We show that pyroelectric/semiconductor granular systems might effectively operate in terahertz range of frequencies due to coupling between electromagnetic waves and movable electron and/or hole islands, which should exist in such media. The optical properties of the system are similar to uniaxial crystals but, in contrast to usual crystal, the main parameters of the system can be easily tuned by an external electric and magnetic field. Such granular systems may find application as tunable selective absorbers and detectors of terahertz radiation. (c) 2007 Elsevier Ltd. All rights reserved.