IET Nanodielectrics最新文献

The authors report a novel electret-based miniature electrostatic motor with an electret film as the stator and a metal electrode as the rotor. A particular commutator is used to transform the polarity of the metal electrode. When the size of the electret-based electrostatic motor (EEM) is 42 × 44 × 15 mm³, the maximum power consumption is only 5.4 mW. The rotation speed of the EEM increases with the increase of the supply voltage, and the maximum rotation speed can reach up to 2864 rpm. Powered by two nickel-hydride batteries with a rated capacity of 1700 mAh, the EEM can drive a fan with a diameter of 40 mm to rotate continuously for 18 h. The EEM has the characteristics of low power consumption and convenient fabrication. Experimental results show that the EEM demonstrates high reliability and has potential applications in micro-electromechanical systems.

We have witnessed the flourish of bioelectronics, brain–computer interface, and brain science programme in recent decades. In this review, the up-to-date advances of dielectric, piezoelectric, and ferroelectric nanomaterials in the biomedical applications are summarised. Biomolecular detection methods have been developed, including dielectric-gated field-effect transistor, dielectrophoresis, non-linear dielectric response, and optical tweezer. Endogenous bioelectricity is a crucial in cell proliferation, migration, differentiation, intracellular communication, neuronal activity, tissue growth. Piezoelectric and ferroelectric materials can be utilised as energy transducer to monitor physiological signal, such as blood pressure or respiration, and directly stimulate cell differentiation, neuronal regeneration, tissue repairment etc. They can also catalyse the electrochemical reaction of organisms through piezoelectricity. The intrinsic relevance between neuronal and ferroelectric polarisation signals inspires the application of the ferroelectrics in the modern intelligent bioelectronics like the artificial retina.

Recently, demands for high-performance polymer film capacitors at elevated temperatures have become more urgent. High dielectric constant is essential for dielectric materials to achieve substantial energy density at relatively low electric fields, which is of great significance to practical applications, while improving the permittivity of high-temperature polymer dielectrics without a remarkable deterioration in other electrical properties still remains a challenge. Here, a polymer nanocomposite containing z-aligned high-k nanowires sandwiched by e-beam evaporation deposited Al₂O₃ films was developed based on the optimal structure proposed by the phase-field simulation. It is found that z-aligned nanowires are more effective in promoting the dielectric constant than random-aligned ones, and a large increase in dielectric constant is observed at relatively low content of nanofillers. Outer insulating layers effectively suppress the electric conduction and improve the breakdown strength. Consequently, the nanocomposite with only 1 volume fraction of z-aligned nanowires exhibits a breakdown strength, electrical resistance, and charge–discharge efficiency as high as neat PEI, but more than twice the discharged energy density than it at 150 °C. This study realises the optimal structure predicted by simulation in experiment, obtaining high-permittivity, high-temperature nanocomposites at no expense of other electrical properties, and making it possible to achieve high discharged energy density at relatively low electric fields.

The flashover threshold (V_flsh) of polymer insulations such as epoxy (EP) in HVDC systems can be augmented by modifying their surface with an appropriate treatment technology. For such purpose, several surface treatment methods such as ion beam, sandpaper and a combination of the two is introduced. Firstly, insulation samples with pure epoxy (EP_pure), different ion beam treatment periods (EP_ion;10, 15, 20 min) and different roughness (EP_sand; R1 = 4.23 μm, R2 = 6.34 μm, R3 = 9.21 μm) are prepared on the laboratory scale. Afterward, based on several characterisations, such as surface conductivity, mean surface roughness and potential distribution of these insulations, multi-modified insulation (EP_multi = EP_ion-20 + EP_sand-R3) is prepared. In the end, the V_flsh of each insulation group is measured and compared to examine the effectiveness of the proposed modifications. It is obtained that the V_flsh of the modified insulations augmented dramatically irrespective of the treatment method. The V_flsh of the insulation group EP_multi augmented by 52.66 % which is the highest improvement among all insulation groups. In short, the proposed surface modifications are effective and could be used as references to enhance the insulation strength of polymer dielectrics in HVDC systems.

