Wireless Underwater Power Transmission (WUPT) for Lithium Polymer Charging

1. Wireless Underwater Power Transmission (WUPT) for Lithium Polymer Charging James D’Amato Shawn French WarsameHeban KartikVadlamani November 2, 2011 School of Electrical and Computer Engineering

2. Problem • Acoustic sensors used to locate oildeposits • High power consumption leads to low lifespan Seismic acoustic sensor (Li-popowered)

3. Project Overview • Goal: Provide wireless solution to recharge submerged battery cells • Target Customer: Upstream oil exploration industry • Motivation: Increase longevity of submerged acoustic sensors • Target Cost: Prototype < $350

4. Design Objectives • Convert an electrical signal to an acoustic signal • Transmit acoustic signal through water • Generate a voltage from the acoustic signal • Amplify voltage • Charge a lithium-ion battery

5. Block Diagram of WUPT System Amplification Circuit Rectification Circuit Transmitter Charging Circuit Electric -> Acoustic Acoustic -> Electric Receiver LithiumPolymer Cell

6. PZT-5H Piezoelectric Transducer • Generates a mechanical force from an electrical signal • Operates at a resonance frequency of 2.2 MHz • US Navy Grade VI Black dot denotes positive terminal

7. Transmitting / Receiving Transducer • ½” Nylon sleeve casing • 30-min. Loctite epoxy (impedance matched to water) • Front epoxy layer has a thickness of 20 microns for ¼ wavelength transmission • RG-178 Teflon coated coaxial cable used for noise reduction • Problem: Low power generation

8. WUPT Testing Configuration • Distance of 22” between transmitting and receiving transducer • Near field to far field transition occurs at 22” for PZT-5H piezoelectric • Rail system used to control variation in x-direction while keeping y, z-direction constant Receiver Transmitter Variable distance

9. Input / Output Waveforms • Input of 10 Vpp,2.2MHz, 50% Duty Cycle square wave • Output of 300 mVpp, 2.2MHz sine wave Input Waveform Output Waveform

10. Amplification Stage • Need a minimum of 5.1 V with a current of 100 mA on the secondary • Step-down transformer: • Amplify current and decrease voltage for charging • Impedance match load to source

11. Transformer Design • Source Impedance • Resistance seen by the primary on the transformer • Found by sweeping load resistance (RL) until V(2)=0.5*V(1) • ? V2 When V(2)=0.5*V(1), Rg=RL

12. AC to DC Rectification • Lithium Polymer charging circuit only accepts a DC voltage • Full-wave bridge rectifier with smoothing capacitor used to convert AC to DC • Problem: 1.4 V drop across two diodes From transformer secondary To MAX1555

13. Lithium Polymer Charging Profile • MAX1555 adheres to this charge profile • Li-po Battery is 3.7 V, 160 mA • Icc is 0.7C Icc = 112 mA • Itc is 0.1C Itc = 16 mA

14. Charging Circuitry • Requires a minimum of 3.7 V at 100 mA • Able to supply power to a system while charging using a linear regulator (MAX8881) • Shuts off charging at 3.7 V and an indicator goes high 3.7 V 100 mA Charge U2 MAX8881 Linear Regulator U1 MAX1555 Li-ion Charger 3.3 V 200 mA System End of Charge Indicator Battery

15. Prototype Cost Analysis

16. Market Analysis • Demand • Oil exploration approved for Shell in Beaufort Sea • Profit (per unit)

17. Current Status of Project • Transmitting and Receiving Transducers • Optimizing final transducer design to receive more power • Amplification/Rectification Circuit • Ordering transformer core • Rectification circuit complete • Charging Circuit • Ordered 3.7 V, 160 mA Lithium Polymer Battery

18. Upcoming Deadlines

19. Questions