Design of Functional Active RF Metamaterials with Embedded Transistor-Based Circuits and Devices
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 demonstrated
using passive metamaterial structures. These structures, based on their passivity and
resonant properties, are typically associated with high loss and signicant bandwidth
limitations.
Enhancing and further exploring novel electromagnetic properties can be done
through embedding active circuits in the constitutive unit cells. Active elements
are able to supplement the passive inclusions to mitigate and overcome loss and
bandwidth limitations. The inclusion of these circuits also signcantly expands the
design space for the development of functional metamaterials and their potential
applications.
Due to the relative diculty of designing active circuits compared with passive
circuits, 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 and
metamaterial design, we aim ll the functional active metamaterial design space.
This document provides the basis for understanding the design and synthesis of
functional 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 emphasize
on linking metamaterial unit cell response with RF/analog circuit design with a brief
introduction to the semiconductor physics important to aid in the understanding of
the 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 versatility
as a combination of tunable elements, motivating the use of embedding transistors
in metamaterials. After establishing a simple application of a transistor in a pas-
sive metamaterial, chapter 3 outlines the design and characterization of an active
metamaterial exhibiting the properties of loss cancellation and gain. Chapter 4 in-
troduces another active metamaterial with the ability to self-adapt to an incident
signal. Within the self-adapting system, several complex RF circuit systems are
simulatenously developed and implemented such as a self-oscillating mixer and a
phase locked loop. Conclusions and additional suggested future research directions
are discussed in chapter 5.
There are also several appendices attached at the end of this document that are
meant to assist future graduate students and other readers. The additional topics
include the experimental verication of a passive magnetic metamaterial acting as a
near eld parasitic, the stabilization and measurement of a tunnel diode, a discussion
on the challenges of realizing active inductors from discrete components, and a basic
strategy for creating a non-volatile metamaterial. It is my aim for these appendices
to help provide additional inspiration for future studies within the eld.
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