ABSTRACT The isothermal charging and discharging currents were recorded for polyamide 11, polyeth... more ABSTRACT The isothermal charging and discharging currents were recorded for polyamide 11, polyethylene terephthalate and low density polyethylene in a large range of temperatures below and above the glass-rubber transition temperature of the amorphous phase, for different electrical fields and different charging and discharging times. The results showed that the low frequency relaxation process is complex and different contributions having the loss peak in the range 0.01 MHz to 0.1 Hz were revealed. The data are in good agreement with those obtained from dielectric relaxation spectroscopy and from thermally stimulated discharge current measurements.
The charge accumulated at a metal-dielectric interface strongly influences the thermally stimulat... more The charge accumulated at a metal-dielectric interface strongly influences the thermally stimulated discharge current measurements at temperatures above room temperature. We propose to improve this method by measuring the released currents on both faces of the sample. The voltages on the two faces of the sample are more different from each other than the currents which flow in external circuit from the two interfaces. In a thermally stimulated discharge current experiment we always start by measuring the current and finish by measuring the voltage. The isothermal voltage discharge measurements clearly show that the charges accumulated at the two contacts are different. The activation energy obtained from initial rising of positive current is higher than that obtained from initial rising of negative current.
Very long time dc measurements have been carried out to analyze charge injection/ejection and tra... more Very long time dc measurements have been carried out to analyze charge injection/ejection and trapping in low-density polyethylene. The basic idea was to compare the total charge involved in the charging step and the total charge stored in the material. The equality of the two charges demonstrates that the charge carriers do not pass through the sample. The injected electrons are trapped very close to the cathode to form a negative layer. It is suggested that near the anode the field ionizes the impurity atoms and/or the neutral molecules associated with structural defects to produce positive ions.
Taking into account the time-consuming trapping and detrapping of electric charge in insulating m... more Taking into account the time-consuming trapping and detrapping of electric charge in insulating materials, a sequential protocol for the investigation the trapping sites and trapped charge stability is proposed. The method is demonstrated for Teflon FEP-A. Elemental peaks are obtained whose maxima shift with increasing field from 456 to 486 K and are characterized by activation energies that increase from 1.1 to 1.9 eV. The relaxation time of the trapped charge, at 523 K, increases as the amount of charge stored in the material decreases and explains the good charge stability for Teflon FEP-A electrets.
An understanding of space charge build-up in the polymeric insulation of power cables is importan... more An understanding of space charge build-up in the polymeric insulation of power cables is important in determining how aging occurs and progresses and, also in predicting cable lifetime. In this investigation electric-field induced space charge in peelings from XLPE (cross-linked polyethylene) cables was measured using two different methods: the pulsed electro-acoustic technique (PEA) and the combined procedure of isothermal and
Proceedings. 11th International Symposium on Electrets
Space charge in electrically aged LDPE was studied using a recently developed technique combining... more Space charge in electrically aged LDPE was studied using a recently developed technique combining isothermal charging and discharging with non-isothermal measurements. Samples were aged in a NaCl aqueous solution at 40°C for 1500 h under an AC field of 6 MV/m (50 Hz). The samples were then isothermally DC charged and discharged (both currents recorded). Next a non-isothermal experiment with constant heating rate was performed. Finally, the sample was kept at the highest temperature and the final isothermal discharge current registered. The last step has to be carried on for a long time to ensure an almost complete discharge of the remnant charge so that results become reproducible and possible to analyze. Selective charging (careful choice of the field, temperature and the ratio of charging/discharging times) revealed the presence of different trapping sites. From the analysis of the isothermal and non-isothermal data the relaxation times and activation energies could be obtained.
Proceedings - International Symposium on Electrets, 2008
The proposed biosensor has successfully detected an immuno-reaction. However, the limit of detect... more The proposed biosensor has successfully detected an immuno-reaction. However, the limit of detection needs to be improved. It has the advantage of using films made from inexpensive materials and using simple methods, and the immobilization protocol is simple.
