Insulator (electricity)

About: Insulator (electricity) is a research topic. Over the lifetime, 15941 publications have been published within this topic receiving 108950 citations. The topic is also known as: electrical insulator.

Electret formation in transition metal oxides by electrochemical amorphization

Abstract: Transition metal oxides (TMOs) are an important class of materials that show a wide range of functionalities involving spin, charge, and lattice degrees of freedom. The strong correlation between electrons in d-orbitals and the multivalence nature give rise to a variety of exotic electronic states ranging from insulator to superconductor and cause intriguing phase competition phenomena. Despite a burst of research on the multifarious functionalities in TMOs, little attention has been paid to the formation and integration of an electret—a type of quasi-permanent electric field generator useful for nanoscale functional devices as an electric counterpart to permanent magnets. Here, we find that an electret can be created in LaMnO3 thin films by tip-induced electric fields, with a considerable surface height change, via solid-state electrochemical amorphization. The surface charge density of the formed electret area reaches ~400 nC cm−2 and persists without significant charge reduction for more than a year. The temporal evolution of the surface height, charge density, and electric potential are systematically examined by scanning probe microscopy. The underlying mechanism is theoretically analyzed based on a drift-diffusion-reaction model, suggesting that positively charged particles, which are likely protons produced by the dissociation of water, play crucial roles as trapped charges and a catalysis to trigger amorphization. Our finding opens a new horizon for multifunctional TMOs. A material that generates its own electric field has been developed by scientists in South Korea. An electret is the electrical equivalent of a magnet in that it is formed of two electric poles rather than two magnetic poles. Just as magnetic dipoles give rise to permanent magnets, electret materials create a quasi-permanent electric field. They are useful for microphones, photocopiers and many other electrical devices. Yong-Jin Kim and Chan-Ho Yang from the Korea Advanced Institute of Science and Technology, Daejeon, have created an electret using transition metal oxides. The researchers used a sharp tip of platinum-coated silicon to “write” a charged pattern with a density similar to that of commercially available electrets into a thin film of lanthanum manganite. These patterns persisted for more than a year. An electret can be created in a complex transition metal oxide LaMnO3 by tip-induced electric fields with a considerable surface height change via solid-state electrochemical amorphization. The surface charge density of the formed electret area reaches ~400 nC cm−2 and persists without significant charge reduction for more than a year. Our finding opens a new horizon for multifunctional transition metal oxides by providing an electric counterpart to permanent magnets.

Investigations on leakage current and phase angle characteristics of porcelain and polymeric insulator under contaminated conditions

Abstract: This paper deals with the analysis of leakage current and phase angle characteristics of porcelain and silicone rubber insulator in order to develop a better diagnostic tool to identify the pollution severity of outdoor insulators In this work, laboratory based pollution performance tests are carried out on porcelain and silicone rubber insulator under ac voltage at different pollution levels and relative humidity conditions with sodium chloride as a contaminant Multi resolution signal decomposition (MRSD) using discrete wavelet transform (DWT) is employed to understand the time-frequency characteristics of the leakage current signal Fast Fourier transform (FFT) spectral analysis is adopted to calculate the phase angle values of the applied voltage and leakage current signals Reported results on porcelain and silicone rubber insulators show that the pollution severity of outdoor insulators could be identified from the DWT STD-MRA (standard deviation multi resolution analysis) distortion ratio pattern analysis of leakage current signals

Insulator layers for magnetoresistive transducers

Abstract: A magnetoresistive (MR) transducer has at least one insulative layer made of tetrahedral amorphous carbon (ta-C). The ta-C layer is formed by filtered cathodic arc deposition, has an essentially zero concentration of hydrogen and can serve as a read gap for the transducer. The hydrogen-free t-aC read gap has high thermal conductivity, keeping an adjoining MR sensor from overheating during operation. This extends sensor lifetimes and/or improves sensor performance. The read gap also has low defects and porosity, preventing unwanted electrical conduction or shorting between a sensor and a shield. The high hardness of the read gap resists plasma and chemical etching processes such as ion milling that are used to form the sensor. The increased hardness and reduced defects and porosity allow the read gaps to be made thinner without risking electrical shorting. Other hydrogen-free t-aC layers are employed for other sensor elements where electrical insulation and reduced thickness are important.

Frequency characteristics of leakage current waveforms of an artificially polluted suspension insulator

Abstract: In order to establish a method for monitoring contamination in insulators based on leakage current waveforms and their frequency characteristics, the leakage current waveforms and frequency characteristics of an artificially polluted 180 mm diameter cap and pin type insulator were investigated by the wet contaminant and the clean fog methods at fixed applied voltages. As a result it was found that leakage current waveforms become similar to the symmetrical wave when strong local arcs occur; hence, the intensity of the odd order of harmonic components, e.g. 50, 150, and 250 Hz, is high. Furthermore, it was clarified that the transition of the leakage current waveforms, until flashover occurs, is classified into six stages and that a threshold exists by which the occurrence of flashover can be predicted.

Impact ionization model for dielectric instability and breakdown

Abstract: A mechanism describing the incipient stages of intrinsic dielectric breakdown is formulated for the case of a wide‐band‐gap insulator with a low hole mobility. Dielectric instability results from the tunnel injection of electrons from the cathode contact and the subsequent impact ionization and field distortion which lead to dielectric breakdown. The model, evaluated for the parameters of SiO2, predicts an intrinsic breakdown voltage which approaches a lower limit of V=9+φ for very thin films, where φ is the cathode contact barrier in volts. As a result, both the electric field at breakdown and the critical current density increase rapidly as the film thickness is reduced below 200 A.