NSF/RISE Workshop/Short Course on the Development and Study of Advanced Sensors and Sensor Materials Sensors for Physical and Chemical Variables: Temperature,

NSF/RISE Workshop/Short Course on the Development and Study of Advanced Sensors and Sensor

Materials

Sensors for Physical and Chemical Variables: Temperature, Pressure,

Corrosion, etc.

Larry DaltonUniversity of Washington

[email protected]

July 10-14, 2006

Sensor Paints

Optimization of individual properties and multi-sensor paints•Pressure sensing paints (PSPs)--Critical commercial application to wind tunnel testing

(planes, cars/trucks, etc.—Boeing, Lockheed Martin, Ford, General Motors)

--Embedded network sensing including infrastructure sensing

--Biocompatible coatings (study of insect flight)--Studies of fluid dynamics--Optimization of all properties (photostability, temperature insensitivity, etc.)•Temperature sensing paints (TSP)--Can be used with PSPs to achieve more accurate wind

tunnel measurements•Shear sensing paints (SSP)—Two approaches

Sensor Paints: New Directions

Infrastructure Monitoring (Smart worms—optical fibers)•Oxygen•Moisture•pH •Corrosion (various ions)•Stress/Strain

NIR Detection

Leak Detection

Smart Clothing

Sensing Materials PSP

•Used in the development of aircraft and other vehicles•Replaces older pressure tap technology•Phosphorescent dye dissolved in oxygen permeable polymer•Cheaper to use and gives continuous information

Coating on substrate

Substrate (wing)

Base coat

DyePSP Layer

O2 O2

O2 O21O2

O2O2

O2

• Theory– Luminescence of certain organometallic molecules (luminophors)

are quenched by oxygen gas– Combining these molecules with a polymer matrix results in PSP

• Advantages– Measures pressure distributions over a surface area– Allows real time modelling– Allows surface flow visualization

• Disadvantages– PSP has temperature dependency– Non-linear response to pressure– Reduced sensitivity at low speed testing

Pressure Sensitive Paint

Dual Luminophor-based PSP

• Dual luminophor-based PSP incorporates two luminophors in the same polymer matrix– Luminophor 1: Pressure independent emission

• Intensity reference; temperature sensor

– Luminophor 2: Pressure dependent emission• Pressure sensor

• Use of a dual luminophor system has advantages– Wind-off measurement is eliminated– Temperature dependency is reduced– Corrects excitation variations

Requirements of a Dual Luminophor System

• Both luminophors must be excited by a single, pulsed excitation source

• Well separated emission spectra

• Low temperature dependency

• Comparable photostabilities

University of Washington’s Dual Luminophor PSP

• Luminophor 1 (Intensity reference):– Platinum tetra-fluorophenylporpholactone

(PtTFPL):

exc 390 nm, det 740 nm

• Luminophor 2 (Pressure sensor):– Magnesium tetra-

hexafluorophenylporphryn (MgTFPP):

exc 390 nm, det 650 nm

Dual Luminophor: Pressure Sensitivity Measurements

0

10

20

30

40

550 600 650 700 750 800 850 900

Wavelength (nm)

0% O2

5% O2

10% O2

15% O2

20% O2

25% O2

30% O2

100% O2

Wavelength (nm)

Rel

ativ

e In

ten

sity

0% O2

5% O2

10% O2

15% O2

20% O2

25% O2

30% O2

100% O2

550 650 700 750 800 850 900600

MgTFPP PtTFPL

0% O2

100% O2

Khalil, Journal of Porphyrin and Phathalocyanines, 6, 135, (2002)Zelelow, Sensors and Actuators, B 96, 304, (2003)Khalil, Sensors and Actuators, B, 97, 13-21, (2004)

Dual Luminophor: Photodegradation

MgTFPP only

PtTFPL only

Dual Luminophor

Dual Luminophor: Ratiometric Intensity

Response

0

4

8

12

16

20

0 20 40 60 80 100

% O 2

I PtT

FP

L/I

MgT

FP

P

00

4

8

12

16

20

20 40 60 80 100

% Oxygen

Dual Luminophor: Comparison to Single

Luminophor PSP

ST=-0.18% per °CSP=68% per bar

ST=+0.05% per °CSP=65% per bar

MgTFPP/PtTFPL PSPPref = 1 bar; Tref = 15° C

Single Luminophor PSPPref = 1 bar; Tref = 15° C

Temperature Sensitivity Correction

PSPcorr = I1 (k/I2 +1-k)

Singlet Oxygen Project Objective

• Develop a new approach to measure 2-D surface pressure by monitoring the 1270 nm singlet oxygen emission

