2009SensorsExpo2 2009Sensors Expo2

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Wireless Power for Battery-Free
Wireless Sensors
powercastco.com
Overview
Powercast technology overview
Applications for wireless sensors
Battery-free reference design
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About Powercast
Driving innovation and commercialization
of wireless power based on RF energy
Custom engineering and components
Applications / Markets
Applications / Markets
Wireless sensors and devices
– Defense
– Aerospace
– Manufacturing
– Others
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2009 Product
Showcase
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Wireless Power (over distance)
Dedicated source transmits common radio waves
Ambient sources augment when available: Cellular, TV, Radio, etc.
• Receiver
Captures the RF energy with an antenna
Converts the RF energy to the appropriate DC voltage
Stores the DC energy
Energy transfer is controllable and predictable by design
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Multiple forms of “wireless power”
Induction Micro-Contacts
Proximity
Wireless Laser / Infrared
Batteries
Solar
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Radio Waves
Harvesting
Vibration
Thermal
Radio Waves
Ambient Energy Harvesting
“Free” Energy
Multiple methods with
many sources
Solar
Energy received is
dependent on the
source
Sources may be
predictable but they
Benefits Drawbacks
Solar
– Vibration
– Thermal
– RF
predictable but they
are uncontrollable
No source = No energy
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EH is fine for some applications, but not all.
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Dedicated Source – Controllable
by Design
System Parameters
RF Power Level
• Frequency
Transmit Antenna
Number of Transmitters
Number of Transmitters
• Distance
Receive Antenna
Device Duty Cycle
• Cost
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Wireless Power Transfer with
Radio Waves…
Governed by Friis Equation
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…Simplified
After parameter selection equation
simplifies to:
There are many parameters to adjust for system
optimization but after selection, calculations are straight
forward.
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Antennas have a significant
impact on power transfer
Patch
)))(((
Sleeve Dipole
Omni-directional
Patch
Directional
Loop
Bi-directional
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Sample Antennas Designs
2.45GHz Tx Array
2.45GHz Rx Array
7.26 x 5.78cm
2.45GHz Patch
Gain =4.9
Beam= 32deg
915 MHz
Sleeve Dipole
Beam = ~20deg
Beam=~90deg
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915 MHz Dipole
915 MHz Short
Dipole
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915 MHz Yagi
Gain = 6
System Comparison
Achieving Higher Performance with Lower Power
Multiple Tx
• Any-to-Any
Even coverage
Lower total Tx power
More robust
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Single Tx
• One-to-Many
Uneven coverage
Higher Tx Power Not enough
power
Minimum
desired
power
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Wireless Power distribution is
similar to a cellular network
Any to Any
• Redundancy
Enables Mobility
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Enables Mobility
• Distributed
Area Coverage
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Gateway Access Points
Power
Data
Power Power
Vision: Unified Power and
Communications for a Ubiquitous
Sensor Network
Power
Data
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The Opportunity – Wireless Sensors
Building automation
Energy management
Location tracking
Reduced wiring
Sealed devices
Reduced maintenance
Applications Benefits of Wireless Power
Location tracking
Condition monitoring
Rotational Machinery
Reduced maintenance
Controllable power
Difficult locations
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Application – Building Automation
Indoor sensors
Low light areas
Behind walls
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Behind walls
Above ceilings
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Application – Location Tracking
Battery-Free Beacons
Active Inside
Inactive Outside
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Longer range “RFID”
Battery-Free “RTLS”
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Application – Industrial Monitoring
Lack of vibration or
heat source
Hazardous areas
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• Distance
Battery trickle-charge
• Non-critical
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Application – Rotating Machinery
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Issues with Primary Batteries
in Wireless Sensor Networks
Intentional constraints to save
power
Design, Operation, Implementation
Majority of energy consumed
sleeping
• Reliability
Retransmissions
Management
Effort
Battery-Powered
Retransmissions
Lifetime vs. cell/pack size
Shelf life?
