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2013 NASA CIPAIR SUMMER RESEARCH INTERNSHIP PROGRAMELECTRICAL ENGINEERING GROUP

M A R I S S A B U E L L , N E H A D D A B A B O , R E N E F I G U E R O A , P E T E R M O A L A

OPTIMIZING A WIRELESSLY POWERED AC-DC BOOSTER FOR BIOMEDICAL IMPLANTS

Supervised by SFSU Student Kang Bai and SFSU Advisor Dr. Hao Jiang

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BIOMEDICAL IMPLANTS

• Cardiac pacemakers

and defibrillators

• Neurological

stimulators

• Muscle Stimulators

• Cochlear implants

• Monitoring devices

• Drug pumpshttp://www.dvclub.info/il-pacemaker-biologico-tutto-naturale/

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BIOMEDICAL IMPLANTS

•Medical implant batteries require replacement every 5-10 years• Effective power storage requires a larger battery• Increased risk with multiple surgeries

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BIOMEDICAL IMPLANTS

• Cost of surgery for replacement ranges from $2000-$45,000+

• Insurance companies do not always cover replacement costs• “She (Plaintiff Paige Riley) alleges that Blue Cross &

Blue Shield of Mississippi refused to cover an operation to replace the batteries of a stomach-pain device she had surgically implanted in 2005. As a result, Riley had to fork over the $43,364.27 in cash”

http://www.forbes.com/2009/11/23/hmo-medical-implants-business-health-care-batteries.html

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THE WIRELESS SOLUTION

• Wireless power transfer for charging of Internal Medical Devices (IMDs) decreases the need for periodic, invasive surgery.

• Dramatically reduces battery size

• Currently, San Francisco State University has developed the most efficient AC-DC Booster• An open circuit input voltage of 200mV yields an output

voltage of 5V

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CIPAIR PROGRAM GOAL

• Optimize, miniaturize, and redesign the circuit by

removing jumper wires and extrinsic components

• Minimize parasitic capacitance, inductance and

resistance

• LT SPICE software—used to simulate testing.

• Printed Circuit Board (PC Board)—used to perform testing experimentally. Simulation cannot account for parasitic aspects, so the usage of a PC Board is mandatory to attain realistic results.

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TRANSFERRING WIRELESS POWER

• Time varying magnetic field induces an electric current in the receiver coil

Faraday’s Law

Self Induction

SETUP• Alternating current passing

through the transmitter coil induces an electromagnetic field.

Baker, et al., "Feedback analysis and design of RF power links for low-power bionic systems." Biomedical Circuits and Systems, IEEE Trans. on 1(1): 28-38.

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AC-DC BOOST CONVERTEROPERATING PRINCIPLE

How does 200mV become 5V?

• Switch is thrown open, large voltage drop occurs across the

other circuit components.

• The coil experiences an abrupt, large decrease in current, generating a

large voltage

• With the switch open, the coil provides the load with the voltage

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VOLTAGE ACROSS AN INDUCTORC

urr

en

t

Time

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FULL WAVE RECTIFIER

• Transforms input AC voltage to output DC voltage required to charge the battery

• Uses two diodes and two MOSFET transistors to avoid the large turn on voltage

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AC VOLTAGE

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TO FULLY RECTIFIED DC VOLTAGE

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WHAT CONTROLS THE SWITCH?

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Signal Coil

Analog Signal Conditioning

Power Coil

AC-DC Boost Converter

Transmitter Coil

Receiver Coil composed of two

coils

DC Output

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SIGNAL CONDITIONER

• Receives and cleans the the input frequency signal for use by the microcontroller, which converts the analog signal to the digital

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Analog Signal Conditioning

Logic Control Circuit

Signal Coil

Power Coil

AC-DC Boost Converter

Transmitter Coil

DC Output

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MICROCONTROLLER

• Small CPU that controls the switch’s on and off time• Uses input signal from the auxiliary coil to control

when switch opens and closes • The switch regulates the current passing through

through the circuit

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CURRENT SETUP

• Uses a transmitter coil to wireless transfer power• Allows for high frequency input and an

adjustable waveform

Why do we want an adjustable waveform and high frequency input?

Higher frequency input allows for a higher duty cycle

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THE SQUARE WAVE ADVANTAGE

Allows us to increase current input—greater duty cycle, less wasted current

• After full-wave rectification, square wave maintains nice steady output line.

