IET Nanodielectrics最新文献

This study focussed on determining the electric field distribution formed by asymmetric agglomerates in order to elucidate the mechanism by which large agglomerates reduce the dielectric breakdown strength of nanocomposites. Epoxy nanocomposite sample was prepared by adding 2.5 vol% of TiO₂ nanoparticles with a primary particle size ranging from 30 to 50 nm. The three-dimensional (3D) structure of the epoxy nanocomposites with a thickness of 5 μm was analysed via focussed ion beam and scanning electron microscopy. The 3D reconstruction was performed using 250 observation images, and a 3D model of the particle in the observational range was obtained. The electric field distribution for the 3D model of the agglomerate with the largest size was determined using the finite element method. In addition, we constructed a calculation model that effectively accommodate changes in the direction of the applied electric field. Subsequently, we examined the changes in the maximum electric field intensity around the agglomerate.

Vibrational energy harvesters, which can convert mechanical energy distributed widely in the surrounding environment to electrical energy in a convenient, eco-friendly and sustainable way, have attracted great attention in both academia and industry. In this study, a resilient electret film-based vibrational energy harvester with a V-shaped counter electrode is introduced, simulated and constructed. A negatively charged fluorinated polyethylene propylene (FEP) electret film with a wavy shape was adopted in the devices, achieving simultaneously a stable embedded biased voltage and a large tensile deformation during vibration. The influences of the factors on the performance of the device, including the initial stretching state of the resilient electret film, seismic mass and depth of the V-shape counter electrode, were analyzed comprehensively with finite element simulation and compared to experiments. Further, the structure of the device was optimised for generating a high output power, and a good agreement between the simulation and experimental data was achieved. Additionally, the resonant frequency of the device can be easily tuned between 28 and 68 Hz by merely adjusting the initial stretching state of the wavy FEP electret film, guaranteeing great superiority for broad bandwidth energy harvesting applications. For an optimised energy harvester with a volume of only 15 × 5 × 1.7 mm³ and a tiny seismic mass of 25 mg, and a normalized output power referring to 1 × g (g is the gravity of the Earth) up to 547 μW was obtained at its resonant frequency of 28 Hz. These results demonstrate that such a miniaturised vibrational energy harvester is a promising electrical energy supplier for low-power-consumption electronic devices, in particular in wireless sensor networks.

A series of high-performance linear and cross-linked polyimide (PI) aerogels with different molecular structures have been successfully synthesised using the freeze-drying process. In this study, the comprehensive regulation of microstructure, thermodynamic, thermal insulation and dielectric properties of PI aerogels are achieved by controlling the rigid/flexible structure and composition of polymerised monomers. The increase in rigidity of PI molecular structure could promote the formation of denser pores, which is beneficial to improve the thermodynamic and thermal insulation properties of aerogels. Notably, the cross-linked PI aerogel prepared by introducing cross-linking agent (tris(4-aminophenyl) amine, [TPA]) into linear PI exhibits high thermal stability (T_d5% > 560°C), excellent ultralow permittivity (ε_r = 1.31, f = 10⁶ Hz) and good thermal insulation property (k = 0.056 W/m · K). This innovative strategy promotes the wider application of the cross-linked polyimide aerogel in the field of integrated circuits and aerospace exploration.

Piezoelectric polymers have been widely used in a variety of applications, including tactile sensors, energy harvesting, polymer actuators, and biological devices. In this investigation, we fabricated the PLLA (poly(L-lactic Acid)-based bimorph structures for piezoelectric motor applications. First, a strain measurement setup was established to measure the strain of the PLLA and PDLA film at different temperatures. The effective piezoelectric constants d₁₄ calculated for the PLLA and PDLA films were 10.2 pC/N and 9.4 pC/N, respectively. Furthermore, the PLLA films showed a strong thermostability of piezoelectricity at 130°C. The PLLA bimorph minimotor showed the maximum load of 1.2 g and the maximum torque of 0.019 cN·m. The minimotors were capable of rotating a plastic hemisphere container in the clockwise and counterclockwise directions at 65 V voltage. Due to the light weight, low driving voltage, and thermal stability, the PLLA/PDLA motors show a great promise in future Braille display, robots, and mini-digital camera applications.

