Wirelessly-Charged UHF Tags for Sensor Data Collection
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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
2
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
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Our Prior Work: WISP
Reader proximity
Benefits
UHF RFID Tag PassiveProgrammableOnboard sensors
Problem
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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 [email protected] 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