Motivation• Availability of NIR InGaAs Camera• Many known efficient photosensitizers for singlet

oxygen• NIR detection allows for multiple sensor

configurations

Oxygenexch P

ke

xc

k1 kp

kq

k2 ko

13T

g1

11S

g30

1S

Energy Diagram

kO2

Porphyrin1270 nm

634 nm

Excitation Source

Radiationless Decay

Bimolecular Quenching

Molecular Emission

Simulation of Singlet Oxygen Production

Kexc=2000 s-1

kp=1.66e4 s-1

kq=1e8 s-1M-1

ko=.01 s-1

ko2=.67 s-1M-1

k1=0 s-1

k2=10000 s-1

[O2]=0.1 mM

[Porphyrin]=0.01 mM

τ(1g) = 1 ms

τ(1g) = 0.1 ms

Excitation on Film Setup

Singlet Oxygen on Film Surface

21% Oxygen ~ 1 % Oxygen

Stern Volmer plots at 650 nm &1270 nm

El Al 747-258F/SCD

Pressure Mapping

Pressure Map of a Boeing Transport Airfoil

Chine Placement

PSP Uses

More PSP Uses

Low Speed Automotive Test Objectives

• Performance evaluation of dual luminophor PSP at low airflow velocities

–Dual luminophor PSP was applied to a model automobile and subject to low speed wind tunnel tests

–Points of evaluation:

• Temperature sensitivity correction

• Model motion

• Excitation variations

Raw Pressure and Temperature Data

Airflow velocity: V = 94 m/s

Corrected Cp Data

Airflow velocity: V = 94 m/s

Corrected Cp Data: V = 42 m/s

Measured Temperature

-20°

0°

20°

T (°C)

With and Without Mirror

Low Speed Automotive Test Summary

• The ratio of the two signals (PSP/TSP)– Simplicity, no need to compute local temperature– Correct for excitation variations – Reduced the temperature sensitivity to -0.07% / C – Minimum effect on the pressure sensitivity.

• PSPcorr algorithm and simple PSP/TSP ratio produced similar results.

Insect Flight: Anticipated Difficulties

• Response Time– Wing beat frequency = 200 Hz– Resolve into 10 positions 2000 Hz– 1/2000 Hz 0.5 ms response time desired

• Sensitivity– The minimum lift pressure required by a

honey bee in hovering flight is ~ 210-4 atm

• Existing PSPs were to stiff, heavy, and slow for insect flight applications P = 210-4 atm

P = 510-1 atm

Insect Flight Studies

• Both wing pairs coated with PSP

• 400 nm laser for excitation and a CMOS video device for detection - Laser pulse and camera shutter phase-locked to the wing beat frequency

• Images will be obtained at different points in the wing beat cycle

• Pressure map used to study lift as a function of wing position

Microphone

Laser

Camera

Tethered bee

Continuous Pressure Map

Polymeric Smart Skin Materials—Biocompatible Coatings

Progress in Pressure Sensitive Paint at University of Washington

Properties 1990 2000 2004

Dynamic range 1.0 bar 50 m bar 1 m bar

Response Time 90%

(m sec)

2500 10 0.07

Temperature coefficient

(% Intensity / degree

-2.5 -0.6 -0.05

Temperature induced error

(m bar / degree)

34 10 1

Applications High speed

(airfoil)

M > 0.3

Re = 106

Low speed

(Auto model)

M> 0.1

Re = 105

Insect flight

M~ 0.02

Re = 103

Shear Stress

• One of the two fundamental forces measured by aerodynamicists.

– Pressure: force normal to airfoil surface, P– Shear Stress: force tangent to airfoil surface,

τw

airfoil

Surface Pressure, P Measured by PSP

airflow, v

Shear Stress, τw

Measured by SSP

Current Shear Stress Measurement Techniques– Mechanical balances– Preston Tubes– Hot wire and hot-film anemometry– MEMS sensors

• But these techniques are still point measurements.

• The resolution of data is dependent upon the number of sensors employed.

Naughton, J., Sheplak, M., Progress in Aerospace Sciences, 38, pp. 515-570 (2002)

SSP Project Objective

• To develop a shear sensitive paint that will provide high-resolution, 2-dimensional shear stress measurements over dynamic surfaces.

• Integrate this technology with current pressure and temperature sensitive paints, ultimately creating a single tool that will measure both pressure and shear stress.

SSP Project Approaches

• Method 1:

– Temperature sensitive paint (TSP)-based shear sensitive paint

• Method 2:

– Dynamic birefringence-based SSP

Method 1: TSP-based SSP

• Theory:– Shear stress can be calculated from the following,

τw = 2cf ρu2

cf = coefficient of friction, a constant that can be derived from the Reynold’s number

ρ = density of the airflow

u = velocity of airflow at a given point on the surface of the airfoil

Steady State Experiment

3 psi (~180 m/s, Re = 8.6x104) 15 psi (~400 m/s, Re = 2.0x105)

C

Wall Jet Wall Jet

Khalil, Rev. Sci Instrum., 75, pp. 192-206 (2004).

Calibration of TSP Temperature Response

• 5 pixel wide linescan at x = 70 (white line)• Standard deviations better than 0.7%

Calibrated TSP Temperature Response

• 5-pixel wide linescan at x=70.

• Note prominent stagnation point at higher pressures.

TSP-based SSP Theory, cont.

