Probing The Of. Experience Pain Pain Team Members Jeff Swift Anna Karas Stacey Hoebel Advisor Prof. Willis Tompkins Client Dr. Christopher Coe UW-Madison.

Probing TheProbing The

Of Of

ExperienceExperience

PainPain

Team MembersJeff Swift

Anna KarasStacey Hoebel

AdvisorProf. Willis Tompkins

Client Dr. Christopher Coe

UW-Madison Dept. of Psychology

AbstractAbstract

Our client, a psychologist at UW, wanted a Our client, a psychologist at UW, wanted a method to study pain disorders without actually method to study pain disorders without actually inflicting pain on patients. inflicting pain on patients. The “thermal grill illusion” accomplishes this by The “thermal grill illusion” accomplishes this by tricking the brain into feeling pain due to tricking the brain into feeling pain due to alternating hot and cold components. alternating hot and cold components. Our device employs solid copper rods as the Our device employs solid copper rods as the cold component (20cold component (20°°C) and strips of stainless C) and strips of stainless steel foil heated electrically as the warm steel foil heated electrically as the warm component (40component (40°°C). C).

Problem StatementProblem Statement

Design a device to test pain sensitivity in Design a device to test pain sensitivity in patients with generalized pain disorders. patients with generalized pain disorders.

The alternating warm and cool The alternating warm and cool components of the device activate sensory components of the device activate sensory receptors and neurological thermal receptors and neurological thermal pathways to create the illusion of pain.pathways to create the illusion of pain.

BackgroundBackground

FIBROMYALGIAFIBROMYALGIAChronic musculoskeletal pain and fatigue disorder Chronic musculoskeletal pain and fatigue disorder Cause of the disease is still unknown Cause of the disease is still unknown Associated sleep disorder called the alpha-EEG Associated sleep disorder called the alpha-EEG anomalyanomalyTreatmentsTreatments

THERMO GRILL ILLUSION OF PAINTHERMO GRILL ILLUSION OF PAINPain and temperature have intersecting neural Pain and temperature have intersecting neural pathwayspathways

Previous DesignPrevious Design

Created by A.D. Craig (Univ. of Arizona)Created by A.D. Craig (Univ. of Arizona)

Alternating warm (40Alternating warm (40°°C) and cool rods (20C) and cool rods (20°°C)C)

About 8” x 8” with 0.5” About 8” x 8” with 0.5” diameter thermal rodsdiameter thermal rods

Presumed to be electricPresumed to be electric

Ominous LookingOminous Looking

Design ConstraintsDesign Constraints

Consistent temperature componentsConsistent temperature components– Warm: 40Warm: 40°C°C Cool: 20°CCool: 20°C

Reach temperatures in 1 sec.Reach temperatures in 1 sec.

SafeSafe

ReusableReusable

Non threatening appearanceNon threatening appearance

Easy to operateEasy to operate

Materials and CostMaterials and Cost

MaterialMaterial Use Use CostCostSt. Steel FoilSt. Steel Foil HeaterHeater $24.00$24.00

Copper BarsCopper Bars Cool ComponentCool Component $65.00$65.00

Wood (scrap)Wood (scrap) Insulator for Insulator for heater, Platformheater, Platform

--------------------

Resistors & WiresResistors & Wires CircuitryCircuitry $1.00$1.00

BreadboardBreadboard CircuitryCircuitry --------------------

Wood ScrewsWood Screws Secure Copper Secure Copper BarsBars

$2.00$2.00

Power AmplifierPower Amplifier CircuitryCircuitry $40.00$40.00

TOTALTOTAL $132.00$132.00

Temperature Controlling CircuitTemperature Controlling Circuit

•Temperature remains constant 40° C

•Rapid heating

•No temperature overshoot

Warm ComponentWarm Component

Stainless Steel foil strips heat when Stainless Steel foil strips heat when voltage is applied by power supplyvoltage is applied by power supply

As temperature changes, the resistance of As temperature changes, the resistance of the stainless steel feeds back to the circuitthe stainless steel feeds back to the circuit

If the resistance of the foil, when heated, If the resistance of the foil, when heated, balances the wheatstone bridge, the balances the wheatstone bridge, the voltage supply is stopped and temperature voltage supply is stopped and temperature is held constantis held constant

Warm Component Material Warm Component Material SelectionSelection

PlatinumPlatinum– Ideal resistivity and temperature coefficient of Ideal resistivity and temperature coefficient of

resistivityresistivity– Very high costVery high cost

Stainless SteelStainless Steel– Large temperature coefficient of resistivityLarge temperature coefficient of resistivity– Large resistivityLarge resistivity– InexpensiveInexpensive– Available in appropriate thicknessAvailable in appropriate thickness

Material SelectionMaterial SelectionElectrical resistivity vs Temperature for Stainless

Steel 321

y = -3E-10x4 + 4E-07x3 - 0.0003x2 + 0.1474x + 69.166

R2 = 1

0

20

40

60

80

100

120

140

0 200 400 600 800 1000

Temperature (C)

