Can you please define what a transponder is?
An RFID transponder is any system that uses radio waves to identify and locate something. There are many different types of radio frequency identification technology. There are passive RFID systems that operate at low, high and ultrahigh frequencies, and there are active RFID systems that operate at 433 MHz, 915 MHz and 2.45 GHz.
Most RFID systems store a serial number on a microchip for identification purposes. The chip is attached to a radio antenna, enabling it to communicate with a reader. But there are systems that do not use chips at all. A company called Inkode embeds tiny metal fibers randomly in paper (see 1-Cent RFID Tags for Supermarkets). When the fibers are hit with radio waves, the waves bounce back with a unique signature that allows a piece of paper or label to be uniquely identified. Another company, Somark Innovations, has created inks that resonate at different frequencies. These can be tattooed onto animals to identify them uniquely (see RFID Tattoos to Make a Mark on Cattle Tagging).
Each system has its own characteristics that make it appropriate for some applications and not for others.
—Mark Roberti, Founder and Editor, RFID Journal
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