Variable capacitor based mechanical energy-to-electrical energy converter

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Author
Aydoğdu, Elif
Advisor
Atalar, Abdullah
Date
2007Publisher
Bilkent University
Language
English
Type
Thesis
Metadata
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http://hdl.handle.net/11693/14552Abstract
Today miniature stand-alone systems highly benefit from the improvements in
IC technology. Shrinking dimensions to submicron technologies and reduced
power consumption in the order of nano-watts open possibilities for new power
applications[1–3]. Such systems demand integrated, long lasting micro energy
sources, and at that power level, ambient energy scavenging arises as an alternative
solution, as energy harvesting units can be integrated conveniently through
MEMS(micro electromechanical systems) technology.
This thesis offers one such solution. A novel generator design with electrostatic
approach is presented. The generator creates new electrical charge, thus
it can be used to recharge a reservoir. It is composed of variable capacitors
and switches. As it does not employ inductive components, it is suitable for
environments in which magnetic fields should be avoided. Throughout the thesis
the design is further improved to overcome the restriction on the achievable
electrostatic field given the dimensions and voltage level. A third electret with
permanent charge is embedded in between the plates of the capacitor creating extra field inside the capacitor at the same potential. On the mechanical side,
more work is done against increased electrostatic force; and on the electrical side
more charge accumulation and a greater charge gain is achieved.
The system is simulated using PSpice and the results are consistent with
the theoretical expectations. An experiment utilizing macro elements is also
carried out with 81% efficiency; when source voltage is 40V, frequency is 1Hz,
and Cmax = 1500pF the power gain is 880nW. For micro applications 1500pF is
achievable, but 40V is very high; so lower voltage sources should be used and
power gain will be much smaller. The electret idea may solve this problem, and
one other considerable solution is to increase the maximum capacitance. For the
future, our purpose is to reach higher capacitance in limited volumes through
new capacitor designs and making use of microfluidics technology.