  We show that resonant tunneling of electromagnetic fields can occur through a
three-layer structure composed of a single-negative (i.e., either
negative-permittivity or negative-permeability) slab paired with bi-layer made
of double-positive (i.e., positive permittivity and permeability) media. In
particular, one of the two double-positive media can be chosen arbitrarily
(even vacuum), while the other may exhibit extreme (either near-zero or very
high) permittivity/permeability values. Our results on this counterintuitive
tunneling phenomenon also demonstrate the possibility of synthesizing
double-positive slabs that effectively exhibit single-negative-like
wave-impedance properties within a moderately wide frequency range.
