Wireless Underwater Power Transmission (WUPT) for Lithium Polymer Charging

James D’AmatoShawn French

Warsame HebanKartik Vadlamani

November 2, 2011

School of Electrical and Computer Engineering

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Problem

Seismic acoustic sensor (Li-po powered)

• Acoustic sensors used to locate oil deposits

• High power consumption leads to low lifespan

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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

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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

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Block Diagram of WUPT System

Electric -> Acoustic

Acoustic -> Electric

Amplification Circuit

Rectification Circuit

Charging Circuit

Lithium Polymer Cell

Transmitter

Receiver

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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

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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

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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 constantReceiverTransmitter

Variable distance

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Input / Output Waveforms

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

Input WaveformOutput Waveform

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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

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Transformer Design

? V2

• Source Impedance– Resistance seen by the primary on the transformer– Found by sweeping load resistance (RL) until

V(2)=0.5*V(1)

When V(2)=0.5*V(1), Rg=RL

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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

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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

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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

U1MAX1555

Li-ion Charger

U2MAX8881

Linear Regulator

Battery

End of Charge Indicator

3.7 V100 mACharge

3.3 V200 mASystem

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Prototype Cost Analysis

Unit PriceNylon Sleeves $50

Epoxy $120

Piezoelectrics Donated

Coaxial Cable Donated

Testing Apparatus $5

Lithium Polymer Battery $10

Circuit Components Donated

Total $185

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Market Analysis

• Demand– Oil exploration approved for Shell in Beaufort Sea

• Profit (per unit)

Method WUPT Replacement Seismic SensorCompany Cost $300 $600

Parts Cost $60

Total Labor $20

Fringe Benefits $5

Overhead $85

Sales Expenses $40

Selling Price $300

Profit $95

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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

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Upcoming Deadlines

Task DeadlineOrder acoustic matching layers and low-frequency piezoelectrics

Nov. 4

Construct low-impedance backing Nov. 8Waterproof transducers Nov. 10Final power efficiency testing Nov. 13Wind transformer Nov. 15Interface circuitry Nov. 20Final testing Nov. 28

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Questions