IET Nanodielectrics最新文献

Polymer nanocomposites with improved dielectric permittivity and high breakdown strength are extremely desirable for the flexible electronic devices and power systems. The compatibility of fillers and polymer matrix is important in determining the dielectric and breakdown strength properties. The core–shell structure concept is useful to improve the compatibility of fillers with polymer matrix. Herein, an organic thermoplastic urethanes (TPU) polymer shell was successfully grafted on the surface of barium titanate (BaTiO₃, BT) and such a TPU shell improved the permittivity and breakdown strength of TPU@BT/PVDF polymer nanocomposites greatly. The permittivity of TPU@BT/PVDF nanocomposites with 12 wt% fillers at 10² Hz was up to 13.5, which was 1.5 times higher than that of pure poly(vinylidene fluoride) (PVDF). The improvement of the dielectric properties could be attributed to the enhanced interfacial polarisation between BT nanoparticles and TPU shell. Besides, the compatibility of BT nanoparticles and PVDF matrix was improved after the introduction of TPU shell. Accordingly, a highest breakdown strength value about 373 MV/m was obtained for the TPU@BT/PVDF nanocomposites with 7 wt% fillers. The core–shell strategy could be extended to a variety of inorganic fillers to improve the dielectric and breakdown strength properties of polymer nanocomposites.

Among the recently insulating materials broadly utilized in high voltage outdoor insulation, silicone rubber (SiR) has gotten the foremost consideration. Actually, SiR is becoming an efficient countermeasure to insulator contamination issues. To enhance different properties of polymeric materials, micro- and nanofillers have been used for dielectric applications. In this study, micron-sized titanium dioxide (TiO₂) and nano-sized TiO₂ fillers were added to the SiR matrix to improve electrical and mechanical properties. Dielectric strength, tensile strength, and elongation at break tests were monitored. Also, a scanning electron microscope was carried out. The samples were prepared by mixing micro-TiO₂ into SiR with the content of 0, 10, 20, 30, and 40 wt% and also mixing nano-TiO₂ into SiR with the content of 0, 1, 3, 5, and 7 wt%. A feed-forward neural network technique was used to estimate the dielectric strength in different conditions and different percentages of fillers. Adding nano TiO₂ filler enhances the electrical and mechanical properties of SiR composites. SiR with 5 wt% nano TiO₂ showed the best improvement in electrical and mechanical properties.

Polymer electrets are increasingly getting application in a very wide range. However, its charge trapped mechanism is still poorly understood. It is always challenging how to improve its charge trapped ability and to enhance its performance stability. In this study, a charge trapped mechanism, quasi-dipole model, is proposed for semi-crystalline polymer electrets. Every grain of crystallite is viewed as a dipole based on the polarisation effect between crystalline and amorphous region when charged. The energy level of the charge trap has a dependence on the crystallite structure. The more regular the crystallite grain structure the better charge stability is. The melt-blown polypropylene (MBPP) electret fabrics with α or mesomorphic crystallite are used as the model material to verify the rationality of the mechanism. The experiment results from thermally stimulating discharge and X-ray diffraction proved that the charge-trapped stability could be improved by means of transformation from meso-crystalline to α crystalline structure. The MBPP fabric containing α-crystallite shows much better charge trapped performance than one containing mesomorphic-crystallite because of more regular structure in α crystallite. The findings not only present new insight into charge-trapped phenomena in polymer electrets, but also provide innovation for the processing technology of polymer electret materials.

This study discusses the design of a low-profile metamaterial-based antenna consisting of a 3 × 5 array of Hilbert shaped unit cells organised as a rectangular patch. The antenna is backed by with a partial ground plane loaded with square electromagnetic band gap defects for energy harvesting applications in the context of ultra-wideband self-powered wearable wireless devices. The antenna is mounted on a 28 × 32 mm FR4 substrate, with a thickness of 0.394 mm, a relative permittivity of 4.2 and a loss tangent of 0.02. The antenna is also printed on a flexible solar panel for self-powered devices through solant–rectenna output terminals. The proposed solant–rectenna is found to cover the frequency range from 0.8 up to 10 GHz. The I–V characteristics of the solar panel are measured with and without the antenna structure to realize low shadowing effects. After that, the solant radiofrequency (RF) port is connected to a rectifier circuit to create a rectenna port that collects the RF energy and converts it to an output DC voltage at 0.915 GHz. It is found that the proposed rectenna provides an output DC voltage of 1.42 V with a conversion efficiency of 90%.

