Wireless Underwater Power Transmission (WUPT) for Lithium Polymer Charging James D’Amato Shawn French Warsame Heban Kartik Vadlamani November 2, 2011 School of Electrical and Computer Engineering

Problem Acoustic sensors used to locate oil deposits High power consumption leads to low lifespan Seismic acoustic sensor (Li-po powered)

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

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

Block Diagram of WUPT System Amplification Circuit Rectification Circuit Transmitter Electric -> Acoustic Acoustic -> Electric Charging Circuit Receiver Lithium Polymer Cell

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

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

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 Transmitter Receiver Variable distance

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

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

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

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

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

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 U1 MAX1555 Li-ion Charger U2 MAX8881 Linear Regulator Battery End of Charge Indicator 3.7 V 100 mA Charge 3.3 V 200 mA System

Prototype Cost Analysis Unit Price Nylon Sleeves $50 Epoxy $120 Piezoelectrics Donated Coaxial Cable Testing Apparatus $5 Lithium Polymer Battery $10 Circuit Components Total $185

Replacement Seismic Sensor Market Analysis Demand Oil exploration approved for Shell in Beaufort Sea Profit (per unit) Method WUPT Replacement Seismic Sensor Company Cost $300 $600 Parts Cost $60 Total Labor $20 Fringe Benefits $5 Overhead $85 Sales Expenses $40 Selling Price $300 Profit $95

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

Upcoming Deadlines Task Deadline Order acoustic matching layers and low-frequency piezoelectrics Nov. 4 Construct low-impedance backing Nov. 8 Waterproof transducers Nov. 10 Final power efficiency testing Nov. 13 Wind transformer Nov. 15 Interface circuitry Nov. 20 Final testing Nov. 28

Questions