Transcript P10022 Transcutaneous Signal Transmission for LVAD

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