TY  - JOUR
A1  - Basso, Heitor Cury
A1  - Monteiro, Jose Roberto B. de A.
A1  - Mazulquim, Daniel Baladelli
A1  - de Paula, Geyverson Teixeira
A1  - Goncalves Neto, Luiz
A1  - Gerhard, Reimund
T1  - Alternating current-generated plasma discharges for the controlled direct current charging of ferroelectrets
JF  - Journal of applied physics
N2  - The standard charging process for polymer ferroelectrets, e. g., from polypropylene foams or layered film systems involves the application of high DC fields either to metal electrodes or via a corona discharge. In this often-used process, the DC field triggers the internal breakdown and limits the final charge densities inside the ferroelectret cavities and, thus, the final polarization. Here, an AC + DC charging procedure is proposed and demonstrated in which a high-voltage high-frequency (HV-HF) wave train is applied together with a DC poling voltage. Thus, the internal dielectric-barrier discharges in the ferroelectret cavities are induced by the HV-HF wave train, while the final charge and polarization level is controlled separately through the applied DC voltage. In the new process, the frequency and the amplitude of the HV-HF wave train must be kept within critical boundaries that are closely related to the characteristics of the respective ferroelectrets. The charging method has been tested and investigated on a fluoropolymer-film system with a single well-defined cylindrical cavity. It is found that the internal electrical polarization of the cavity can be easily controlled and increases linearly with the applied DC voltage up to the breakdown voltage of the cavity. In the standard charging method, however, the DC voltage would have to be chosen above the respective breakdown voltage. With the new method, control of the HV-HF wave-train duration prevents a plasma-induced deterioration of the polymer surfaces inside the cavities. It is observed that the frequency of the HV-HF wave train during ferroelectret charging and the temperature applied during poling of ferroelectrics serve an analogous purpose. The analogy and the similarities between the proposed ferroelectret charging method and the poling of ferroelectric materials or dipole electrets at elevated temperatures with subsequent cooling under field are discussed.
Y1  - 2013
U6  - https://doi.org/10.1063/1.4821113
SN  - 0021-8979
SN  - 1089-7550
VL  - 114
IS  - 10
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Altafim, Ruy Alberto Pisani
A1  - Basso, Heitor Cury
A1  - Altafim, Ruy Alberto Pisani
A1  - Lima, L.
A1  - de Aquino, C. V.
A1  - Goncalves Neto, Luiz
A1  - Gerhard, Reimund
T1  - Piezoelectrets from thermo-formed bubble structures of fluoropolymer-electret films
N2  - The acetone extracts of the root bark and stem bark of Erythrina sacleuxii showed antiplasmodial activities against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of Plasmodium falciparum. Chromatographic separation of the acetone extract of the root bark afforded a new isoflavone, 7-hydroxy-4 -methoxy-3'- prenylisoflavone (trivial name 5-deoxy-3' - prenylbiochanin A) along with known isoflavonoids as the antiplasmodial principles. Flavonoids and isoflavonoids isolated from the stem bark of E. sucleuxii were also tested and showed antiplasmodial activities. The structures were determined on the basis of spectroscopic evidence.
Y1  - 2006
UR  - http://ieeexplore.ieee.org/servlet/opac?punumber=94
U6  - https://doi.org/10.1109/TDEI.2006.247822
SN  - 1070-9878
ER  -