<p>Nonlinear transmission lines (NLTLs) are of great interest
for high power microwave (HPM) generation because they can sharpen pulses to
create an electromagnetic shockwave to produce oscillations from 100 MHz to low
GHz. NLTLs provide frequency agility, compactness, durability and reliability,
providing a solid-state radiofrequency (RF) source for producing HPM. The
essential component of NLTLs is the nonlinear material, typically a dielectric
that varies with voltage or a magnetic material whose permeability varies with
current, incorporated in the transmission line in various topologies. This
thesis presents an alternative approach involving designing composites comprised
of nonlinear dielectric inclusions (barium strontium titanate (BST)) and/or
nonlinear inductive inclusions (nickel zinc ferrites (NZF)) in a polymer base
host material, analogous to electromagnetic interference designs that
incorporate stainless steel inclusions of various shapes in a plastic to tune
the composite’s electromagnetic properties at GHz. Appropriately designing NLTL
composites requires predicting these effective properties both in linear (for a
fixed and low voltage and current) and nonlinear regions (permittivity and
permeability become voltage dependent and current dependent, respectively) prior
to designing HPM systems comprised of them. As a first step, this thesis
evaluates and benchmarks composites models in the commercial software CST
Microwave Studios (CST MWS) to various effective medium theories (EMTs) to
predict the permittivity and permeability of composites of BST and/or NZF
inclusions in the linear regime, compared with experimental measurements. The manufacturing
and measurement of the nonlinear composites will be briefly discussed with an
analysis of the homogeneity of a composite sample using 3D X-ray scan.
Long-term application of these approaches to predicting the effective nonlinear
composite permittivity and permeability and future work will be discussed.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/11127839 |
| Date | 27 November 2019 |
| Creators | Xiaojun Zhu (8039564) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Assessing_effective_medium_theories_for_designing_composites_for_nonlinear_transmission_lines/11127839 |
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