This work investigated the effect of polyethylene glycol (PEG) as an additive on barium titanate (BaTiO₃, BT) nanoparticles (NPs) synthesised by a hydrothermal process. The structure, morphology, dispersion and crystallinity of BT NPs were tested by differential scanning calorimetry–thermogravimetric analysis, X-ray diffraction, field emission scanning electron microscope, transmission electron microscope and Raman spectroscopy, respectively. The results showed that the main phase of BT NPs includes the cubic BT phase with a tiny tetragonal phase. Also, the addition of PEG with different concentrations has a very positive effect on the control of the grain size and grain shape of the samples during the hydrothermal process. When the concentration of PEG is 1 g/l, BT NPs possess the best morphologies and highest dispersibility, and the average size is about 71.86 nm.

High permittivity materials are currently in use for mitigation of electrical stress in high-voltage apparatus and energy storage systems. In this work, epoxy-based high permittivity nanocomposites with Barium titanate (BaTiO₃) nanofillers are considered, for the purpose of stress mitigation. Uniform dispersion of the fillers in the polymer up to 10% by volume is achieved. Apart from the use of as-received fillers, the effect of using surface-functionalised nanoparticles (with 3-glycidoxypropyltrimethoxy-silane) before use is also investigated. The nanocomposite is characterised in terms of its complex permittivity, DC conductivity, short-term AC breakdown strength and space charge accumulation, to gauge its suitability for use in high-voltage insulation. Complex permittivity is measured using broadband dielectric spectroscopy over a broad frequency range of 1 mHz to 1 MHz. DC conductivity is studied from polarisation–depolarisation current measurements. Short-term AC breakdown strength tests are performed at power frequency (50 Hz). Space charge density along the sample thickness is obtained using pulsed electro-acoustic technique. A computational case-study is presented to show the feasibility of using the high permittivity nanocomposite for electric stress control in high-voltage equipment (viz., at mounting flanges of 69 kV bushings).

The development of reliable, environmentally safe and economic insulating oil for the transformer is an endless effort of the electrical industry. Recent research is based on natural ester fluid, the green insulating oil which exhibits excellent dielectric performance and environment friendly characteristics. Nanofluids are also emerging as potential replacement for the conventional mineral oil used in transformers. Characterisation of nanoparticle filled mineral oil and natural esters have validated their improved dielectric behaviour in comparison to the unfilled oil. Although the applications are wide, the state of the art technology requires a deeper understanding of the underlying phenomenon. Much work is expected to be done in the application of nanofluids prepared with mineral oil and natural ester, particularly its effect on the cellulose insulation. The study provides an overview of the different materials that have been used as alternatives to the conventional transformer mineral oil, with special emphasis on natural esters and natural ester nanofluids, their advantages and challenges.

The dielectric effect, investigated using dielectric spectroscopy and DC dielectric breakdown strength measurements, of introducing xylene into a composite system containing polyethylene, a co-polymer of ethylene and vinyl acetate and an organoclay can be understood in light of X-ray diffraction data. In dielectric spectroscopy, although organoclay alone changes the dielectric response of the polymer blend and xylene has no effect on the unfilled polymer blend, when both xylene and organoclay are present, a synergistic response is revealed at the 1 V_rms amplitude voltage used to acquire the dielectric data. In contrast to this, in DC, dielectric breakdown strength measurements revealed that, under high field conditions, both the xylene and organoclay, independently, caused a decreased breakdown strength. This work was undertaken in order to examine the generality of the possible effects of labile, low molar mass impurities on electrical properties of comparable systems, which may be processed through solvent-based routes.

Silicone rubber is widely used for electrical insulation and may be exposed to a harsh environment. The present study envisaged to improve insulation properties of silicone rubber by adding an optimised quantity of nanofillers. The fundamental space charge and charge trap characteristics were studied by adopting the pulsed electroacoustic analysis technique and through surface potential measurement. The dielectric properties of the materials were analysed through measurement of permittivity and loss factor of the material at different frequencies and temperatures. The influence of gamma irradiation on variations in fundamental properties of the material was characterised. The results of the study indicate that 5 wt.% alumina added nanocomposites had better space charge performance under gamma irradiation compared with virgin silicone rubber.