Experimental and Analysis of Electromagnetic Characterization of Biological and Non-Biological Materials in Microwave, Millimeter-wave, and Terahertz Frequency Bands

The goal of this research is to characterize the electromagnetic properties of biological and non-biological materials at terahertz (THz), millimeter-wave, and microwave frequency bands. The biological specimens are measured using the THz imaging and spectroscopy system, whereas the non-biological materials are measured using the microwave and millimeter-wave free-space system. These facilities are located in the Engineering Research Center at the University of Arkansas. The THz imaging system (TPS 3000) uses a Ti-Sapphire laser directed on the photoconductive antennas to generate a THz time domain pulse. Upon using the Fourier Transform, the spectrum of the pulsed THz signal includes frequencies from 0.1 THz to 4 THz. On the other hand, the free space system uses a PNA network analyzer to produce a signal at frequencies ranging from 10 MHz to 110 GHz. For the biological specimens, the research focused on imaging the freshly excised breast tumors to detect the cancer on the margins using THz radiation. The tumor margin assessment depends on the THz contrast between cancer, collagen, and fat tissues in the tumor. Three models of breast tumors are investigated in this research: humans, mice (xenograft and transgenic), and Sprague Dawley rats. The results showed good differentiation between the cancerous and non-cancerous tissues in all three models. In addition, an excellent distinction was observed between cancer, collagen, and fat in the formalin-fixed paraffin-embedded (FFPE) block tissue with ~ 90-95% correlation with the pathology images. Furthermore, the FFPE ductal carcinoma in situ (DCIS) tumors are investigated, also using the THz imaging. The THz images of the DCIS samples are compared with those of the FFPE invasive ductal carcinoma (IDC) specimens. The results demonstrated that THz electric field reflection from the IDC were higher than that from the collagen, DCIS, and then the fat tissue region. Furthermore, a pilot study is conducted to investigate the effect of optical clearance (e.g., glycerol solution) on THz images of freshly excised tumors. The results showed that the glycerol reduced the absorption coefficients of pre-treated tissues compared with those of untreated tissues. For the non-biological materials, the research focuses on characterizing highly conductive non-magnetic radar absorbing materials (RAM) for the automotive industry. The ingredients of material components in the RAM samples are unrevealed under a non-disclosure agreement (NDA). The material characterization involves the extraction of the complex relative permittivity utilizing the transmission measurement data obtained at the K-band (18 GHz to 26.5 GHz) and the W-band (75 GHz to 110 GHz). The measurements are obtained using the free-space conical horn antenna system. A transmission line based extraction model is implemented, and the results are validated with the experimental measurements of the S-parameters. The maximum error reported between the measured and the calculated S-parameters was less than 1 dB. In conclusion, the THz imaging of breast cancer tumors presents a potential margin assessment of other solid tumors, and the microwave, millimeter-wave, and THz spectroscopy of materials demonstrate a potential application in the fifth and sixth generations of wireless communications

Measurement and Characterization of Terahertz Radiation Propagating Through a Parallel Plate Waveguide

As the amount of study into the terahertz (THz) region of the electromagnetic spectrum steadily increases, the parallel plate waveguide has emerged as a simple and effective fixture to perform many experiments. The ability to concentrate THz radiation into a small area or volume enables us to analyze smaller samples and perform more repeatable measurements, which is essential for future research. While the fundamental physics of PPW transmission are understood mathematically, the practical knowledge of building such a fixture for the THz domain and taking measurements on it with a real system needs to be built up through experience. In this thesis, multiple PPW configurations are built and tested. These include waveguides of different lengths and opening heights, using lenses and antennas to focus and collect radiation from the input and output, and different amounts of polish on the waveguide surface. A basic resonator structure is also built and measured as a proof of concept for future research. The two most useful propagation modes through the waveguide, the lowest order transverse magnetic (TEM) and transverse electric (TE) modes, were characterized on all of the setups. Additionally, a flexible fixture was designed and measured which will allow future work in the THz field to be much more reliable and repeatable

Terahertz (THz) Waveguiding Architecture Featuring Doubly-Corrugated Spoofed Surface Plasmon Polariton (DC-SSPP): Theory and Applications in Micro-Electronics and Sensing