Proceedings - International Symposium on Electrets, 2008
Cork is a natural cellular material and is the outer bark of the Mediterranean tree Quercus Suber... more Cork is a natural cellular material and is the outer bark of the Mediterranean tree Quercus Suber-L. Its many different applications derive from the unique set of properties: cork is a good thermal, vibratic and acoustic insulator, prevents fire propagation, it is impervious to water. In this study shows that the main problem for charge storage during long periods is related to the small amount of humidity present in cork. Therefore control of the water content is essential.
Proceedings - International Symposium on Electrets, 2011
ABSTRACT Polarization can accelerate the bioactivity of HAp immersed in an SBF solution. However ... more ABSTRACT Polarization can accelerate the bioactivity of HAp immersed in an SBF solution. However a careful choice of polarization conditions has to be made. One relevant issue is to have long relaxation times of the polarization and this is related to the amount of water in Hap, which was to be kept as low as possible during poling. It was shown that the precipitation mechanism needs negative charges on the Hap surface. Under positive charge the mechanism is inhibited.
2008 13th International Symposium on Electrets, 2008
ABSTRACT The authors have presented a new electrical method to investigate the molecular dynamics... more ABSTRACT The authors have presented a new electrical method to investigate the molecular dynamics in polar and non-polar materials at nanoscopic level. During a charging process electric charge is injected in material, in other words the structure is decorated with space charge. During the subsequent heating of the sample we are observing an apparent peak and the genuine peaks that are related to charge detrapping determined by the molecular movement. The method allows to reveal details that are not observed when other electrical and nonelectrical techniques are employed. The parameters for local and collective molecular movements can be determined.
ABSTRACT The final thermally stimulated discharge current (FTSDC) technique can be used to analyz... more ABSTRACT The final thermally stimulated discharge current (FTSDC) technique can be used to analyze charge trapping and transport in insulating materials. The experimental conditions can be selected so that the FTSDC is mainly determined by the space charge detrapping. Measurements of the FTSDC in a wide temperature range including the local (secondary) (β relaxation and the non-local (primary) α relaxation, for different polymers, demonstrate the existence of an apparent peak. The shift of peak temperature Tm with respect to the charging temperature Tp is analyzed. The interval Tm - Tp decreases from about 25 K to zero, as Tp approaches the glass transition Tg. Tm - Tp is lower for materials of lower conductivity. The peak width at the half maximum intensity decreases as Tp increases and the thermal apparent activation energy increases. The variations are not monotonous revealing the temperature range where the molecular motion is stronger and consequently the charge trapping and detrapping processes are affected by the strong thermal motion.
An analytical expression for the pull-in voltage is deduced for an RF micro-electromechanical sys... more An analytical expression for the pull-in voltage is deduced for an RF micro-electromechanical system (MEMS) switch, by tacking into account the presence of a dielectric layer deposited on the coplanar waveguide. The model allows investigation of the influence of the dielectric permittivity and the geometry of the device on the displacement d of the bridge and on the pull-in voltage. A comparison of the experimental data and the simulated data gives indication about the best way to estimate the pull-in voltage. The difference between the value obtained for the pull-in voltage, when the contribution of the dielectric layer is taken into account and the value of the pull-in voltage obtained by neglecting the presence of the dielectric layer is significant indicating that the presence of the dielectric layer cannot be neglected.
HDPE/iron powder composites have been characterized from the point of view of mechanical, thermal... more HDPE/iron powder composites have been characterized from the point of view of mechanical, thermal and electrical properties. Results for iron powder contents varying between 0 and 24 % by volume are presented. Generally, the composites show poorer mechanical properties as compared with the unfilled polymer. The density and hardness of HDPE/iron composites are higher than those of HDPE. The incorporation of iron powder in HDPE increases the thermal diffusivity and conductivity and decreases the specific heat and the electrical resistivity. The experimental data were interpreted using appropriate theoretical models.
