The electromagnetic power is generated and radiated by antennas. Timevarying current radiates electromagnetic waves (radiated electromagnetic fields). Radiation pattern, beam width, directivity, and other major characteristics can be studied using Maxwell’s equations, see Section . We use the vectors of the electric field intensity E, electric flux density D, magnetic field intensity H, and magnetic flux density B. The constitutive equations are D = εE and B = µH where ε is the permittivity; µ is the permiability. It was shown in Section that in the static (time-invariant) fields, electric and magnetic field vectors form separate and independent. | CHAPTER 4 CONTROL OF NANO- AND MICROELECTROMECHANICAL SYSTEMS . FUNDAMENTALS OF ELECTROMAGNETIC RADIATION AND ANTENNAS IN NANO- AND MICROSCALE ELECTROMECHANICAL SYSTEMS The electromagnetic power is generated and radiated by antennas. Timevarying current radiates electromagnetic waves radiated electromagnetic fields . Radiation pattern beam width directivity and other major characteristics can be studied using Maxwell s equations see Section . We use the vectors of the electric field intensity E electric flux density D magnetic field intensity H and magnetic flux density B. The constitutive equations are D eE and B pH where is the permittivity U is the permiability. It was shown in Section that in the static time-invariant fields electric and magnetic field vectors form separate and independent pairs. That is E and D are not related to H and B and vice versa. However for timevarying electric and magnetic fields we have the following fundamental electromagnetic equations r. y H x y z t V X E x y z t -p-- n y y E x y z t . Vx H x y z t sE x y z t ----- J x y z t V-E X. y z t P ZH V- H x y z t 0 where J is the current density and using the conductivity S we have J SE pv is the volume charge density. The total current density is the sum of the source current Js and the conduction current density SE due to the field created by the source Js . Thus JS J S SE. The equation of conservation of charge continuity equation is f J - ds -d f pvdv dtJv and in the point form one obtains V-J x y z t -ipv x-y z-t dt 2001 by CRC Press LLC Therefore the net outflow of current from a closed surface results in decrease of the charge enclosed by the surface. The electromagnetic waves transfer the electromagnetic power. That is the energy is delivered by means of electromagnetic waves. Using equations Vx E -u and Vx H J M dt dt we have dE dt V ExH H VxE -E VxH -H m -E edE J . dt dt In a media where the constitute parameters are constant time-invariant we have the so-called .
