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Prof. Ji Chen

ECE 3317. Prof. Ji Chen. Spring 2014. Notes 4 Maxwell’s Equations. Adapted from notes by Prof. Stuart A. Long. Electromagnetic Fields. Four vector quantities E electric field strength [Volt/meter] D electric flux density [ Coulomb/meter 2 ]

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Prof. Ji Chen

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  1. ECE 3317 Prof. Ji Chen Spring 2014 Notes 4 Maxwell’s Equations Adapted from notes by Prof. Stuart A. Long

  2. Electromagnetic Fields Four vector quantities E electric field strength [Volt/meter] D electric flux density [Coulomb/meter2] Hmagnetic field strength [Amp/meter] B magnetic flux density [Weber/meter2] or [Tesla] each are functions of space and time e.g.E(x,y,z,t) J electric current density [Amp/meter2] ρv electric charge density [Coul/meter3] Sources generating electromagnetic fields

  3. length – meter [m] mass – kilogram [kg] time – second [sec] MKS units Some common prefixes and the power of ten each represent are listed below femto - f - 10-15 pico - p - 10-12 nano - n - 10-9 micro - μ - 10-6 milli - m - 10-3 mega - M - 106 giga - G - 109 tera - T - 1012 peta - P - 1015 centi - c - 10-2 deci - d - 10-1 deka - da - 101 hecto - h - 102 kilo - k - 103

  4. Maxwell’s Equations (Time-varying, differential form)

  5. Maxwell James Clerk Maxwell (1831–1879) James Clerk Maxwell was a Scottish mathematician and theoretical physicist. His most significant achievement was the development of the classical electromagnetic theory, synthesizing all previous unrelated observations, experiments and equations of electricity, magnetism and even optics into a consistent theory. His set of equations—Maxwell's equations—demonstrated that electricity, magnetism and even light are all manifestations of the same phenomenon: the electromagnetic field. From that moment on, all other classical laws or equations of these disciplines became simplified cases of Maxwell's equations. Maxwell's work in electromagnetism has been called the "second great unification in physics", after the first one carried out by Isaac Newton. Maxwell demonstrated that electric and magnetic fields travel through space in the form of waves, and at the constant speed of light. Finally, in 1864 Maxwell wrote A Dynamical Theory of the Electromagnetic Field where he first proposed that light was in fact undulations in the same medium that is the cause of electric and magnetic phenomena. His work in producing a unified model of electromagnetism is considered to be one of the greatest advances in physics. (Wikipedia)

  6. Maxwell’s Equations (cont.) Faraday’s law Ampere’s law Magnetic Gauss law Electric Gauss law

  7. Law of Conservation of Electric Charge (Continuity Equation) Flow of electric current out of volume (per unit volume) Rate of decrease of electric charge (per unit volume)

  8. Continuity Equation (cont.) S V Integrate both sides over an arbitrary volume V: Apply the divergence theorem: Hence:

  9. Continuity Equation (cont.) S V Physical interpretation: (This assumes that the surface is stationary.) or

  10. Maxwell’s Equations (cont.)

  11. Maxwell’s Equations (cont.) Time-harmonic (phasor) domain

  12. Constitutive Relations The characteristics of the media relate Dto E and Hto B Free Space c = 2.99792458  108 [m/s] (exact value that is defined)

  13. Constitutive Relations (cont.) # 1 Definition of the Amp: I d Two infinite wires carrying DC currents # 2 Fx2 I x From ECE 2317 (see next slide): Definition of I=1 Amp:

  14. Constitutive Relations (cont.) Force calculation: # 1 I d Two infinite wires carrying DC currents y # 2 Fx2 I x (Lorentz force law for force on a wire) The contour C runs in the reference direction of the current on the wire. Hence we have

  15. Constitutive Relations (cont.) Free space, in the phasor domain: This follows from the fact that (where a is a real number)

  16. Constitutive Relations (cont.) In a material medium: r= relative permittivity r= relative permittivity

  17. Terminology Properties of or Variation Independent of Dependent on space homogenous inhomogeneous frequency non-dispersive dispersive time stationary non-stationary field strength linear non-linear direction of isotropic anisotropic Eor H

  18. Isotropic Materials ε(and μ) are scalarquantities, which means that E|| D(and H|| B) y y x x

  19. Anisotropic Materials ε (or μ) is a tensor (can be written as a matrix) Example: or This results in Eand DbeingNOTproportional to each other.

  20. Anisotropic Materials (cont.) Teflon substrate Fibers Practical example: uniaxial substrate material

  21. Anisotropic Materials (cont.) RT/duroid® 5870/5880/5880LZ High Frequency Laminates The column indicates that v is being measured. http://www.rogerscorp.com/acm/products/10/RT-duroid-5870-5880-5880LZ-High-Frequency-Laminates.aspx

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