Ultra-Low Power Wireless Sensor Nodes for IoT

Lunghammer – TU Graz

S C I E N C E n _{P A S S I O N} n _{T E C H N O L O G Y}

Jasmin Grosinger, Graz University of Technology

Ultra-Low Power

Wireless Sensor Nodes for IoT

IEEE IoT Vertical and Topical Summit

Wireless Sensing, with Wireless Sensors, in Wireless Sensor Networks for IoT Applications

Overview

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Motivation

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HF and UHF RFID technologies

§

SoC and SiP concepts

§

Ultra-low power wireless sensor nodes

§

Passive UHF RFID sensor tags

§

Signal pattern-based sensor system

§

Dependability investigations

§

Related work

Motivation

Internet of things (IoT) and digitalization of economy and society

§ Massive deployment of wireless communication and sensor systems: sustainability issues on environmental and

economic levels

§ RF design challenges

§ Ultra-low power wireless communication

§ Eco-toxicity of batteries, costs of battery replacement

§ High level of integration

§ Carbon footprint, production and end-of-life costs

§ Passive sensing capabilities in wireless systems

§ Passive communication based on HF and UHF RFID technologies

§ SoC and SiP concepts based on CMOS technologies

J. Grosinger, RF Design for Ultra-Low Power Wireless Communication Systems, Habilitation thesis, 2020. J. Grosinger, et al., Tag Size Matters, IEEE Microwave Magazine, 2018.

RF … radio frequency HF … high frequency UHF … ultra-high frequency RFID … radio frequency identification SoC … system on a chip SiP … system in package CMOS … complementary metal-oxide-semiconductor

HF and UHF RFID Technologies

Wireless communication between reader and batteryless/passive tags (antenna and chip)

§ Reader–tag: RF power and data

§ Tag–reader (no transmitter): reader signal modulated/reflected by tag (tag ID)

§ Operating frequency/wavelength: 13.56 MHz / 22.1 m (HF), 868 MHz / 30 cm (UHF)

Tag: antenna (largest part ~ fraction of wavelength) and chip

§ Tag/antenna miniaturization: read range reduction

§ Near-field communication: inductive (coils) or capacitive (electrodes) coupling

§ Read range extension: booster antennas

Tag … transponder ID … identification number Chip … microchip

Antenna array

UHF RFID tag UHF RFID reader

SoC and SiP Concepts

CMOS technology-based SoC and SiP concepts

§ Classes of RFID (sensor) tags

§ CoS: additional components (sensor chip, etc.)

J. Grosinger, et al., Tag Size Matters: Miniaturized RFID Tags to Connect Smart Objects to the Internet, IEEE Microwave Magazine, 2018. W. Pachler, et al., A Novel 3D Packaging Concept for RF Powered Sensor Grains, Proc. IEEE ECTC, 2014.

W. Pachler, et al., An On-Chip Capacitive Coupled RFID Tag, Proc. EuCAP, 2014. W. Pachler, et al., A Miniaturized Dual Band RFID Tag, Proc. IEEE RFID-TA, 2014.

CoM / CoS tags CoC/OC3 tags Read range ₊ -Losses ₊ -Costs _{- +} Conventional tags A > 200 mm² Coil-on-module (CoM) / coil-on-system (CoS) tags 200 mm² > A > 2 mm² Coil-on-chip (CoC) / on-chip capacitive coupling (OC3) tags A ~ 1 mm²

Ultra-Low Power Wireless Sensor Nodes

P. Greiner et al., A System-on-Chip Crystal-less Wireless Sub-GHz Transmitter, IEEE Trans. Microw.Theory Techn. (TMTT), Vol. 66, No. 3, 2018 J. Grosinger et al., Tag Size Matters: Miniaturized RFID Tags to Connect Smart Objects to the Internet, IEEE Microw. Mag., Vol. 19, No. 6, 2018

R. Fischbacher et al., Localization of UHF RFID Magnetic Field Sensor Tags, Proc. IEEE RWS, 2020 J. Grosinger and J. Griffin, Backscatter RFID Sensor with a Bend Transducer, US Patent: US8917202 B2, 2014

