diff --git a/paper/paper.tex b/paper/paper.tex index acc2ee1..71257d0 100644 --- a/paper/paper.tex +++ b/paper/paper.tex @@ -29,6 +29,7 @@ \newcommand{\degree}{\ensuremath{^\circ}} \newcolumntype{P}[1]{>{\centering\arraybackslash}p{#1}} \newcommand{\partnum}[1]{\texttt{#1}} +\newcommand{\todo}[1]{\textbf{TODO}\footnote{#1}} \begin{document} @@ -138,6 +139,36 @@ and other cooling components, which directly translates to a decrease in cost. \section{Twisted Inductor Design} +We can approach twisted inductors by construction. Let us first consider a simple, planar, circular spiral coil with a +fixed pitch. We will ignore trace width for now, and consider the trace a thin wire. We will also ignore the placement +of the two electrical ports of the inductor for now. The trace trajectory of a standard planar spiral inductor can be +parameterized in polar coordinates $r, \phi$ based on an Archimedean spiral: \todo{For the lulz, cite Archimedes here} + +\begin{equation} + r &= a\cdot\phi + \label{eqn_arch_spi_basic} +\end{equation} + +An Archimedean spiral defined this way always starts at the origin, and it continues to infinity. Let us re-parameterize +this spiral taking into account that our spiral inductor has a defined inner radius $r_0$ and outer radius $r_1$, and a +fixed turn count $n$. Let us further re-parameterize the spiral to a curve parameter $t$ with range $\left\[0, +1\right\]$. Taking into account that the input ports of a spiral inductor are usually placed on the outside of the +spiral, we define the inductor's first port to lie at $\left\(\phi, r\right\)=\left\(0, r_1\right\)$, and we define that +this corresponds to $t=0$. The resulting parametrization is: + +\begin{align} + r &= r_1 - \frac{t}{n} \cdot \left\(r_1 - r_0\right\) \\ + \phi &= 2\pi \cdot n \cdot t + \label{eqn_simple_spiral_ind} +\end{align} + +For integer $n$, the spiral's second port will lie at $\left\(\phi, r\right\)=\left\(0, r_0\right\)$, however, other +values of $n$ are possible, which will rotate the second port around the coordinate origin. + +%Let us further flip the radial coordinate axis such that the spiral's outer end is at $\phi=0$ +%because spiral inductors usually have their input ports at the outside. By normalizing the coordinate axes substituting +%$\phi' = \frac{1}{2\pi}\phi$ and $r' = \left\(r - r_0\right\) \cdot \frac{1}{r_1 - r_0}$: + \subsection{From Spiral to Twisted Inductor} \subsubsection{Ohmic Resistance}