EEG Monitoring System The EEG Porto-Cap Team 5 ENGN4017 - Engineering Design Autumn 1999.
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Transcript of EEG Monitoring System The EEG Porto-Cap Team 5 ENGN4017 - Engineering Design Autumn 1999.
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EEG Monitoring SystemThe EEG Porto-Cap™
Team 5
ENGN4017 - Engineering Design
Autumn 1999
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Design Process
• Examine project domain– EEG measurement systems
• Meet with intended customer– Dr Richard Clark, Flinders University SA
• Identifying problems with existing skull cap system– Requirements for new system were formulated
• Develop conceptual solutions to problems– Brainstorming
• Project Decomposition– Sub-system groups focussing on specific problems
• Integration– System integration
• Presentation, Final Report
March
June
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What is EEG?
• EEG = Electroencephalogram• Measurement of brain wave patterns
in hopes of understanding the mysteries of the mind.
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Problem Statement
The reliable measurement, over extended periods, of scalp EEG on
consecutive occasions, during mental functions in everyday environments.
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Key Problem Areas
• Lack of repeatability• Different Head Sizes• Long setup times• Difficulty with lengthy experiments• Use of conductive gels• Scalp abrasion• Noise in signal• Lack of portability/environmental constraints
Issues that needed to be addressed in any new system developed by the group:
In finding a solution, we have taken an ambitious approach to solving these problems in a medical research application
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Problem Decomposition
P os it ion in gR ep eatab ility
A ccu racyD iffe ren t H ead S izes
M ech an ica lG rou p
S e lec tion o f M ate ria lP o la risa tion
H yg e in eIrrita t ion
E lec trod eG rou p
N o ise R ed u c tionR eso lu tion
P ortab le S ys tem
S ig n a l P rocess in gG rou p
D eta iled D es ig nD ecom p os it ion
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Key Requirements
Category Requirement DesignElectrodes positionedaccording to 10/20system
Yes/No Yes/NoFlexible
Position accuracy forrepeatedmeasurements
< 1mm2
deviationRequires 2nd
prototypetesting
Head size Circumferencerange:> 53-60cm
Circumferencerange:> 53-66cm
Setup time < 15 minutes < 15 minutes
M e
c h
a n
i c
a l
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Cap DesignM
e c
h a
n i c
a l
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Positioning• Nasion/Ear reference points• Adjustable straps for different head
dimensions (53cm - 66cm)• Electrodes retractable to suit
M e
c h
a n
i c
a l
Nathan in an early model. Current model.
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Demonstration of
Skull Cap Setup . . .
M e
c h
a n
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Key RequirementsCategory Requirement DesignSkull impedance < 5 k Expect < 1k,
2nd prototypetesting req.
I rritation J ury Test:< 2%experienceirritation
Requires 2nd
prototypetesting
Electrodepolarisation
< 1%Deviation
Expected,2nd prototypetesting req.
Cleaning Compliancewith Aust.Standard
Yes
Scalp preparation No No
E l e
c t
r o
d e
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Electrode Selection
• Silver/silver chloride selected– Minimal polarisation characteristic
• Dry electrode used (no gel required)– Uses local impedance converting amplifier
• Pellet electrode, 2mm diameter– Small electrode size ensures good hair
penetration and contact with scalp
2mm
E l e
c t
r o
d e
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Irritation Issues
• Initial model- helmet supported by electrodes• Prototype - straps support the load
– allows smaller electrodes to be used without increasing irritation
– straps allow for more comfortable fit• No preparation or abrasion of skin surface
required
E l e
c t
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Cleaning
• Electrodes detachable for cleaning• Cleaning processes include disinfecting
and sterilisation via autoclave• Use of two sets of electrodes allows
continuous use
E l e
c t
r o
d e
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Key Requirements
Category Requirement DesignSignal noise < 1% Expect 0.1%,
2nd prototypetesting req.
Signal resolution .15V 30.5nV
Signal drift Eliminate below0.05Hz
Adjustablehigh-pass filter(.005-.1Hz)
Wireless operation Yes Yes
Sampling rates Variousselectable
8 selectable(0.5, 1, 1.25,2.5, 5, 10kHz)
S i g
n a
l s
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ComponentsS
i g
n a
l s
Amplifiers,Filters,ADC’s,
CPU
CAP
Transmitter,Power Supply,
Batteries
BELT PACK
Receiver
COMPUTERSerial Data and
Control Line
Power Lines Wireless SerialData Line
CAP
Buffer,1000x Amplifier,
Analog Switch
ELECTRODE(x4)
HP/LP Filters,10x Amplifier,Samp. & Hold,
ADC
GROUP(x6)
CPU,Clocks
CENTRAL(x1)
AnalogData Line
Power Lines SerialData Line
DigitalControl Lines
Power Lines
DigitalControl Line
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Signal FlowS
i g
n a
l s
ElectrodeHighpass
Filter
Sample andHold
1000
10ADCCPU
WirelessTransmitter
WirelessReceiver
1Lowpass
Filter
Computer
EEG Signal Flow Control Signal Flow
Conditioning
Conversion
Transm
ission
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Signal FlowS
i g
n a
l s
ElectrodeHighpass
Filter
Sample andHold
1000
10ADCCPU
WirelessTransmitter
WirelessReceiver
1Lowpass
Filter
Computer
EEG Signal Flow Control Signal Flow
Conditioning
Conversion
Transm
ission
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Signal FlowS
i g
n a
l s
ElectrodeHighpass
Filter
Sample andHold
1000
10ADCCPU
WirelessTransmitter
WirelessReceiver
1Lowpass
Filter
Computer
EEG Signal Flow Control Signal Flow
Conditioning
Conversion
Transm
ission
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Signal FlowS
i g
n a
l s
ElectrodeHighpass
Filter
Sample andHold
1000
10ADCCPU
WirelessTransmitter
WirelessReceiver
1Lowpass
Filter
Computer
EEG Signal Flow Control Signal Flow
Conditioning
Conversion
Transm
ission
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Other Features
• EMF Shielding– Faraday cage– Cable shielding
• Auto-Zero Function– Remove constant DC offset introduce by
electronic components
S i g
n a
l s
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Areas of Further Research
• Gauging depth of electrodes• Improving setup time• Ag/AgCl dry electrodes• Electrode polarisation• Effectiveness of Faraday cage• Noise analysis• Artifacts from physiological rhythms
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Manufacturing Materials Cost
• Total - around US$4k– Mechanical - US$100– Electrode - US$2300– Signals - US$1800
• Prototype materials - estimated US$50k
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Why you should upgrade to the Porto-Cap™ . . .
Wireless communication – no huge cables to lug around, you are free to walk around the house just like with a cordless phone.
Data recorded from each different electrode is clocked at exactly the same instant – at last, a device which accurately maps which bits of your brain that weren’t working during that embarrassing moment.
No scalp preparation required – the feeling of blunt needles scraping your scalp will only be remembered in your nightmares.
Porto-Cap™ uses dry electrodes only – that gooey conducting paste can now be used as axle grease.
Zero signal drift – the amplifier and filter package has been hand picked so that the only interruptions during a testing period will involve rubble entering your building.
Eight selectable sampling frequencies – if flexible data rates is you, then you won’t die hungry when wearing the Porto-Cap™.
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ConclusionThe EEG Porto-Cap™ successfully enables repeatable and reliable measurements of
EEG signals. It achieves this with little discomfort, no paste or gel and in
conventional environments.
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Thank you for coming,
we would like to take this
opportunity to answer any
questions you may have.
Team 5
ENGN4017 - Engineering Design
Autumn 1999