IET Nanodielectrics最新文献

An electret-based electrostatic energy harvester featuring tuneable resonance frequency, small size, light weight, and high output power was designed and its performance predicted by the finite element method and verified by experiment. The device consists of a resilient fluorinated polyethylene propylene (FEP) electret film that is metallised on one side with a small seismic mass attached to its centre and an arc-shaped counter electrode. In principle, such an energy harvester is mechanically a mass-spring system and electrically a self-bias voltage variable capacitor and converts vibrational energy into electrical energy by electromechanical coupling. For an energy harvester sample with dimensions of 30 × 10 × 9 mm for which the last dimension denotes the initial depth of the centre of the harvester, the resonance frequency can be tuned from 17 to 70 Hz by stretching the length of the FEP film loaded with a given seismic mass of 0.06 g. For a seismic mass of 0.1 g, the harvester generated a power up to 797 μW to a matching resistor at its resonance frequency of 17 Hz at an acceleration of 1×g, where g is the gravity of the earth. Such energy harvesters are promising candidates for use in self-powered electronic devices and wireless sensor network nodes.

The authors report the key findings from an experimental study that explored the use of activated bentonite for the reclamation of thermally aged ester-based transformer nanofluids to improve their insulation performance. Bentonite activated with acid treatment caused an increase in the specific surface area and pore volume of bentonite compared to the bentonite sample before treatment, thus imparting an improved adsorption capability. Physico-chemical diagnostic studies were carried out to characterise the activated bentonite. The insulation performance of the reclaimed natural ester and nano-filled ester fluid samples was assessed by measuring the corona inception voltage and breakdown voltage of each fluid sample, apart form measuring the flow electrification current using the spinning disk method. The results revealed that the reclamation process improved the corona inception voltage, dissipation factor and the breakdown voltage of the base ester fluid sample due to attraction of carbon particles to activated bentonite, but no significant variation was observed with nanofluids due to the depletion of the electrical double layer. The flow electrification current of ester and ester nanofluids reduced after treatment with activated bentonite, may be attributed to the interaction between copper and bentonite that alters the double layer formation responsible for the separation of charges.

Nanoparticles of Ni_0.5Co_0.2Zn_0.3Fe₂O₄ were prepared using the sol-gel combustion route. The nanoparticles were characterised by x-ray diffraction to confirm single-phase formation in a cubic spinel structure. Micro- and nanostructural analyses were carried out using field emission-scanning electron microscopy and field emission-transmission electron microscopy, respectively. A planetary ball milling technique was used to grind the powder into nanoparticles; the average particle size was 64 nm. Energy-dispersive X-ray spectroscopy was used to determine the atomic composition of the sample. Radio-frequency characteristics were recorded for dielectric measurement in a frequency range of 1 Hz to 15 MHz using a broadband dielectric spectrometer. Terahertz (THz) time-domain spectroscopy was performed to study THz-optical parameters such as refractive index, dielectric constant, and conductivity at room temperature in a frequency range of 0.3−2.2 THz using an indigenously developed THz time-domain spectroscopy setup. The magnetic properties of the sample were studied using a SQUID vibrating sample magnetometer under an applied magnetic field of ±10 kOe. An examination of M-H loops revealed that the saturation magnetization $��\left(�M_s�\right)�$, remanent magnetization $��\left(�M_r�\right)�$ and coercivity $��\left(�H_c�\right)�$ increased with an increase in temperature from 300 to 50 K.

The synthesis of core@double-shells structured TiO₂@C@SiO₂ nanowires (NWs) with variable thickness of carbon inner shell and SiO₂ outer shell was achieved by individually controlling the chemical vapour deposition time and amount of silicon precursor added in the sol–gel synthesis. The resultant TiO₂@C@SiO₂ NWs filled nanocomposites exhibited an excellent dielectric performance with simultaneously improved dielectric constant and suppressed dielectric loss, which could be further regulated by individually controlling the carbon inner shell and SiO₂ outer shell thickness. More importantly, the influences of the conductive carbon inner shell and insulated SiO₂ outer shell thickness on the dielectric performance of nanocomposites were clearly revealed. The increase of the conductive carbon inner shell thickness would lead to an increase in dielectric constant and loss of nanocomposites, while the insulated SiO₂ outer shell exhibited a totally opposite law that the dielectric constant and loss of nanocomposites decrease with increasing SiO₂ outer shell thickness. Numerical simulations were also carried out to theoretically verify the relationship between the dielectric loss and SiO₂ outer shell thickness. This promising controllable multi-shell structure could be extended to a variety of hybrids to develop high-performance dielectric nanocomposites.

Avalanche photodiode (APD) is an indispensable receiver component because of its high bandwidth and low noise performance. Recently, APD reliability, under harsh environmental stresses such as high heat and humidity, has drawn great interest in the applications of passive optical network, wireless, military, and free space optics. The authors study the APD degradation under the harsh environment of high humidity and high bias. The failure morphology through cross-sectional scanning electron microscopy is shown, and a new moisture degradation model based on electrochemical oxidation to account for the failure mechanism is developed.

Researchers are devoted to developing dielectric elastomers (DEs) with excellent electromechanical properties as an artificial muscle material. The authors report a new class of semi-interpenetrating network (semi-IPN) composites that contains siloxane-modified linear polyurethane (PU) and silicone rubber through reasonable design of polymer structure. The organic-filler copper phthalocyanine (CuPc) is chemically grafted into the semi-interpenetrating network as a cross-linking point and exhibits excellent dispersibility in the matrix. The various properties of the obtained composite films are also evaluated. The dielectric constant (8.65 at 1 kHz) and maximum actuation strain at 30 MV m⁻¹ (5.32%) are significantly higher than those of semi-IPN composites.

Polymer nanocomposites have attracted increased attention for use in the field of high-voltage direct current (HVDC) cable insulation. To study the use of polymer nanocomposites for this purpose, 3D flower-like MgO (flower-MgO) particles with hierarchical surface morphology are first synthesised. Polypropylene (PP) was simultaneously mixed with styrene-(ethylene-co-butylene)-styrene triblock copolymer (SEBS) and flower-MgO to obtain PP/SEBS/flower-MgO composites. The microstructural, thermal, electrical, and mechanical properties of the obtained nanocomposites were then studied in detail. The results showed that flower-MgO particles loaded at low concentration were well dispersed in the PP/SEBS matrix. The incorporation of flower-MgO particles has been found to significantly suppress the injection of homocharges and strengthen the ability to release the charge, thus containing accumulation of the space charge. The DC breakdown strength of PP/SEBS/flower-MgO composites was increased to 323 MV/m. Meanwhile, the tensile strength and elongation at break of the obtained composites was improved by loading 0.5 phr flower-MgO because of the synergistic toughening effects of SEBS and MgO. The investigation demonstrates the immense potential to replace nonrecyclable cross-linked polyethylene as an HVDC cable insulating material.

In this article, the dielectric response of epoxy resin and epoxy-based barium titanate (BaTiO₃) nanocomposites is characterised in the time-domain, based on polarisation and depolarisation current measurements. The aim of this article is to understand the dominant polarisation mechanisms in neat epoxy and its nanocomposites and validate the findings in frequency-domain spectroscopy (FDS). The effect of various parameters on the dielectric response of the material is investigated to this end, namely, polarisation–depolarisation time, electrode material, electric field and specimen thickness. The effect of pre-processing the nano-particles before use is also studied. In order to validate the findings of FDS, time-domain spectroscopy (TDS) of neat epoxy and its nanocomposites is performed.