development of a wireless sensors network powered by energy harvesting techniques
DESCRIPTION
Develer Workshop: A workshop focused on the principles and benefits of applying the Energy Harvesting techniques on Wireless Sensor Networks. The contents come from my Better Embedded 2013 talk.TRANSCRIPT
DEVELOPMENT OF A WIRELESS SENSOR NETWORK POWERED BY ENERGY HARVESTING TECHNIQUES
Daniele Costarella
Develer – Campi Bisenzio, FI, Italy – November 6th, 2013
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
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Common EH Systems
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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.
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Common EH Sources
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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)
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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
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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
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Wireless Sensor Node
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Power unit
Piezoelectric generator
Solar source
TEG
Sensing subsystem
Sensors
ADC
Computing subsystem
MCU • Memory • SPI • UART
Communication subsystem
Radio
Main subsystems
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Wireless Sensor Node
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25%
15%
60%
Computing Subsystem Sensing Subsystem Communication Subsystem
Power consumption distribution for a wireless sensor node
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• 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
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• 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
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Energy Storage
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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
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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
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Supply management: LTC3588
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A simple circuit simulation
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Supply management: LTC3588
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A simple circuit simulation with a 47uF output capacitor
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Supply management: LTC3588
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We could increase the output capacitance to 2200uF
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Supply management: LTC3588
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And if we choose an even larger capacity? Ex. 1F
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Anatomy of the WSN node
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Battery Output vs. EH Module Output
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Energy Available vs. Time
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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
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Power supply circuit
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Piezo
Solar
TEG
Supercap
Primary Charge
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Prototyping On board: • 40-Pin Flash Microcontroller
with nanoWatt XLP Technology
• Low Power 2.4GHz GFSK Transceiver Module
• Low Power Linear Active Thermistor
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Signal analysis
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Fig. A: Duty cycle Fig. B: TX pulse length (Zoom View)
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Code Diagram
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Fig. A: Init Fig. B: Main Loop
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Payload structure
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Data analysis • Web interface
• Real time graphics • History
• Views • Temperature • Supercapacitor Voltage • Input Voltage • Charging • Backup status
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Data analysis: examples
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Fig. A: Temperature Fig. B: Input Voltage (VIN)
Fig. C: Supercap charging Fig. D: Supercap discharge
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DEMO
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
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References
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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
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Thank you
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@dcostarella
http://it.linkedin.com/in/danielecostarella
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