L. Görtschacher and J. Grosinger, UHF RFID Sensor System Using Tag Signal Patterns: Prototype System, IEEE Antennas Wireless Propag. Lett., Vol. 18, No. 10, 2019

F unc ti onal ity Costs Passive HF/UHF RFID sensor tags Passive HF/UHF RFID sensor tags (sensor circuitry) Sub - 1 GHz battery-assisted sensor nodes NXP NTAG 213 TT Bimetal switch NXP UCODE G2iM+ Reed switch w. permanent magnet RF bend sensor Sub-1 GHz transmitter

Passive UHF RFID Sensor Tags

State-of-the-art UHF RFID system

§ Amplitude modulation of the backscattered signal for tag ID transfer Sensor add-on for passive RFID chips

§ Additional modulation in amplitude/phase of the backscattered tag signal via additional impedance states

RFID Tag Leistung und Daten Moduliertes rückgestreutes Signal RFID Reader A nt enn e Chip

RFID reader _{RF power and}

data RFID tag Chip A nt e nn a Modulated backscatter signal Z_Abs Z_Ref Z_Ant ID … identification number Z … impedance

Passive UHF RFID Sensor Tags

Antenna transducer Z_Ant(ψ)

§ Use of commercial off-the-shelf UHF RFID chips

Challenges

§ Constant WPT towards passive chip: Additional analog modulation of

digital signal due to sensing

S_Abs(Z_Abs,Z_Ant(ψ)) ≠0

§ Setup independence: Variations of tag signal due to changes in wireless communication channel

Sensor tag mounted on infusion bag Wireless communication channel Reader antenna Sensing state: Water filling level

J. Grosinger et al, Passive RFID Sensor Tag Concept and Prototype Exploiting a Full Control of Amplitude and Phase of the Tag Signal, IEEE Trans. Microw. Theory Tech., Vol. 64, No. 12, 2016

L. Görtschacher et al, UHF RFID Sensor Tag Antenna Concept for Stable and Distance Independent Remote Monitoring, Proc. IEEE IMBioC, 2018

L. Görtschacher and J. Grosinger, UHF RFID Sensor System Using Tag Signal Patterns: Prototype System, IEEE Antennas Wireless Propag. Lett., Vol. 18, No. 10, 2019

L. Görtschacher and J. Grosinger, Localization of Signal Pattern Based UHF RFID Sensor Tags, IEEE Microw. Wireless Compon. Lett., Vol. 29, No. 11, 2019

S … reflection coefficient

Signal Pattern-Based Sensor System

Challenge

§ Constant WPT towards passive chip: 𝜏𝜏(S_Abs(ψ)) ≥ 0.9, ∀ψ

𝜏𝜏… power transmission coefficient

Sensor tag Plastic Water 0 mm 50 mm 100 mm NXP UCODE 7 chip 𝜏𝜏= 0 _{𝜏𝜏= 0.9} 𝜓𝜓stop 𝜓𝜓start Tag response diagram Solution

§ Optimized antenna design for smart modulation of amplitude and phase

Signal Pattern-Based Sensor System

Challenge

§ Setup independence: Correct detection although tag signal amplitude and phase changes

E … electric field I … current 𝜓𝜓stop= 100 mm 𝜓𝜓start= 0 mm 𝜓𝜓mid 𝜓𝜓stop 𝜓𝜓start 𝜓𝜓mid Signal constellation diagram 𝜓𝜓stop 𝜓𝜓start 𝜓𝜓mid 𝜓𝜓start 𝜓𝜓start 𝜓𝜓mid 𝜓𝜓start 𝜓𝜓stop Solution

§ Pronounced tag signal pattern versus water filling level (infusion bag full or empty)

Dependability Investigations

Repeated measurement of tag signals versus filling level ψ

§ Four reader antennas: A1-A4

§ Six different canister positions: P1, P3-P6 (z = 1.05 m), P2 (z = 1.52 m)

