An RFID tag includes a plastic container having at least one particle that is disposed therein and that is formed from metal or metal coated and/or fabricated from a plurality of different metals. A receiver unit detects RF pulses which are generated by the Triboelectric effect of the particles....http://www.google.com/patents/US7568630?utm_source=gb-gplus-sharePatent US7568630 - RF tag and RF tagging system
