Patent ID: 8111138

Claim:
A method for use with a base station and with a plurality of tags, each tag lacking a battery, each tag having a respective unique identifier, each tag having digital logic, each tag defining a first state internal thereto, the method comprising the steps of: at the base station, transmitting a radio-frequency power signal at a first frequency, the first frequency being below 1 MHZ; at each tag among the plurality of tags, receiving the radio-frequency power signal by means of a first antenna, the first antenna comprising a high-Q circuit; at each tag among the plurality of tags, deriving DC power from the radio-frequency power signal; at each tag among the plurality of tags, developing a power-on-reset signal from the radio-frequency power signal; at each tag among the plurality of tags, deriving a first clock signal from the radio-frequency power signal, the first clock signal being higher than the first frequency, the derivation of the first clock signal from the radio-frequency power signal being performed without use of a crystal and without use of a phase-locked loop and without use of a resonator; at each tag among the plurality of tags, resetting the digital logic by the power-on-reset signal, and resetting the first state; at the base station, transmitting a data signal at a second frequency, the data signal comprising a start signal followed by a serial digital message; at each tag among the plurality of tags, receiving the data signal by means of a second antenna, the second antenna comprising a low-Q circuit; at each tag among the plurality of tags, detecting the start signal of the data signal; at each tag among the plurality of tags, comparing the serial digital message of the data signal with the respective unique identifier; at each tag among the plurality of tags, in the event of a match between the serial digital message of the data signal and the respective unique identifier, transmitting a first message by means of the second antenna if the first state was not set, and transmitting a second message by means of the second antenna if the first state was set; at each tag among the plurality of tags, in the event of a match between the serial digital message of the data signal and the respective unique identifier, setting the first state.