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