require a time-consuming simulation of the antenna structure with a finite number of unit cells of the periodic substrate, chosen to be large enough to achieve convergence. On the contrary, the present work employs periodic boundary conditions applied at the substrate, to dramatically reduce the computational domain and hence, the cost of such simulations. Emphasis is given on radiation pattern calculation, and the consequences of the truncated computational domain of the proposed method on the computation of the electric and magnetic surface currents invoked in the near-to-far field transformation. The theoretical aspects of the proposed methodology are complemented by numerical examples of a wire and an integrated patch antenna over electromagnetic band-gap substrates.

A high-gain antenna with U-slot using zero-index metamaterial superstrate

A zero-index metamaterial unit cell working over a wide frequency band is presented. A three layer superstrate with metamaterial unit cells arranged in a 5 by 5 array is designed and placed over a mircostrip patch antenna with U-slot for antenna gain enhancement. The simulation results show that the gain of the metamaterial antenna is improved by nearly 4 dB throughout the operating band.