dc.contributor.advisor |
McCormick, D |
en |
dc.contributor.advisor |
Gallichan, R |
en |
dc.contributor.advisor |
Budgett, D |
en |
dc.contributor.author |
Lim, Hendrick |
en |
dc.date.accessioned |
2020-01-09T00:12:12Z |
en |
dc.date.issued |
2019 |
en |
dc.identifier.uri |
http://hdl.handle.net/2292/49415 |
en |
dc.description.abstract |
This thesis presents a design methodology for wireless power transfer (WPT) frequency
optimisation which incorporates specific absorption rate (SAR) limitations that account
for adverse tissue heating effects, for near-field loosely-coupled inductive links used in
deeply implanted millimetre-sized biomedical devices. Current approaches to WPT
frequency optimisation do not consider the SAR within their design optimisation process,
but instead verify their link meets SAR limits after optimising to other parameters. A
figure-of-merit which incorporates SAR into the optimisation process is proposed, using
a peak spatial-average SAR limit of 2 W/kg. Using the measured implant coil single-turn
equivalent resistance, and the permissible SAR constrained magnetic field found in-silico,
the optimal operating frequency and receiving coil design based on geometric constraints
are calculated such that power delivered to load (PDL) is maximised, whilst remaining
within SAR limits. The findings indicate that when adhering to SAR limits, at an implant
depth of 100 mm, operating frequencies in the sub MHz to low MHz range, results in
greater PDL in midbrain tissue. The main factor influencing PDL is the ratio of the tissue
resistivity to coil resistance. Maximising this ratio leads to the highest achievable power
transfer when SAR is the limiting factor. The implant coil resistance increases with
frequency due to skin and proximity effects. Additionally, tissue resistivity decreases with
frequency, and thus a lower operating frequency implies a greater PDL, irrespective of
implanted coil geometry. Consequently, there is no optimal frequency when only
considering SAR, but only a trend where lower frequencies are preferred, as the ratio of
tissue resistivity to pickup coil resistance is inversely proportional to frequency. In light
of these findings, application of induced electric field limits, which account for harmful
effects due to electrostimulation, were applied to obtain a lower bound, and thus an
optimum. In accordance with IEEE C95.1-2005 and ICNIRP 2010 human electromagnetic
exposure guidelines, the optimal WPT frequency due to SAR and induced electric field
limits is found to be 500 kHz and 700 kHz, respectively. Considering a 38AWG coil and an
anatomical in-silico phantom: at 500 kHz, a PDL of 14.25 mW was calculated; and at 700
kHz, a PDL of 14.11 mW was calculated. |
|
dc.publisher |
ResearchSpace@Auckland |
en |
dc.relation.ispartof |
Masters Thesis - University of Auckland |
en |
dc.relation.isreferencedby |
UoA |
en |
dc.rights |
Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. |
en |
dc.rights |
Restricted Item. Thesis embargoed until 2/2021. Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. |
en |
dc.rights |
Restricted Item. Full Text is available to authenticated members of The University of Auckland only. |
en |
dc.rights.uri |
https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm |
en |
dc.rights.uri |
http://creativecommons.org/licenses/by-nc-sa/3.0/nz/ |
en |
dc.title |
Safely Powering Inductively Coupled Deeply Implantable Millimetre-Sized Devices |
en |
dc.type |
Thesis |
en |
thesis.degree.discipline |
Bioengineering |
en |
thesis.degree.grantor |
The University of Auckland |
en |
thesis.degree.level |
Masters |
en |
dc.rights.holder |
Copyright: The author |
en |
pubs.elements-id |
790719 |
en |
pubs.record-created-at-source-date |
2020-01-09 |
en |
dc.identifier.wikidata |
Q112949247 |
|