• Consider an airfoil that is heated to a given temperature with a thermal pulse of energy.

The rate of cooling over a given point on the surface of the airfoil will be a function of the velocity of airflow, u, above it.

TSP-based SSP Theory, cont.

Airflow II > Airflow I

Tem

pera

ture

Thermal Pulse

Airflow II

Airflow I

No Airflow

Time

Temperature Profile of a Thermally Pulsed Airfoil Under Varying Airflow Velocities

Experiment Parameters• TSP: 1:200 EuTTA:FIB, 7.5% FIB in TFT• Test surface: steel ribbon (0.5 cm x 2 cm)• Compressed air is directed over the test surface

using a 26-gauge needle.– Airflow is varies from 3 to 7 psig (~180 m/s – 400 m/s,

Re = 8.6 x 104 to 2.0 x 105)

• The ribbon is heated by application of a direct current.– Final temperature varies between 29 and 31 C

• Data acquisition begins when direct current is switched off.– A series of 10 images are acquired at an exposure

time of 100 ms.

Results τw = 2cf ρu2

TSP Response to Varying Airflows

y = -3E-05x + 1.0031

R2 = 0.9977

y = -2E-05x + 1.0022

R2 = 0.9974

y = -1E-05x + 1.0015

R2 = 0.9831

0.965

0.97

0.975

0.98

0.985

0.99

0.995

1

1.005

0 200 400 600 800 1000

Time (ms)

Io/I

No Flow Condition

5 psig

7 psig

Method 2: Dynamic Birefringence-based SSP

• Theory:– Most transparent solids are anisotropic:

• Anisotropic solids have two indices of refraction.– The difference between these axes is known as birefringence.– The birefringence of an anisotropic material will change when a stress

is applied to the object.

lightly sheared liquid crystal molecules

n1 n2

sin n

Kaminsky, W., Proc. R. Soc. Lond. A, 452, pp. 2751-2765, (1996).

Infrastructure Monitoring: Sensor Needs

• Properties of interest in civil engineering:– Oxygen concentration– Moisture content– Metal oxidation– pH

% Oxygen pH (unit) % Moisture

Range 1 - 30 8 – 14 1 - 100

Use life/years: Up to 10

Performance Specifications

Evanescent Field in Optical Fibers

• Light traveling through a waveguide by total internal reflection generates an interface specific, electromagnetic disturbance.

• The transverse component of the reflecting beam generates a standing wave at every point of strike to the interface.

• This harmonic wave, which penetrates the cladding over a small distance is called the evanescent wave.

•400 m

cladding

core •z

•x

dp

Detection of Corrosion

• Methods of Detection include– Visual– Ultrasonic– X-Ray– Magnetic Flux

The zinc sensor will be integrated into the sacrificial paint layer that contains zinc particles.

Oxidation Process Zn Zn2+

The rate of Zn2+ production is diagnostic for the corrosion process.

Optical chemical sensor that detect the presence of Zn2+ will be the diagnostic tool of detecting corrosion.

Corrosion Sensor Concept

Corrosion Sensor

Monitoring Zinc oxidation

Detection of Corrosion• Aluminum

Detection of Corrosion

Cement pH 

Unlike natural rocks and minerals, concrete is a basic material: high [Na+], [K+], and [OH-] create a pH in range 12.5 to 13.5. Reduction in the pH is expected to destabilize the hydration products in the cement. Aqueous acidity is harmful to concrete. 

Sensor for high pH environments

Based on luminescence changes

Oxygen Sensor: Cement Curing

• Monitoring of air pocket formation in curing cement– System 1: Ordinary cement– System 2: Cement with surfactant additive

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

0 20 40 60 80 100 120 140

Time (hour)

% O

xyge

n

% Oxygen (Cement with Air)

% Oxygen (Cement No Air)

System 2 (Surfactant additive)

System 1 (Cement Only)

Leak Detection--Motivation

• Natural gas is becoming a more appealing source of energy as the world’s natural sources of crude oil diminish.– 200,000 miles of pipeline in the U.S.– 200,000 miles of pipeline in Canada– $700 per mile spent each year on

maintenance and inspection, – Market expected to increase by 50% in next

20 years.

• Pipeline safety is becoming a BIG issue!

Our Solution• A fiber optic gas leak detection system based

on PSP and evanescent field spectroscopy.

outer cladding/buffer (~150m) inner cladding (~12 m)

core (1mm)

Oxygen sensor film

Experiment Set Up

Data Processing

Signal Detector(650 nm filter)

LED(400 nm filter)

Flow Meter

Gas Flow Out

O2/Air

N2/CH4

Test Chamber

Natural Gas Leak Detection

Leak Detection Results

PSP-coated FOC Simulated Methane LeakOpen Air Environment

0.9

1

1.1

1.2

1.3

1.4

1.5

0 10 20 30 40 50 60

Time (min.)

PSP-coated FOC Simulated Methane LeakPipe Buried in Sand

0.9

1

1.1

1.2

1.3

1.4

1.5

0 10 20 30 40 50

Time (min.)