Use of a Pulsed Terahertz Sensor for Coat Weight, Non ...€¦ · Overview • Motivation for...

Use of a Pulsed Terahertz Sensor for Coat Weight, Noncontact

Caliper Thickness and Moisture

Jeffrey White, Jason Morgan, John Riccardi, Mike FrieseIrl Duling AppletonAd anced PhotoniAdvanced PhotonixPicometrix

PaperCon 2011 Page 480

Overview

• Motivation for developing THz sensor- Capability of improved performance single sensor for multiple

simultaneous measurements

- Department of Homeland Security - reduce / eliminate procurement of l d i h h inuclear sources due to security threats → they got you coming

- Environmental Protection Agency - reduce / eliminate procurement of nuclear sources due to disposal issues → they got you goingnuclear sources due to disposal issues → they got you going

• Pilot coater trial results

• Factory trial results

PaperCon 2011 Page 481

THz Sensor Comparisons

Compared to existing sensors, THz systems are:• single sided• single sided, • faster (up to 1 kHz),• smaller lightersmaller, lighter,• higher precision,• completely safe, poses no regulatory burden or p y , p g y

exposure concerns• Offer simultaneous measurements with a single sensor

PaperCon 2011 Page 482

What is Terahertz

• In general:a portion of the EM spectrum

THzIn / Out

25between IR and microwaves

• In practice:

25 mm

Time-Domain Terahertz is a pulsed EM (< 1ps) method used for sample measurement, defect detection and imaging

• Often sed like an EM analog of ltraso nd• Often used like an EM analog of ultrasound

PaperCon 2011 Page 483

Industrial Sensor

2.5”

5”

7”

PaperCon 2011 Page 484

Terahertz Characteristics

• Excellent penetration through paper, coatings, foams, plastics, fiberglass, paint, insulation; nearly all dielectric materials

• Non-contact, transmission or reflection (1” – 12” standoff typical)

• Fast Measurement Rate (up to 1 kHz)

• High precision (exceptional for time based measurements)

• Non-nucleonic, non-ionizing – Completely Safe• Additional measurement capabilities (caliper, moisture, formation?)

• Very insensitive to sample variations, environmental conditions

• Flexible sensor positioning (fiber coupled up to 60m)

• Imaging, more

PaperCon 2011 Page 485

THz Applications

• Foam on Shuttle External Fuel Tank (adhesion, voids)• Building materials in-process - rubbers, asphalt shingles• Coatings - paper, pharmaceutical tablets, automotive, ceramic

F-35 low observable materials• Basis weightg• Non-contact

Caliper• AerospaceAerospace • Security• CT Imaging• Art Inspection• Defect Detection (voids, crack, disbonds)• Pharmaceutical Products (compression force)• Pharmaceutical Products (compression force)

PaperCon 2011 Page 486

Transmission Measurements

2.0

2.5

Time Domain Terahertz Waveforms - Plastic Shim Samples

olts

)

No Sample 1 mil 2 mil 5 mil 10 mil 15 mil20 mil

0.0

0.5

1.0

1.5

rtz T

ime

Dom

ain

Sign

al (V

20 mil 25 mil 30 mil

0 10 20 30 40 50 60 70 80-1.5

-1.0

-0.5

Tera

he

Time (ps)700

800

RI Values<2 um - 2.095 2-5 um - 1.8337 5 30 um 1 692

Establishes THz Time of Flight

400

500

6007.5-30 um - 1.692 10 um - 1.798

him

Thi

ckne

ss (u

m)

Time-of-Flightmeasurement to

basis weight100

200

300

Pre

dict

ed S

h

Measured Values Linear Fit

R^2 = 0.9999

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.60

RI Corrected Delta ToF Value (ps)

PaperCon 2011 Page 487

Reflection Measurements

Reflection creates“ lf f d”“self-referenced”

measurement

PaperCon 2011 Page 488

THz Measurement Precision

Sample: 0.125” thick Fused SilicaSample Sets measured: 34Total Measurements: 388,000Data Collection Time: 6450 min

30000

Data Collection Time: 6450 min(4.5 days)

Results for Reflection measurements:20000

25000

nts

Mean Value = 41.164 ± 0.010 ps (±2σ)(0.014% RSD)

