Pavel Nikitin Intermec Technologies

TU Graz, Austria, May 5, 2011

Sensing with UHF RFID: an Overview

6th IEEE UWB Forum on Sensing and Communications

Slide 2

Outline

Introduction

Wireless Sensing

Bands, low power technologies, battery life

Some UHF RFID Basics

UHF RFID Sensing

On/off sensing

ID modulation

Analog sensing

Dedicated sensors

Conclusions

Slide 3

Quantities of Interest in Sensing

Temperature

Light

Touch

Pressure

Humidity

Position

Activity

Alerts

Health

Slide 4

Unlicensed Wireless Bands in US

433 MHz

Active RFID, DASH7

902-928 MHz (UHF)

UHF RFID, ZigBee

2.4-2.483 GHz (SHF)

WiFi, ZigBee, Bluetooth, ANT

5.725-5.875 GHz (microwave)

WiFi

3.1-10.6 GHz (UWB)

UWB: PSD < 41.3 dBm/Hz, spectrum >500 MHz or 20% of center frequency)

24-24.25 GHz

Automotive radars

61-61.5 GHz (EHF)

Wireless HD

Slide 5

Low Power Wireless Sensor Topology

Radio

EnergySource

Sensors Actuators

EnergyHarvesting

Antenna

MicroControllerInformation

Connectivity

Actions

Energy

Slide 6

Low Power Wireless Technologies

Zigbee

~1 mA average current

Bluetooth Low Energy (BLE)

~0.1 mA average current

ANT

~ 50 uA average current

DASH7 and UHF RFID (battery assisted)

~1 uA average current

Passive UHF RFID

~0.1 uA average current

Slide 7

Coin Cell Battery Lifetime

Coin cell capacities range from 25 mAh to 1000 mAh

CR2330 (~250 mAh) lasts:

~30 years with 1 uA current

~3 years with 10 uA current

~3 months with 0.1 mA current

~2 weeks with 1 mA current

Shelf life: 5 to 10 years Image from http://www.ipanasonic.com

Slide 8

Passive UHF RFID Systems

RFID tag

Chip

1 2

RCS 2

RCS 1

Reader transmits and receives simultaneously

Tag is powered by RF, scatters data back by modulating its impedance

Attractive features: low cost of the tags, long lifetime

Standardized protocol: Gen2 (ISO 18000-6C)

Slide 9

What is Measured in UHF RFID Sensing

On/OFF Sensing

Powered tag presence (read /no read)

ID modulation

Which ID is readable

Analog sensing with tag antenna

Minimum power to read the tag, RSSI and phase of the received tag signal

Dedicated sensors

Tag user data is supplied by specific sensors

Slide 10

Tag signal constellation

-30

-20

-10

0

10

20

30

-30 -20 -10 0 10 20 30I (mV)

Q (m

V) Qac

Iac

Minimum Power, Tag RSSI and Phase

Simple microwave model of the tag

Minimum transmit power to read the tag

Tag signal power at the reader

tagpathtmin PpGGP

ac

ac

2ac

2ac

22path

2tt

IQarctan

IQKpGGPRSSI

mismatch onpolarizati

gain pathgain antenna transm.

ysensitivit taggain rbackscatte

power incident

p

GG

PKP

path

t

tag

inc

Pinc

K Pinc

Slide 11

First RFID Sensing Tag –

The Great Seal Bug (1945)

Eavesdropping device designed by Leon Theremin was built into the Great Seal and given to US ambassador in Moscow in 1945

Backscattered a harmonic of the 330 MHz CW signal, AM modulated by sound

Was discovered only in 1952 by accident by British radio operator

On display in NSA National Cryptologic Museum (Washington, DC)

Images from http://www.spybusters.com/Great_Seal_Bug.html

Slide 12

On/Off Sensing with Tag Antenna

Tag either receives enough power to turn on and respond or not. This allows to sense the environment (material the tag is placed on, etc.)

RFID tag antenna based sensing: Does your beverage glass need a refill? Bhattacharyya, R.; Floerkemeier, C.; Sarma, S.; RFID, 2010 IEEE International Conference on Publication Year: 2010 , Page(s): 126 –

133

Slide 13

Analog Sensing with Tag Antenna

With proper calibration, change in tag signal RSSI and phase (or in the minimum power needed to activate the tag) due to change in tag antenna performance can be related to the change in the environment.

