Optimum Transparent Absorbers of Electromagnetic Waves

Electromagnetic wave absorbers consisting of thin transparent sheets of conducting medium are studied in this paper. In particular, a result known since the 1930 s that, for plane waves normally incident on a conducting sheet, the maximum achievable absorption is one half of the incident power is proved and generalized to multiple layers. The case of arbitrary incidence angle and polarization is discussed and illustrated with examples, and the resistance providing maximum absorption when the angle of incidence and polarization is arbitrary is derived. We also consider an absorber consisting of two resistive sheets and optimize its resistances to yield the best possible absorption for normal incidence, such that the total absorption at all frequencies is ges 0.5. Finally, conditions for an optimal absorber for a spherical sheet surrounding a dipole antenna are derived.