IET Nanodielectrics最新文献

Smart sensors with excellent performance are accelerating the development of biomedicine and the Internet of Energy. Nanodielectrics exhibit unique electrical and mechanical properties. As the predominant materials in optical magnetic field sensor (MFS), they can not only exert the anti-interference of optical sensing, but improve the measuring characteristics of optical sensors. For instance, the optical fibre quantum probe for the magnetic field can obtain a higher sensitivity of 0.57 nT/Hz^1/2, while the measurement range of the sensor that uses Co-doped ZnO nanorods as cladding is 17–180 mT. Here, these exciting recent achievements in the realm of optical sensing methods for magnetic field detection are reviewed, with a focus on nanodielectrics, which provide an emerging opportunity to achieve higher sensitivity and a wider measurement range of MFS.

Semiconductor packaging materials play a critical role in the development of semiconductor devices. They not only provide reliable protection and support, but also contribute to the electrical connection between the chip and the external circuit. Among many choices of packaging materials, polymer-based nanocomposites have become the mainstream candidate due to their low cost, easy processability, and tunable properties. Materials with low dielectric constant and dielectric loss, high glass transition temperature, fast thermal conductivity, suitable coefficient of thermal expansion, low viscosity, and good processability are commonly required in semiconductor packaging, yet most polymers do not meet these criteria. Therefore, modulation of the polymer matrix, introduction of suitable fillers, and modification of the filler surface are often effective approaches to enhance the performance of the composites. Here, the authors first review current research progresses of polymer-based nanocomposites for five different types of packaging applications, namely moulding compounds, thermal interface materials, underfills, die attach materials, and substrates. The authors then present prospects of developing next-generation polymer-based nanocomposites for advanced semiconductor packaging and propose some suggestions to solve the existing challenges.

Bacterial biofilm formation is an important factor in bacterial resistance. The commonly used methods to inhibit bacterial biofilms are synthetic drugs such as antimicrobial peptides, but physical methods are often safe, non-toxic and simple to prepare. This work proposes an environmentally friendly method to use electret films to provide a stable electric field during the formation of bacterial biofilms, inhibit the formation of bacterial biofilms through the action of the electric field and weaken the adhesion of bacterial biofilms. The total amount of Staphylococcus aureus biofilm decreased by 20% compared to the control group after the treatment of positive electret. The distribution of exopolysaccharides showed that the activity of biofilm also decreased. In addition, the negative electret can also inhibit the formation of bacterial biofilm. The result can be generalised to other Gram-positive bacteria and could contribute to reduce the resistance of bacteria, improve the effect of related antibiotics, reduce the dosage of antibiotics and reduce the side effects of drugs.

Environmental protection is the future trend of power equipment development, and is also a research hotspot in the field of power cable insulation in recent years. Due to the excellent electrical properties and recyclability, polypropylene (PP) based composites are regarded as promising insulating materials for eco-friendly next-generation power cables. However, the high modulus and hardness of pure PP make it difficult to be directly employed as cable insulations, which needs to be further optimised. General methods of mechanical performance regulation often result in the deterioration of electrical performance, such as breakdown strength, space charge and so on. Therefore, it is recognised that the major challenge impeding practical applications of PP power cable insulation arises from the synergetic regulation of multi-performances. The multi-level structures influencing the multi-performances of PP are introduced by the authors and the researches on the performance enhancement of PP through nanoscale structure regulation in recent years are reviewed in detail. Seven kinds of modification methods including nano-doping, chemical grafting, in-suit copolymerisation, heat treatment, nucleating agent, voltage stabiliser and elastomer blending are paid special attention. Based on the full understanding of the research status, the challenges and issues of future research are put forward for eco-friendly PP power cable insulation.

Hybrid vibration energy harvesting technology converts vibration energy into electricity using multiple transduction mechanisms to improve output power. A frequency-tunable resonant hybrid vibration energy harvester using a piezoelectric cantilever with electret-based electrostatic coupling is proposed in this article. The electrostatic coupling including electrostatic force coupling and electrical damping coupling is introduced by an electret film placed below the cantilever, where the electrostatic force acting on the cantilever realises a tunable resonant frequency and additional electrical damping boosts power output. A coupling electromechanical model is derived using Euler–Bernoulli beam theory and Kirchhoff's law. By investigating the static and dynamic stability of cantilever, the maximum electret surface potential is defined to prevent the pull-in phenomenon. The damping of the device is evaluated, and the optimal electret surface potential is determined to obtain the matching of the electrical and mechanical damping for maximum power output. The resonant frequency of hybrid vibration energy harvester can be adjusted in range of 176.1 rad/s by changing the electret surface potential and resistive load. The experimental output power of hybrid vibration energy harvester was 5.2 μW, 27.4 times higher than that of the individual piezoelectric generator. The proposed hybrid vibration energy harvester exhibits a promising potential to power microelectronic devices and wireless sensor network node.

Flexible solar wings with high energy density, lightweight, small size and large deployment area are one of the first choices for next-generation spacecraft. However, the flexible solar wings are subjected to irradiation in space and tensile mechanical stress, which produce the charge accumulation effect and result in electrostatic discharge. It is necessary to establish a test method for the conductivity and space charge behaviour of polyimide under tensile stress. The stress–strain characteristics of polyimide under different tensile stresses are studied by the authors. The longitudinal length-strain characteristics and transverse thickness evolution characteristics under different stresses are also obtained. The results show that the variation of film thickness with tensile force is only about 1% before the yield point. The polyimide films from 50 to 200 μm thick have similar yield and tensile strengths. The ultimate stress of the specimen decreases from approximately 126 to 103 MPa with increasing thickness. The thickness model of polyimide under tensile stress were obtained, which could accurately calculate the voltage amplitude applied on the specimens for measuring the conductivity under different tensile stresses. A basis for investigating the stress–strain characteristics of polyimide films under different tensile stresses are provided, which will facilitate the formulation selection and performance improvement of polyimide for flexible solar wings of spacecraft.