Self-sensing passive RFID: From theory to tag design and experimentation Marrocco, G.; Amato, F.; Microwave Conference, 2009. EuMC 2009. European Publication Year: 2009 , Page(s): 001 –

004

Coupling sensors to UHF RFID tags Huan-Yang Chen; Bhadkamkar, A.; van der Weide, D.W.; Wireless Sensing, Local Positioning, and RFID, 2009. IMWS 2009. IEEE MTT-S Workshop, 2009 , Page(s): 1 –

4

Slide 14

Analog Sensing Example: Proximity Sensor

Reader is mounted on construction equipment

Smart hat emits audible tone when RSSI becomes too high

S. Thomas, J. Teizer, M. Reynolds, SmartHat: A Battery-Free Worker Safety Device Employing Passive RFID Technology", Proceedings IEEE RFID 2011

Slide 15

Analog Sensing: Tag Localization

With proper calibration, tag signal RSSI and phase can be related to the tag position (and, possibly orientation) relative to the reader antenna system

Several methods exist in standard Gen2 UHF RFID:

Markers (readers or tags)

Transmit power control

Antenna beam steering

Tag RSSI based

Tag phase based (time, frequency, spatial domains)

For more information, come to PhD defense “Tag Localization in Passive UHF RFID”

by Daniel Arnitz, TU Graz, May 6, 2011

Slide 16

ID Modulation

Switches (pushed or triggered by change in the environment) connecting ICs with different IDs to the tan antenna

Battery-free wireless identification and sensing Philipose, M.; Smith, J.R.; Jiang, B.; Mamishev, A.; Sumit Roy; Sundara-Rajan, K.; Pervasive Computing, IEEE Volume: 4 , Issue: 1, 2005

, Page(s): 37 –

45

A Cost-Effective UHF RFID Tag for Transmission of Generic Sensor Data in Wireless Sensor Networks Catarinucci, L.; Colella, R.; Tarricone, L.; IEEE Tran. MTT, Volume: 57 , Issue: 5 , 2009 , pp: 1291 –

1296

UHF RFID remote controller, www.favite.com

Image from http://www.favite.com

Slide 17

Custom ICs with Integrated Sensors

A number of custom Gen2 ICs from universities with integrated temperature sensors

A 9 uA, Addressable Gen2 Sensor Tag for Biosignal

Acquisition, Yeager, D.; Fan Zhang; Zarrasvand, A.; George, N.T.; Daniel, T.; Otis, B.P.; Solid-State Circuits, IEEE Journal of, Volume: 45 , Issue: 10, 2010 , Page(s): 2198 –

2209

A System-on-Chip EPC Gen-2 Passive UHF RFID Tag With Embedded Temperature Sensor Jun Yin;

Jun Yi; Law, M.K.; Yunxiao

Ling; Man Chiu Lee; Kwok Ping Ng; Bo Gao; Luong, H.C.; Bermak, A.; Mansun

Chan; Wing-Hung Ki; Chi-Ying Tsui; Yuen, M.; Solid-State Circuits, IEEE Journal of Volume: 45 , Issue: 11, 2010 , Page(s): 2404 –

2420

Slide 18

BAP UHF Gen2 ICs with Serial Interfaces

Direct access to tag memory via serial port interface allows to connect external microprocessor and any sensors to these ICs

Several commercial products:

NXP UCODE (I2C)

IDS SL900A (SPI)

Ramtron

WM72016 (SPI)

EM Microelectronic –

EM4324 (SPI)

Image from http://www.ids-microchip.com

Slide 19

Flexible Architecture: Discrete Tag

Discrete off-the-shelf element based tag with standard low power microcontroller (TI MSP430) and a lot of capabilities (sensing, security, etc.).

Design of an RFID-Based Battery-Free Programmable Sensing Platform, Sample, A.P.; Yeager, D.J.; Powledge, P.S.; Mamishev, A.V.; Smith, J.R.; Instrumentation and Measurement, IEEE Transactions on, 2008 , Page(s): 2608 -

2615

Image from http://ils.intel-research.net

Slide 20

Dedicated Sensing Example with WISP

A separate capacitive touch sensor can be integrated with UHF tag antenna

A capacitive touch interface for passive RFID tags, Sample, A.P.; Yeager, D.J.; Smith, J.R.; RFID, 2009 IEEE International Conference on , Publication Year: 2009 , Page(s): 103 -

109

Best IEEE RFID 2009 conference paper award

Slide 21

Conclusions

The choice of a wireless sensing system requires tradeoffs and depends on things such as:

Number of nodes for peer-to-peer, readers vs tags for master-slave

Desired range

Total cost

Lifetime

Packaging

UHF RFID is attractive due to low tag cost and power consumption

Low power sensing or sensing in close range may use passive mode

More sensors and features and longer range sensing require battery assisted passive mode

Several commercial BAP Gen2 ICs with serial port are available now

Slide 22

Thank You!

Questions or comments?pavel.nikitin@intermec.com

AcknowledgementsRene Martinez and Mike Hansen

(Intermec Technology Office)