An expression is derived for the scattering of electromagnetic radiation by small, nonabsorbing, compound ellipsoids that contain an inner ellipsoidal region and an outer confocal ellipsoidal shell. For certain combinations of dielectric constant, the scattering is zero, thereby rendering the body invisible.
Milton Kerker, "Invisible bodies," J. Opt. Soc. Am. 65, 376-379 (1975)