Development of a wireless sensor network powered by energy harvesting techniques

DEVELOPMENT OF A WIRELESS SENSOR NETWORK POWERED BY ENERGY HARVESTING TECHNIQUES

Daniele Costarella

Grand Hotel Mediterraneo - Florence - July 9th, 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

July 9th, 2013 Energy Harvesting Demoboard 2

Common EH Systems


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.


Common EH Sources


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)

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


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


Wireless Sensor Node


Power unit

Piezoelectric generator

Solar source

TEG

Sensing subsystem

Sensors

ADC

Computing subsystem

MCU •  Memory •  SPI •  UART

Communication subsystem

Radio

Main subsystems

Wireless Sensor Node


25%

15%

60%

Computing Subsystem Sensing Subsystem Communication Subsystem

Power consumption distribution for a wireless sensor node

•  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


•  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

Energy Storage


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

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


Anatomy of the WSN node


Battery Output vs. EH Module Output


Energy Available vs. Time


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


Power supply circuit


Piezo

Solar

TEG

Supercap

Primary Charge

Prototyping On board: •  40-Pin Flash Microcontroller

with nanoWatt XLP Technology

•  Low Power 2.4GHz GFSK Transceiver Module

•  Low Power Linear Active Thermistor


Signal analysis


Fig. A: Duty cycle Fig. B: TX pulse length (Zoom View)

Data analysis •  Web interface

•  Real time graphics •  History

•  Views •  Temperature •  Supercapacitor Voltage •  Input Voltage •  Charging •  Backup status


Data analysis: examples


Fig. A: Temperature Fig. B: Input Voltage (VIN)

Fig. C: Supercap charging Fig. D: Supercap discharge

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


References


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

Thank you


@dcostarella

http://it.linkedin.com/in/danielecostarella