Res

isti

vity

(m

icro

oh

m*c

m)

Material SelectionMaterial Selection

Calculations for foil dimensions:Calculations for foil dimensions:– Want total resistance of heaters Rs = 2.5Want total resistance of heaters Rs = 2.5ΩΩ– Heaters to be connected in series so Heaters to be connected in series so

resistance of each of 6 heaters = 0.42resistance of each of 6 heaters = 0.42ΩΩ– Thickness of foil = 5.08 x 10Thickness of foil = 5.08 x 10-5-5 m m

Length of foil strip = 0.2032 mLength of foil strip = 0.2032 m

Resistivity of steel at 40Resistivity of steel at 40°°C = 7.46 x 10C = 7.46 x 10-7-7 ΩΩ-m-m– R=R=ρρ*L/A *L/A width of foil strip = 0.7 cm width of foil strip = 0.7 cm

Cool ComponentCool Component

Copper barsCopper bars– Heat transfer equation:Heat transfer equation:

Q=A * k * Q=A * k * ΔΔTT

T=(m * CT=(m * Cp p * * ΔΔT) / QT) / Q

– Time to change 1ºK = 6.4 secTime to change 1ºK = 6.4 sec

Heat sinkHeat sink– Adds thermal mass (absorbs heat)Adds thermal mass (absorbs heat)– Adds surface area (dissipates heat)Adds surface area (dissipates heat)

Prototype ConstructionPrototype Construction

Cool ComponentCool Component– Cut copper bar into six Cut copper bar into six

smaller bars (8” long)smaller bars (8” long)– Drilled holes in ends of Drilled holes in ends of

each copper bareach copper bar– Used a countersink to Used a countersink to

accommodate screw accommodate screw headsheads

– Hammered wood Hammered wood screw through copper screw through copper hole and into plywood hole and into plywood platformplatform

Prototype ConstructionPrototype Construction

Warm ComponentWarm Component– Cut wood blocks to Cut wood blocks to

same size as copper same size as copper bars (8” x 1” x ½”)bars (8” x 1” x ½”)

– Cut stainless steel foil Cut stainless steel foil strips to size for strips to size for optimal heating control optimal heating control (8” x ¼”)(8” x ¼”)

– Tacked foil and wire to Tacked foil and wire to wood at endswood at ends

Prototype TestingPrototype Testing

Verified total resistance of foil heatersVerified total resistance of foil heaters

Tested prototype with feedback circuit: Tested prototype with feedback circuit: – Power Source: +/- 20V and 1 ampPower Source: +/- 20V and 1 amp– Resulted in overload of power sourceResulted in overload of power source– Failure AnalysisFailure Analysis

Tested prototype without feedback circuit:Tested prototype without feedback circuit:– Applied direct voltage of 3V to foil Applied direct voltage of 3V to foil – Resulted in successful heat generationResulted in successful heat generation

Assessment of Cool ComponentAssessment of Cool Component

– AdvantagesAdvantagesSimple operator interfaceSimple operator interface

Easy to manufactureEasy to manufacture

Constant temperatureConstant temperature

ReusableReusable

Aesthetically pleasing– conductive paintAesthetically pleasing– conductive paint

– DisadvantagesDisadvantagesRemains at the room temperature Remains at the room temperature

Assessment of Warm ComponentAssessment of Warm Component

– Advantages:Advantages:Quickly heats up to 40Quickly heats up to 40°°C (1-2 sec) C (1-2 sec)

Remains at constant temperatureRemains at constant temperature

No temperature overshootNo temperature overshoot

No risk of burning patientNo risk of burning patient

Easy to manufactureEasy to manufacture

– Disadvantages:Disadvantages:Somewhat primitive in appearanceSomewhat primitive in appearance

Improvement of control circuitry necessaryImprovement of control circuitry necessary

EthicsEthics

Inducing pain in human subjectsInducing pain in human subjects

Adequate testing to assure engineering Adequate testing to assure engineering temperature controls are reliable and safetemperature controls are reliable and safe

Future WorkFuture Work

Improve the aesthetics of deviceImprove the aesthetics of deviceDevelop and test circuitry to control temperatureDevelop and test circuitry to control temperature– Order 3W resistors for power ampOrder 3W resistors for power amp

Look into possibilities of creating a switch Look into possibilities of creating a switch operated deviceoperated deviceUse an aluminum sheet to serve as a heat sink Use an aluminum sheet to serve as a heat sink for the cold copper barsfor the cold copper barsReplace wood blocks with ceramic as the Replace wood blocks with ceramic as the thermal insulator for stainless steel heater thermal insulator for stainless steel heater

Special ThanksSpecial Thanks

Prof. Willis Tompkins Prof. John WebsterProf. Willis Tompkins Prof. John Webster

Prof. Jay MartinProf. Jay Martin