1. 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

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

3. 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

4. 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

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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. Questions