Terahertz (10^12 Hz) has long been considered a missing link between microwave and optical IR spectra. This frequency range has attracted enormous research attentions in recent years, with ever-growing anticipation for its applications in remote sensing, molecular spectroscopy, signal processing and next-generation high-speed electronics. However, its development has been seriously hindered by the lack of waveguiding and manipulating architectures that could support the propagation of THz radiations without excessive signal distortion and power loss. Facing this challenge, this work exploits the spoofed surface plasmon polariton (SSPP) mode of the THz oscillation and introduces the doubly corrugated SSPP (DC-SSPP) architecture to support sub-wavelength, low-dispersion THz transmission. DC-SSPP displays unique bandgap structure, which can be effectively modulated via structural and material variables. These unequaled properties make DC-SSPP the ideal solution to support not only signal transmission but also THz sensing and THz-electronics applications. In this thesis, theoretical analysis is carried out to thoroughly characterize the THz propagation, field distribution and transmission band structures in the novel architecture. Via numerical approximation and finite element simulations, design variations of the DC-SSPP are further studied and optimized to fulfill application-specific requirements. We demonstrate effective DNA sensing by adopting the Mach-Zehnder interferometer (MZI) or waveguide-cavity-waveguide insertions, which showed detectability with minuscule sample size even in the aqueous environment. We manifest high-speed analog-to-digital conversion via a combination of MZI DC-SSPP with nonlinear, partial-coupling detector arrays. Full characterization of the proposed ADC is carried out where high operation speed, small signal distortion, and great output linearity is shown. Also included in this work is a detailed review of the THz emitters and detectors, which are indispensable constituents of the THz system discussed herein. The future of the DC-SSPP in building THz bio-computing and THz digital circuits, considered as the next step of this research work, is also explored and demonstrated with the novel concept of directed logic network.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/137130/1/xuzhao_1.pd

Multiscale optical patterning: using micro and nano periodic structures to create novel optical devices with applications to biosensing

Patterning, the utilisation and manipulation of geometric properties, is important both for the rational design of technological devices and also to the understanding of many natural phenomena. In this thesis I examine the way in which micro and nano patterning can alter optical properties across a large range of wavelength scales and how these novel phenomena can be utilised. Micro patterned electrodes can tune the geometry of radio frequency electric fields to generate dielectrophoretic microfluidic devices. These devices use the dielectrophoretic force to sort, position and characterise the properties of micro and nano particles.. I develop a new image processing algorithm that radically improves experimental efficiency allowing for real-time supervisor free dielectrophoretic characterisation of nanoparticles. Metamaterials are composite structures that have repeating units that are much smaller than the wavelength of radiation they are designed to work with. The optical properties of the materials are derived from these units rather than the bulk characteristics of the materials they are composed of. I demonstrate the development of novel THz metamaterial absorber devices. These devices provide a means to design and control the absorption of THz radiation, modulating bandwidth, polarization dependence and frequency in a form that is readily integrable with other standard fabrication processes. Finally by periodically patterning materials on the nanometer scale I demonstrate the development of novel photonic crystal devices and complementary optical components. In these devices the periodicity of the electromagnetic wave is modulated by the periodicity of the structures themselves resulting in band gaps and resonances analogous to the band gaps and defect states found commonly in semi-conductor physics. I demonstrate the theory, fabrication and measurement of these devices using novel broadband supercontinuum sources and propose a future application for biosensing. Further topics covered in the appendix include the development of a spin out technology, a $100 open source atomic force microscope developed while spending time in China. Finally I examine the role of patterning for optimising the performance of nanomechanical cantilever biosensors, and show how geometrical effects on the microscopic scale are crucial to understanding the workings of the vancomycin family of antibiotics, as screened using microcantilevers. Portions of this report are edited extracts from published articles resulting from this work, a full list of which is given in Appendix A

