2013 NASA CIPAIR SUMMER RESEARCH INTERNSHIP PROGRAM ELECTRICAL ENGINEERING GROUP MARISSA BUELL, NEHAD DABABO, RENE FIGUEROA, PETER MOALA OPTIMIZING A WIRELESSLY POWERED AC-DC BOOSTER FOR BIOMEDICAL IMPLANTS Supervised by SFSU Student Kang Bai and SFSU Advisor Dr. Hao Jiang 1

BIOMEDICAL IMPLANTS Cardiac pacemakers and defibrillators Neurological stimulators Muscle Stimulators Cochlear implants Monitoring devices Drug pumps 2

BIOMEDICAL IMPLANTS Medical implant batteries require replacement every 5-10 years Effective power storage requires a larger battery Increased risk with multiple surgeries 3

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 As a result, Riley had to fork over the $43, in cash ” 4

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 5

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. 6

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):

AC-DC BOOST CONVERTER OPERATING PRINCIPLE 8

VOLTAGE ACROSS AN INDUCTOR Current Time 9

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 10

AC VOLTAGE 11

TO FULLY RECTIFIED DC VOLTAGE 12

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Signal Coil Analog Signal Conditioning Power Coil AC-DC Boost Converter Transmitte r Coil Receiver Coil composed of two coils DC Output 14

SIGNAL CONDITIONER Receives and cleans the the input frequency signal for use by the microcontroller, which converts the analog signal to the digital 15

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Analog Signal Conditioning Logic Control Circuit Signal Coil Power Coil AC-DC Boost Converter Transmitte r Coil DC Output 17

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 18

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 19

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 20

DUTY CYCLE VS OUTPUT VOLTAGE FOR SINUSOIDAL WAVEFORM Peaks at 62% 21

Green Wave – Input AC VoltageBlue Wave – Control Signal Square Wave 78% Duty Cycle Sinusoidal Wave 62% Duty Cycle Rising edge of control signal must be properly aligned with input AC to maximize current input 22

OUTPUT VOLTAGE VS OPEN CIRCUIT INPUT VOLTAGE Sinusoidal Wave V out =10.9V in Square Wave V out =25V in Smaller input yields same output 23

DESIGNING A PC BOARD 24

THE PREVIOUS SCHEMATIC 25

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 26

LAYOUT FOR THE MOST RECENT PC BOARD Microcontroller Boost Converter Signal Conditioner 27

CURRENT SCHEMATIC OF CIRCUIT 28

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 FOR MANUFACTURE 29

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PC Board Design 31

CONCLUSION To minimize input voltage: Use a transmitter coil to generate a square-wave to maximize power efficiency V out =25V in Align the rising edge of the control signal with the zero crossing of the AC input Minimal input voltage occurs at a duty cycle of 78% for a transmitter coil San Francisco State University’s setup currently holds the greatest ratio of output to input voltage 32

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 33

PC BOARD MEASUREMENTS Time On (µs)Time Off (µs)End of Period (µs) Duty CycleOutput Voltage Data for 1.43 mH coil 34

DUTY CYCLE VS. OUTPUT VOLTAGE Peaks at 76% 35

LOAD RESISTANCE VS. OUTPUT VOLTAGE Load Resistance (kΩ)Output Voltage (V)

LOAD RESISTANCE VS. OUTPUT VOLTAGE The output voltage is dependent on the load resistance; their relationship is somewhat linear. 37

POWER EFFICIENCY Input Voltage (V) Output Voltage (V) Load Resistance (kΩ) Power Output (mW) Power Input (mW) Power Efficiency (%) Crude Power Efficiency for the 1.43mH coil using a 76% duty cycle. 38

OUTPUT VOLTAGE VS. FREQUENCY 39 ƒ=n/τ n=1,2,3,4 τ=L/R S Output voltage vs frequency for various coil sizes. An input voltage of 0.89 V is held constant at 1kHz for each coil.

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), 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”, batteries.html 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):

QUESTIONS? 41