use of a pulsed terahertz sensor for coat weight, non ...€¦ · overview • motivation for...
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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”
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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
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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
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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