Proc. SPIE. 8035, Energy Harvesting and Storage: Materials, Devices, and Applications II
KEYWORDS: Fabrication, Microelectromechanical systems, Energy efficiency, Solar energy, Capacitors, Dielectrics, Computing systems, Energy conversion efficiency, Thermal modeling, Temperature metrology
The efficient conversion of waste thermal energy into electrical energy is of considerable interest due to
the huge sources of low-grade thermal energy available in technologically advanced societies. Our group at the
Oak Ridge National Laboratory (ORNL) is developing a new type of high efficiency thermal waste heat energy
converter that can be used to actively cool electronic devices, concentrated photovoltaic solar cells, computers and
large waste heat producing systems, while generating electricity that can be used to power remote monitoring
sensor systems, or recycled to provide electrical power. The energy harvester is a temperature cycled pyroelectric
thermal-to-electrical energy harvester that can be used to generate electrical energy from thermal waste streams
with temperature gradients of only a few degrees. The approach uses a resonantly driven pyroelectric capacitive
bimorph cantilever structure that potentially has energy conversion efficiencies several times those of any
previously demonstrated pyroelectric or thermoelectric thermal energy harvesters. The goals of this effort are to
demonstrate the feasibility of fabricating high conversion efficiency MEMS based pyroelectric energy converters
that can be fabricated into scalable arrays using well known microscale fabrication techniques and materials.
These fabrication efforts are supported by detailed modeling studies of the pyroelectric energy converter
structures to demonstrate the energy conversion efficiencies and electrical energy generation capabilities of these
energy converters. This paper reports on the modeling, fabrication and testing of test structures and single
element devices that demonstrate the potential of this technology for the development of high efficiency thermal-to-electrical energy harvesters.
Au, Au-V solid solution, and Au-V<sub>2</sub>O<sub>5</sub> dispersion films were fabricated for comparison of electrical and mechanical
characteristics. Resistivity and nanoindentation hardness increased with increasing V content in all films, but the ratio of
resistivity increase to hardness increase was much lower for the Au-V<sub>2</sub>O<sub>5</sub> films. Measurements of contact force and
electrical contact resistance between pairs of Au or Au-V films show that increased hardness and resistivity in the alloy
films results in higher contact resistance and less adhesion than in pure Au. These results imply that the Au-V<sub>2</sub>O<sub>5</sub> films
may exhibit attractive behavior when used in a contact configuration, but this has not yet been tested.
The present work examines how the characteristics of the large thermal-compressive response of a 20 vol. % NiTi fiber 6082-T0 composite change with variations in the value of maximum tensile strain imposed during a preceding room temperature tensile process. We observe that the self thermal compression process is shifted to higher temperatures with increasing maximum room temperature tensile strain, and that the maximal thermal compression versus temperature slope becomes larger as the maximum tensile strain is increased from 4 to 6% and then becomes smaller as the maximum tensile strain is further increased to 7%.