Is this something universal?
No, not all antennas are composed of metal. Passive low-frequency (LF) and high-frequency (HF) antennas are made of copper, and many passive ultrahigh-frequency (UHF) transponders contain etched copper antennas as well. Many also use aluminum, but antennas can be printed with metallic inks (there is usually silver in the ink). Some also use conductive polymers. Generally speaking, metallic antennas perform better (that is, they have a longer read range) than printed inks or polymer antennas.
—Mark Roberti, Founder and Editor, RFID Journal
Can SharePoint and RFID Be Used in Tandem? »