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Electrical Aspects
Published in Frank R. Spellman, The Science of Wind Power, 2022
The ratio of the electric charge on each conductor of the capacitor to the potential difference (voltage) between them is known as capacitance. The capacitance value of a capacitor is measure in farads (F). One farad is a very large quantity of capacitance; thus, most commonly used household type capacitors are rated at only a fraction of a farad, often in microfarads (µf—a thousandth of a farad) or smaller in picofarads (a trillionth, pF). Supercapacitors (sometimes used to store energy produced by wind turbines) can store very large electrical charges of thousands of farads.
Introduction to Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
Capacitance of a conductor is the charge produced on it per unit potential applied. Capacitor is a circuit component for storing electric charge, designed to provide a fixed or variable value of capacitance in a circuit. A parallel plate capacitor consists of two metal plates separated by an insulator.
Active Wearable Antennas for 5G and Medical Applications
Published in Albert Sabban, Wearable Systems and Antennas Technologies for 5G, IOT and Medical Systems, 2020
The varactor diode consists of a standard PN junction, see Figure 15.1. The diode is operated under reverse bias conditions and this gives rise to three regions and there is no conduction. The left and right ends of the diode are P and N regions, where current can be conducted. However, around the junction is the depletion region where no current carriers are available. As a result, current can be carried in the P and N regions, but the depletion region is an insulator. This is similar to a capacitor structure. It has conductive plates separated by an insulating dielectric. The capacitance of a capacitor depends on the plate area, the dielectric constant of the insulator between the plates and the distance between the two plates. In the case of the varactor diode, it is possible to increase and decrease the width of the depletion region by changing the level of the reverse bias. This has the effect of changing the distance between the plates of the capacitor. However, to be able to use varactor diodes to their best advantage it is necessary to understand features of varactor diodes, including the capacitance ratio, Q, gamma, reverse voltage and the like.
Study of an interesting physical mechanism of memory effect in nematic liquid crystal dispersed with quantum dots
Published in Liquid Crystals, 2019
Ayushi Rastogi, Kaushlendra Agrahari, Govind Pathak, Atul Srivastava, Jakub Herman, Rajiv Manohar
Capacitance is a measure of charge storage capacity. In the present work, sample cell holder behaves as capacitor plates. These capacitor plates are filled with dielectric material (LC and LC+ QD mixtures). In case of pure nematics, the increase in capacitance in first cycle has been due to the presence of ionic charges in LC medium. However, in LC-QDs mixtures, presence of core/shell QDs effectively stores these ionic charges on the surface of shell and the charge storage capacity of LC-QDs dispersed system increases because as the concentration of QDs increases, LC-QDs and QDs-QDs interaction plays the dominant role apart from LC-substrate and LC-LC interaction. Core/Shell QD are semiconducting in nature. When an electric field is applied to LC-core/shell QDs dispersed system, the dipole moment of core/shell QDs affects the dipole moment of nematic LC molecules up to higher extent. The higher conc. of core/shell QDs increases the number of ions produced by doping therefore dielectric constant increases for dispersed system [3]. When the reverse voltage is applied, the stored charge on the QDs leaks from its surface therefore the capacitance decreases in reverse cycle (Due to charge leakage).
Nanomaterial-based wearable pressure sensors: A minireview
Published in Instrumentation Science & Technology, 2020
As we all know, for a parallel plate capacitor with a fixed area, the capacitance (C) is proportional to the relative permittivity (ε) value of the dielectric layer and inversely proportional to the distance (d) between the two plates. A dielectric layer with a porous structure may be considered to be a composite of air and a dielectric material. The ε value of the polymer usually used for dielectric materials is similar to that of air, and the resulting ε of the composite material does not change significantly. At this time, the capacitance is only related to the distance (d).
Demulsification of crude oil emulsion by capacitative sensor system measurement: introduction to apparatus and methodology
Published in Journal of Dispersion Science and Technology, 2019
Vaibhav Kedar, Sunil S. Bhagwat
A basic capacitor can be constructed by dipping two parallel conductive plates into a dielectric liquid. Capacitance is the measure of the amount of charge that a capacitor can hold at a given voltage. As the water phase in the emulsion rises in the cylinder, the dielectric effect of the liquid changes the effective capacitance of a sensing capacitor which is detected by electronic processing unit coupled to the sensor.