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Development of a wireless sensor network powered by energy harvesting techniques

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Energy Harvesting for Wireless Sensor Networks

Energy Harvesting for Wireless Sensor Networks

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  • 1. DEVELOPMENT OF A WIRELESS SENSOR NETWORK POWERED BY ENERGY HARVESTING TECHNIQUES Daniele Costarella Grand Hotel Mediterraneo - Florence - July 9th, 2013
  • 2. Outline •  Energy Harvesting Basics •  What are the benefits? Where is it useful? Important aspects. •  Piezoelectric, Thermoelectric and Solar Sources •  Selecting the Right Transducers, piezogenerator models, capabilities, limitations •  Converting Harvested Energy into a Regulated Output •  Rectification, start-up, efficiency, and over-voltage concerns •  Integrated solution in a WSN •  Challenges Design of a EH-WSN node, prototyping •  Data analysis July 9th, 2013 Energy Harvesting Demoboard 2
  • 3. Common EH Systems July 9th, 2013 Energy Harvesting Demoboard 3
  • 4. Energy Harvesting Basics •  Energy Harvesting is the process by which energy readily available from the environment is captured and converted into usable electrical energy •  This term frequently refers to small autonomous devices, or micro energy harvesting •  Ideal for substituting for batteries that are impractical, costly, or dangerous to replace. July 9th, 2013 Energy Harvesting Demoboard 4
  • 5. Common EH Sources July 9th, 2013 Energy Harvesting Demoboard 5 Energy Source Performance (Power Density) Notes Solar: •  Outdoor, direct sunlight •  Outdoor, cloudy •  Indoor 15 mW / cm2 0.15 mW /cm2 10 uW / cm2 Power per unit with a Conversion efficiency of 15% Mechanical •  Machinery •  Human body •  Acoustic noise •  Airflow 100-1000 uW /cm3 110 uW / cm3 1 uW / cm2 @ 100 dB 750 uW / cm2 @ 5 m/s Ex. 800 uW / cm3 @ 2mm e 2.5 kHz Ex. 4 uW / cm3 @ 5 mm and 1 Hz It depends on the specific conditions with respect to the Betz limit Thermic •  Temperature gradients •  EM radiation 1-1000 uW / cm3 Depends on the average temperature. Distance: 5 m from a 1W source @ 2.4 GHz (free space)
  • 6. Design challenges in conventional WSN •  Sensor node has limited energy supply •  Hard to replace/recharge nodes’ batteries once deployed, due to •  Number of nodes in network is high •  Deployed in large area and difficult locations like hostile environments, forests, inside walls, etc •  Nodes are ad hoc deployed and distributed •  No human intervention to interrupt nodes’ operations •  WSN performances highly dependent on energy supply •  Higher performances demand more energy supply •  Bottleneck of Conventional WSN is ENERGY July 9th, 2013 Energy Harvesting Demoboard 6
  • 7. Energy Harvesting in Wireless Sensor Networks •  Wireless Sensor nodes are designed to operate in a very low duty cycle •  The sensor node is put to the sleep mode most of the time and it is activated to perform sensing and communication when needed •  Moderate power consumption in active mode, and very low power consumption while in sleep (or idle) mode •  Advantages: •  Recharge batteries or similar in sensor nodes using EH •  Prolong WSN operational lifetime or even infinite life span •  Growing interest from academia, military and industry •  Reduces installation and operating costs •  System reliability enhancement July 9th, 2013 Energy Harvesting Demoboard 7
  • 8. Wireless Sensor Node July 9th, 2013 Energy Harvesting Demoboard 8 Power unit Piezoelectric generator Solar source TEG Sensing subsystem Sensors ADC Computing subsystem MCU •  Memory •  SPI •  UART Communication subsystem Radio Main subsystems
  • 9. Wireless Sensor Node July 9th, 2013 Energy Harvesting Demoboard 9 25% 15% 60% Computing Subsystem Sensing Subsystem Communication Subsystem Power consumption distribution for a wireless sensor node
