  Binary disordered systems are usually obtained by mixing two ingredients in
variable proportions: conductor and insulator, or conductor and
super-conductor. and are naturally modeled by regular bi-dimensional or
tri-dimensional lattices, on which sites or bonds are chosen randomly with
given probabilities. In this article, we calculate the impedance of the
composite by two independent methods: the so-called spectral method, which
diagonalises Kirchhoff's Laws via a Green function formalism, and the Exact
Numerical Renormalization method (ENR). These methods are applied to mixtures
of resistors and capacitors (R-C systems), simulating e.g. ionic
conductor-insulator systems, and to composites consituted of resistive
inductances and capacitors (LR-C systems), representing metal inclusions in a
dielectric bulk. The frequency dependent impedances of the latter composites
present very intricate structures in the vicinity of the percolation threshold.
We analyse the LR-C behavior of compounds formed by the inclusion of small
conducting clusters (``$n$-legged animals'') in a dielectric medium. We
investigate in particular their absorption spectra who present a pattern of
sharp lines at very specific frequencies of the incident electromagnetic field,
the goal being to identify the signature of each animal. This enables us to
make suggestions of how to build compounds with specific absorption or
transmission properties in a given frequency domain.
