Artificial opal-like structures based on spheres and colloidal particles have been fabricated in a
controlled way, presenting optical band-gap properties in the optical frequency range. Nonclose
packed artificial opals have also been fabricated and studied recently. In order to gain a better
understanding of these phenomena, we have studied macroscopic models of nonclose packed fcc
lattices using glass spheres (ε = 7) of 8 mm diameter, and measuring in the microwave region from
10 to 30 GHz. The results have shown a Bragg resonance tunable with filling factor of the opal, and
a strong rejected band similar, also present in close packed samples, much less affected by
compactness. The relation of this high order band with spheres single layer behavior is also
discussed
