Vibration-to-electric energy conversion using a mechanically-varied capacitor

Past research in vibration energy harvesting has focused on the use of variable capacitors, magnets, or piezoelectric materials as the basis of energy transduction. How- ever, few of these studies have explored the detailed circuits required to make the energy harvesting work. In contrast, this thesis develops and demonstrates a circuit to support variable-capacitor-based energy harvesting. The circuit combines a diode-based charge pump with an asynchronous inductive flyback mechanism to re- turn the pumped energy to a central reservoir. A cantilever beam variable capacitor with 650 pF DC capacitance and 347.77 pF zero-to-peak AC capacitance, formed by a 43.56 cm2 spring steel top plate attached to an aluminum base, drives the experimental charge pump near 1.56 kHz. HSPICE simulation confirms that given a maximum to minimum capacitance ratio larger than 1.65 and realistic models for the transistor and diodes, the circuit can harvest approximately 1 lW of power. This power level is achieved after optimizing the flyback path to run at approximately 1/4 of the mechanical vibration frequency with a duty ratio of 0.0019. Simulation also shows that unless a source-referenced clock drives the MOSFET, spurious energy injection can occur, which would inflate the circuit's conversion efficiency if the harvester is driven by an external clock. A working vibration energy harvester comprising a time varying capacitor with a capacitance ratio of 3.27 converted sufficient energy to sustain 6 V across a 20 MQ load.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2005

Author dc:creator

• Yen, Bernard Chih-Hsun, 1981-

Advisor dc:contributor.advisor

• Jeffrey H. Lang.

• Electrical Engineering and Computer Science.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/30177

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/30177