Non-Linearities in Passive RFID Systems: Third Harmonic Concept and Applications

By Gianfranco Andia, Yvan Duroc and Smail Tedjini

This book concerns a new paradigm in the field of UHF RFID systems: the positive exploitation of nonlinear signals generated by the chips integrated into the RFID tags.

After having recalled the main principles in RFID technology and its current challenges notably with the emergence of Internet of Things or the smart connected environments, the purpose is to focus on the presence of nonlinearities produced by the nonlinear circuits of RFID chips: effects, nuisances and solutions but also and especially use of the phenomena.   

The presentation covers all aspects from the characterization of the nonlinear behavior of RFID tags and the associated platforms (distinguishing conducted and radiated measurement) to the design of new types of tags where nonlinearities are exploited in order to offer new capabilities or enhanced performance.

• Language: English
• Publisher: Wiley
• Release date: Jan 19, 2018
• ISBN: 9781119490746

Book preview

Table of Contents

Cover

Title

Copyright

Acknowledgments

Introduction

1 History of Radio-frequency Identification: from Birth to Advanced Applications

1.1. Early facts about the genesis of RFID

1.2. Birth of RFID

1.3. Early modern RFID

1.4. The 1970s: the infancy age of RFID

1.5. The 1980s and 1990s: implementation of RFID

1.6. RFID chip age

1.7. Maturation of RFID

1.8. Internet of Things: the next RFID frontier

1.9. Summary

2 RFID Technology: Main Principles and Non-linear Behavior of Tags

2.1. RFID: a multilayer vision

2.2. Focus on passive UHF RFID technology

2.3. Non-linear RF networks and harmonic generation

2.4. Non-linear behavior and associated applications in the RFID field

2.5. Summary

3 Characterization Platforms for Passive RFID Chips and Tags

3.1. Introduction

3.2. Measuring the backscattered tag response

3.3. Characterization of RFID tags – radiated measurements

3.4. Characterization of RFID chips–conducted measurements

3.5. Summary

4 Modeling the Harmonic Signals Produced by RFID Chips

4.1. Introduction

4.2. Analysis of harmonic currents in RFID chips

4.3. Third harmonic in traditional RFID tags

4.4. How to profit from the third harmonic signal

4.5. Summary

5 Applications: Augmented RFID Tags

5.1. Introduction

5.2. Harmonic communication in passive UHF RFID

5.3. Harmonic harvesting: empowering the RFID tag

5.4. Conclusion

Conclusion

Bibliography

Index

End User License Agreement

List of Tables

1 History of Radio-frequency Identification: from Birth to Advanced Applications

Table 1.1. The most exploited tag categories. These tags are passive devices that can be used for short range (less than 1 m) and long range (up to 28 m). Depending on the constraints of an application, the tags can be inserted into a suitable package before their attachment or integration to the item to be tracked

Table 1.2. Evolution of RFID chip sensitivity. Theoretical read range considering: operating frequency at 868 MHz, reader power at 2W ERP, reader antenna gain at 2 dBi, tag antenna as an ideal dipole and perfect matching between the RFID chip and the tag antenna

2 RFID Technology: Main Principles and Non-linear Behavior of Tags

Table 2.1. Measured power of harmonics at a 10 dBm input signal

3 Characterization Platforms for Passive RFID Chips and Tags

Table 3.1. Free-space path loss

Table 3.2. Details of the evaluated UHF RFID tags

Table 3.3. Backscattered harmonics from the tag response

Table 3.4. Impedance results at the fundamental frequency

Table 3.5. Harmonic responses from RFID chips

Table 3.6. Harmonic treatment

5 Applications: Augmented RFID Tags

Table 5.1. Yagi-Uda antenna type without a director: design parameters

Table 5.2. Yagi-Uda antenna type with a director: design parameters

Table 5.3. LF-inverted antenna parameters

Table 5.4. Different configurations of the HTs under test

List of Illustrations

1 History of Radio-frequency Identification: from Birth to Advanced Applications

Figure 1.1. Depiction of the device designed by L. Theremin and used as a wireless passive microphone. Left: the device as it was embedded in a carved wooden plaque of the US Great Seal. Right: the composition of The Thing

Figure 1.2. Description of the EAS system. The tag is primarily an LC circuit whose presence is detected by a reader which is primarily a sweep generator

Figure 1.3. Examples of EAS tags. We clearly see the magnetic loop connected to the chip capacitor to form the LC resonant tank circuit. Typical operation frequencies are in the range of 1.75 MHz to 9.5 MHz band. The standard frequency for retail use is 8.2 MHz

Figure 1.4. Examples of implanted tags for pet tracking. These tags are based on inductive systems at LF (low-frequency) and HF (high-frequency) bands to take into account the electromagnetic characteristics of biological tissues

