From d103b16e0307739904b63c9a5d9c74785a944830 Mon Sep 17 00:00:00 2001 From: jaseg Date: Fri, 8 Nov 2024 17:59:27 +0100 Subject: [PATCH] Related work mostly done --- paper/paper.tex | 66 +++++++++++++++++++++++++++---------------------- 1 file changed, 36 insertions(+), 30 deletions(-) diff --git a/paper/paper.tex b/paper/paper.tex index 9a1d30f..f8b92da 100644 --- a/paper/paper.tex +++ b/paper/paper.tex @@ -178,7 +178,6 @@ condition between the number of turns and the number of inversions within each t inductors below, although in contemporary literature, this condition is never explicitly stated \cite{eppenAnforderungenEinzelteileRundfunkempfanger1927, kleinSpulenUndSchwingungskreise1941, wiggeRundfunktechnischesHandbuch1930}. -% TODO cite \cite{querfurthCoilWindingDescription1954} \subsection{PCB inductor design for wireless power transfer} @@ -213,27 +212,34 @@ a pure air-core inductor. \subsection{Twisted Inductors in RFIC Design} +Planar inductors are commonly used in RF ICs. In RFIC design, the major challenges are area optimization, and precisely +predicting the inductor's characteristics during the design phase. Common optimizations include applying a variable +trace pitch to reduce distributed capacitance\cite{lopez-villegasImprovementQualityFactor2000}, and applying variable +trace width to decrease equivalent series resistance while preserving total inductance and quality +factor\cite{hsuAnalyticalDesignAlgorithm2008}. + +In RFICs, inductors are commonly designed as \emph{balanced} inductors with a grounded central node. Such designs +interleave two counter-wound planar spiral inductors on the same layer with the help of some jumper connections on a +second layer\cite{daneshDifferentiallyDrivenSymmetric2002,martinMultiturnTwistedInductor2016}. The use of such designs +in RFIC design is mainly focused on their electrical symmetry, so that the two input ports can be fed with a fully +differential signal, with the inductor loading both driver outputs equally across the inductor's frequency range. + The simplest twisted inductor as shown below with $k=1$ inversion corresponds to the counterwound scheme that is commonly used for two-layer planar inductors\cite{lopeFirstSelfResonant2021,sproHighVoltageInsulationDesign2021,leePrintedSpiralWinding2011a}, and which has been used to stack planar coils for more than a century\cite{flemingPrinciplesElectricWave1910}. -Another, more recent design interleaves two counter-wound planar spiral inductors on the same layer with the help of -some jumper connections on a second layer, as shown in \cite{daneshDifferentiallyDrivenSymmetric2002}. The use of this -design in RFIC design is mainly focused on its electrical symmetry, so that the two input ports can be fed with a fully -differential signal, with both driver outputs being loaded equally across the inductor's frequency range. - % They note that the main point behind the design is electrical symmetry of the two ports to make driving the thing % differentially cleaner. We should adopt this observation for our inductors, which likewise are electrically symmetric % when compared to a single-layer spiral inductor. \subsection{Inductive Wireless Power Transfer in Practice} -Inductive WPT has been proposed in a large number of scenarios\cite{zhangWirelessPowerTransfer2019}, each of which comes -with a set of unique constraints. When WPT is used to charge an electric toothbrush, the implementation cost of the -system is critical, while efficiency and total power output are of little concern. Mechanically, in an electric -toothbrush's charging system, the position and spacing of the transmitter and receiver coils can easily be controlled -down to millimeter precision. +Inductive WPT has been proposed in a large number of +scenarios\cite{zhangWirelessPowerTransfer2019,mouWirelessPowerTransfer2015}, each of which comes with a set of unique +constraints. When WPT is used to charge an electric toothbrush, the implementation cost of the system is critical, while +efficiency and total power output are of little concern. Mechanically, in an electric toothbrush's charging system, the +position and spacing of the transmitter and receiver coils can easily be controlled down to millimeter precision. In contrast to this, wireless smartphone charging is a much more demanding application. Here, the total cost of the system is only secondary, but the receiver's form factor is critical, and total power output as well as efficiency @@ -241,33 +247,33 @@ become major objectives. At the same time, in wireless smartphone charging, posi