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paper: Add coupling experiment section

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jaseg 2024-09-26 18:51:54 +02:00
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paper/paper.tex
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@ -306,10 +306,10 @@ In conclusion, we observe that twisted inductors \emph{improve} high-frequency p
inductors while closely matching them in ESR and inductance. While they peform worse than simple single-layer inductors
in high-frequency performance, the increased trace width that two-layer inductors allow for lowers resistive losses by
approximately a factor of four. In applications where resistive losses lead to the choice of a two-layer inductor,
twisted inductors provide improved high-frequency performance at no additional cost and without compromising on other
twisted inductors provide improved high-frequency performance at no additional cost and without compromising other
performance parameters.
\begin{table}
\begin{table*}
\begin{tabular}{cc|ccc|}
Turn Count $n$&
Trace pair count $k$&
@ -319,10 +319,33 @@ performance parameters.
\end{tabular}
\caption{Inductor sample design parameters and measured characteristics. All inductors have outer diameter
\qty{35}{\milli\meter} and inner diameter \qty{15}{\milli\meter}.}
\end{table}
\end{table*}
\subsection{Coupling}
The key performance criterion in our application is the voltage ripple that appears on the secondary side of a WPT link
when one of the inductors is rotating. To experimentally evaluate the magnitude of this ripple in a realistic scenario
across a large set of rotations and relative displacements, we created a test setup consisting of a 3D gantry built from
an old 3D printer, with a fourth rotation axis provided by a small servo that allows us to position two inductor test
coupons at arbitrary offsets and angles to one another while measuring their coupling.
To evaluate a realistic scenario, we loaded the secondary inductor with a resistive load of \qty{10}{\ohm}, while
providing a signal at a \qty{300}{\kilo\hertz} carrier frequency to the primary inductor from a Siglent SDG6022X
function generator. We measured both the input and output voltages of the coupled inductor pair using Keysight 34465A
multimeters in AC RMS mode. The results of these measurements, with the voltage ratio between the coupled inductors'
input and output voltages graphed across one revolution in Figure\ \ref{symmetry_3turn_n_twist} for a set of three-turn
inductors and in Figure\ \ref{symmetry_10turn_n_twist} for a set of 10-turn inductors with multiple trace pair amounts
$k$.
From these graphs we observe slightly lower coupling for $k>0$ compared to a single-layer spiral inductor, which is
in line with our previous inductance measurements. Across one revolution, we find that single-layer spiral inductors
exhibit the worst voltage ripple, with simple two-layer inductors with $k=1$ already improving ripple by a large margin.
Increasing $k$ above $1$ does not decrease the amplitude of this ripple further, but it does shift the ripple into
higher frequencies that are easier to passively filter, as we originally intended.
\todo{new ripple measurements, concrete coupling factor measurements}
\todo{schematics for illustration of measeurement circuits}
\begin{figure}
\begin{center}
%\includegraphics[width=0.7\linewidth]{figures/symmetry_3turn_n_twist.pdf}