Industrial and Social Applications of Wireless Sensor Nets with “Energy Scavenging”

1. Industrial and Social Applications of Wireless Sensor Nets with “Energy Scavenging” With a case study on “battery-less” tiny-temperature nodes for “smart building applications” Paul Wright, Jan Rabaey, David Culler, Eli Leland, Elaine Lai, Sue Mellers, Michael Montero, Jessy Baker, Brian Otis, Rob Scewczyk, and Shad Roundy (now at The Australian National University)

2. Energy Scavenging GOAL: Design an ‘infinite life’ power source for a sensor node APPLICATION: Wireless Sensor Networks in Buildings VISION: Millions of self-powered sensor/transceivers, each the size of a speck of dust, will infiltrate a building and create a smart environment PROOF OF CONCEPT: To power a Mica2Dot Mote using vibrations from a wooden stairway in the Naval Architecture Building

3. Battery, Solar, and Vibrational Energy

4. Common Sources of Vibrations

5. Constitutive Equations 3 2 33 Mode 1 + V - 3 31 Mode 2 1 + V F - The Piezoelectric Effect Usable Modes of PZT d = strain s = stress Y = Young’s modulus d = piezoelectric coeff. D = electrical displacement e = dielectric constant E = electric field

6. Tungsten proof mass, glued base, PZT bender Pirelli Piezoelectric Device Staircase Piezoelectric device

7. Piezoelectric generator Rs C Vs Load Piezoelectric Bimorph Generators

8. Wooden Stairs Peak Frequency at 26.8 Hz FFT of frequencies Power generator must match peak frequency of vibration source for max power output Vibrations from walking down stairs

9. Bender Design • Characteristics • Piezoelectric: PZT • Tungsten Alloy Mass: 52 g • Beam Dimensions: • 1.25” x 0.5” x 0.02” • Behavior • Resonant Frequency: 26.8 Hz • Power Output: 450 μW 40V peak–to-peak output from bender when someone walks down the stairs

10. Tiny Temp Storage Capacitor Power Circuit Mote Piezoelectric Power Generator Thermistor

11. Rectifier Power Circuit Voltage Out to Mote Voltage In from Bender Rectifier Voltage Regulator Storage Capacitor Comparator (3.5V – 5V) Regulator Enable ~ VIN Piezo Bender Vout = 3.3V DC Comparator CST 6600μF

12. Load Requirements • Mica2Dot Mote • 3.3 Input Voltage • 800 ms ‘Startup Time’ • 45 mW to take temperature reading and transmit information

13. FDM Packaging Upper Case Temperature Sensor Hole Capacitor Holders PCB Holder Bridge Bender Platform Case Tabs Lower Case

14. Capacitor Discharging 5 V 3.5 V 816 ms Power Out Proof of Concept #1 (CEC) • Procedure • 3 people ran on the stairs for 40 minutes • Results • 3.28 V for 816 ms • 2 temperature readings transmitted

15. Proof of Concept #2 (Fire)

16. Proof of Concept #2 (Fire)

17. Next Steps: Short Term Mica2dot mote Charge Up Time PicoRadio-based node Efficiency

19. TMSM PDMS SiO2 Si Inertial Mass Platinum PZT Cantilever Beam Si3N4 SiO2 Si Substrate Aluminum Flip and Bond Assembly Next Steps: Long Term Design a variable resonant frequency MEMS bender which adapts to vibration sources with different peak frequencies.

20. Thanks to CITRIS, NSF & the California Energy Commission for their sponsorship Many Thanks!