Method to increase RFID tag sensitivity

• US 10,452,968 B2
• Filed: 06/14/2017
• Issued: 10/22/2019
• Est. Priority Date: 06/14/2017
• Status: Active Grant

• Current Assignee: Intermec (Honeywell International Inc.)
• Original Assignee: Intermec (Honeywell International Inc.)
• Inventors: Nikitin, Pavel, Kelly, Stephen J., Martinez, Rene
• Primary Examiner(s): Lee, Michael G
• Assistant Examiner(s): Tardif, David
• Application Number:
  US15/622,839
• Publication Number:
  US 20180365549A1
• Time in Patent Office: 860 Days
• Field of Search: 235487
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 19/07773 Antenna details antennas for wireless devices, e.g. RFID tags, in general H01Q1/22
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10158 methods and means used by the interrogation device for reliably powering the wireless record carriers using an electromagnetic interrogation field
• CPC Class Codes: H01Q 1/2225 used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
• CPC Class Codes: H01Q 1/248 provided with an AC/DC converting device, e.g. rectennas
• CPC Class Codes: H01Q 15/0006 Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices H01Q15/12, H01Q15/22, H01Q15/24 take precedence

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.

Claims

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 a first portion of the main antenna and a separate length of antenna; and

a circuit connected to a second portion of the main antenna, wherein the second portion of the main antenna is different than the first portion of the main antenna, 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;

control the switch to intermittently connect the separate length of antenna to the main antenna;

change a resonant frequency of the main antenna, based on the controlled switching, to generate a high reflectance period and a low reflectance period; and

reduce a reflectance of the main antenna below a predefined amount during the high reflectance period without shorting the main antenna to enable the main antenna for continuous wireless power harvesting while transmitting the reflected signal to the RFID reader, wherein the reflectance of the main antenna during the high reflectance period is reduced based on the change in the resonant frequency of the main antenna.

2. The RFID tag of claim 1, wherein the predetermined amount is a reflection coefficient magnitude of between 0 and 0.5.

3. The RFID tag of claim 1, wherein the predefined amount is a reflection coefficient magnitude of 0.5.

4. The RFID tag of claim 1, wherein the circuit is an application-specific integrated circuit (ASIC).

5. The RFID tag of claim 1, wherein the main antenna is a linearly polarized antenna.

6. 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; 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 a high reflectance period when an amount of reflectance by the main antenna of the RF signal is greater than a predetermined amount, and a low reflectance period when an amount of reflectance by the main antenna of the RF signal is lower than the predetermined amount,

wherein a reflectance of the main antenna is reduced below a predefined amount during the high reflectance period without shorting the main antenna to enable the main antenna for continuous wireless power harvesting while transmitting the reflected signal to the RFID reader, wherein the reflectance of the main antenna during the high reflectance period is reduced based on a change in a resonant frequency of the main antenna,

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.

7. The RFID tag of claim 6, wherein the predetermined amount is a reflection coefficient magnitude of between 0 and 1.

8. The RFID tag of claim 6, wherein the circuit increases the duty cycle of the low reflectance periods to greater than 50%.

9. The RFID tag of claim 6, wherein the circuit is an application-specific integrated circuit (ASIC).

10. The RFID tag of claim 6, wherein the main antenna is a linearly polarized antenna.

11. 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; 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 a first reflectance period and a second reflectance period when an amount of reflectance by the main antenna of the RF signal is different than during the first reflectance period,

wherein a reflectance of the main antenna is reduced below a predefined amount during the first reflectance period without shorting the main antenna to enable the main antenna to continuously harvest power while transmitting the reflected signal to the RFID reader, wherein the reflectance of the main antenna is reduced based on a change in a resonant frequency of the main antenna.

12. The RFID tag of claim 11, wherein the circuit changes the resonant frequency of the main antenna to generate the first and second reflectance period.

13. The RFID tag of claim 12, wherein the circuit adds a separate length of antenna to the main antenna during the first reflectance period.

14. The RFID tag of claim 13, further comprising:

a switch that adds the separate length of antenna by connecting the separate length of antenna to the main antenna during the first reflectance period, the switch being located on a first portion of the main antenna and the circuit being located on a second portion of the main antenna, wherein the first portion of the main antenna is different than the second portion of the main antenna.

15. The RFID tag of claim 11,

wherein the main antenna includes a first antenna for receiving the RF signal, and a second antenna for receiving power, and

the second antenna continues to absorb a portion of the RF signal during the first reflectance period and the second reflectance period to generate a low reflectance to enable wireless power harvesting during both the first reflectance period and the second reflectance period.

16. The RFID tag of claim 11, further comprising:

a switch controlled by the circuit that connects an RF impedance to the main antenna during the first reflectance period.

17. The RFID tag of claim 11, wherein the amount of reflectance by the main antenna of the RF signal is greater than the predetermined amount during the first reflectance period, and

the amount of reflectance by the main antenna of the RF signal is lower than the predetermined amount during the second reflectance period.

18. The RFID tag of claim 11, wherein the amount of reflectance of the main antenna of the RF signal during the first reflectance period is of greater magnitude to the amount of reflectance of the main antenna of the RF signal during the second reflectance period.

19. The RFID tag of claim 11, wherein the circuit is an application-specific integrated circuit (ASIC).

20. The RFID tag of claim 11, wherein the main antenna is a linearly polarized antenna.