An Efficient Hybrid Method for 3D Scattering from Inhomogeneous Object Buried beneath a Dielectric Randomly Rough Surface

An efficient iterative analytical-numerical method is proposed for three-dimensional (3D) electromagnetic scattering from an inhomogeneous object buried beneath a two-dimensional (2D) randomly dielectric rough surface. In the hybrid method, the electric and magnetic currents on the dielectric rough surface are obtained by current-based Kirchhoff approximation (KA), while the scattering from the inhomogeneous object is rigorously studied by finite element method (FEM) combined with the boundary integral method (BIM). The multiple interactions between the buried object and rough surface are taken into account by updating the electric and magnetic current densities on them. Several numerical simulations are considered to demonstrate the algorithm’s ability to deal with the scattering from the inhomogeneous target buried beneath a dielectric rough surface, and the effectiveness of our proposed method is also illustrated

Multiple Volume Scattering in Random Media and Periodic Structures with Applications in Microwave Remote Sensing and Wave Functional Materials

The objective of my research is two-fold: to study wave scattering phenomena in dense volumetric random media and in periodic wave functional materials. For the first part, the goal is to use the microwave remote sensing technique to monitor water resources and global climate change. Towards this goal, I study the microwave scattering behavior of snow and ice sheet. For snowpack scattering, I have extended the traditional dense media radiative transfer (DMRT) approach to include cyclical corrections that give rise to backscattering enhancements, enabling the theory to model combined active and passive observations of snowpack using the same set of physical parameters. Besides DMRT, a fully coherent approach is also developed by solving Maxwell’s equations directly over the entire snowpack including a bottom half space. This revolutionary new approach produces consistent scattering and emission results, and demonstrates backscattering enhancements and coherent layer effects. The birefringence in anisotropic snow layers is also analyzed by numerically solving Maxwell’s equation directly. The effects of rapid density fluctuations in polar ice sheet emission in the 0.5~2.0 GHz spectrum are examined using both fully coherent and partially coherent layered media emission theories that agree with each other and distinct from incoherent approaches. For the second part, the goal is to develop integral equation based methods to solve wave scattering in periodic structures such as photonic crystals and metamaterials that can be used for broadband simulations. Set upon the concept of modal expansion of the periodic Green’s function, we have developed the method of broadband Green’s function with low wavenumber extraction (BBGFL), where a low wavenumber component is extracted and results a non-singular and fast-converging remaining part with simple wavenumber dependence. We’ve applied the technique to simulate band diagrams and modal solutions of periodic structures, and to construct broadband Green’s functions including periodic scatterers.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135885/1/srtan_1.pd

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Impedance Transformers

Non

Integrated Silicon-Based Photonic, Acoustic and Optomechanical Devices

Integration of photonic and other types of micro- and nanoscale devices in silicon and silicon- based material platforms allows one to leverage existing large-scale wafer-based manufacturing infrastructure and tools developed for the integrated circuit (IC) industry. This thesis explores chip- scale silicon photonic structures that include physical contacts that are intimate with the optical field, evanescent confinement of acoustic waves using slowness contrast silicon-based materials, and the implementation of optomechanical devices in monolithic CMOS microelectronics platforms. The unifying objective of this work was to make progress toward photonic and optomechanical devices that are densely integrable on chip, and potentially also monolithically with state-of-the- art transistors, in optical and optomechanical circuits.Loss avoidance in photonic structures with contacts is designed and explained using a novel mechanism, imaginary coupling of modes. Periodic contacts are treated as an index perturbation and designed to radiatively couple two eigenmodes of the unperturbed structure, so as to construct a low-loss supermode with a field distribution pattern that “avoids” the contacts. Using this concept, a linear waveguide crossing array and a circular “wiggler” resonator are designed and experimentally demonstrated. The “wiggler” resonator is further suspended while sustaining a high quality factor above 100,000.Evanescent confinement and guiding of elastic waves on chip based on material contrast is investigated theoretically in the context of silicon-based materials, as an alternative to confining acoustic waves using air-solid interfaces in suspended structures. Calculations of material intrinsic and radiation losses suggest that compact wavelength-scale acoustic/phononic devices can be built on chip to form complex circuitries.Combining optics and acoustics, optical forces and integration of suspended optomechanical devices in CMOS microelectronics processes are explored. Waveguide design to maximize static radiation pressure in a vertically coupled dual ring structure, and the initial design of an optome- chanical “wiggler” resonator are discussed. Post processing steps to suspend devices fabricated in an unmodified CMOS microelectronics process are proposed with current experimental progress presented