Figure 1.5. Examples of tags for toll applications. Toll tags are based on RF technologies and in most cases are powered by a battery

Figure 1.6. Evolution of tags from the PCB circuit to the RFID chip. First tags used PCB and a suitable external package. Actual tags with reduced size have a label format with only two elements: RFID chip and antenna

Figure 1.7. The microchip developed by Hitachi. Known also as Powder or Dust, these chips consist of 128-bit ROM (read-only memory) that can store a 32-digit number. They can be integrated into very thin substrates like paper and notes. Microchips may also have advanced applications such as smartdust

Figure 1.8. Implanted tags developed by VeriChip Corp. The tag consists of an RFID microchip, a capacitor and a loop antenna wrapped around a ferrite core. It is enclosed in medical-compliant glass and coated in a substance called Biobond to avoid the migration of the tag within the body. The implant has the size of a grain of rice

Figure 1.9. Classification of RFID tags following different parameters. Several duties should be considered when selecting a tag category for an application. Due to their low cost, batteryless feature and long read range, passive UHF tags are very often selected

2 RFID Technology: Main Principles and Non-linear Behavior of Tags

Figure 2.1. Air interface protocol stack

Figure 2.2. Working principle of passive UHF RFID systems

Figure 2.3. Reader and tag in a passive UHF RFID system

Figure 2.4. Simulated RFID tag reflection coefficient when varying its distance to an infinitively extended metal plate [DOB 05]. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 2.5. Architecture of a UHF RFID passive chip

Figure 2.6. Non-linear device or network

Figure 2.7. Localization system exploiting the intermodulation phenomena

3 Characterization Platforms for Passive RFID Chips and Tags

Figure 3.1. Measurement procedure based on the PSD analysis of UHF RFID signals

Figure 3.2. Frame timing in the forward and return links [EPC]

Figure 3.3. Query command structure [EPC]

Figure 3.4. Miller sequences for M = 2 [EPC]

Figure 3.5. Tag → Reader preamble with Miller M = 2 [EPC]

Figure 3.6. a) Bistatic configuration in the anechoic chamber. b) Equipment setup

Figure 3.7. Time domain response from nine UHF RFID tags. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 3.8. PSD at the fundamental frequency for tag T5 when Pout=15.6 dBm. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 3.9. PSD at the second harmonic frequency for tag T5 when Pout=15.6 dBm. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 3.10. PSD at the third harmonic frequency for tag T5 when Pout=15.6 dBm. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 3.11. Measured PSD at CW harmonic frequencies with Pout considering each tag sensibility. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 3.12. Current distribution until the fifth harmonic along the length of a half-wave dipole designed for the fundamental frequency. The half-wave dipole requires zero admittance at even harmonics to be able to radiate

Figure 3.13. PSD of the tag response at the BLF. Pout considers each tag’s sensibility

Figure 3.14. PSD of the periodic and random sequences of bits in the response of tag T4 at the fundamental frequency. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 3.15. PSD of the periodic and random sequences of bits in the response of tag T5 at the third harmonic. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 3.16. Comparison of PSD levels from the periodic and random sequence responses for tag T5

Figure 3.17. Comparison of harmonic levels generated from the RFID tester and one commercial reader

Figure 3.18. Effect of the transmitted power on the backscattered response at the fundamental frequency. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 3.19. Effect of the transmitted power on the second backscattered harmonic. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 3.20. Effect of the transmitted power on the third backscattered harmonic. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 3.21. Power on frequency hopping channels at the fundamental frequency

Figure 3.22. Power on frequency hopping channels at the third harmonic

Figure 3.23. Illustration of the presence of multiple channels in the tag-to-reader communication link. The impedance modulation is still present in the harmonic signal

Figure 3.24. Structure of the RFID-NTP used to characterize the backscattered harmonics by RFID chips

Figure 3.25. RFID-NTP with the connected RFID chip

Figure 3.26. a) RFID chips and calibration kit. b) LPF used to reject harmonics from the RFID tester

Figure 3.27. Flow diagram of the measurement procedure in the RFID-NTP

Figure 3.28. Harmonic characterization method in the DSO. The visualization allows the optimal position of the impedance tuners to be set by minimizing the CW level

Figure 3.29. Measured power sensitivity of RFID chips

Figure 3.30. Impedance for chips 1 and 3 in the scavenging state for a sweep of power

Figure 3.31. Harmonic responses measured for the three chips for a sweep of power. A characterization until the fourth harmonic is presented

Figure 3.32. Harmonic characterization for chip 1 after the harmonic treatment

Figure 3.33. Measured chip input impedance at the fundamental frequency in a temporal sweep. Scavenging and reflecting states can be seen

