METHOD TO INCREASE RFID TAG SENSITIVITY
First Claim
1. A radio-frequency identification (RFID) tag comprising:
- a main antenna that receives a radio-frequency (RF) signal from an RFID reader and wirelessly harvests power from the RF signal;
a switch connected to the main antenna and a separate length of antenna; and
a circuit connected to a different portion of the main antenna than the switch, the circuit being configured to;
vary a reflection coefficient of the main antenna to transmit a reflected signal to the RFID reader, the reflected signal having high reflectance periods when an amount of reflectance by the main antenna of the RF signal is greater than a predetermined amount, and low reflectance periods when an amount of reflectance by the main antenna of the RF signal is lower than the predetermined amount;
reduce the reflectance of the main antenna below a predefined amount during the high reflectance periods to enable wireless power harvesting during the high reflectance periods by changing a resonant frequency of the main antenna to generate the high reflectance periods and low reflectance periods; and
change the resonant frequency by controlling the switch to intermittently connect the separate length of antenna to the main antenna.
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Accused Products
Abstract
A radio-frequency identification (RFID) tag with improved sensitivity includes an antenna that receives a radio-frequency (RF) signal and wireless power from an RFID reader. The RFID tag further includes a circuit that varies a reflection coefficient of the antenna to transmit a reflected signal to the reader, the reflected signal having periods of high reflectance when a relatively high amount of the RF signal is reflected, and low reflectance periods when a relatively low amount of the RF signal is reflected. The reflectance of the antenna is sufficiently low during the high reflectance periods to enable wireless power reception during the high reflectance periods.
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Citations
20 Claims
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1. A radio-frequency identification (RFID) tag comprising:
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a main antenna that receives a radio-frequency (RF) signal from an RFID reader and wirelessly harvests power from the RF signal; a switch connected to the main antenna and a separate length of antenna; and a circuit connected to a different portion of the main antenna than the switch, the circuit being configured to; vary a reflection coefficient of the main antenna to transmit a reflected signal to the RFID reader, the reflected signal having high reflectance periods when an amount of reflectance by the main antenna of the RF signal is greater than a predetermined amount, and low reflectance periods when an amount of reflectance by the main antenna of the RF signal is lower than the predetermined amount; reduce the reflectance of the main antenna below a predefined amount during the high reflectance periods to enable wireless power harvesting during the high reflectance periods by changing a resonant frequency of the main antenna to generate the high reflectance periods and low reflectance periods; and change the resonant frequency by controlling the switch to intermittently connect the separate length of antenna to the main antenna. - View Dependent Claims (2, 3, 4, 5)
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6. A radio-frequency identification (RFID) tag comprising:
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a main antenna that receives a radio-frequency (RF) signal from an RFID reader and wirelessly harvests power from the RF signal; and a circuit that is configured to vary a reflection coefficient of the main antenna to transmit a reflected signal to the RFID reader, the reflected signal having high reflectance periods when an amount of reflectance by the main antenna of the RF signal is greater than a predetermined amount, and low reflectance periods when an amount of reflectance by the main antenna of the RF signal is lower than the predetermined amount, wherein the circuit increases a duty cycle of the low reflectance periods and decreases a duty cycle of the high reflectance periods to increase a time period of wireless power transmission. - View Dependent Claims (7, 8, 9, 10)
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11. A radio-frequency identification (RFID) tag comprising:
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a main antenna that receives a radio-frequency (RF) signal from an RFID reader and wirelessly harvests power from the RF signal; and a circuit that is configured to vary a reflection coefficient of the main antenna to transmit a reflected signal to the RFID reader, the reflected signal having first reflectance periods, and second reflectance periods when an amount of reflectance by the main antenna of the RF signal is different than during the first reflectance periods, wherein the main antenna continuously harvests power while transmitting the reflected signal to the RFID reader. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification