Space charge behavior of XLPE/silica nanocomposites under high electric field
Space charge formation behavior is compared among crosslinked polyethylene and its two nanocomposites with silica nanofillers with and without surface treatment. By conducting a degassing treatment, we have prepared nine kinds of samples in total. As a result, it was found that the presence of cross-linking by-products suppresses space charge formation. As far as the present silica nanofillers are concerned, their addition to XLPE enhances the formation of negative space charge near the cathode.
Space charge formation in LDPE/MgO Nano-composite under high electric field at high temperature
Time dependence of space charge formation under high dc electric field at various temperatures between 30 and 60degC in nanocomposite of low density polyethylene (LDPE) mixed with nano-size filler of magnesium oxide (MgO) were studied using pulsed electro-acoustic (PEA) method. In LDPE without MgO, it is found that huge amounts of both positive and negative packet-like charges injection at all measured temperatures, and they makes a local electric field in bulk higher. On the other hand, there is almost no such huge packet-like charge was observed in LDPE/MgO with MgO content of more than 1 phr even under high electric field at high temperature, while it was observed in that with MgO content of 0.2 phr. To study the reason of such space charge suppression effect by nano-filler, we tried to calculate the potential distribution which is induced by the difference of relative permittivities between LDPE and MgO under such high electric field. By a numerical analysis, it is found that the induced potential distribution induced around the nano-filler under high electric field works as a deep trap to capture and to prevent the movement of injected carriers from electrode.
New Low-Profile Applicators for Local Heating of Tissues
A new type of low-profile applicator is described giving efficient power transfer to tissue with low leakage. It consists of a resonant element spaced from a ground plane by low-loss material having high relative permittivity and some relative permeability. This combination is covered by similar material which can be placed in direct contact with the tissue to be heated, or separated from it by a water bolus as required. Laboratory measurements using phantom materials show that these applicators are well matched and produce well defined and relatively uniform heating profiles. Applicators having maximum dimensions of 3-15 cm covering the frequency range 1000-100 MHz, respectively, are described. Penetration depths of at least 4 cm at 100-200 MHz are achieved. Tests on anesthetised pigs and some clinical assessment have confirmed the usefulness of this compact low-frequency type of applicator and have shown that performance compares favorably with that of other recently reported types. The design can be optimized for treatment of specific sites, and suitable choice of dimensions and electrical characteristics of the layer material allow the low-profile concept to be extended over a wide range of operating frequencies.