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Define inductance of a coil as: • A.k.a self-inductance • Φ: magnetic flux • N: number of turns • I: current flowing in the coil • H (henry) ↔ weber-turn/A • Stands for linear inductor

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Maxwell’s First Equation (2) • Apply to electrostatic & steady magnetic fields • The electric flux per unit volume leaving a vanishingly small volume unit is exactly equal to the volume charge density there

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Energy Density in the Electrostatic Field (1) • Carrying a positive charge (1) from infinity into the field of another fixed positive charge (2) needs work • If the charge 1 is held near the charge 2, it has a potential energy • If then the charge 1 is released, it will accelerate away from the charge 2, acquiring kinetic energy • Problem: f...

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Using Field Sketches to Estimate Capacitance (1) • A conductor boundary is an equipotential surface • The electric field intensity E & the electric flux D are both perpendicular to the equipotential surfaces • E & D are perpendicular to the conductor boundaries & posses zero tangential values • The lines of electric flux, or streamlines, begi...

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Dipole: the plane between the 2 charges is zero potential • That plane can be represented by a vanishingly thin conducting plane, infinite in extent • → the dipole can be substituted for a system of a charge and a conducting plane, & then the fields above the conducting plane obtain equivalence

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Sheet Charge (1) • Charge is distributed on the surface of a plate (e.g. of a parallel-plate capacitor) • Sheet/surface charge density ρS (unit: C/m2)

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Stepping Motors (2) • The angular resolution of a VRM is determined by the number of rotor & stator teeth & can be greatly enhanced by techniques such as castleation. • Have a wide variety of designs & configurations. • The use of permanent magnets in combination with a variable-reluctance geometry can significantly enhance the torque & po...

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Polyphase synchronous motors with permanent – magnet rotors. • Similar to the synchronous machines discussed up to this point, with the exception that the field windings are replaced by permanent magnets  can be analysed with the techniques of this chapter by assuming that the machine is excited by a field current of constant value. • ...

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The phenomenon of hysteresis can be used to produce mechanical torque. • The rotor is a smooth cylinder of magnetically hard steel, without windings or teeth. • The rotor is placed inside a slotted stator carrying distributed windings designed to produce as nearly as possible a sinusoidal space distribution of flux. • In single-phase motors,...

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Magnetic Saturation • Magnetic materials are less than ideal. As their magnetic flux is increased, they begin to saturate. • Therefore saturation may influence the characteristics of the machines. • With saturation, it is more difficult to obtain analytical results. • Saturation characteristics of rotating machines are typically presented i...

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