Design of Functional Active RF Metamaterials with Embedded Transistor-Based Circuits and Devices

Abstract

Recent advances in electromagnetics introduced tools that enable the creation of arti-cial electromagnetic structures with exotic properties such as negative material pa-rameters. The ability to express these parameters has experimentally demonstratedusing passive metamaterial structures. These structures, based on their passivity andresonant properties, are typically associated with high loss and signicant bandwidthlimitations.Enhancing and further exploring novel electromagnetic properties can be donethrough embedding active circuits in the constitutive unit cells. Active elementsare able to supplement the passive inclusions to mitigate and overcome loss andbandwidth limitations. The inclusion of these circuits also signcantly expands thedesign space for the development of functional metamaterials and their potentialapplications.Due to the relative diculty of designing active circuits compared with passivecircuits, using active circuits in the construction of metamaterials is still an under-developed area of research. By combining the two elds of active circuit design andmetamaterial design, we aim ll the functional active metamaterial design space.This document provides the basis for understanding the design and synthesis offunctional active metamaterials.To provide necessary background matter, chapter 1 will function as an introduc-tion chapter, discussing how active electromagnetic metamaterials are created and characterized. There are also several required design techniques necessary to suc-cessfully engineer a functional active metamaterial. The introduction will emphasizeon linking metamaterial unit cell response with RF/analog circuit design with a briefintroduction to the semiconductor physics important to aid in the understanding ofthe full active metamaterial design and fabrication process.The subsequent chapters detail our specic contributions to the eld of func-tional active RF metamaterials. Chapter 2 introduces and characterizes a meta-material designed to have a tunable quality factor (tunable resonant bandwidth).This metamaterial is essentially passive but demonstrates the transistor's versatilityas a combination of tunable elements, motivating the use of embedding transistorsin metamaterials. After establishing a simple application of a transistor in a pas-sive metamaterial, chapter 3 outlines the design and characterization of an activemetamaterial exhibiting the properties of loss cancellation and gain. Chapter 4 in-troduces another active metamaterial with the ability to self-adapt to an incidentsignal. Within the self-adapting system, several complex RF circuit systems aresimulatenously developed and implemented such as a self-oscillating mixer and aphase locked loop. Conclusions and additional suggested future research directionsare discussed in chapter 5.There are also several appendices attached at the end of this document that aremeant to assist future graduate students and other readers. The additional topicsinclude the experimental verication of a passive magnetic metamaterial acting as anear eld parasitic, the stabilization and measurement of a tunnel diode, a discussionon the challenges of realizing active inductors from discrete components, and a basicstrategy for creating a non-volatile metamaterial. It is my aim for these appendicesto help provide additional inspiration for future studies within the eld.