Figure 3.34. Measured chip input impedance at the third harmonic frequency in a temporal sweep. Both states of modulation can be distinguished

4 Modeling the Harmonic Signals Produced by RFID Chips

Figure 4.1. Passive tag architecture

Figure 4.2. Equivalent circuit of the Schottky diode for the analysis in DC and RF. a) Equivalent circuit of the Schottky diode. b) Equivalent rectifier circuit under the steady state. c) RF equivalent circuit: the capacitors become short circuits and the 2N diodes are in parallel. d) DC equivalent circuit: the capacitors do not allow the current to pass through and the diodes are in series

Figure 4.3. Current–voltage curve for a rectifier of N voltage-multiplier stages, modeled using the modified series of Bessel. The total current is composed only of the odd harmonic components. A similarity between the current amplitude at f0 and current amplitude at 3f0 can be noted. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 4.4. Comparison of I30, the amplitude of the current in the rectifier at 3f0, and I10, the amplitude of the current in the rectifier at f0. At V0/Vt = 6 (V0 = 0.15 V), I30 is the half of I10 which becomes closer as V0 increases

Figure 4.5. Equivalent circuit of the RF section of a passive RFID tag

Figure 4.6. Transmission coefficient of the LC network with different Q values. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 4.7. Equivalent circuit of the tag when the current at 3f0 is being reflected in the antenna

Figure 4.8. Law decay of the power P3 at 3f0 with respect to the power P1 at f0 as a function of Q and V0/Vt for traditional tags. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

Figure 4.9. Proposed matching network to exploit the signal generated by the RFID chip at 3f0. The cascade LC matching network allows the chip to transmit a maximum power towards the antenna at 3f0. L' is always considered in the analysis

Figure 4.10. Transmission coefficient of the cascade LC network of the HT antenna (Q* = 2.01) compared to an original LC network in traditional tags (Q = 4.96)

Figure 4.11. Law decay of the power at 3f0 with respect to the power at f0 for the HT. a) Law decay as a function of Q*, Q and V0 for the HT. b) Law decay as a function of V0. If the matching network is well dimensioned, the ratio depends only on the non-linearity of the chip. For a color version of this figure, see www.iste.co.uk/andia/non-linearites.zip

5 Applications: Augmented RFID Tags

Figure 5.1. RFID HT antenna design process

Figure 5.2. a) Equipment setup for bi-static configuration; b) anechoic chamber configuration

Figure 5.3. HT prototype. a) Fundamental resonator; b) harmonic resonator; and c) reflector

Figure 5.4. Simulated reflection coefficient of the HT, normalized to the chip impedance

Figure 5.5. Simulated directivity in the plane E for the HT

Figure 5.6. Simulated directivity in the plane H for the HT

Figure 5.7. New version of the HT prototype with a director element. a) Harmonic resonator; b) fundamental resonator; c) reflector and d) director

Figure 5.8. Simulated directivity in the plane E for the Yagi-Uda HT with and without a director

Figure 5.9. Simulated directivity in the plane H for the Yagi-Uda HT with and without a director

Figure 5.10. HT prototype in the LF-inverted structure

Figure 5.11. Simulated directivity in the plane E for the LF-inverted HT

Figure 5.12. Simulated directivity in the plane H for the LF-inverted HT

Figure 5.13. ERP transmitted by the RFID-TP as a function of the frequency for the tags of type HT1 compared with a commercial tag. The analysis is performed at f0

Figure 5.14. ERP transmitted by the RFID-TP as a function of the frequency for the tags of type HT2 compared with a commercial tag. The analysis is performed at f0

Figure 5.15. Power of the tag response from the tags of type HT1 at f0 as a function of the EIRP transmitted by the RFID-TP. The measured power considers an isotropic antenna at reception

Figure 5.16. Power of the tag response from the tags of type HT2 at f0 as a function of the EIRP transmitted by the RFID-TP. The measured power considers an isotropic antenna at reception

Figure 5.17. Power of the tag response from the tags of type HT1 at 3f0 as a function of the EIRP transmitted by the RFID-TP. The measured power considers an isotropic antenna at reception

Figure 5.18. Power of the tag response from the tags of type HT2 at 3f0 as a function of the EIRP transmitted by the RFID-TP. The measured power considers an isotropic antenna at reception

Figure 5.19. Read range for the tags of type HT1 at f0 as a function of 35 dBm EIRP transmitted by the RFID-TP. The measured power considers a 6 dBi antenna at reception

Figure 5.20. Read range for the tags of type HT2 at f0 as a function of 35 dBm EIRP transmitted by the RFID-TP. The measured power considers a 6 dBi antenna at reception

Figure 5.21. Read range for the tags