Ferroelectrets (also called piezoelectrets) are relatively young members in the family of piezo-, pyro- and ferroelectric materials. They exhibit ferroic behaviour phenomenologically undistinguishable from that of traditional ferroelectrics, although the materials per se are essentially non-polar space-charge electrets with artificial macroscopic dipoles (i.e. internally charged cavities). Since ferroelectrets not only represent a scientific curiosity but also have great application potential, they have attracted tremendous attention from science and industry. The research and development of ferroelectrets has witnessed significant progress in the past few years. New ferroelectrets with large transverse piezoelectric activity, biodegradable ferroelectrets as well as 3-D printed ferroelectrets are reported. Charging methods of high efficiency are proposed based on better understanding of the physico-chemical processes during charging. New insights into the piezoelectricity of ferroelectrets are provided. The development of ferroelectret-based piezoelectric-magnetic multimodal transducer films opens up new avenues for the research of ferroelectrets. Particularly, more and more novel applications of ferroelectrets in flexible pressure sensors, health monitoring, energy harvesting, air-coupled ultrasonic non-destructive testing etc. are reported. Here, these exciting recent advancements in the field of ferroelectret research are reviewed and discussed.

Al electrodes with different thickness (sheet resistance 2–100 Ω/□) were deposited onto the films of polypropylene (PP), polyester (PET) and polyimide (PI) by vacuum evaporation. The root-mean-square (RMS) and peak-to-valley roughness of Al electrodes were characterised by atomic force microscopy (AFM). It was found that the PET and PI substrates showed the reduced threshold thickness of the continuous growth of Al electrodes compared with the PP substrate. The sheet resistance of Al electrodes decreases with the increase of peak-to-valley roughness. The current surge capability of the Al electrode decreases with the increase of RMS roughness. The Al electrode deposited on the PET film has higher sheet resistance and better current carrying capability, and the self-healing performance of metallised film is also excellent among three kinds of films.

Improving the energy storage density of dielectric capacitors has absorbed extensive attention for energy storage. However, a decrease in breakdown strength may be aroused after the addition of abundant fillers, it is necessary to design the composite film with a sandwich structure without the sacrifice of mechanical properties. The PPy-TiO₂/PVDF monolayer film and PVDF/PPy-TiO₂/PVDF sandwich-structured composite films were successfully prepared via electrospinning and a hot-press treatment. The experiment results show that the dielectric constant of the composite films can be enhanced effectively by adding PPy-TiO₂.When the filling amount is 30 wt%, the energy storage density of PVDF/PPy-TiO₂/PVDF sandwich-structured composite films is outstanding before the breakdown strength, which is higher than that of the pure PVDF film. The energy storage density of PVDF/PPy-TiO₂/PVDF sandwich-structured composite films could be achieved to 2.68 J/cm³ under the electric strength of 1700 kV/cm.

Most commonly used dielectric elastomers (DEs) such as acrylic dielectric elastomers VHB^TM 4910 need a high actuation voltage and pre-stretching to obtain a large actuation strain, and present high mechanical loss caused by viscoelasticity. In this work, we fabricated a new acrylic elastomer by UV curing based on CN9021 and lauryl acrylate. By manipulating crosslinker content, crosslink density changed and physical entanglements of the new material can be affected. Therefore, mechanical properties such as Young's Modulus and mechanical loss of the new material can be controlled, and little change of its glass transition temperature was induced. Results of the actuation test show that the new DE is capable of 9.0% actuation area strain under 11 kV/mm and a good performance under oscillating voltage with different waveforms and frequencies.

The agglomeration causes a significant challenge to nanodielectrics. Identification of agglomerates in scanning electron microscopy (SEM) images is an important step of solving this issue. Motivated by the fast development of image recognition in computer vision, we propose a new approach for agglomerates identification in SEM images of nanodielectrics by semantic segmentation, which is more efficient and accurate than traditional methods. Three models based on convolutional neural networks are investigated in this work, namely pixel blocks classification network, full convolutional segmentation network employed with data augmentation and unsupervised self-encoding network. All three networks can preliminarily identify agglomerates of spherical silica-based blend polyethylene nanocomposites. The mean intersection over union (mIoU) of pixel blocks classification network is 0.843 and it takes 25 s to process an image. Full convolutional segmentation network only needs 0.059 s to process a sample, with a mIoU of 0.777. Unsupervised self-encoding network can reach a mIoU of 0.747 at a speed of 5.806 s. According to the amount of data sets, and requirements for different speed and accuracy, three kinds of networks can be flexibly selected.

Focussing on the insulating material of power transformer—cellulose insulation paper, this paper first introduces the basic characteristics and engineering application background of insulation paper. Then, the research progress of improving the mechanical properties, thermal stability and electrical properties of insulation paper by nano modification in recent years is compared, and the promotion mechanism is analysed. In addition, in practical engineering application, the oil–paper composite insulation system composed of insulation paper and insulating oil is used for the internal insulation of oil immersed transformer. Therefore, the influence of modified insulation paper on the performance of oil–paper composite insulation system is analysed. Finally, the newly reported new insulation paper is introduced, and the future development trend of modification of traditional insulation paper is analysed.