Wirelessly-Charged UHF Tags for Sensor Data Collection

Dan Yeager

Pauline Powledge

Richa Prasad

David Wetherall

Joshua Smith

Intel Research Seattle

University of Washington Electrical Engineering

University of Washington Computer Science and Engineering

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Outline

• Motivation for Wireless Sensing

• Prior Work

• The Wirelessly-Charged Power Model

• The Passive Data Logger (PDL)

• Experimental Results

• Future Work

3

Motivation: Wireless Sensing

RFID Sensor Applications

Sensor-enhanced RFID tags exist, what is the problem?

Blood plasma

Chemicals Frozen & Refrigerated Food

4

Motivation: Wireless Sensing

Problem: No visibility during transport

No RFID Coverage

Supplier Shipping Customer

RFIDReader

TaggedGoods

RFIDReader

TaggedGoods

5

Prior Work

Active Passive Ideal

Power Source Battery-poweredRF-powered (battery-free)

RF-powered (battery-free)

Physical Operating Range

UnlimitedRequires proximity to RF power source

Unlimited

Lifespan Months to yearsNo fundamental

limitationNo fundamental

limitation

Example

Iris Mote (Berkeley)

Passive RFID Tag + Sensor

No devices

DEVICE COMPARISON

6

Our Prior Work: WISP

Reader proximity

Benefits

UHF RFID Tag PassiveProgrammableOnboard sensors

Problem

7

A New Power Model: Wirelessly Charged Sensors

MOTIVATION

Supplier Shipping Customer

CONCEPT

Wirelessly charge via RF power

Battery-free sensor data loggingPassive TagsActive Tags

RFID Wireless Charge

RFID Wireless Data DownloadTagged

Goods No RFID Coverage TaggedGoods

Data Logging

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A New Power Model: Wirelessly Charged Sensors

1 day runtime, 2 hour charge time at 1 meter

echechddedchstored TPVVCE argarg22

arg2

1

t

vCI

CAPACITANCE REQUIREMENT CHARGE TIME

Our Prototype

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Passive Data Logger (PDL) Tag

Power Management

Antenna

Analog Front End

Storage Capacitor

Microcontroller

Sensor

Flash Memory

RFIDReader

WISP-PDL Implementation - Hardware

+

Storage Capacitor

IC + Antenna

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Sensor Measurement

Data Logging

Sleep Mode RFID Communication

WISP-PDL Implementation - Firmware

STATE DIAGRAM

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Sending Data in RFID Gen 1

Reader Tag

Tag Memory

EPC ID

Historical Sensor Measurements

Time elapsed since last reset

Charge remainingSensor Data

Lack of address space!

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Sending Data in RFID Gen 2

Reader Tag

Tag Memory

EPC ID

ID Memory User Memory

• Sensor Data

• Charge remaining

• Time elapsed since last reset

• Historical Sensor Measurements

• Fully compatible with Gen 2 specification

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Milk Monitoring Study

Capacitive Fluid Level

Sensor

UHF Antenna

Storage Capacitor

RefrigeratorWISP-PDL

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Milk Monitoring Study

Refrigerator

Reader Antenna

Reader Laptop

RFID Reader

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Study Results

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8

Time (hours)

Per

cent

Ful

l (%

) / T

empe

ratu

re (°

C) Temperature (°C)

Percent Fill

Controlled Experiment

Carton Tilted to Pour

Fluid Level Decreases After Use

Temperature Increases

When Removed

From Fridge

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Study Results

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20Time (hours)

Per

cent

Ful

l (%

) / T

empe

ratu

re (C

)

Temperature (°C)

Percent Full

Uncontrolled Experiment

Level Sensor Detects Nearby Cartons

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Future Work / Conclusion• Wirelessly charged power model is feasible

• New hybrid devices can improve RFID sensing

• Key challenge: Increase runtime / decrease required capacitance– Reduce quiescent current draw– Design custom IC for key hardware blocks

• Begin collaborative projects– Come pick up information to get involved!

Email yeagerd@gmail.com for information

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Prior WorkExamples of Active Solutions

• Berkeley Motes (Zigbee)– Programmable Atmel MCU– Wide array of sensors– 4 month battery life (coin cell)– Zigbee radio (2.4 GHz)

• Intel Mote– Zigbee radio (2.4 GHz)– Extensible for arbitrary sensors

• MIT CargoNet– Low power analog sensor event detection– Programmable MCU, 1MB Flash– 2-year battery life (coin cell)– Custom 2.4 GHz radio protocol