THE APPLICATION AND CHARACTERIZATION OF DIELECTRIC AND PIEZOELECTRIC POLYMER DEVICES
Open Access
- Author:
- Wang, Yong
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- January 08, 2009
- Committee Members:
- Qiming Zhang, Dissertation Advisor/Co-Advisor
Qiming Zhang, Committee Chair/Co-Chair
Heath Hofmann, Committee Member
Zhiwen Liu, Committee Member
Michael T Lanagan, Committee Member - Keywords:
- polymer
PVDF
aromatic polyurea
dielectric
piezoelectric
electrical conduction
capacitor - Abstract:
- Two important families of electro-polymers: aromatic polyurea and polyvinylidene fluoride (PVDF) based polymer, are studied in this dissertation for: dielectric and piezoelectric applications. High quality aromatic polyurea thin films made through chemical vapor deposition (CVD) exhibit many advantages for high temperature capacitors. The relative high dielectric constant (~4.2) and high breakdown strength (800MV/m) yield the released energy density as high as 12J/cm3 at room temperature. TGA and dielectric measurement show the material has a good thermal stability up to 200oC. High temperature characterizations demonstrate the material has a high breakdown strength (>500MV/m) and high released energy density (>6 J/cm3) even at high temperatures such as 180oC. The properties of aromatic polyurea films highly depend on the composition ratio between two monomers, diphenylmethane-diisocyanate (MDI) and diphenylmethane-diamino (MDA). MDA-rich polyurea has been reported to exhibit a dielectric constant as high as 15 with low loss to temperatures above 150oC. Surface morphology study with SEM and AFM revealed that the apparent high-k in MDA-rich polyurea films originates from the non-uniformity of its thickness and erroneous interpretation of the data rather than from its intrinsic properties. The new P(VDF-HFP) 10wt% copolymer exhibits a high transverse piezoelectric response with both high piezoelectric d31 (d31=43.1pm/V) and electromechanical coupling k31 coefficients (k31=0.187) under quasi-static condition. The phase change nature also results in a large frequency dispersion of the piezoelectric response and a smaller d31 (=20.5 pm/V) at 50 kHz. The direct piezoelectric response of PVDF was investigated under high mechanical stress. The piezoelectric polymer can withstand high strain (~3%) without degrading the piezoelectric responses, which is very attractive for energy harvesting applications. Through an optimized system design including high strain active material selection, mechanical amplification design and active electronic circuit control, an active energy harvesting system from ocean waves was developed. Experiment results show 3~5 times improvement in energy conversion efficiency compared with passive approaches at the same conditions.