Development of a wireless sensor network powered by energy harvesting techniques

Project and development of a smart Wireless Sensor Network node powered by ambient Energy Harvesting. The demoboard is capable of accepting piezoelectric, solar and thermal-powered energy sources simultaneously. The project comes with a web based real-time data view.

Transcript

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