TIRFID low frequency tags operate on a carrier frequency of 134.2 kHz. The "uplink" from the RFM Reader (Radio Frequency Module) to the RFID Tag Transponder is a Frequency Shift Keyed (FSK) transmission with a bandwidth of 25 kHz. The "downlink" from the RFID Tag Transponder to the RFM is an Amplitude Shift Keyed (ASK) transmission replying with identification and stored data information.
Classical radio transmission is comprised of a combination of an electrostatic field and a magnetic field component. These fields are depicted as orthogonal vectors that propagate a transverse electro-magnetic (TEM) disturbance that can be received at a distance from the source. Although Low Frequency RFID Tags are generating TEM waves their magnetic component becomes most the significant source of energy transfer for the link of the near field.
As the energy is coupled from the RFM to the antenna, magnetic flux waves extend into the space surrounding the coils. Similar to a transformer coupling energy from its primary winding to its secondary winding, the expanding field from the transmitter antenna coils can induce a voltage in a second coil in its proximity, such as an antenna coil within an RFID tag present in the field. The induced voltage in the tag's coil is utilized to charge a capacitor. Acting as a temporary battery, the capacitor then powers a chip that provides the data and intelligent protocol for transponding back to the RFM.
This is what they look like:
And this is what you use to stick them in:
Yes, it hurts, bleeds, and yes I'm serious. :)