Temperature performance
Battery replacement cost
Device location / placement
• Ecology
Limitations of scale
10s 100s 1000s
Management
Size of Sensor Network
Battery-Free
Battery
Replacement
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Majority of battery life is
consumed in sleep mode
60.0%
80.0%
100.0%
% Power Consumed in Sleep Mode
10uA
30uA
20uA
0.0%
20.0%
40.0%
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2
3
4
5
6
7
8
9
10
30
60
Daily
Wake-up Every X Minutes
Transmit current: 50mA
Other current: 30mA
Transmit time: 5 ms
Other time: 20ms
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Average energy ≈ Sleep energy
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Capacitor
Voltage
Power
Broadcast
Battery-Free Concept
Send power as needed - 1) On-Demand, 2) Scheduled, or 3) Continuously
VMIN
VMAX
Power Output
Sensor Active
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GND
Sensor Dormant
“Zero Stand-By” Power
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Battery-Free Reference System
P2100 Powerharvester™ Module
Front Back
Sleeve Dipole Antenna
Simple “2 wire” hardware integration for any RF module
Integrated, 915 MHz
High Efficiency
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TI eZ430-RF2500T
CAP-XX GZ115
Low Power
Small Form Factor
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Powerharvester™ Module
P2100 – 915MHz, Charge & Fire
High Conversion Efficiency
Internal Charge Management
High Sensitivity
Configurable Output Voltage
Features
50mA Output Current
Capacitor Overvoltage Protection
Internally Matched to 50 ohms
Low Quiescent Current (<1µA)
Simple Integration
Small Footprint
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Energy Storage
Choosing the Supercap Value
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2
3
4
Output Voltage (V)
Voltage Window (Hysteresis)
Energy Available
Capacitor Value
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0
1
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
1.40
1.45
1.50
Capacitor Voltage (V)
DC-DC conversion
efficiency
Capacitor Value
= required load energy GZ115 cap size = 0.16F (measured)
Stored energy = 22.7 mJ
VMIN VMAX
C = 7.02E/e e 0.82
C= 8.57E
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TI eZ430-RF2500T
Start-up and Data
3.70 mJ @ 3.3V
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Note: V1.5 Software
Initial start-up Data
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P2100 Charge Current
100
1000
10000
Output Current (uA)
P2100 Capacitor Charge Current at 1.1V
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1
10
-15 -10 -5 0 5 10 15
Output Current (uA)
Module Input Power (dBm)
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Energy Harvesting Performance
1000
10000
Charge Time (sec)
Charge Time vs. Distance
Measured @10ft
(152 sec)
Measured @ 15 ft
(103 sec)
3W EIRP Patch Antenna Transmitter
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1
10
100
5 10 15 20 25 30 40 45 50
Charge Time (sec)
Sleeve Dipole (G=1.5)
Air Dipole (G=4.1)
Yagi (G=6.1)
Distance (ft)
Measured @20ft
(145sec)
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Reference System Summary
Stored energy = 22.7 mJ
Usable energy = 18.6 mJ (current design)
Initial start-up and data transmission = 3.7 mJ
20ft range (3W source, sleeve-dipole Rx antenna)
Temperature and voltage sensing
Extremely long life – NO BATTERIES!!!
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Reference System On-Going Efforts
Optimizing Performance
Reduce the capacitor size by modifying the software start-
up sequence
Target joule usage of 100uJ will require less than 1000uF capacitor
Improve charge management efficiency
Lower the harvester sensitivity to extend range
Targets
100uJ per activation
Credit card form factor
100+ ft range (2-4X increase)
3Q09 timeframe
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Summary
Wireless power via RF energy harvesting is capable
of powering wireless sensors over distance
Capacitors offer an attractive alternative to
disposable batteries
Wireless power uniquely provides controllable
Wireless power uniquely provides controllable
power options: on-demand, scheduled, continuous
Zero Stand-By operation eliminates design
concerns of driving down sleep current:
Average Current ≈ Sleep Current ≈ 0
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Thank You
Visit us in Booth #1026
www.powercastco.com
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