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)

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

Battery, Solar, and Vibrational Energy

Vibration Source Frequency of Peak (Hz) Peak Acceleration (m/s 2 ) Kitchen Blender Casing Clothes Dryer Door Frame (just after door closes)1253 Small Microwave Oven HVAC Vents in Office Building Wooden Deck with People Walking Bread Maker External Windows (size 2ftx3ft) next to a Busy Street Notebook Computer while CD is Being Read Washing Machine Second Story of Wood Frame Office Building Refrigerator Common Sources of Vibrations

The Piezoelectric Effect Constitutive Equations  = strain  = stress Y = Young’s modulus d = piezoelectric coeff. D = electrical displacement  = dielectric constant E = electric field Usable Modes of PZT V Mode 31 Mode F V

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

Piezoelectric Bimorph Generators Load Vs C Rs Piezoelectric generator

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

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

Tiny Temp Piezoelectric Power Generator Storage Capacitor Thermistor Power Circuit Mote

6600μF Enable Comparator Regulator V out = 3.3V DC C ST ~ V IN Piezo Bender Rectifier Voltage Out to Mote Voltage In from Bender Voltage Regulator Comparator (3.5V – 5V) Storage Capacitor Power Circuit Rectifier

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

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

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

Proof of Concept #2 (Fire)

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

Next Steps: Long Term Design a variable resonant frequency MEMS bender which adapts to vibration sources with different peak frequencies. Si SiO 2 PDMS TMSM Si SiO 2 Si 3 N 4 PZT Platinum Aluminum Inertial Mass Substrate Cantilever Beam Flip and Bond Assembly

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