ABSTRACT The isothermal charging and discharging currents were recorded for polyamide 11, polyeth... more ABSTRACT The isothermal charging and discharging currents were recorded for polyamide 11, polyethylene terephthalate and low density polyethylene in a large range of temperatures below and above the glass-rubber transition temperature of the amorphous phase, for different electrical fields and different charging and discharging times. The results showed that the low frequency relaxation process is complex and different contributions having the loss peak in the range 0.01 MHz to 0.1 Hz were revealed. The data are in good agreement with those obtained from dielectric relaxation spectroscopy and from thermally stimulated discharge current measurements.
The charge accumulated at a metal-dielectric interface strongly influences the thermally stimulat... more The charge accumulated at a metal-dielectric interface strongly influences the thermally stimulated discharge current measurements at temperatures above room temperature. We propose to improve this method by measuring the released currents on both faces of the sample. The voltages on the two faces of the sample are more different from each other than the currents which flow in external circuit from the two interfaces. In a thermally stimulated discharge current experiment we always start by measuring the current and finish by measuring the voltage. The isothermal voltage discharge measurements clearly show that the charges accumulated at the two contacts are different. The activation energy obtained from initial rising of positive current is higher than that obtained from initial rising of negative current.
Very long time dc measurements have been carried out to analyze charge injection/ejection and tra... more Very long time dc measurements have been carried out to analyze charge injection/ejection and trapping in low-density polyethylene. The basic idea was to compare the total charge involved in the charging step and the total charge stored in the material. The equality of the two charges demonstrates that the charge carriers do not pass through the sample. The injected electrons are trapped very close to the cathode to form a negative layer. It is suggested that near the anode the field ionizes the impurity atoms and/or the neutral molecules associated with structural defects to produce positive ions.
Taking into account the time-consuming trapping and detrapping of electric charge in insulating m... more Taking into account the time-consuming trapping and detrapping of electric charge in insulating materials, a sequential protocol for the investigation the trapping sites and trapped charge stability is proposed. The method is demonstrated for Teflon FEP-A. Elemental peaks are obtained whose maxima shift with increasing field from 456 to 486 K and are characterized by activation energies that increase from 1.1 to 1.9 eV. The relaxation time of the trapped charge, at 523 K, increases as the amount of charge stored in the material decreases and explains the good charge stability for Teflon FEP-A electrets.
An understanding of space charge build-up in the polymeric insulation of power cables is importan... more An understanding of space charge build-up in the polymeric insulation of power cables is important in determining how aging occurs and progresses and, also in predicting cable lifetime. In this investigation electric-field induced space charge in peelings from XLPE (cross-linked polyethylene) cables was measured using two different methods: the pulsed electro-acoustic technique (PEA) and the combined procedure of isothermal and
Proceedings. 11th International Symposium on Electrets
Space charge in electrically aged LDPE was studied using a recently developed technique combining... more Space charge in electrically aged LDPE was studied using a recently developed technique combining isothermal charging and discharging with non-isothermal measurements. Samples were aged in a NaCl aqueous solution at 40°C for 1500 h under an AC field of 6 MV/m (50 Hz). The samples were then isothermally DC charged and discharged (both currents recorded). Next a non-isothermal experiment with constant heating rate was performed. Finally, the sample was kept at the highest temperature and the final isothermal discharge current registered. The last step has to be carried on for a long time to ensure an almost complete discharge of the remnant charge so that results become reproducible and possible to analyze. Selective charging (careful choice of the field, temperature and the ratio of charging/discharging times) revealed the presence of different trapping sites. From the analysis of the isothermal and non-isothermal data the relaxation times and activation energies could be obtained.
Proceedings - International Symposium on Electrets, 2008
The proposed biosensor has successfully detected an immuno-reaction. However, the limit of detect... more The proposed biosensor has successfully detected an immuno-reaction. However, the limit of detection needs to be improved. It has the advantage of using films made from inexpensive materials and using simple methods, and the immobilization protocol is simple.
