where [ W α α ] = [ W ] is the energy flow through the surrounding surface, and [ I inc ] = [ W m 2 ] is the intensity of the incident wave. For a plane wave the intensity is going to be I inc = | E | 2 / ( 2 η η ) , where η η = μ μ μ μ 0 / ( ε ε ε ε 0 ) is the impedance of the host medium.