Passive RFID tag reader/locator
First Claim
1. A reader/locator system for reading and locating RFID (radio frequency identification) tags, the system comprising:
- a transmitter circuit for transmitting a signal;
a receiver circuit for receiving a received signal;
a frequency changing circuit for providing a frequency changing signal to said transmitter circuit for transmission to said tags, said frequency changing signal having a frequency which changes over time for estimating a range between said system and an RFID tag, said frequency changing signal having a frequency which is swept across a specific frequency band;
a calculation circuit for determining a beat frequency derived from a modulated version of said frequency changing signal received from a specific tag and said frequency changing signal;
whereinsaid system is for use with passive RFID tags;
said beat frequency is used to calculate a distance between said system and a specific tag;
said beat frequency is a difference in frequency between said modulated version of said frequency changing signal received by said system and said frequency changing signal transmitted from said system.
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Abstract
Systems and methods for use in reading and locating passive RFID tags. A reader/locator system sends out a signal with varying frequency. A tag reflects the signal back and the receiver portion of the reader/locator system receives the signal after a certain propagation delay. Since during this propagation delay the transmit frequency has changed, the received signal frequency differs from the one is currently transmitted. The received signal gets mixed with the currently transmitted signal and the resulting beat frequency depends on the frequency variation pattern (which is known) and the signal propagation delay. This beat frequency is directly proportional to the distance between the reader/locator and the RFID tag. The beat frequency can therefore be used to estimate this distance between the reader/locator and the RFID tag. Also provided are methods for determining if an incoming signal is data bearing and a method to obtain a cleaner incoming signal by storing a “carbon footprint” or background clutter and subtracting the carbon footprint from the incoming signal. A novel type of passive RFID tag is also disclosed.
27 Citations
19 Claims
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1. A reader/locator system for reading and locating RFID (radio frequency identification) tags, the system comprising:
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a transmitter circuit for transmitting a signal; a receiver circuit for receiving a received signal; a frequency changing circuit for providing a frequency changing signal to said transmitter circuit for transmission to said tags, said frequency changing signal having a frequency which changes over time for estimating a range between said system and an RFID tag, said frequency changing signal having a frequency which is swept across a specific frequency band; a calculation circuit for determining a beat frequency derived from a modulated version of said frequency changing signal received from a specific tag and said frequency changing signal; wherein said system is for use with passive RFID tags; said beat frequency is used to calculate a distance between said system and a specific tag; said beat frequency is a difference in frequency between said modulated version of said frequency changing signal received by said system and said frequency changing signal transmitted from said system. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method for estimating a distance between a reader/locator system and a passive RFID (radio frequency identification) tag, the method comprising:
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a) transmitting a frequency changing signal from said system to said tag b) receiving at said system a modulated version of said frequency changing signal from said tag c) mixing said modulated version of said frequency changing signal with an original frequency changing signal d) determining a frequency of a result of step c), said frequency of said result being a beat frequency, e) estimating said distance based on said beat frequency. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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19. A long range battery assisted passive RFID tag comprising:
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an on-board battery; a receive amplifier for receiving a received signal and for amplifying said received signal; a signal control block for receiving an amplified received signal from said receive amplifier and for producing a modulated version of said received signal, said modulated version of said received signal being for transmission to an RFID reader/locator; a transmit amplifier for amplifying said modulated version of said received signal; a coupler coupled to at least one antenna and to said receive amplifier and to said transmit amplifier, said coupler coupling said receive amplifier and said transmit amplifier to said at least one antenna wherein said signal control block modulates said received signal based on data to be transmitted to said RFID reader/locator.
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Specification