wireless underwater power transmission (wupt) for lithium polymer charging james d’amato shawn...
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Wireless Underwater Power Transmission (WUPT) for Lithium Polymer Charging
Wireless Underwater Power Transmission (WUPT) for Lithium Polymer Charging
James D’AmatoShawn French
Warsame HebanKartik Vadlamani
December 5, 2011
School of Electrical and Computer Engineering
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Project OverviewProject 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
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Design ObjectivesDesign 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
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Technical SpecificationsTechnical Specifications
Features Proposed Specifications Specifications
Operating Frequency 2.1-2.3 MHz 41 - 47 kHz
Phase Velocity 1482 m/s 1482 m/s
Input Signal 20 V Square Wave 30 V Square Wave
Distance to Transmit 22” 22”
Matching Layer Thickness
0.0008” 0.667”
Transfer Efficiency 10% 10%
Battery 3.7 V, 160 mAh 3.7 V, 160 mAh
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Transducer DimensionsTransducer Dimensions
2.1”
2.5”
• Acrylic matching layer
• Stainless steel conduit sleeve
• Weight of 2.1 lbs
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Piezo Electric PropertiesPiezo Electric Properties
• SM111 piezo materialo PZT-4
• 50 mm diameter, 3 mm thickness
• 44 kHz +/- 3 kHz resonance
• 60% electromechanical coupling coefficient
• 8 Ω resonant impedance
• 7200 pF static capacitancePositive terminal
Negative terminal
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Transducer Cross SectionTransducer Cross Section
Piezoelectric 30 MRayl
Acrylic (0.67”)3.67 MRayl
Acrylic (0.67”)3.67 MRayl
Polyurethane1.6 MRayl 5 minute epoxy
(water-proofing)
Stainless Steel Sleeve
• Water has an
acoustic impedance of 1.438 MRayl
• Polyurethane has high attenuation
• Stainless steel sleeve acts as heat sink
Front
Back
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Energy Harvesting CircuitEnergy 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
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Energy Harvesting ProfileEnergy 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
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Battery Charging CircuitBattery Charging Circuit
• Low operating current (450 nA)
• 1% voltage accuracy
• 50 – 500 mA output current
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Lithium Polymer Charging ProfileLithium 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
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WUPT Demo ConfigurationWUPT Demo Configuration
• Distance of 22” between transmitting and receiving transducer• Transmitter connected to function generator• Receiver connected to energy harvesting circuit
Receiver
Transmitter
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ResultsResults
• 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
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ProblemsProblems
• 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
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Final Cost AnalysisFinal Cost Analysis
Unit Price
Nylon Sleeves $50
Epoxy $120
Small Piezoelectrics Donated
Coaxial Cable Donated
Testing Apparatus $5
Lithium Polymer Battery $10
Circuit Components Donated
Large Piezoelectrics $36
Epoxy, Polyurethane, RTV, Caulk Gun $54
Acrylic Plexiglas $67
Total $342
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Future WorkFuture 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