De-tuned RFID tags having increased sensitivity
A radio-frequency identification (RFID) tag includes an antenna with a relatively large number of turns and is de-tuned from an excitation frequency of an RFID reader. The RFID tag, when grouped with other similar RFID tags, uses resonant inductive coupling to channel the magnetic flux density field (B-field) through the group to power each of the tags in the group. As a result, the sensitivity is increased as compared to using an antenna having a smaller number of turns.
1 . A radio-frequency identification (RFID) tag, comprising:
RFID tag electronics; and
an antenna assembly coupled to the RFID electronics, wherein the antenna assembly includes an antenna, wherein the antenna has more than 5 turns and has a capacitance,
wherein the RFID tag has a resonant frequency resulting from the antenna assembly, wherein the resonant frequency of the RFID tag is higher than an excitation frequency of a transmission generated by an RFID reader,
wherein the RFID tag is one of a plurality of RFID tags in proximity in a grouping, wherein the grouping of RFID tags shapes a magnetic flux density field of the transmission generated by the RFID reader through the grouping of RFID tags, wherein the grouping of RFID tags has a resonant frequency that is lower than the resonant frequency of each of the plurality of RFID tags considered individually due to resonant coupling, and wherein the transmission generated by the RFID reader powers the RFID tag electronics via the resonant coupling, and
wherein a sensitivity of the RFID tag increases as a number of turns of the antenna increases.
2 . The RFID tag of claim 1 , further comprising:
a circuit element connected in series between the antenna and the RFID tag electronics, wherein the circuit element includes at least one of a capacitor, an inductor, and a resistor.
3 . The RFID tag of claim 2 , wherein the capacitor has a capacitance of between 1.8 and 3.0 pF.
4 . The RFID tag of claim 2 , wherein the capacitor has a capacitance of between 1.8 and 3.9 pF.
5 . The RFID tag of claim 2 , wherein the circuit element is a component of the antenna assembly.
6 . The RFID tag of claim 1 , wherein the capacitance of the antenna assembly results from a self-capacitance of the antenna.
7 . The RFID tag of claim 1 , wherein the antenna assembly further comprises a capacitor in parallel with the antenna.
8 . The RFID tag of claim 7 , wherein the capacitor in parallel with the antenna has a capacitance of between 0.125 and 1.0 pF.
9 . The RFID tag of claim 1 , wherein the RFID electronics further comprises a capacitor in parallel with the antenna.
10 . The RFID tag of claim 1 , wherein the antenna has between 6 and 19 turns.
11 . The RFID tag of claim 1 , wherein the antenna has between 20 and 34 turns.
12 . The RFID tag of claim 1 , wherein the antenna has 35 or more turns.
13 . The RFID tag of claim 1 , wherein a read range between the RFID tag and the RFID reader increases as the number of turns of the antenna increases.
14 . The RFID tag of claim 1 , wherein a resonant frequency of the grouping of RFID tags is within 10% above and 10% below the excitation frequency of the RFID reader.
15 . A system for determining locations of objects in a gaming environment, the system comprising:
a plurality of radio-frequency identification (RFID) antennas arranged at a plurality of locations on a gaming table;
one or more RFID readers coupled to the plurality of RFID antennas; and
a plurality of RFID tags, wherein a given RFID tag of the plurality of RFID tags comprises:
RFID tag electronics; and
an antenna assembly coupled to the RFID electronics, wherein the antenna assembly includes an antenna, wherein the antenna has more than 5 turns and has a capacitance,
wherein the given RFID tag has a resonant frequency resulting from the antenna assembly, wherein the resonant frequency of the given RFID tag is higher than an excitation frequency of a transmission generated by the one or more RFID readers,
wherein the given RFID tag is one of the plurality of RFID tags in proximity in a grouping, wherein the grouping of RFID tags shapes a magnetic flux density field of the transmission generated by the one or more RFID readers through the grouping of RFID tags, wherein the grouping of RFID tags has a resonant frequency that is lower than the resonant frequency of each of the plurality of RFID tags considered individually due to resonant coupling, and wherein the transmission generated by the one or more RFID readers powers the RFID tag electronics via the resonant coupling, and
wherein a sensitivity of the given RFID tag increases as a number of turns of the antenna increases.
16 . The system of claim 15 , wherein the given RFID tag further comprises:
a circuit element connected in series between the antenna and the RFID tag electronics, wherein the circuit element includes at least one of a capacitor, an inductor, and a resistor.
17 . The system of claim 15 , wherein the capacitance of the antenna assembly results from a self-capacitance of the antenna of the given RFID tag.
18 . The system of claim 15 , wherein the antenna assembly further comprises a capacitor in parallel with the antenna of the given RFID tag.
19 . The system of claim 15 , wherein the RFID electronics further comprises a capacitor in parallel with the antenna of the given RFID tag.
20 . The system of claim 15 , wherein the antenna of the given RFID tag has 35 or more turns.