ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 Energy Harvesting Methodologies for Wireless Sensor Nodes Dinesh Bhatia Associate Professor Abhiman Hande Research Associate Erik Jonsson School of Engineering November 23, 2005

ZigBee TM Alliance | Wireless Control That Simply Works Embedded 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

ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 Technology Trends Relative improvements in laptop computing technology from 1990–2003.

ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 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 technologyPower density Solar cells (outdoors at noon)15 mW/cm 2 Piezoelectric (shoe inserts)330 μW/cm 3 Vibration (small microwave oven)116 μW/cm 3 Thermoelectric (10 o C gradient)40 μW/cm 3 Acoustic noise (100dB)960 nW/cm 3 Power densities of energy harvesting technologies

ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 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

ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 Energy Harvesting for Wireless Sensor Nodes VCC Raw data Packetized samples MicrocontrollerA/D converter SensorsProgram 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

ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 Solar Cell Characteristics  % efficiency outdoors  <1% efficiency indoors  Needs power management scheme  Maximum power point might need tracking V-I characteristics of a Solar World solar panel

ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 Solar Cell Efficiencies Under Different Light Conditions

ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 Vibrations to Electricity

ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 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/cm 3 vs. 100 μW/cm 3 for capacitive MEMS devices.  Electromagnetic converters provide maximum voltage of 0.1 volts

ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 Piezo Converter Set-up Piezoelectric converter with rectifier and DC-DC converter

ZigBee TM Alliance | Wireless Control That Simply Works Embedded 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 Management Optional rectification Solar panels / piezoelectric element Dual energy storage mechanism for a wireless sensor node

ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 Research at UTD’s EACG  Crossbow TM MICAz motes  2.4GHz, IEEE compliant ZigBee TM 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 moteMICA2 motes

ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 Battery Life Estimation for a MICAz Mote Battery life estimation for a MICAz mote operating at 1% duty cycle

ZigBee TM Alliance | Wireless Control That Simply Works Embedded 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 FA 2006 (Y1) SP SU FA 2007 (Y2) SP SU FA 2008 (Y3) Indicates publications Tentative research timeline

ZigBee TM Alliance | Wireless Control That Simply Works Embedded and Adaptive Computing Group Hande, Nov 2005 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.