초록 ▼

A method of reading multiple RFID tags located in a field of an interrogating antenna is based on periodic transmissions from the tags with large, non-transmission intervals between transmissions. The non-transmission intervals are fixed for a given tag, but are random between tags due to manufactur

A method of reading multiple RFID tags located in a field of an interrogating antenna is based on periodic transmissions from the tags with large, non-transmission intervals between transmissions. The non-transmission intervals are fixed for a given tag, but are random between tags due to manufacturing tolerances in electrical components from which the tag is constructed, such that no coordination of transmissions from the interrogating antenna is required.

대표청구항 ▼

[ We claim:] [1.] A method of reading data from a plurality of radio frequency intelligent devices located within an interrogation zone comprising the steps of:an interrogation device transmitting a generally continuous interrogation signal, the interrogation signal comprising an electromagnetic fie

[ We claim:] [1.] A method of reading data from a plurality of radio frequency intelligent devices located within an interrogation zone comprising the steps of:an interrogation device transmitting a generally continuous interrogation signal, the interrogation signal comprising an electromagnetic field at a first predetermined radio frequency, wherein a strength of the electromagnetic field defines the interrogation zone;a plurality of radio frequency intelligent devices located within the interrogation zone being acted upon by the electromagnetic field, the electromagnetic field inducing a voltage in each intelligent device which provides power to the intelligent devices;each of the plurality of intelligent devices within the interrogation zone reading a respective prestored data field and repeatedly transmitting a message stored therein at a second predetermined radio frequency at predetermined periodic intervals with a fixed length non-transmission interval between each transmission interval, wherein a length of the non-transmission interval is much greater than a length of the message transmission interval, the length of the non-transmission interval for each intelligent device being different due solely to manufacturing tolerances in electrical components of the intelligent devices; andthe interrogation device reading the message transmissions of each of the plurality of intelligent devices, wherein a probability of two or more of the plurality of intelligent devices transmitting their respective messages simultaneously is significantly reduced due to variations among the intelligent devices in the fixed non-transmission time and by making the length of the non-transmission interval much greater than the length of the message transmission interval, and wherein the manufacturing tolerances are sufficiently large so as to significantly vary the fixed non-transmission time among the plurality of intelligent devices and thereby significantly reduce the probability that two or more of a plurality of intelligent devices will transmit their respective messages simultaneously.