Propagation of Electromagnetic Signals

Maxwell's equations have been the basis of electromagnetic theory for a century. They were very successful in providing solutions with sinusoidal time variation, but these solutions are outside the causality law and the conservation law for energy. Signal solutions, which satisfy these two laws, generally do not exist, but can be obtained by adding a term for magnetic dipole currents to Maxwell's equations. Such currents are caused by the rotation of magnetic dipoles, ranging from the hydrogen atom to the magnetic compass needle. Many computer plots of the time variation of electric and magnetic field strengths excited by signals are given in this useful book.