february 19, 2009 sara carr, carl hoge, keith lesser, robert macgregor, oxana petritchenko
TRANSCRIPT
February 19, 2009Sara 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 transplantThey help the LVAD to pump blood
throughout the bodyDepending on patient, they can be
implanted for months or yearsEventually will have ability to
become a permanent solution
Dangers of Wired SystemsWired systems pose a danger to
heart pump patientsAround 40% deaths in patients
come from infectionMost susceptible to infection after
surgery or traumatic eventWired 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
Heat Shrink Boots
Power Cable
Outside case
DisplayPort Connector
Signal cable(Through Skin)
Final Product: Signal Transmission
Grommets
PICDAC
Outside PCB
Inner Case
PIC
VoltageDividers
VoltageRegulatorRelay
SwitchInner PCB
PIC
Programming Wires
Final Product: Wireless Power
Pulse Generator
H-BridgeRectifier
Voltage Regulator
Powered LED
Primary CoilSecondary Coil
Testing: Cable
Cables measured at multiple locations
300% thinner
Weights applied to wire between supports spaced at a fixed distance
370% more flexible
Old Cable: Diameter = 8 mm
New Cable: Diameter = 2.7 mm
Testing: SignalsTesting
Position monitor signals: 0-600Hz 0-3.3V
PWM control signals: 20kHz 0-100% Duty Cycle
Motor Controller signal: 50Hz 0-100% Duty Cycle
ResultsPosition monitor and
PWM control signals were accurately transmitted with delay of 32μsec
Method used to transmit motor controller signal was not sufficient
HESA Signal In
HESA Signal Out
PWM Signal Out
PWM Signal In
Motor Controller Signal In
Motor Controller Signal Out
Testing: Power EfficiencyTesting
Coils were set at different distances between 0.5cm – 2cm
Different loads were placed at the output to measure output power
ResultsEfficiency 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 StatusSize and flexibility needs metWireless power concept proven to work
10% efficiency over system 35% over the coils
12 of 13 signals met performance requirementsMotor control signal duty cycle not within 5% of
target valueSampling rate of some signals is too slow
Meeting Customer NeedsDescription
Specification (Ideal/Marginal)
Test Results Status
Cable Flexibility 200% / 150% 370% AchievedCable Diameter 2mm / 3 mm 2.7 mm (300% decrease) Achieved
Wires Elimination All / 15 wires15 wires eliminated using SPI protocol
7 wires remainAchieved
Wireless Power Optional Delivers power with 15 – 30% efficiency Achieved
SafetyApproved for medical
applicationsMedical grade LOCTITE 5248™
silicone.Achieved
Heat damage to tissueSurface temperature of the
case does not exceed 50ºC. Not verified because prototype was not
functional.Not verified
Heat damage to electronicsTemperature of electronics
does not exceed 120ºC.Functional at 120ºC. Not verified
Shock Protection 5 drops from 1.5 m height Passed Achieved
Water proof/ Pressure 1m under waterDid not pass – the silicone layer was too
thin, no time to re-coatWill be achieved
Function: continuous, no user intervention, and
reliable13 signals
Final prototype – not functionalPartial functionality : 12/13 signals
Need not met
Available space in body cabvity
Less than 650 cm3 Inner case: 90 cm3 Achieved
Dimensions and Weight Less than 900gInner case: 9 x 5 x 2 cm, 125g
Outer case: 11 x 3.5 x 2 cm, 125gAchieved
Budget $2750/ $3500 $2550 Achieved
Future ImprovementsModify PIC firmware to be capable of
sampling all signals at the correct rateImplement PCBs without jumper wiresModify 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 HzPackaging
Questions