ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

Hande, Nov 2005

Energy Harvesting Methodologies for Wireless Sensor Nodes

Dinesh BhatiaAssociate Professor

Abhiman HandeResearch Associate

Erik Jonsson School of EngineeringNovember 23, 2005

ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

Hande, Nov 2005

Outline

Present power requirements in PANs Necessity for alternate sources of energy Available alternative energy sources Energy harvesting issues Energy storage issues Power management strategies Research at UTD’s EACG

ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

Hande, Nov 2005

Technology Trends

Relative improvements in laptop computing technology from 1990–2003.

ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

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Feasible Sources of Energy

Photovoltaic solar cells Amorphous Crystalline

Vibrations Piezoelectric Capacitive Inductive

Radio-Frequency (RF) Thermoelectric conversion Human power Wind/air flow Pressure variations

Harvesting technology Power density

Solar cells (outdoors at noon) 15 mW/cm2

Piezoelectric (shoe inserts) 330 μW/cm3

Vibration (small microwave oven) 116 μW/cm3

Thermoelectric (10oC gradient) 40 μW/cm3

Acoustic noise (100dB) 960 nW/cm3

Power densities of energy harvesting technologies

ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

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Feasible Devices for Energy Storage

Batteries Li-ion NiCD NiMH

Ultracapacitors Maxwell Samsung NEC

Micro-fuel cells Micro-heat engines Radioactive power sources Maxwell 5V 2F 2.7 mAhr ultracapacitor

VoltaFlex thin film rechargeable lithium batteries

ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

Hande, Nov 2005

Energy Harvesting for Wireless Sensor Nodes

VCC

Raw data

Packetized samples

MicrocontrollerA/D converter

Sensors Program and data flash memory

RF communication link

Energy harvesting and energy storage

Energy source

Antenna

Block diagram of an energy harvesting wireless sensing node with data logging and bidirectional RF communications capabilities

ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

Hande, Nov 2005

Solar Cell Characteristics

10-20 % efficiency outdoors <1% efficiency indoors Needs power management scheme Maximum power point might need tracking

V-I characteristics of a Solar World 4-4.0-100 solar panel

ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

Hande, Nov 2005

Solar Cell Efficiencies Under Different Light Conditions

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Vibrations to Electricity

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Comparison of Vibrations to Electricity Methods

Scavenging the power from commonly occurring vibrations for use by low power wireless systems is both feasible and attractive for certain applications.

Piezoelectric converters appear to be the most attractive for meso-scale devices with a maximum demonstrated power density of approximately 200 μW/cm3 vs. 100 μW/cm3 for capacitive MEMS devices.

Electromagnetic converters provide maximum voltage of 0.1 volts

ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

Hande, Nov 2005

Piezo Converter Set-up

Piezoelectric converter with rectifier and DC-DC converter

ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

Hande, Nov 2005

Power Management

Charge energy storage devices Route stored energy to sensor node Monitor available energy level Low power buck/boost converter required

VCC to system

Ultracapacitors Batteries

Power ManagementOptional rectification

Solar panels / piezoelectric

element

Dual energy storage mechanism for a wireless sensor node

ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

Hande, Nov 2005

Research at UTD’s EACG

CrossbowTM MICAz motes 2.4GHz, IEEE 802.15.4 compliant ZigBeeTM transceiver. Mesh networking protocol Potential applications include temperature and light monitoring in

remote locations, measuring tire pressure, monitoring acceleration in automobiles, medical applications, etc.

MICAz mote MICA2 motes

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Battery Life Estimation for a MICAz Mote

Processor Currents Example duty cycle Full operation 8 mA 1 %

Sleep mode 8 A 99 % Radio Currents Example duty cycle

Receive mode 8 mA 0.75 % Transmit mode 12 mA 0.25 %

Sleep mode 2 A 99 % Logger Memory Currents Example duty cycle

Write operation 15 mA 0 % Read operation 4 mA 0 %

Sleep mode 2 A 100 % Sensor Board Currents Example duty cycle

Full operation 5 mA 1 % Sleep mode 5 A 99 %

Computed mAhr used each hour Processor 0.0879

Radio 0.0920 Logger Memory 0.0020

Sensor Board 0.0550 Total mAhr used 0.2369

Computed battery life vs. battery size Battery Capacity (mAhr) Battery Life (months)

250 1.45 1000 5.78 3000 17.35

Battery life estimation for a MICAz mote operating at 1% duty cycle

ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

Hande, Nov 2005

Research Challenges

Set-ups for both solar and vibrational energy Dual energy storage scheme Power management Low power buck converter design

Task 1: Develop designs for energy scavenging prototypes

Task 2: Develop an appropriate power management scheme

Task 3: Identify appropriate components for procurement

Task 4: Implement the prototype designs

Task 5: Testing and modifications

SP SU FA2006 (Y1)

SP SU FA2007 (Y2)

SP SU FA

2008 (Y3)Indicates publications

Tentative research timeline

ZigBeeTM Alliance | Wireless Control That Simply WorksEmbedded and Adaptive Computing Group

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Conclusions

Acceptable power sources remain perhaps the most challenging technical hurdle to the widespread deployment of wireless sensor networks.

While significant progress has been made in many areas including indoor photovoltaic systems, micro-fuel cells, thermoelectrics, micro-heat engines, and vibration-to-electricity conversion, much more research and new approaches need to be pursued.