Roll-to-roll production of RFID tags
A method and apparatus for manufacturing thin RFID tags adapted to be mounted proximate an interfering substance, such as metal or liquid. Each tag comprises: a web substrate having a predetermined thickness; an antenna attached to the substrate; and an RFID integrated circuit connected to the antenna, the RFID integrated circuit comprising a tank circuit adapted to be tuned in response to an RF signal after the tag has been mounted proximate the interfering substance. In one embodiment, the tag is manufactured using roll-to-roll manufacturing technology.
1. A radio frequency identification (RFID) tag comprising:
a substrate having a predetermined thickness;
an antenna mounted on the substrate;
a variable tank circuit coupled to the antenna;
a tuner coupled to the variable tank circuit, wherein, when the RFID tag is not exposed to an interfering substance, the RFID tag has a first resonant frequency, and when the RFID tag is exposed to the interfering substance, impedance of the antenna is changed causing a change in resonant frequency of the RFID tag to a second resonant frequency, wherein the tuner adjusts impedance of the variable tank circuit to substantially compensate for the antenna impedance change thereby adjusting the resonant frequency of the RFID tag to be substantially the first resonant frequency, and wherein the tuner generates a digital value indicative of an amount of impedance adjustment of the variable tank circuit, wherein the digital value is operable to be interpreted by a radio frequency (RF) reader to determine characteristics of the interfering substance, wherein the characteristics include one or more of a proximity of the interfering substance to the RFID tag, an environmental condition, a metal, a free space, and a liquid; and
a transmitter operable to convert the digital value into an outbound RF signal and to transmit the outbound RF signal to the RF reader.
2. The RFID tag of claim 1 wherein the substrate comprises a roll of flexible web and wherein thickness of the substrate is within the range of 0.02 millimeter (mm) to 0.2 mm.
3. The RFID tag of claim 1 further comprises:
an integrated circuit mounted on the substrate, wherein the integrated circuit includes the variable tank circuit, the tuner, and the transmitter.
4. The RFID tag of claim 3 further comprises:
a protective layer attached to a first surface of the substrate and substantially covering the antenna and the integrated circuit.
5. The RFID tag of claim 4 further comprises:
an adhesive layer attached to a second surface of the substrate, wherein the second surface is substantially opposite of the first surface of the substrate.
6. The RFID tag of claim 1 further comprises:
a power regulator operable to convert an inbound radio frequency (RF) signal into a direct current (DC) power supply voltage; and
a power detector operable to detect a received signal strength of the inbound RF signal and generate a second digital value indicative of the received signal strength.
7. The RFID tag of claim 1 wherein the tuner is further operable to:
adjust the impedance of the variable tank circuit to the digital value within a range of digital values, wherein the range of digital values corresponds to impedance adjustments of the variable tank circuit when the RFID tag is in free space, in a liquid, or within 1 millimeter of metal.
8. A method for manufacturing a radio frequency identification (RFID) tag, the method comprising:
connecting a plurality of RFID integrated circuits to a web substrate, wherein the web substrate has attached thereto a plurality of antennas, wherein an RFID integrated circuit of the plurality of RFID integrated circuits is electrically connected an antenna of the plurality of antennas, wherein the RFID integrated circuit includes:
a variable tank circuit coupled to the antenna;
a tuner coupled to the variable tank circuit, wherein, when the RFID tag is not exposed to an interfering substance, the RFID tag has a first resonant frequency, and when the RFID tag is exposed to the interfering substance, impedance of the antenna is changed causing a change in resonant frequency of the RFID tag to a second resonant frequency, wherein the tuner adjusts impedance of the variable tank circuit to substantially compensate for the antenna impedance change thereby adjusting the resonant frequency of the RFID tag to be substantially the first resonant frequency, and wherein the tuner generates a digital value indicative of an amount of impedance adjustment of the variable tank circuit, wherein the digital value is operable to be interpreted by a radio frequency (RF) reader to determine characteristics of the interfering substance, wherein the characteristics include one or more of a proximity of the interfering substance to the RFID tag, an environmental condition, a metal, a free space, and a liquid; and
a transmitter operable to convert the digital value into an outbound RFsignal and to transmit the outbound RF signal to the RF reader;
adhering a layer of a first surface of the web substrate; and
separating the RFID integrated circuit and the antenna from the web substrate to produce the RFID tag.
9. The method of claim 8 , wherein the web substrate comprises a roll of flexible web.
10. The method of claim 8 , wherein the RFID tag is manufactured using roll-to-roll manufacturing technology.
11. The method of claim 8 further comprises:
attaching the plurality of antennas to the web substrate using one or more of printing, depositing, and adhering.
12. The method of claim 8 , wherein the thickness of the web substrate is preferably within the range of 0.02 mm to 0.2 mm.
13. The method of claim 8 wherein the interfering substance comprises a selected one of a metal and a liquid.