two coils in the charging base and in the phone may be positioned more than a centimeter off-axis, with a gap of several millimeters and potentially not even in parallel planes. -Power transfer across large distances is even more of a concern in implantable medical devices. Where a wireless phone -charger must be able to bridge distances of a few millimeters, an implantable medical device might be situated -underneath several centimeter of tissue and bones. At the same time, cost is of (almost) no concern in this medical -application, which enables the use of complex manufacturing techniques, customized electronic components and exotic -materials. +Power transfer across large distances is even more of a concern in implantable medical +devices\cite{mooreApplicationsWirelessPower2019}. Where a wireless phone charger must be able to bridge distances of a +few millimeters, an implantable medical device might be situated underneath several centimeter of tissue and bones. At +the same time, cost is of (almost) no concern in this medical application, which enables the use of complex +manufacturing techniques, customized electronic components and exotic materials. While all of the aforementioned applications transfer somewhere between a few hundred milliwatts and several watts of power, at the other end of the spectrum there is a large body of research suggesting the use of inductive wireless power -transfer for the charging of electric vehicles (EVs). In this application, the wireless power transfer system replaces -the conventional wired charging connector, which improves the systems' user experience given the strong force required -to seat or unseat these rather large connectors, as well as the heft of the required water-cooled cables. In this -application, size is of (almost) no concern, but at several kilowatt up to dozens or even a hundred kilowatt, the -transferred power is enormous and consequentially efficiency becomes of utmost importance. When charging an EV at a -rate of 30 kW, an efficiency improvement of just $0.1\%$ corresponds to a reduction in power dissipation of 30 W. -Besides the monetary cost of the power lost this way, each small improvement enables a reduction in size of heat sinks -and other cooling components, which directly translates to a decrease in cost. +transfer for the charging of electric vehicles +(EVs)\cite{liWirelessPowerTransfer2015,mouEnergyEfficientAdaptiveDesign2017}. In this application, the wireless power +transfer system usually replaces the conventional wired charging connector, which improves the systems' user experience +given the strong force required to seat or unseat these rather large connectors, as well as the heft of the required +water-cooled cables. In this application, size is of (almost) no concern, but at charging rates up to tens of kilowatt, +efficiency becomes critical. When charging an EV at a rate of 10 kW, an efficiency improvement of just $0.1\%$ +corresponds to a reduction in power dissipation of 10 W. Besides the monetary cost of the power lost this way, each +small improvement enables a reduction in size of heat sinks and other cooling components, which directly translates to a +decrease in cost. \subsection{Air-Core Inductors for Inductive Power Transfer} -In inductive wireless power transfer, air-core inductors are often used since in most applications, an air gap of -several millimeters or more is expected, and adding a ferrite core would not change the system's performance by much in -these circumstances. A common way to use ferrites in WPT applications is magnetically shielding the inductor's back side -with a ferrite plate such that the field does not extend beyond the coil's back side, and to reduce eddy current losses -when the WPT coils are placed near metal +Across application areas, air-core inductors are often used for wireless power transfer since in most applications, an +air gap of several millimeters or more is expected, and adding a ferrite core would not change the system's performance +by much in these circumstances. A common way to use ferrites in WPT applications is magnetically shielding the +inductor's back side with a ferrite plate such that the field does not extend beyond the coil's back side, and to reduce +eddy current losses when the WPT coils are placed near metal objects\cite{batraEffectFerriteAddition2015,leeSimpleWirelessPower2017,muehlmannMutualCouplingModeling2012}. - \section{Twisted Inductor Design} We can approach twisted inductors by construction. Let us first consider a simple, planar, circular spiral coil with a