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Defense Date


Document Type


Degree Name

Master of Science


Mechanical Engineering

First Advisor

Dr. Karla Mossi


Wireless sensors are an emerging technology that has the potential to revolutionize the monitoring of simple and complex physical systems. One of the biggest challenges with wireless sensors technology is power management and hence cost. A wireless sensor system incapable of managing its power consumption either by maintaining long battery life and/or harvesting from its surroundings, is simply not cost effective. Prolonging or eliminating the battery entirely would reduce the cost of battery replacement and maintenance. A viable family of materials for this purpose is piezoelectric materials because of their inherent ability to convert vibrations into electrical energy. Currently, a wide variety of piezoelectric materials are available and the appropriate choice for harvesting energy depends on their characteristics and properties. In addition to the material choice, energy harvesting circuitry is needed to efficiently convert and filter the signal from the piezoelectric device into a form that can be used by a load (battery). This thesis addresses the theoretical and experimental use of a type of pre-stressed PZT-5A Unimorph called a Thunder® to actively convert mechanical vibrations into useable power. Two types of devices of Thunder diaphragms are used: (1) a composite made of stainless steel, plain polyimide, a piezoelectric layer, plain polyimide, and copper; (2) and a second composite made with the same materials except that micro nickel inclusions are suspended into the polyimide layer. The first type produced a maximum average power of 2,585μW (~2.6mW) with a power density of 1411μW/cm2 (~1.4mW). The maximum total energy was 541,114μJ (~0.54J). The second type produced a maximum average power of 3,800μW (~3.8mW) with a power density of 2,073μW/cm2 (~2mW/cm2). The maximum total energy produced 1,187,939μJ (~1.19J). Based on these energy calculations, it was found that a plain polyimide diaphragm could theoretically charge a 1000mA-hr battery in a range from 3.32 hours to 32.32 hours depending on the energy harvesting circuit while nickel polyimide diaphragm could charge it in a range from 3.38 hours to 20.01 hours. These results show that THUNDER can effectively generate power from a steady sinusoidal source at frequencies below 10 Hz for the charging of batteries or for directly powering a device.


Part of Retrospective ETD Collection, restricted to VCU only.


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Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

June 2008