  • 10. •  Vibrating piezos generate an A/C output •  Electrical output depends on frequency and acceleration •  Open circuit voltages may be quite high at high g-levels •  Output impedances also quite high Energy sources July 9th, 2013 Energy Harvesting Demoboard 10 •  TEGs are simply thermoelectric modules that convert a temperature differential across across the device, and resulting heat flow through it, into a voltage •  Based on Seebeck effect •  Output voltage range: 10 mV/K to 50 mV/K •  A solar cell converts the energy of light directly into electricity by the photovoltaic effect •  The output power of the cell is proportional to the brightness of the light landing on the cell, the total area and the efficiency
  • 11. Energy Storage July 9th, 2013 Energy Harvesting Demoboard 11 Option 2: Capacitors •  Efficient charging •  Limited capacity Option 3: Super Capacitors •  Small size •  High efficiency •  Very high capacity ( from 1 up to 5000F or so) Option 1: Traditional Rechargeable Batteries •  Inefficient charging (lots of energy converted to heat) •  Limited numbed of charging cycles
  • 12. Supply management: LTC3588 •  The LTC3588 is a high efficiency integrated hysteretic buck DC/DC converter •  Collects energy from the piezoelectric transducer and delivers regulated outputs up to 100mA •  Integrated low-loss full-wave bridge rectifier •  Requires 950nA of quiescent current (in regulation) and 450nA in UVLO July 9th, 2013 Energy Harvesting Demoboard 12
  • 13. Anatomy of the WSN node July 9th, 2013 Energy Harvesting Demoboard 13
  • 14. Battery Output vs. EH Module Output July 9th, 2013 Energy Harvesting Demoboard 14
  • 15. Energy Available vs. Time July 9th, 2013 Energy Harvesting Demoboard 15
  • 16. Demoboard Project •  Design of a multisource Energy Harvesting Wireless Sensor Node •  Development of a demoboard with Energy Harvesting capabilities, including RF communication and Temperature sensor •  Additional supercap for longer backup operation •  Very customizable to the end users’ needs July 9th, 2013 Energy Harvesting Demoboard 16
  • 17. Power supply circuit July 9th, 2013 Energy Harvesting Demoboard 17 Piezo Solar TEG Supercap Primary Charge
  • 18. Prototyping On board: •  40-Pin Flash Microcontroller with nanoWatt XLP Technology •  Low Power 2.4GHz GFSK Transceiver Module •  Low Power Linear Active Thermistor July 9th, 2013 Energy Harvesting Demoboard 18
  • 19. Signal analysis July 9th, 2013 Energy Harvesting Demoboard 19 Fig. A: Duty cycle Fig. B: TX pulse length (Zoom View)
  • 20. Data analysis •  Web interface •  Real time graphics •  History •  Views •  Temperature •  Supercapacitor Voltage •  Input Voltage •  Charging •  Backup status July 9th, 2013 Energy Harvesting Demoboard 20
  • 21. Data analysis: examples July 9th, 2013 Energy Harvesting Demoboard 21 Fig. A: Temperature Fig. B: Input Voltage (VIN) Fig. C: Supercap charging Fig. D: Supercap discharge
  • 22. DEMO
  • 23. Board specifications Feature Description Sources: Solar / TEG / Piezoelectric Input voltage ranges: Solar: 5 ÷ 18 VDC TEG: 20 ÷ 500 mVDC Piezoelectric: max 18 VAC Temperature Sensor: 0 ÷ 50 °C Resolution: 0.4 °C Wireless communication: 2400-2483.5 MHz ISM (GFSK) Transmission rate: 1 and 2 Mbps support Current/Power IDLE mode: 9 uA / 30 uW Current/Power TX mode: 18.9 mA / 62 mW Maximum TX distance: 100 m Backup operation: > 24 h July 9th, 2013 Energy Harvesting Demoboard 23
  • 24. References July 9th, 2013 Energy Harvesting Demoboard 24 Energy Harvesting Technologies Springer By Shashank Priya and Daniel J. Inman Covers a very wide range of interesting topics My Master Thesis Università degli Studi di Napoli “Federico II” By Daniele Costarella Available online: http://danielecostarella.com
  • 25. Thank you July 9th, 2013 Energy Harvesting Demoboard 25 @dcostarella http://it.linkedin.com/in/danielecostarella