The high permittivity of polymer dielectrics facilitates their use in the electronics industry. Compared to inorganic ceramics and composites, intrinsic high permittivity polymer dielectrics have the advantages of easy solution processing and better homogeneity. The permittivity of common polymers is generally low, hence it would be worthwhile to explore avenues for augmenting the permittivity of polymer dielectrics via judicious and efficient structural design. The effective strategies used to increase the permittivity of intrinsic polymers encompass elevating local polarisabilities by fortifying electron delocalisation capabilities, exploiting ion pairs to generate atomic clusters with larger dipole moments, amplifying dipole density, augmenting dipole mobility, and so forth. Due to the rigidity and flexibility of the polymer backbone's decisive influence on the dielectric's all-around performance, its selection also requires a total consideration of the requirements of practical applications. This work provides an overview and a brief evaluation of the dominant design strategies and mentions possible future design paradigms for polymer dielectrics.

The concept of self-healing dielectric polymers has been heatedly discussed, with the expectation of high damage resistance and longer service time. However, there is still a lack of analysis on the competitive relationship between electrical degradation and self-healing. The authors discussed this relationship in two stages: the design of self-healing strategies and the operation of self-healing polymers. Since the requirements for excellent insulating or mechanical properties are not consistent with the demands for high self-healing capability, trade-offs are necessary during the design of self-healing polymeric systems. In the operation stage of dielectric polymers, some key factors that affect the service lifetime of non-autonomous self-healing dielectric polymers are analysed, including the efficiency and repeatability of self-healing, and the frequency of healing maintenance. For autonomous self-healing dielectrics, the simultaneous processes of ageing and healing are investigated using a self-healing epoxy resin based on microcapsules and in situ-generated radicals. A quicker recovery of insulating properties, in terms of partial discharge magnitude, was observed under appropriate healing voltages. However, the self-healing ability might vanish when the voltage was too high, verifying the competitive relationship between electrical degradation and self-healing.

Piezoelectrets, also called ferroelectrets, can exhibit promising piezoelectric properties and have plenty of applications in wearable health monitoring. Usually, the cellular structure of piezoelectrets is of outstanding importance for their sensing properties, and structure improvement and optimisation would be a possible way to realise high-performance piezoelectrets. The authors proposed a compound-structured piezoelectret system, where a layer of polypropylene foam was sandwiched between two layers of solid polytetrafluoroethylene, resulting in a combination of a foam-structured and a layer-structured piezoelectrets. The compound systems are thin and flexible, they can exhibit stable electrical outputs, they have relatively broader linear working range under pressure, and promising mechanical sustainability for multiple testing. The results reveal that the compound system can be considered as a simple addition of both components, and each component contributes linearly and independently to the whole system. The application potential of this proposed compound system has been demonstrated by sleep monitoring together with carotid and radial pulse recordings, where many useful physiological information including breath, heartbeat, and pulse details can be extracted from the signals acquired by the compound system. A type of flexible sensor system that is very competitive for future portable and wearable applications may be provided.

Collection and conversion of widespread mechanical energy is one promising way to alleviate environmental pollution and energy crisis. Piezoelectric materials can effectively realise this conversion between mechanical and electrical energies. Here, via near-field electrospinning, piezoelectric poly(vinylidene fluoride) microfibers were fabricated on flexible polyethylene terephthalate substrate. Bending measurement indicated that open-circuit voltage response from piezoelectric microfibers was strain dependent but insensitive to bending frequency. The microfiber sensor could detect acoustic signals with sound pressure level between 70 and 120 dB and the recorded acoustic frequency was well consistent with the nominal frequency. Light wind from a low-power hand fan was also detected by this microfiber sensor. This simply structured and highly flexible piezoelectric microfiber sensor provided a promising and low-cost fabrication measure for weak mechanical excitation sensing.

Heat dissipation has become an important challenge and technical bottleneck for the rapid development of high-frequency microelectronic devices and high-voltage electrical equipment. Thus, there is a great urgent need for high-performance intrinsically thermally conductive polymer (ITCP) to realise effective heat dissipation. In recent year, the ITCP has received extensive attention due to excellent overall performances and clear advantages over conventional heat conductive polymer composites. The thermal transport physics and its relation with the multiscale chain conformations in polymers with diverse morphologies are reviewed. Then, the current understanding of how the chemistry of polymers, multiscale chain morphologies and conformations would affect phonon transport and the resulting thermal conductivity (TC) in both amorphous and crystalline polymers to unveil the important chemistry-structure-property relationships is discussed and anaysed. The latest advances in engineering ITCP from oriented fibre to bulk amorphous states for a high TC are summarised. Lastly, the challenges, prospects and outlook of ITCP have been proposed. The authors anticipate that the present paper will spire more fundamental and applied research in the intrinsic polymer dielectrics field to advance scientific understanding and industrial applications.