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

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