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February 19, 2009 Sara Carr, Carl Hoge, Keith Lesser, Robert MacGregor, Oxana Petritchenko Left Ventricular Assist Devices (LVAD) Typically LVADs are used while a patient is awaiting for heart transplant They help the LVAD to pump blood throughout the body Depending on patient, they can be implanted for months or years Eventually will have ability to become a permanent solution Dangers of Wired Systems Wired systems pose a danger to heart pump patients Around 40% deaths in patients come from infection Most susceptible to infection after surgery or traumatic event Wired systems also limit mobility, and may cause discomfort Customer Needs The cable entering the body is more flexible. The cable entering the body is smaller in diameter. Eliminate as many wires as possible from XPC Control Target to the LVAD, position sensors, and Active Magnetic Bearings Wireless Power System to eliminate power wires (15V and Ground) through the human skin and biological tissues. The cable, packaging, and connections are safe to human tissue. Heat generated by the inner transceiver does not cause tissue damage. The heat created by a body does not damage the electronics. Inner and outer transceivers must be protected from the outside forces. The device must function continuously, without user intervention, and be reliable with the currently established system components. The interior transceiver must fit within the human chest cavity. The exterior transceiver must be small and light enough to wear on a belt. System Architecture Final Product: Signal Transmission Programming Wires PIC PIC Voltage Dividers Voltage Regulator Relay Inner Switch PCB Inner Case Power Cable Heat Shrink Boots Outside case Signal cable (Through Skin) DisplayPort Connector DAC PIC Outside PCB Grommet Final Product: Wireless Power Secondary Coil Primary Coil Voltage Regulator H-Bridge Rectifier Pulse Generator Powered LED Testing: Cable Old Cable: Diameter = 8 mm New Cable: Diameter = 2.7 mm Cables measured at multiple locations 300% thinner Weights applied to wire between supports spaced at a fixed distance 370% more flexible Testing: Signals Testing Position monitor signals: 0600Hz 0-3.3V PWM control signals: 20kHz 0-100% Duty Cycle Motor Controller signal: 50Hz 0-100% Duty Cycle Results Position monitor and PWM control signals were accurately transmitted with delay of 32μsec Method used to transmit motor controller signal was not sufficient HESA Signal Out HESA Signal In PWM Signal In PWM Signal Out Motor Controller Signal In Motor Controller Signal Out Testing: Power Efficiency Testing Coils were set at different distances between 0.5cm – 2cm Different loads were placed at the output to measure output power Results Efficiency over full system was between 10-36% Efficiency over coils was between 16-28% at 0.5 cm Testing Power Efficiency Various materials were placed between the coils to study performance over a 15Ω load and spacing of 0.75cm Materials Used Paper Cardboard Aluminum Foil Magnet Material Vin (V) Vout (V) Air 10 2.4 Paper 10 2.04 Cardboard 10 2.0 Aluminum 10 0.6 Magnet 10 1.0 Project Status Size and flexibility needs met Wireless power concept proven to work 10% efficiency over system 35% over the coils 12 of 13 signals met performance requirements Motor control signal duty cycle not within 5% of target value Sampling rate of some signals is too slow Meeting Customer Needs Description Specification (Ideal/Marginal) Test Results Status Cable Flexibility Cable Diameter 200% / 150% 2mm / 3 mm 370% 2.7 mm (300% decrease) Achieved Achieved Wires Elimination All / 15 wires 15 wires eliminated using SPI protocol 7 wires remain Achieved Wireless Power Optional Delivers power with 15 – 30% efficiency Achieved Safety Approved for medical applications Medical grade LOCTITE 5248™ silicone. Achieved Surface temperature of the case does not exceed 50ºC. Temperature of electronics does not exceed 120ºC. Not verified because prototype was not functional. Not verified Functional at 120ºC. Not verified Shock Protection 5 drops from 1.5 m height Passed Achieved Water proof/ Pressure 1m under water Heat damage to tissue Heat damage to electronics Function: continuous, no user intervention, and reliable Available space in body cabvity Did not pass – the silicone layer was too Will be achieved thin, no time to re-coat 13 signals Final prototype – not functional Partial functionality : 12/13 signals Need not met Less than 650 cm3 Inner case: 90 cm3 Achieved Dimensions and Weight Less than 900g Inner case: 9 x 5 x 2 cm, 125g Outer case: 11 x 3.5 x 2 cm, 125g Achieved Budget $2750/ $3500 $2550 Achieved Future Improvements Modify PIC firmware to be capable of sampling all signals at the correct rate Implement PCBs without jumper wires Modify circuitry to transmit motor control signal with more accuracy. TET efficiency Alternative H-Bridge to dissipate less heat Alternative H-Bridge/driver circuit to run at ~170 Hz Packaging Questions