Metamateriais electromagnéticos baseados em geometria fractal

In the growing trends in different technological areas, metamaterials opened new opportunities for controlling electromagnetic radiation for advanced applications. There are different types of metamaterials that a) offer negative values for the real parts of effective permittivity and/or permeability [doublenegative (DNG) media]; b) provide for extremely high and/or anisotropic parameters (e.g., wire media); and c) have near-zero values of these parameters as in electric near-zero (ENZ) or magnetic near-zero (MNZ) media. One of the most common forms of the metamaterials designed for microwave applications are regular periodic structures. Although periodicity can be sometimes a necessary property (like, for example, in the photonic band-gap (PBG) metamaterials), some other forms such as wire medium (WM) do not really need to be periodic to provide the same plasma-like effective permittivity. Moreover, periodicity in metamaterials designed for suppression of the propagation may open new bands in which waves can propagate. Recently, electrodynamics of fractal structures caught a vast attention in the design of microwave and optical devices and their applications. Fractals are geometric patterns whose topological dimensions cannot be always represented by an integer number. Instead, dimensions in fractals are described by other definitions such as the Hausdorff dimension. Due to their self-repeating pattern, fractals can bring new opportunities in the design of metamaterials. In this work, the fractal-geometric approach has been studied in order to build different types of metamaterials. Specifically, the project objectives are to model electromagnetic characteristics of these metamaterials based on different types of fractals; and to provide new homogenization techniques for this group of metamaterials. To further expand the idea of fractal applications, the new concept of fractal coding metamaterials also has been developed and studied in the framework of this project.Nas tendências de crescimento de diversas áreas tecnológicas, os metamateriais abriram novas oportunidades no controlo da radiação eletromagnética para aplicações avançadas. Existem diferentes tipos de metamateriais que: a) oferecem valores negativos para as partes reais da permitividade e/ou permeabilidade efetivas [meio duplamente negativo (DNG)]; b) proporcionam valores extremamente elevados e/ou anisotrópicos desses parâmetros [por exemplo, meios de fios condutores (WM)]; e c) apresentam valores próximos de zero desses parâmetros, como nos meios de permitividade elétrica próxima de zero (ENZ) ou de permeabilidade magnética próxima de zero (MNZ). Uma das formas mais comuns dos metamateriais concebidos para aplicações de microondas são estruturas periódicas regulares. Embora a periodicidade possa às vezes ser uma propriedade necessária (como, por exemplo, nos metamateriais fotónicos de bandas proibidas (PBG)), algumas outras formas, como os meios de fios condutores (WM), não precisam ser periódicas para oferecer a mesma permitividade efectiva do material de tipo plasma. Além disso, a periodicidade em metamateriais projetados para a supressão da propagação pode abrir novas bandas nas quais as ondas podem se propagar. Recentemente, a eletrodinâmica de estruturas fractais tem vindo a atrair uma grande atenção na conceção de dispositivos de microondas e ópticos e nas suas aplicações. Os fractais são padrões geométricos cujas dimensões topológicas não pode ser sempre representada por um número inteiro. Em vez disso, as dimensões nos fractais são descritas por outras definições, como a dimensão de Hausdorff. Devido ao seu padrão de auto-repetição, os fractais trazem novas oportunidades à conceção de metamateriais. Neste trabalho, a abordagem fractal-geométrica foi estudada para construir diferentes tipos de metamateriais. Especificamente, os objetivos do projeto são modelar as características eletromagnéticas desses metamateriais com base em diferentes tipos de fractais; e fornecer novas técnicas de homogeneização para este grupo de metamateriais. Para expandir ainda mais as aplicações da geometria fractal neste contexto, o novo conceito de metamateriais de codificação fractal foi também desenvolvido e estudado no âmbito deste projeto.Programa Doutoral em Telecomunicaçõe

Emerging Nanophotonic Applications Explored with Advanced Scientific Parallel Computing

The domain of nanoscale optical science and technology is a combination of the classical world of electromagnetics and the quantum mechanical regime of atoms and molecules. Recent advancements in fabrication technology allows the optical structures to be scaled down to nanoscale size or even to the atomic level, which are far smaller than the wavelength they are designed for. These nanostructures can have unique, controllable, and tunable optical properties and their interactions with quantum materials can have important near-field and far-field optical response. Undoubtedly, these optical properties can have many important applications, ranging from the efficient and tunable light sources, detectors, filters, modulators, high-speed all-optical switches; to the next-generation classical and quantum computation, and biophotonic medical sensors. This emerging research of nanoscience, known as nanophotonics, is a highly interdisciplinary field requiring expertise in materials science, physics, electrical engineering, and scientific computing, modeling and simulation. It has also become an important research field for investigating the science and engineering of light-matter interactions that take place on wavelength and subwavelength scales where the nature of the nanostructured matter controls the interactions. In addition, the fast advancements in the computing capabilities, such as parallel computing, also become as a critical element for investigating advanced nanophotonic devices. This role has taken on even greater urgency with the scale-down of device dimensions, and the design for these devices require extensive memory and extremely long core hours. Thus distributed computing platforms associated with parallel computing are required for faster designs processes. Scientific parallel computing constructs mathematical models and quantitative analysis techniques, and uses the computing machines to analyze and solve otherwise intractable scientific challenges. In particular, parallel computing are forms of computation operating on the principle that large problems can often be divided into smaller ones, which are then solved concurrently. In this dissertation, we report a series of new nanophotonic developments using the advanced parallel computing techniques. The applications include the structure optimizations at the nanoscale to control both the electromagnetic response of materials, and to manipulate nanoscale structures for enhanced field concentration, which enable breakthroughs in imaging, sensing systems (chapter 3 and 4) and improve the spatial-temporal resolutions of spectroscopies (chapter 5). We also report the investigations on the confinement study of optical-matter interactions at the quantum mechanical regime, where the size-dependent novel properties enhanced a wide range of technologies from the tunable and efficient light sources, detectors, to other nanophotonic elements with enhanced functionality (chapter 6 and 7)

