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Wireless Underwater Power Transmission (WUPT) for Lithium Polymer Charging

Wireless Underwater Power Transmission (WUPT) for Lithium Polymer Charging. James D’Amato Shawn French Warsame Heban Kartik Vadlamani December 5, 2011. School of Electrical and Computer Engineering. Project Overview. Goal: Provide wireless solution to recharge submerged battery cells

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Wireless Underwater Power Transmission (WUPT) for Lithium Polymer Charging

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  1. Wireless Underwater Power Transmission (WUPT) for Lithium Polymer Charging James D’Amato Shawn French WarsameHeban KartikVadlamani December 5, 2011 School of Electrical and Computer Engineering

  2. 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

  3. Design Objectives • Convert an electrical signal to an acoustic signal • Transmit acoustic signal through water • Generate a voltage from the acoustic signal • Rectify and amplify voltage • Charge a lithium-ion battery

  4. Technical Specifications

  5. WUPT System Energy Harvesting Circuit Transmitter Battery Charging Circuit Receiver

  6. Transducer Dimensions 2.1” • Acrylic matching layer • Stainless steel conduit sleeve • Weight of 2.1 lbs 2.5”

  7. Piezo Electric Properties • SM111 piezomaterial • PZT-4 • 50 mm diameter, 3 mm thickness • 44 kHz +/- 3 kHz resonance • 60% electromechanical coupling coefficient • 8 Ω resonant impedance • 7200 pF static capacitance Negative terminal Positive terminal

  8. Transducer Cross Section Front • Water has an acoustic impedance of 1.438 MRayl • Polyurethane has high attenuation • Stainless steel sleeve acts as heat sink Acrylic (0.67”) 3.67 MRayl Piezoelectric 30 MRayl Acrylic (0.67”) 3.67 MRayl Polyurethane 1.6 MRayl 5 minute epoxy (water-proofing) Back Stainless Steel Sleeve

  9. Energy Harvesting Circuit Piezoelectric • 2.7 – 20 V Input Operating Range • Low-loss Full-Wave Bridge Rectifier • 100 mA Output Current • Buck DC/DC Converter • Selectable Output Voltages of 1.8 V, 2.5 V, 3.3 V, 3.6 V

  10. Energy Harvesting Profile • 3 min. 30 sec charging time • PGOOD goes high when Vout is 92% of target value • Buck Converter outputs constant voltage independent of Vin

  11. Battery Charging Circuit • Low operating current (450 nA) • 1% voltage accuracy • 50 – 500 mA output current

  12. Lithium Polymer Charging Profile • LTC4070 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

  13. WUPT Demo Configuration • Distance of 22” between transmitting and receiving transducer • Transmitter connected to function generator • Receiver connected to energy harvesting circuit Receiver Transmitter

  14. Results • Input of 20 Vpp square wave at 46.77 kHz • Output of 2.38 Vpp sine wave at 46.77 kHz • Efficiency of 12% • Specifications satisfied

  15. Problems • Initial transducers were operating at too high of a frequency • Matching layer was not a precise thickness nor was effectively impedance matched • Backing layer was not acoustically matched to transmission medium • Nylon sleeves were reflecting heat • Energy harvesting circuit currently not matching output profile

  16. Final Cost Analysis

  17. Future Work • Implement piezoelectric transducers with more suitable internal acoustic impedance for better matching • Develop polymer matching layer that can meet desired requirements • Implement charging and end-of-charge feedback signals to charging source • Increase effective range

  18. Questions

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