The significant progresses of polymer-based nanocomposites with improved dielectric performances are urgently calling for an effect way to realise commercial production. Up to now, the biaxial stretching technology is still a powerful method to produce the high-performance dielectric films applied in the film capacitors due to its full-blown applications. In this work, a classical composite system of BaTiO₃/polypropylene was applied to reveal the connection between the microstructure changes and dielectric properties of the corresponding nanocomposite films in the biaxial stretching process. The permittivity of BT-30 wt% nanocomposite reached 2.8 at 10³ Hz after stretching, and its breakdown strength reached 340 MV/m. In addition, the breakdown strength of BT-10 wt% nanocomposite could even be promoted to 452 MV/m, which was 1.3 times higher than that before stretching. The microstructure test demonstrated that the rearrangement of nanofillers, high crystallinity and the oriented polypropylene crystals were advantageous to the improvement of breakdown strength for the stretched nanocomposite films. Therefore, the application of biaxial stretching technology into the preparation of nanocomposite dielectric film is an enormous potential way for the energy storage film capacitors.

Dielectric energy storage capacitors with excellent high temperature resistance are essential in fields such as aerospace and pulse power. However, common high-temperature resistant polymers such as polyimide (PI) and polyether sulfone have low energy storage densities and energy efficiencies at high temperature, which are greatly limited in practical applications. The polymer nanocomposites prepared by doping modification can regulate the charge injection and transport process, and improve the high-temperature energy storage performance. However, the quantitative relationship between charge injection and charge trapping and the energy storage performance of linear polymer nanocomposites still needs further study. An energy storage and release model considering the charge trapping effects is constructed by the authors. We simulate the high-temperature energy storage properties of polyimide nanocomposite dielectrics (PI PNCs) with different charge injection barriers and trap parameters at 150°C. A triangular voltage is applied to the electrodes at both sides of the PI PNCs, the electric displacement-electric field loop is simulated, and the discharged energy densities and energy efficiencies are calculated. The simulation results are consistent with the experimental results. Increasing the charge injection barrier, deep trap energy and deep trap density can effectively reduce the charge injection and the carrier mobility, thereby improving the discharged energy densities and energy efficiencies of dielectric capacitors. In the case of low charge injection barrier (1.3 eV), with the increase of deep trap energy (0.7–1.5 eV) and deep trap density (1 × 10²¹–1 × 10²⁵ m⁻³), the discharged energy density changes from 0.20 to 1.44 Jcm⁻³, the energy efficiency changes from 9.0% to 99.9%, and the high-temperature energy storage performance improves significantly. This research provides theoretical and model support for the improvement of the high-temperature energy storage performance of nanocomposites.

High-performance dielectric capacitors are essential components of advanced electronic and pulsed power systems for energy storage. Because of their high breakdown strength and excellent flexibility, polymer-based capacitors are regarded as auspicious energy storage material. However, the energy storage capacity of polymer-based capacitors is severely limited due to their low polarisation and low dielectric permittivity. The modified Stöber method was used to construct two types of CNT@SiO₂ (CS) one-dimensional core-shell structured nanowires with different shell thicknesses. By integrating the procedures of solution mixing, melt blending, hot-stretching orientation and hot pressing, sandwich-structured poly (vinylidene fluoride) (PVDF)-based composites were fabricated. The CS core-shell nanowires dispersed in the inter-layer serve as electron donors, leading to a high permittivity, while two PVDF outer layers provide the favourable overall breakdown strength. The insulating SiO₂ shell can effectively limit the migration of carriers and keep the dielectric loss at a relatively low level in the composites. The CS/PVDF composite exhibited an enhanced discharged density (~6.1 J/cm³) and breakdown strength (~241 kV/mm) when the interlayer filled with as small as 1 wt% CS nanowires with the SiO₂ shell thickness of 8 nm, which is 203% and 18.7 % higher than pure PVDF (~2.01 J/cm³ at 203 kV/mm), respectively. This research presents a practical strategy for designing and fabricating advanced polymer film capacitor energy storage devices.

Barium titanate (BaTiO₃, BT) was co-doped by solid-state sintering with niobium pentoxide (Nb₂O₅) and cobalt trioxide (Co₃O₄) as dopants. The modified barium titanate containing Nb and Co (BTNC) with larger particle size (0.5–1 μm) and silver powder (Ag) with smaller particle size (25 nm) were co-filled with polyvinylidene fluoride (PVDF) to prepare (BTNC-Ag)/PVDF three-phase composites. The morphology and crystal structure of composites were characterised by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. SEM shows that when the volume ratio of BTNC and Ag in the composite is 4:1, the two fillers have good dispersion in polymer matrix and could intersperse with each other to reduce voids. XRD patterns display that the filling of BTNC and Ag powders was conducive to promoting the enhancement of the diffraction peaks of β phase and γ phase in PVDF. The dielectric properties of the composites are effectively enhanced through the synergistic effect of the micro-nano bicomponent ceramic BTNC and conductive particles Ag co-filled polymer PVDF. When the volume ratio of filler (BTNC:Ag = 4:1) to matrix PVDF is 2/1, the dielectric properties of the composite are the best, the dielectric constant reaches 134.1 at 10² Hz and the dielectric loss is 0.04.