Sensor tag Canister A1 _A2 A3 A4 y x 𝜓𝜓 z NXP UCODE7 A1 A2 A3 A4 P1 P2 P5 P4 P3 P6 x y

Dependability Investigations

24 measured tag signal patterns (A1-A4, P1-P6)

§ Comparison to reference pattern

ℎ_P1,A1 𝜓𝜓

§ Tag signal phase: rotate with angle 𝛼𝛼

§ Tag signal amplitude: scale with 𝑎𝑎

§ Comparison with simulation

§ Two port simulation and tag signal calculation

§ Good agreement with measurements

§ Dependable sensor system: Filling level monitoring possible

𝜓𝜓stop 𝜓𝜓start 𝜓𝜓mid 𝜓𝜓stop 𝜓𝜓start 𝜓𝜓mid 𝜓𝜓start

Related Work

Year Reference Analog modulation Constant power transfer

Setup

independence

2009 Bhattacharyya, et al. (Auto ID Labs, MIT)

Amplitude No No

2009 Marrocco, et al. (Univ. Rome Tor Vergata)

Amplitude No Yes (analog

identifier) 2013 Marrocco, et al. (Univ.

Rome Tor Vergata)

Amplitude Yes Yes (analog

identifier) 2014 Grosinger, et al. (TU

Vienna/Graz)

Amplitude and phase Yes No

2015 Marrocco, et al. (Univ. Rome Tor Vergata)

Phase Yes No

2016 Marrocco, et al. (Univ. Rome Tor Vergata)

Amplitude Yes (self-tuning chip)

No 2018 Grosinger, et al. (TU

Vienna/Graz)

Conclusions

RF design solutions to include passive sensing capabilities in IoT nodes to solve sustainability issues on

environmental and economic levels

§ Ultra-low power wireless communication

§ High level of integration

Other (future) RF design challenges for wireless systems in IoT

§ Rapid testing of novel designs in specific application environments

§ Efficient miniaturization of IoT nodes

§ Robust operation in harsh application environments

J. Grosinger, RF Design for Ultra-Low Power Wireless Communication Systems, Habilitation thesis, 2020. G. Saxl, et al., Software Defined RFID Readers, IEEE Microwave Magazine, in press.

L. Görtschacher and J. Grosinger, UHF RFID Sensor System Using Tag Signal Patterns: Prototype System, IEEE Antennas Wireless Propagation Letters, 2019. L. Görtschacher, et al., Passive HF RFID Repeater for Communicating with Tags in Metal Housings, , IEEE Antennas Wireless Propagation Letters, 2020.

P. Greiner et al., A System-on-Chip Crystal-less Wireless Sub-GHz Transmitter, IEEE Transactions on Microwave Theory Techniques, 2018.

HF coil UHF coil

OC3 tagOC3

DeSSnet Project

Dependable, secure and time-aware sensor networks (DeSSnet)

§ Goals

§ Enable the future use of wireless sensor networks as dependable and as cost-efficient as possible

§ Cover the whole value chain of wireless sensor networks

§ Develop key enabling technologies for

§ Sensor and communication technologies

§ Security

§ Network dependability

§ Time-aware analytics

Acknowledgements

Special thanks to the (former) members of the RFID technologies group of the

Institute of Microwave and Photonic Engineering, Graz University of Technology, in particular to

§ Dr. L. Görtschacher: Novel UHF RFID Tracking and Sensing Systems, PhD Thesis, 2019.

§ Dr. W. Pachler: Miniaturized RFID Tags Exploring Passive Boosting Technologies, PhD Thesis, 2015 (awarded with the Austrian Award of Excellence).

§ Dr. P. Greiner: Highly Stable All CMOS Frequency Reference for SoC Wireless Sub-GHz Applications, 2017.

Ass.-Prof. Jasmin Grosinger

Ultra-Low Power Microwave Components and Systems – RFID Technologies Institute of Microwave and Photonic Engineering

Graz University of Technology Inffeldgasse 12, 8010 Graz jasmin.grosinger@tugraz.at