• Sinusoidal wave requires some manipulation

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DUTY CYCLE VS OUTPUT VOLTAGEFOR SINUSOIDAL WAVEFORM

0 10 20 30 40 50 60 70 80 90 1000

1

2

3

4

5

6

DC Output (V) v.s. Duty Cycle(%)

DC Output (V)

duty cycle %

DC

Outp

ut

Volt

age (

V)

Peaks at 62%

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Green Wave – Input AC Voltage Blue Wave – Control Signal

Square Wave78% Duty Cycle

Sinusoidal Wave62% Duty Cycle

Rising edge of control signal must be properly aligned with input AC to maximize current input

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OUTPUT VOLTAGE VSOPEN CIRCUIT INPUT VOLTAGE

Sinusoidal WaveVout=10.9Vin

Square WaveVout=25Vin

Smaller input yields same output

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DESIGNING A PC BOARD

LayoutSchematicSolder & Test PC Board

Results and

Conclusion

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THE PREVIOUS SCHEMATIC

OBSOLE

TE

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RECREATING THE CURRENT SCHEMATIC

• Working backwards from the manufacturer’s file, the schematic for the presently utilized PC board was generated• Extra components, headers, and jumpers were

then removed Recreation of the layout

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LAYOUT FOR THE MOST RECENT PC BOARD

Microcontroller

Boost Converter

Signal Conditioner

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CURRENT SCHEMATIC OF CIRCUIT

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GENERATION OF THE LAYOUT

PLACE

• Organize the components

• Minimize parasitic aspects

COMPLETE WIRING

DESIGN RULE

CHECK (DRC)

• Ensure regulations are met

• Distance, drill hole size,

REVISE LAYOUT

SEND FORMANUFACTUR

E

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31PC Board Design

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WHAT’S NEXT?

• Manufacturing of the board takes 2 weeks

• Wind coils of different wire lengths and measure resulting inductance and resistance to minimize input voltage

• Run measurements on the old PC Board

• After receiving the new PC Board, solder components and rerun testing

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PC BOARD MEASUREMENTS

Time On (µs)

Time Off (µs)

End of Period (µs)

Duty Cycle Output Voltage

-395.2 66.8 126.6 88.53967037

4.2449

1126.5 1592 1671.5 85.41284404

4.2611

498.1 893.3 967.1 84.26439232

4.2449

1125.9 1575.5 1665.4 83.33642261

4.2189

-424.4 2.3 122.6 78.00731261

4.013

518.56 894.04 1004.32 77.29743083

4.1612

704.51 1051.19 1160 76.11144043

5.1192

1707.5 2053 2164.1 75.66798073

5.1192

249.96 527.92 723.84 58.65619988

5.02

482.8 715.7 995 45.47051933

4.7

1003 1191.12 1522.6 36.2047729 4.1381

Data for 1.43 mH coil

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DUTY CYCLE VS. OUTPUT VOLTAGE

0 10 20 30 40 50 60 70 80 90 1000

1

2

3

4

5

6

Duty Cycle (%)

Outp

ut

Volt

age (

V)

LR=1.43mHRS=4.1Ω

Peaks at 76%

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LOAD RESISTANCE VS. OUTPUT VOLTAGE

Load Resistance (kΩ) Output Voltage (V)

47.7 20.969

41 19.22

32.7 16.28

29.9 16.8

25.1 14.26

19.6 10.1

14.9 8.39

11.4 7.48

5.6 4.16

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LOAD RESISTANCE VS. OUTPUT VOLTAGE

0 10 20 30 40 50 600

5

10

15

20

25

Load Resistance (kΩ)

Outp

ut

Volt

age (

V)

The output voltage is dependent on the load resistance; their relationship is somewhat linear.

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POWER EFFICIENCY

Input Voltage (V)

Output Voltage (V)

Load Resistance (kΩ)

Power Output (mW)

Power Input (mW)

Power Efficiency (%)

0.235 4.06 27 0.611 0.003 18.1

0.235 5.12 47 0.558 0.003 16.6

0.88 15 27 8.333 0.047 17.6

0.89 20.969 47 9.355 0.048 19.4

Crude Power Efficiency for the 1.43mH coil using a 76% duty cycle.

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OUTPUT VOLTAGE VS. FREQUENCY

0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 4.4 4.8 5.2 5.6 6 6.4 6.8 7.2 7.60

2

4

6

8

10

12

14

16

18

20

22L=1.43mH, R=4.1Ω

L=2.46mH, R=4.3Ω

L=2.08mH, R=4.2Ω

Frequency (kH)

Outp

ut

Volt

ages (

V)

ƒ=n/τn=1,2,3,4τ=L/RS

Output voltage vs frequency for various coil sizes. An input voltage of 0.89 V is held constant at 1kHz for each coil.

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REFERENCES

1. H. Jiang, D. Lan, D. Lin, J. Zhang, S. Liou, H. Shahnasser, M. Shen, M. Harrison, and S.Roy, “A Feed-Forward Controlled AC-DC Booster for Biomedical Implants”, in Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2012

2. H. Jiang, B. Lariviere, J. Zhang, S. Liou, H. Shahnasser, M. Shen, M. Harrison, and S. Roy, “A Low Switching Frequency AC-DC Boost Converter for Wireless Powered Miniaturized Implants”, 2012

3. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1502062/

4. http://www.forbes.com/2009/11/23/hmo-medical-implants-business-health-care-batteries.html

5. http://www.dvclub.info/il-pacemaker-biologico-tutto-naturale/

6. http://www.atlantichealth.org/gagnon/our+services/treatment+services/cardiac+surgery/pacemaker+and+defibrillator+implantation

7. Baker, et al., "Feedback analysis and design of RF power links for low-power bionic systems." Biomedical Circuits and Systems, IEEE Trans. on 1(1): 28-38.

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QUESTIONS?