UniversityUniversity of Wisconsin – Madisonof Wisconsin – Madison

Engineering Projects In Community Service

BIOFEEDBACK / STRESS MANAGEMENT

May 9, 2001

Professor John Webster, AdvisorProfessor John Webster, AdvisorDepartment of Biomedical EngineeringDepartment of Biomedical Engineering

Dr. Dan Muller, ClientDr. Dan Muller, ClientDepartment of Medicine and Med Micro/ImmunologyDepartment of Medicine and Med Micro/Immunology

Group MembersElectrodes:

Ben Birkenstock Ji ChoeElizabeth NeeChristy Palmer

Feedback:Chris KoenigsAmy Li

Electronics:Steve Almasi Jacob FealaWilliam LauSarah Michaels

Problem Statement

To design and build a portable, inexpensive To design and build a portable, inexpensive electroencephalogram (EEG) device that electroencephalogram (EEG) device that would enable users to monitor brain states would enable users to monitor brain states during meditation.during meditation.

Meditation

Self-induced calming of mind and bodySelf-induced calming of mind and body Linked to health benefitsLinked to health benefits

ADDADD Blood pressureBlood pressure CreativityCreativity

Electroencephalogram (EEG)

Electrodes attached to Electrodes attached to scalpscalp

Action potentials of Action potentials of cells amplified and cells amplified and averagedaveraged

Oscilloscope provides Oscilloscope provides visual representation visual representation of brain wave signalsof brain wave signals

Brain Wave States

Beta: waking activity Beta: waking activity (above 13 Hz)(above 13 Hz)

Alpha: relaxed, eyes Alpha: relaxed, eyes closed (8-13 Hz)closed (8-13 Hz)

Theta: drowsy, Theta: drowsy, dreamlike (4-7 Hz)dreamlike (4-7 Hz)

Delta: deep sleep Delta: deep sleep (below 4 Hz)(below 4 Hz)

Meditation can alter Meditation can alter brain waves over timebrain waves over time

Subgroups

ElectrodesElectrodesDetermine number, type, placement and Determine number, type, placement and

attachment of electrodesattachment of electrodes ElectronicsElectronics

Design and build circuitryDesign and build circuitry FeedbackFeedback

Determine system of feedback to userDetermine system of feedback to user

Basic Design Concept

Electrodes

Elizabeth NeeElizabeth Nee

Electrode Selection

StyleStyle ReusableReusable DisposableDisposable Dry/activeDry/active

Type of electrolyteType of electrolyte GelGel PastePaste SalineSaline HydrogelHydrogel

Electrode Placementtheta—central

alpha—occipital

Current Design ProsPros

InconspicuousInconspicuous Not distracting to userNot distracting to user AdjustableAdjustable Easy to place properlyEasy to place properly

ConsCons Possible noisePossible noise Problems Problems

achievingachieving good good contact through contact through long hairlong hair

side view

rear view

Accomplishments This Semester

Research Research Full EEG electrode set-up not necessaryFull EEG electrode set-up not necessary Placement of electrodes confirmedPlacement of electrodes confirmed

Existing products Existing products Ordered FlexTrodes systemOrdered FlexTrodes system Investigated HydroDot electrodesInvestigated HydroDot electrodes

Tested deviceTested device

Electronics

Steve AlmasiSteve Almasi

General Specifications PortablePortable

SmallSmall LightweightLightweight Battery poweredBattery powered

Inexpensive Inexpensive Most existing products > $700Most existing products > $700

Measure strength of alpha (Measure strength of alpha (aa) and theta () and theta (JJ)) Provide feedbackProvide feedback

Dominant stateDominant state Strength of dominant stateStrength of dominant state

Signal Flow Diagram

electrodes amplifier

filter

(4-8 Hz)

rectifier+

averager

audio output

filter

(8-13 Hz)

rectifier+

averager

voltage-controlled oscillator

[from Gevins, 1994].

Signal Processing

t

v(t)original signal filtered signal rectified signal averaged signal

[from Gevins, 1994].

Amplifier Specifications

High input impedanceHigh input impedance High noise rejectionHigh noise rejection Amplify 10-100 Amplify 10-100 V input signalV input signal Minimal power consumptionMinimal power consumption Low costLow cost

Amplifier Design

Test Results

Gain of approximately 19,000 at 10 HzGain of approximately 19,000 at 10 Hz

High common mode rejection ratioHigh common mode rejection ratio

Attenuated DC offsetAttenuated DC offset

Filter Specifications

Distinguish alpha, theta bandsDistinguish alpha, theta bands Low complexityLow complexity Minimal power consumptionMinimal power consumption Low costLow cost

Alpha Circuit

Theta Circuit

Test ResultsFrequency Response of Theta Filter

0

100

200

300

400

500

600

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Hz

Am

pit

ud

e (

mV

)

Feedback

Amy LiAmy Li

Specifications

Make meditation more fulfillingMake meditation more fulfilling Pleasant, easy to understand feedbackPleasant, easy to understand feedback Low costLow cost Technically feasibleTechnically feasible

Feedback Essential Points

Starts with high pitched toneStarts with high pitched tone User chooses to train for alpha or theta stateUser chooses to train for alpha or theta state Pitch varies in proportion to strength of Pitch varies in proportion to strength of

desired statedesired state

04/21/23

FeedbackStrategy

High pitch

High Volume Lower pitch

Lower Volume

**Attained Ideal Deep Meditative State**

Silence

Pitch and volume increases

again

If meditative state is lost

TargetTarget

1. 2.3.

4.

5.

Feedback Circuit - Summing Amplifier

Feedback Circuit - Variable Gain Amplifier

Research Results

Best performed with eyes closedBest performed with eyes closed Auditory signals most effectiveAuditory signals most effective

Volume change difficult to detectVolume change difficult to detect Pitch change easy to detectPitch change easy to detect

Vibrations, thermal signals, artificial tones Vibrations, thermal signals, artificial tones less effectiveless effective

Changing Tone

ProsPros Technically simpleTechnically simple Less distracting Less distracting

than musicthan music Easy to detect pitch Easy to detect pitch

changechange

ConsCons ““tone deafness”tone deafness” Intrusive soundIntrusive sound

Questions?