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?