The theoretical basis for the design comes from
the effective medium theory; MMs can be characterized
by complex permittivity ˜ε(ω) and permeability
µ˜(ω). In practice, loss is measured by the amount
of EM power absorbed, which is defined as A(ω) =
1 − T(ω) − R(ω), where R(ω) and T(ω) represent
the reflectivity and transmission as functions of frequency
ω, respectively. It is possible to absorb both
the incident electric and magnetic fields tremendously
by properly tuning ˜ε(ω) and ˜µ(ω), and achieve perfect
impedance-matching to free space. To achieve
unity absorption of the MA, simultaneously minimizing
R(ω) and T(ω) to near zero is necessary.