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 powercastco.com 2 About Powercast • Driving innovation and commercialization of wireless power based on RF energy • Custom engineering and components • Applications / Markets – – – – – Wireless sensors and devices Defense Aerospace Manufacturing Others powercastco.com 2009 Product Showcase 3 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 powercastco.com 4 Multiple forms of “wireless power” Proximity Wireless Micro-Contacts Induction Laser / Infrared Batteries Radio Waves Thermal Harvesting Solar powercastco.com Vibration Radio Waves Ambient Energy Harvesting Benefits Drawbacks • “Free” Energy • Energy received is dependent on the source • Sources may be predictable but they are uncontrollable • No source = No energy • Multiple methods with many sources – – – – Solar Vibration Thermal RF EH is fine for some applications, but not all. powercastco.com 6 Dedicated Source – Controllable by Design System Parameters • • • • • • • • RF Power Level Frequency Transmit Antenna Number of Transmitters Distance Receive Antenna Device Duty Cycle Cost powercastco.com 7 Wireless Power Transfer with Radio Waves… Governed by Friis Equation powercastco.com 8 …Simplified After parameter selection equation simplifies to: ∴There are many parameters to adjust for system optimization but after selection, calculations are straight forward. powercastco.com 9 Antennas have a significant impact on power transfer Patch Directional Sleeve Dipole Omni-directional ( ( ( ))) Loop Bi-directional powercastco.com Sample Antennas Designs 7.26 x 5.78cm 2.45GHz Patch Gain =4.9 Beam= 32deg 915 MHz Sleeve Dipole powercastco.com 915 MHz Yagi Gain = 6 2.45GHz Rx Array Gain =12 Beam=~90deg 915 MHz Short Dipole 2.45GHz Tx Array Gain =43 Beam = ~20deg 915 MHz Dipole 11 System Comparison Achieving Higher Performance with Lower Power • • • • Single Tx One-to-Many Uneven coverage Higher Tx Power powercastco.com Minimum desired power Not enough power • • • • • Multiple Tx Any-to-Any Even coverage Lower total Tx power More robust 12 Wireless Power distribution is similar to a cellular network • Any to Any • Redundancy • Enables Mobility • Distributed • Area Coverage powercastco.com 13 Vision: Unified Power and Communications for a Ubiquitous Sensor Network Gateway Data Power Access Points Power Power Power Data powercastco.com The Opportunity – Wireless Sensors Applications Benefits of Wireless Power • Building automation • Reduced wiring • Energy management • Sealed devices • Location tracking • Reduced maintenance • Condition monitoring • Controllable power • Rotational Machinery • Difficult locations powercastco.com 15 Application – Building Automation • Indoor sensors • Low light areas • Behind walls • Above ceilings powercastco.com 16 Application – Location Tracking • Battery-Free Beacons • Active Inside • Inactive Outside • Longer range “RFID” • Battery-Free “RTLS” powercastco.com 17 Application – Industrial Monitoring • Lack of vibration or heat source • Hazardous areas • Distance • Battery trickle-charge • Non-critical powercastco.com 18 Application – Rotating Machinery powercastco.com 19 Management Effort Issues with Primary Batteries in Wireless Sensor Networks • Intentional constraints to save power Battery-Powered – Design, Operation, Implementation – Majority of energy consumed sleeping • Reliability Battery Replacement Battery-Free • 10s 100s 1000s • Size of Sensor Network • • powercastco.com – – – – Retransmissions Lifetime vs. cell/pack size Shelf life? Temperature performance Battery replacement cost Device location / placement Ecology Limitations of scale 20 Majority of battery life is consumed in sleep mode % Power Consumed in Sleep Mode 100.0% 30uA 80.0% 20uA 60.0% 10uA 40.0% 20.0% Transmit current: 50mA Other current: 30mA Transmit time: 5 ms Other time: 20ms 0.0% 1 2 3 4 5 6 7 8 9 10 30 60 Daily Wake-up Every X Minutes Average energy ≈ Sleep energy powercastco.com 21 Battery-Free Concept Send power as needed - 1) On-Demand, 2) Scheduled, or 3) Continuously Power Broadcast VMAX Capacitor Voltage VMIN GND Power Output Sensor Active powercastco.com Sensor Dormant “Zero Stand-By” Power 22 Battery-Free Reference System Simple “2 wire” hardware integration for any RF module Sleeve Dipole Antenna Integrated, 915 MHz Front Back P2100 Powerharvester™ Module High Efficiency TI eZ430-RF2500T Low Power CAP-XX GZ115 Small Form Factor powercastco.com 23 Powerharvester™ Module P2100 – 915MHz, Charge & Fire Features • High Conversion Efficiency • Internal Charge Management • High Sensitivity • Configurable Output Voltage • 50mA Output Current • Capacitor Overvoltage Protection • Internally Matched to 50 ohms • Low Quiescent Current (<1µA) • Simple Integration • Small Footprint powercastco.com 24 Energy Storage Choosing the Supercap Value Voltage Window (Hysteresis) Energy Available Capacitor Value C = 7.02E/e C = 8.57E e ≈ 0.82 DC-DC conversion efficiency 3 2 1 VMIN VMAX 0 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 Output Voltage (V) 4 Capacitor Voltage (V) = required load energy GZ115 cap size = 0.16F (measured) Stored energy = 22.7 mJ powercastco.com 25 TI eZ430-RF2500T Start-up and Data 3.70 mJ @ 3.3V Initial start-up powercastco.com Data Note: V1.5 Software 26 P2100 Charge Current P2100 Capacitor Charge Current at 1.1V Output Current (uA) 10000 1000 100 10 1 -15 -10 -5 0 5 10 15 Module Input Power (dBm) powercastco.com 27 Energy Harvesting Performance Charge Time vs. Distance 10000 3W EIRP Patch Antenna Transmitter Measured @ 15 ft (103 sec) Charge Time (sec) 1000 Measured @10ft (152 sec) 100 Measured @20ft (145sec) 10 Sleeve Dipole (G=1.5) Air Dipole (G=4.1) Yagi (G=6.1) 1 5 powercastco.com 10 15 20 25 Distance (ft) 30 40 45 50 28 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!!! powercastco.com 29 Reference System On-Going Efforts Optimizing Performance • Reduce the capacitor size by modifying the software startup 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 powercastco.com 30 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 power options: on-demand, scheduled, continuous • Zero Stand-By operation eliminates design concerns of driving down sleep current: Average Current ≈ Sleep Current ≈ 0 powercastco.com 31 Thank You Visit us in Booth #1026 www.powercastco.com powercastco.com 32
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