ENERGY HARVESTING USING MICRO AND NANO STRUCTURES

1. ENERGY HARVESTING USING MICRO AND NANO STRUCTURES FALL 2008 MAE 589M FINAL PROJECT KARTHIK TIRUTHANI

2. AGENDA • Motivation • Introduction • Motion based energy conversion model • Review • Comparison of energy harvesting techniques • Issues • Existing solutions • Proposed solution • Analysis and Conclusion

3. MOTIVATION • Increasingly intelligent systems • Complexity of wiring • Increased costs of wiring • Reduced costs of embedded intelligence • Increasing popularity of wireless networks • Limitations of batteries • Limitations of power management techniques

4. INTRODUCTION Energy Harvesting Mechanisms • Ambient radiation sources • Pyroelectric energy harvesting • Photonic energy harvesting • Energy harvesting using Electroactive Polymers • Piezoelectric energy harvesting • Electrostatic energy harvesting • Electromagnetic energy harvesting • Thermoelectric energy harvesting • Magnetostrictive energy harvesting Properties of energy harvesting devices desired to power sensors • “Small” • “Light weight” • “Long life” • “Inexpensive” • “Flexibility” • “High power density” • “Easy fabrication” • “Easy implementation with microelectronics” • “Low wattage electronics without parasitics”

5. MODEL FOR MOTION BASED ENERGY HARVESTING • The equation for this system is given by • The solution for the system is given by • The power output is

6. EXISTING METHODS FOR MOTION OR VIBRATIONBASED ENERGY HARVESTING Piezoelectric Strain in piezoelectric material causes a charge separation (voltage across capacitor) Capacitive Change in capacitance causes either voltage or charge increase. Piezoelectric generator Rs C Vs Load

7. EXISTING METHODS FOR MOTION OR VIBRATIONBASED ENERGY HARVESTING Inductive Coil moves through magnetic field causing voltage in wire through Faradays Law Magnetostrictive Strain induced on a MsM produces a change in the magnetization of the material(Villari Effect). Upon dynamic or cyclic loading, this change in magnetization is converted into electrical energy using a pick-up coil surrounding the magnetostrictive layer. The constitutive equations are and Electromagnetic energy conversion device Amirtharajah et. al., 1998 MsM Energy harvesting device, Lei Wang 2007 Cross-Section of Micromachined Generator Williams et. al., 2001

8. THERMOELECTRIC ENERGY HARVESTING • Seebeck effect describes the potential generated when the junction of two dissimilar metals experiences a temperature difference • Thermoelectric generators (TEGs) use the Seebeck effect to harvest energy. • ZT, called Figure of Merit is a very convenient figure for comparing the potential efficiency of different materials for use in devices. Values of ZT=1 are considered good. • A simple charging circuit is shown • Power output is calculated using Seebeck Effect Illustration Simple Charging Circuit

9. COMPARISON OF ENERGY HARVESTING TECHNIQUES

10. ISSUES • Voltage required to be produced and energy density of the harvesting process for example as supply voltage for a sensor or to charge a battery or capacitor • Low wattage circuitry and eliminating parasitic • Size of the device • Ease of fabrication • Ease of implementation with CMOS processes and microelectronics • Flexibility • Adaptability and maximization of power (Resonance Tuning) Performance Characteristics

11. EXISTING SOLUTIONS • Synchronized switch harvesting on inductor • Adaptive control technique for the dc–dc converter • DC-DC PWM Boost Converter with feedforward and feedback control • Piezoelectric nanogenerators using aligned Zinc Oxide nanowire (NW) arrays • Flexible Microfibre–nanowire hybrid structures for energy scavenging • Tunable nanoresonators constructed from telescoping nanotubes Piezoelectric Nanogenerator Flexible nanogenerators Telescoping Nanotubes

12. EXISTING SOLUTIONS • Multiple spring mass systems • Tuning the effective non-linear stiffness by particular design of the electrostatic drive combs and mechanical springs • Alter beam stiffness by changing the axial preloads and causing buckling of beam • The apparent stiffness of a beam is dependent on both the elastic constant of the material, and the electric field across the material. The stiffness of a structure can be varied by changing field

13. PROPOSED SOLUTION • Mass of the silicon structure free to vibrate ~ 0.02 grams (Assuming 2.33g/cc) • Mass of fluid filled in the enclosure ~ 0.28 g (Assuming 4.95g/cc) • Total proof mass can be varied by varying the amount of fluid in the enclosure • If the initial quantity of fluid is a quarter of the enclosure then the frequency can be tuned by 100% Wafer #1 Side and Top View Wafer #2 Side and Top View Wafer #3 Side View of Microchannel Assembled Microstructure

14. RESULTS AND ANALYSIS Displacement Profile under loading

15. RESULTS AND ANALYSIS Stress distribution profile under loading

16. RESULTS AND ANALYSIS Factor of Safety plot under loading

17. CONCLUSIONS • Minimum Factor of Safety for the design is 10.2 • Maximum stress occurs at beam supports and it has factor of safety 12 • Designing the beams in a trapezoidal shape maximizes the average strain on the beam thus increasing power produced • Future research could focus on improving the efficiency, implementing microstructures with microelectronics, developing nanostructures, improving properties like ZT, piezoelectric and magnetostrictive constants, factor of coupling, etc

18. QUESTIONS