Papers by Author: Jong Soon Lee

Abstract: In this paper, the surface crystalline morphology and piezoelectricity of P(VDF/TrFE)(72/28) copolymer ultrathin films were studied using different scanning probe microscopy (SPM) techniques. Atomic force microscopy (AFM) was used to study the changes in their crystalline morphology with varying temperature conditions. From electric force microscopy (EFM) studies, the change in dipole moment vectors along the applied field direction and the resultant change in amplitude image for '1 or 0' state were monitored and used to 'write/erase and read' the data on the memory bit. These results indicate the possibility of using SPM-based high density data storage with these copolymer ultrathin films.

Abstract: Flexible piezoelectric polymer materials for smart apparel and wearable computer applications are of great interest. Among known ferroelectric and piezoelectric polymers, polyvinylidene fluoride (PVDF) exhibit β-phase under poling and is known to give highest piezo-, pyro-, and ferroelectric properties. Previous reports suggests that, during corona poling of the PVDF film, a high surface electric potential is generated resulting in a high internal electric field within the polymer film causing the polarization of the dipoles along the direction of the applied electric field. The resultant phase change from α- to β-phase and the dipole switching generates displacement of charges or piezoelectricity. And also mechanical variation would change dipole density of PVDF film. In this report, we measured human heartbeat signal from an DAQ interfaced with a custommade voltage-amplifier with specific frequency filtering function using the corona-poled PVDF film of various sizes and thickness as a piezoelectric sensor and analyzed it. We employed elastic textile band to sensor system for comfortable fit on wrist or ankle. And then, we found the feasibility of applying flexible PVDF film sensor to smart apparel application which can sense heartbeat rate, blood pressure, respiration rate, accidental external impact on human body, etc.