Proceedings - International Symposium on Electrets, 2008
Cork is a natural cellular material and is the outer bark of the Mediterranean tree Quercus Suber... more Cork is a natural cellular material and is the outer bark of the Mediterranean tree Quercus Suber-L. Its many different applications derive from the unique set of properties: cork is a good thermal, vibratic and acoustic insulator, prevents fire propagation, it is impervious to water. In this study shows that the main problem for charge storage during long periods is related to the small amount of humidity present in cork. Therefore control of the water content is essential.
Proceedings - International Symposium on Electrets, 2011
ABSTRACT Polarization can accelerate the bioactivity of HAp immersed in an SBF solution. However ... more ABSTRACT Polarization can accelerate the bioactivity of HAp immersed in an SBF solution. However a careful choice of polarization conditions has to be made. One relevant issue is to have long relaxation times of the polarization and this is related to the amount of water in Hap, which was to be kept as low as possible during poling. It was shown that the precipitation mechanism needs negative charges on the Hap surface. Under positive charge the mechanism is inhibited.
2008 13th International Symposium on Electrets, 2008
ABSTRACT The authors have presented a new electrical method to investigate the molecular dynamics... more ABSTRACT The authors have presented a new electrical method to investigate the molecular dynamics in polar and non-polar materials at nanoscopic level. During a charging process electric charge is injected in material, in other words the structure is decorated with space charge. During the subsequent heating of the sample we are observing an apparent peak and the genuine peaks that are related to charge detrapping determined by the molecular movement. The method allows to reveal details that are not observed when other electrical and nonelectrical techniques are employed. The parameters for local and collective molecular movements can be determined.
ABSTRACT The final thermally stimulated discharge current (FTSDC) technique can be used to analyz... more ABSTRACT The final thermally stimulated discharge current (FTSDC) technique can be used to analyze charge trapping and transport in insulating materials. The experimental conditions can be selected so that the FTSDC is mainly determined by the space charge detrapping. Measurements of the FTSDC in a wide temperature range including the local (secondary) (β relaxation and the non-local (primary) α relaxation, for different polymers, demonstrate the existence of an apparent peak. The shift of peak temperature Tm with respect to the charging temperature Tp is analyzed. The interval Tm - Tp decreases from about 25 K to zero, as Tp approaches the glass transition Tg. Tm - Tp is lower for materials of lower conductivity. The peak width at the half maximum intensity decreases as Tp increases and the thermal apparent activation energy increases. The variations are not monotonous revealing the temperature range where the molecular motion is stronger and consequently the charge trapping and detrapping processes are affected by the strong thermal motion.
An analytical expression for the pull-in voltage is deduced for an RF micro-electromechanical sys... more An analytical expression for the pull-in voltage is deduced for an RF micro-electromechanical system (MEMS) switch, by tacking into account the presence of a dielectric layer deposited on the coplanar waveguide. The model allows investigation of the influence of the dielectric permittivity and the geometry of the device on the displacement d of the bridge and on the pull-in voltage. A comparison of the experimental data and the simulated data gives indication about the best way to estimate the pull-in voltage. The difference between the value obtained for the pull-in voltage, when the contribution of the dielectric layer is taken into account and the value of the pull-in voltage obtained by neglecting the presence of the dielectric layer is significant indicating that the presence of the dielectric layer cannot be neglected.
HDPE/iron powder composites have been characterized from the point of view of mechanical, thermal... more HDPE/iron powder composites have been characterized from the point of view of mechanical, thermal and electrical properties. Results for iron powder contents varying between 0 and 24 % by volume are presented. Generally, the composites show poorer mechanical properties as compared with the unfilled polymer. The density and hardness of HDPE/iron composites are higher than those of HDPE. The incorporation of iron powder in HDPE increases the thermal diffusivity and conductivity and decreases the specific heat and the electrical resistivity. The experimental data were interpreted using appropriate theoretical models.
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Papers by Eugen Neagu