Computational Explorations of Enhanced Nonlinearities and Quantum Optical Effects in Photonic Nanostructures

In this thesis, we present a comprehensive theoretical analysis and computataional study of optical nonlinearities in the graphene-based and silicon-based metamaterials. The novel numerical methods and corresponding results described in this work give a significant impact on our understanding of surface plasmon resonance in artificial optical materials, which facilitates the design and fabrication of new photonic devices with enhanced nonlinear optical functionalities. // Two generic nonlinear metasurfaces are elaborated in this dissertation, namely, graphene-based metasurfaces and silicon-based metasurfaces. Employing a novel homogenization technique, the effective second-order susceptibility of graphene metasurfaces is calculated, which can be enhanced by more than two orders of magnitude as compared to the intrinsic value of graphene sheet. There is excellent agreement between the predictions of the homogenization method and those based on rigorous numerical solutions of Maxwell equations. Moreover, we also illustrate that the effective Raman susceptibilities of silicon-based metasurfaces can be enhanced by 3 to 4 orders of magnitude as compared to the intrinsic value of silicon. Even though the homogenization method for silicon-based metasurfaces is not as accurate as graphene-based, this result still gives a qualitative analysis on the effective Raman susceptibility of silicon-based metasurfaces. // Additionally, the optical nonlinearity is utilized to design a two-mode quantum waveguide made of coupled silicon photonic crystal nanocavities in the last part of the thesis. Finally, we also explore the implications of our work to the development of new active photonic nano devices with new or improved functionalities

Doctor of Philosophy

dissertationPhotonic integration circuits (PICs) have received overwhelming attention in the past few decades due to various advantages over electronic circuits including absence of Joule effect and huge bandwidth. The most significant problem obstructing their commercial application is the integration density, which is largely determined by a signal wavelength that is in the order of microns. In this dissertation, we are focused on enhancing the integration density of PICs to warrant their practical applications. In general, we believe there are three ways to boost the integration density. The first is to downscale the dimension of individual integrated optical component. As an example, we have experimentally demonstrated an integrated optical diode with footprint 3 Ã- 3 m2, an integrated polarization beamsplitter with footprint 2.4 Ã- 2.4 m2, and a waveguide bend with effective bend radius as small as 0.65 m. All these devices offer the smallest footprint when compared to their alternatives. A second option to increase integration density is to combine the function of multiple devices into a single compact device. To illustrate the point, we have experimentally shown an integrated mode-converting polarization beamsplitter, and a free-space to waveguide coupler and polarization beamsplitter. Two distinct functionalities are offered in one single device without significantly sacrificing the footprint. A third option for enhancing integration density is to decrease the spacing between the individual devices. For this case, we have experimentally demonstrated an integrated cloak for nonresonant (waveguide) and resonant (microring-resonator) devices. Neighboring devices are totally invisible to each other even if they are separated as small as /2 apart. Inverse design algorithm is employed in demonstrating all of our devices. The basic premise is that, via nanofabrication, we can locally engineer the refractive index to achieve unique functionalities that are otherwise impossible. A nonlinear optimization algorithm is used to find the best permittivity distribution and a focused ion beam is used to define the fine nanostructures. Our future work lies in demonstrating active nanophotonic devices with compact footprint and high efficiency. Broadband and efficient silicon modulators, and all-optical and high-efficiency switches are envisioned with our design algorithm