China
Africa
Explore chapters and articles related to this topic
Introduction
Published in Shoogo Ueno, Tsukasa Shigemitsu, Bioelectromagnetism, 2022
Shoogo Ueno, Tsukasa Shigemitsu
The properties of electromagnetic waves necessary for understanding the various effects of electromagnetic fields on biological systems will be briefly presented. They describe the fundamental aspects of electric and magnetic fields as well as the electromagnetic wave. To begin, consider the case where a direct current (DC) power supply is connected to a single wire stretched in the air. The wire is being charged by the electric charge from the power source, and electric lines of force are generated from the wire to the ground. Although the electric lines of force are invisible to the eye, their existence can be confirmed by the fact that when another charged particle is placed between the wire and the ground, it can receive either an attractive or repulsive force in the direction of the electric lines of force. The space where these electric lines of force exist, that is the field where the electric force act, is called electric field. Its strength is defined by the force that acts when a unit charge is placed there. Now, if an alternating current (AC) power source is connected to the same cable instead of a DC power supply, the polarity of the cable charge reverses direction with its frequency. Therefore, the direction of the electric lines of force is also reversing with its frequency, but the pattern of distribution remains the same. In short, an electric field is a region of space over which an electric charge exerts a force on charged objects in its vicinity. The unit of the electric field strength is Newton/Coulomb (N/C), and in practical use, the unit is expressed in Volt/Meter (V/m).
Introduction to Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
Electrical energy is a form of energy arising from the existence of charged bodies. A body is said to be electrically charged if, on rubbing with another body, it acquires the ability to attract light objects, like pieces of paper, fur, etc. The charge produced on a glass rod rubbed with silk is called positive charge, whereas that created on an ebonite rod rubbed with flannel is known as negative charge. Unlike charges attract each other and like charges repel. Electric field is the region of space in which force is exerted by the charge. Electric field strength or intensity (E) at a point in an electric field is defined as the force per unit charge experienced by a small charge placed at that point. Electric current (I) is the flow of electric charge and its magnitude is given by the rate of flow of charge, that is, the amount of charge per unit time. Circuit is the closed path around which electric current flows. Electrical potential (V) at a point in an electric field is the work done in transferring a unit positive charge from infinity to that point, whereas potential difference between two points (ΔV) is the work done in transferring a unit positive charge from one point to the other.
Selection of Sensors, Transducers, and Actuators
Published in Wasim Ahmed Khan, Ghulam Abbas, Khalid Rahman, Ghulam Hussain, Cedric Aimal Edwin, Functional Reverse Engineering of Machine Tools, 2019
Memoon Sajid, Jahan Zeb Gul, Kyung Hyun Choi
Capacitance is defined as the ability of a material to store charge. Capacitive sensors are the second most common type of sensors and have the same reason behind their popularity: low cost and simple integration [4]. In case of capacitive sensors, the transducers are again a simple pair of electrodes that provide an interface between the sensing region and the electrical readout circuit. Capacitive sensors work on two basic principles: change in the dielectric constant of the active area material resulting in change of the capacitance and change in the physical distance between the two transducer electrodes that can be expressed using equation 1.3. Capacitance=(area×ε×dielectriccoefficient)/distance
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).
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.
Dielectric and electro-optical properties of zinc ferrite nanoparticles dispersed nematic liquid crystal 4’-Heptyl-4-biphenylcarbonnitrile
Published in Liquid Crystals, 2020
Fanindra Pati Pandey, Ayushi Rastogi, Rajiv Manohar, Ravindra Dhar, Shri Singh
Capacitance is a measure of charge storage capacity. Capacitor cells are filled with dielectric material (pure and NPs dispersed LCs). In case of pure nematic, the increase with respect to voltage in capacitance in the first cycle has been due to the presence of ionic charges in the nematic medium. However, in NPs dispersed systems, the presence of zinc ferrite NPs effectively stores these ionic charges on its magnetic iron surface and the charge storage capacity of NPs dispersed systems increase. However, in NPs dispersed systems, the presence of zinc ferrite NPs effectively stores these ionic charges on its magnetic iron surface and the charge storage capacity of NPs dispersed systems increase. When the reverse voltage is applied, the stored charge on the NPs leaks from its surface leading to the decrease in capacitance value in reverse cycle. After 15 V applied to bias the charge retention capacity saturates. Therefore, 15 V may be regarded as the saturation voltage for charge retention capacity in pure LC and its NPs dispersed counterparts. Now, when the voltage is applied in the reverse direction the LC molecules do not relax back to its original orientation and therefore, original path is not retraced. As the voltage reduces the charge retention capacity or capacitance also reduces due to the release of ionic charges. The complete removal of bias voltage in reverse direction shows that there exists residual capacitance which indicates pronounced memory in 0.3 wt% system in comparison to pure and other dispersed systems. Therefore, the dielectric hysteresis curve for pure LC and its mixture with NPs confirms the dielectric stored in the form of reminiscence or memory (Table 2). The amount of remnant capacitance indicates the distinguished memory effect in pure LC and its mixtures with NPs. The increased percentage of remnant capacitance for the dispersed system with 0.3 wt% NPs indicates pronounced memory in compression to pure and other dispersed systems. Therefore, the dielectric hysteresis curve for pure LC and its mixture with NPs confirms the dielectric memory effect. The memory effect, in the present work, has been evaluated using the method as described by Rastogi et al. [31]. Figure 12 shows the variation of transmittance as a function of applied DC voltage at 40°C for pure and NPs dispersed LC systems. The memory effect in pristine and NPs dispersed LC systems is clearly confirmed by Figure 12. The percentage of memory parameter has been calculated by the relation [44],