Power management of transponders and sensors in an RFID security network

A method for managing the power of an RFID transponder having an associated sensor and being configured for use in a security network including at least a first RFID reader, the method comprising:

• (a) sending signals from the RFID transponder to the first RFID reader at a second frequency representing relatively low power;
• (b) transmitting return signals from the first RFID reader at a first frequency representing relatively high power;
• (c) receiving the return signals at at least one diode of the RFID transponder;
• and
• (d) applying at least one of an on-off keyed modulation and an amplitude modulation scheme to the signal obtained by the diode.

A security network comprising:

• at least a first RFID reader transmitting signals at a first frequency and including:
• (a) a first diversity antenna sending a first message,
• (b) a second diversity antenna sending a second message, and
• (c) a receiver;
• and
• an RFID transponder having an associated sensor, the RFID transponder including:
• (a) a processor controlling other components of the RFID transponder,
• (b) transmitter circuitry coupled to a transmit antenna for transmitting signals to the first RFID reader at a second frequency,
• (c) a receive antenna receiving signals in a frequency band that includes the first frequency,
• (d) at least one RF diode obtaining the signal from the receive antenna and configured to output a power envelope signal representing the power level of the signal obtained from the receive antenna, and
• (e) an amplifier coupled to the output of the RF diode and amplifying the power envelope signal received from the RF diode;
• wherein the processor receives the amplified power envelope signal and decodes any data that have been encoded using an on-off keyed modulation scheme applied to the signal obtained from the receive antenna.