overhead6 - Amirkabir University of Technology
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Transcript overhead6 - Amirkabir University of Technology
University of Wisconsin – Madison
Engineering Projects In Community Service
BIOFEEDBACK / STRESS MANAGEMENT
May 9, 2001
Professor John Webster, Advisor
Department of Biomedical Engineering
Dr. Dan Muller, Client
Department of Medicine and Med Micro/Immunology
Group Members
Electrodes:
Ben Birkenstock
Ji Choe
Elizabeth Nee
Christy Palmer
Feedback:
Chris Koenigs
Amy Li
Electronics:
Steve Almasi
Jacob Feala
William Lau
Sarah Michaels
Problem Statement
To design and build a portable, inexpensive
electroencephalogram (EEG) device that
would enable users to monitor brain states
during meditation.
Meditation
Self-induced calming of mind and body
Linked to health benefits
ADD
Blood pressure
Creativity
Electroencephalogram (EEG)
Electrodes attached to
scalp
Action potentials of
cells amplified and
averaged
Oscilloscope provides
visual representation
of brain wave signals
Brain Wave States
Beta: waking activity
(above 13 Hz)
Alpha: relaxed, eyes
closed (8-13 Hz)
Theta: drowsy,
dreamlike (4-7 Hz)
Delta: deep sleep
(below 4 Hz)
Meditation can alter
brain waves over time
Subgroups
Electrodes
Determine number, type, placement and
attachment of electrodes
Electronics
Design and build circuitry
Feedback
Determine system of feedback to user
Basic Design Concept
Electrodes
Elizabeth Nee
Electrode Selection
Style
Reusable
Disposable
Dry/active
Type of electrolyte
Gel
Paste
Saline
Hydrogel
Electrode Placement
theta—central
alpha—occipital
Current Design
Pros
Inconspicuous
Not distracting to user
Adjustable
Easy to place properly
side view
rear view
Cons
Possible noise
Problems
achieving good
contact through
long hair
Accomplishments This Semester
Research
Full EEG electrode set-up not necessary
Placement of electrodes confirmed
Existing products
Ordered FlexTrodes system
Investigated HydroDot electrodes
Tested device
Electronics
Steve Almasi
General Specifications
Portable
Small
Lightweight
Battery powered
Inexpensive
Most existing products > $700
Measure strength of alpha (a) and theta (J)
Provide feedback
Dominant state
Strength of dominant state
Signal Flow Diagram
q filter
(4-8 Hz)
electrodes
rectifier
+
averager
amplifier
a filter
(8-13 Hz)
rectifier
+
averager
[from Gevins, 1994].
voltagecontrolled
oscillator
audio
output
Signal Processing
v(t)
original signal
filtered signal rectified signal
averaged signal
[from Gevins, 1994].
t
Amplifier Specifications
High input impedance
High noise rejection
Amplify 10-100 mV input signal
Minimal power consumption
Low cost
Amplifier Design
Test Results
Gain of approximately 19,000 at 10 Hz
High common mode rejection ratio
Attenuated DC offset
Filter Specifications
Distinguish alpha, theta bands
Low complexity
Minimal power consumption
Low cost
Alpha Circuit
Theta Circuit
Test Results
Frequency Response of Theta Filter
Ampitude (mV)
600
500
400
300
200
100
0
0
1
2
3
4
5
6
7
8
Hz
9 10 11 12 13 14 15 16
Feedback
Amy Li
Specifications
Make meditation more fulfilling
Pleasant, easy to understand feedback
Low cost
Technically feasible
Feedback Essential Points
Starts with high pitched tone
User chooses to train for alpha or theta state
Pitch varies in proportion to strength of
desired state
Feedback
Strategy
1. High pitch
2.
Lower pitch
High Volume
Lower Volume
Target
3.
*Attained Ideal Deep
Meditative State*
Silence
4.
5.
Pitch and
volume increases
again
If
meditative
state is lost
Feedback Circuit - Summing
Amplifier
Feedback Circuit - Variable Gain
Amplifier
Research Results
Best performed with eyes closed
Auditory signals most effective
Volume change difficult to detect
Pitch change easy to detect
Vibrations, thermal signals, artificial tones
less effective
Changing Tone
Pros
Technically simple
Less distracting
than music
Easy to detect pitch
change
Cons
“tone deafness”
Intrusive sound
Questions?