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Magnetic Circuits
Published in Ahmad Shahid Khan, Saurabh Kumar Mukerji, Electromagnetic Fields, 2020
Ahmad Shahid Khan, Saurabh Kumar Mukerji
Consider a time-invariant, linear, lossless, uniformly wound long cylindrical inductor with time-varying current i at its terminals. The voltage (v), applied across its terminals opposes the induced electromotive force (EMF). The EMF (e), is caused due to the change in the magnetic flux linking the inductor winding (coil). Faraday’s law of electromagnetic induction (discussed in Chapter 15), states that the EMF induced around a closed path c, is equal to the rate of decrease of the magnetic flux Φc linking to the closed path c. Therefore, e=−dΦcdt
Switch Mode Power Converters
Published in K. Kit Sum, Switch Mode Power Conversion, 2017
To understand the nature of the three basic configurations, it is convenient to recall Lenz's law. In 1834, Lenz, a Russian physicist, supplemented Faraday's work on electromagnetic induction by pointing out that the direction of the induced emf is the same as that of a current whose magnetic action would neutralize or oppose the flux change. This statement is known as Lenz's law.
A.c. theory
Published in W. Bolton, Higher Engineering Science, 2012
Faraday's law of electromagnetic induction states that the size of the induced e.m.f is proportional to the rate of change of flux linked by a coil. One way of changing the flux linked by a coil when in a magnetic field is to rotate the coil so that the angle between the field direction and the plane of the coil changes (Figure 8.1(a)). When the plane of the coil is at right angles to a field of flux density B then the flux linked per turn of wire is a maximum and given by BA, where A is the area of the coil. When the plane of the coil is parallel to the field then there is no flux linked by the coil. When the axis of the coil is at an angle θ to the field direction then the flux linked per turn is Φ = BA cos θ. The flux linked thus changes as the coil rotates. If the coil rotates with an angular velocity ω then its angle θ at a time t is ωt and so the flux linked per turn varies with time according to: Φ=BAcosωt
Performance optimization of energy harvesting solutions for 0.18um CMOS circuits in embedded electronics design
Published in Cogent Engineering, 2020
Electromagnetic Energy Harvesting can be achieved by the principle of electromagnetic induction. Electromagnetic induction is defined as the process of generating voltage in a conductor by changing the magnetic field around the conductor. One of the most effective ways of producing electromagnetic induction for energy harvesting is with the help of permanent magnets, a coil and a resonating cantilever beam (Cevik et al., 2015). El-Hami, et al. describe a vibration-based electromechanical power generator that consisted of a cantilever beam and a pair of magnets. Since the late 1990 s, various researchers (Martinez et al., 2018; Peters et al., 2011; Qiang et al., 2010; Shenck & Paradiso, 2001; Sterken et al., 2003) have identified the techniques employed to generate power from electromagnetic resources. The electromagnetic generators designed have the advantage of being enclosed and can be protected from the outside environment. Electromagnetic induction provides the advantage of improved reliability and reduced mechanical damping as there would not be any mechanical contact between any parts; also, no separate voltage source is required. However, electromagnetic materials are bulky in size and are complicated to integrate with MEMs. Bayrashev, et al. and Staley, et al. concentrated on harvesting energy from magnetostrictive materials (Li & Bashirullah, 2017). These magnetostrictive materials are used to build actuators and sensors as they have the capability of converting magnetic energy into kinetic energy. These materials are highly flexible, are suited to high frequency vibration and overcome the limitations of the other vibrational sources. To harvest energy by using magnetostrictive materials and provide power to wireless sensors in Structural Health Monitoring is explained by Wang and Yuan of North Carolina State University. It is difficult to integrate these materials with MEMs. The Electrostatic and Piezoelectric harvesters are capable of producing voltage ranging 2–10 V, whereas the electromagnetic harvesters have limitation of producing max. voltage of 0.1 V. The advantage of using mechanical vibrations to harvest energy is that they are the most prevalent energy source available in many environments. In summary, three main converters enable to turn mechanical energy into electricity: piezoelectric devices, electromagnetic devices and electrostatic devices (Table 2). 1-Piezoelectric devices: they use piezoelectric materials that present the ability to generate charges when they are under stress/strain. 2-Electromagnetic devices: they are based on electromagnetic induction and ruled by Lenz’s law. An electromotive force is generated from a relative motion between coil and magnet. 3-Electrostatic devices: they use a variable capacitor structure to generate charges from a relative motion between two plates.