Range < 0 05 ps 5000

10000

15000

Cou

n

Range < 0.05 psover all 388,000 measurements

41.14 41.15 41.16 41.17 41.180

5000

ICE Reflection Time (ps)

PaperCon 2011 Page 489

Reflection / Time Measurement Properties

• No effect with standoff distance variation

S d ff di f 1” 12” i• Standoff distances from to 1” - 12” are routine

• No effect with pass-line variation

• No measureable effect with dirt / debris on sensor

• Time based measurement not affected by• Time based measurement not affected by misalignment of sensor, source decay, othersignal loss modessignal loss modes

PaperCon 2011 Page 490

Sensor on Coater – Western Michigan Univ.

PaperCon 2011 Page 491

Multilayer

PaperCon 2011 Page 492

Multi-layer Measurement

Web profile over 1 hour (approx 30 100 ft product rolls)

24

26

28

30

Total Upper Lower

PaperCon 2011 Page 493

Low Adhesion Detection• Complete delamination was created.• Slowly returned to proper operation.

Full delamination

PaperCon 2011 Page 494

Coatings

ThickThickCoating

ThinCoating

PenetratingCoatingg

PaperCon 2011 Page 495

Two-Sided Paper Thick Coating

PaperCon 2011 Page 496

Measurement Classes

• Reflection Only- Basis weight- Coat weight (thick non-penetrating coatings)- Moisture

• Differential Reflection Measurements- Coat weight for thin or penetrating coatings

• External Reference Structure (ERS) Measurements- Non-contact Caliper thickness- Basis weight + thickness Density (formation?)- Improved basis weight

Improved moisture- Improved moisture

PaperCon 2011 Page 497

The ERS

• An external structure consisting of a window in front of the sample and a reflector behind the sample. The spacing between the window and reflector is used in calculationsand has to be known or measured.

Uses• Non-contact Caliper• Mass / Thickness Density• Improved transmission ToF

measurement (basis weight)

Window

measurement (basis weight)• Improved Moisture Reflector

PaperCon 2011 Page 498

Double Pass TransmissionCaliper MeasurementCaliper Measurement

Double Pass Transmission(Ref - Pk3 + Pk0)Ref

Caliper thickness(Ref - Pk1 - Pk3 + Pk2) c( )

PaperCon 2011 Page 499

Spot External Reference StructureStock inspection at unwind Coated Product Inspection

THzReceiver

THzERS

WindowTHz Window

ERS

THz Transmitter

ERSRear Reflector

PaperCon 2011 Page 500

Scanning with ERS

PaperCon 2011 Page 501

Pilot Coater Trial

Objective: demonstrate on-line measurement of:basis weight coat weight caliper thickness andbasis weight, coat weight, caliper thickness and percent moisture• Two sensors: unwind, windupTwo sensors: unwind, windup

• Three differing stock materials

• Two differing coatingsTwo differing coatings

• Two differing applicators

• Three or four differing coat weights caliper thickness or• Three or four differing coat weights, caliper thickness or percent moisture measurements.

• Typical data collection: 3 minutes per settingTypical data collection: 3 minutes per setting

PaperCon 2011 Page 502

Stock Nominal Basis Weight

PaperCon 2011 Page 503

High Pigment Coat Weight

PaperCon 2011 Page 504

Low Pigment Coat Weight

PaperCon 2011 Page 505

Low Pigment Coat Weight – Rod Coater

PaperCon 2011 Page 506

Non-contact Caliper – All Grades

PaperCon 2011 Page 507

Non-contact Caliper – Individual Grades

#28 Stock

#43 Stock

#100 Stock

PaperCon 2011 Page 508

Moisture• Moisture levels adjustments made with oven and

fan parameters, not line speed• Adjustments made from higher moisture levels to lowerAdjustments made from higher moisture levels to lower

PaperCon 2011 Page 509

Summary

• Single THz sensor able to simultaneously measure:- Basis Weight- Non-contact Caliper Thickness- Percent Moisture

• Dual Differential THz sensors for Coat Weight• No regulated nuclear material, no exposure g , p

concerns, no high voltages• Completely safep y• Very fast, high precision measurements• Optimized for operation in factory environment• Optimized for operation in factory environment.

PaperCon 2011 Page 510