EEG Monitoring SystemThe EEG Porto-Cap™
Team 5
ENGN4017 - Engineering Design
Autumn 1999
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
What is EEG?
• EEG = Electroencephalogram• Measurement of brain wave patterns
in hopes of understanding the mysteries of the mind.
Problem Statement
The reliable measurement, over extended periods, of scalp EEG on
consecutive occasions, during mental functions in everyday environments.
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
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
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
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Cap DesignM
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Positioning• Nasion/Ear reference points• Adjustable straps for different head
dimensions (53cm - 66cm)• Electrodes retractable to suit
M e
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Nathan in an early model. Current model.
Demonstration of
Skull Cap Setup . . .
M e
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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
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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
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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
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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
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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
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ComponentsS
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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
Signal FlowS
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ElectrodeHighpass
Filter
Sample andHold
1000
10ADCCPU
WirelessTransmitter
WirelessReceiver
1Lowpass
Filter
Computer
EEG Signal Flow Control Signal Flow
Conditioning
Conversion
Transm
ission
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
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
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
Other Features
• EMF Shielding– Faraday cage– Cable shielding
• Auto-Zero Function– Remove constant DC offset introduce by
electronic components
S i g
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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
Manufacturing Materials Cost
• Total - around US$4k– Mechanical - US$100– Electrode - US$2300– Signals - US$1800
• Prototype materials - estimated US$50k
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™.
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.
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