Progress in On-Aircraft Application of Thermography Dr. Steven Shepard Thermal Wave Imaging, Inc.

Thermography System Evolution

Anatomy of a Thermography System Detector Excitation Processing Application Requirements Physics Inspection NDT System

Today… Frame rate: 30 – kHz Array size: 64x64 – 1k x 1K NETD mK Cooled / uncooled Cost: $2K - $250K

Many Excitation Choices 500 W1500 W4800 J [watt-sec] 250 W 600 W / m 2 10 W / in 2

Best Solution? Flash Close proximity Non-contact FOV: ~ 1 sq ft Projection Long range (45) Non-contact FOV: ~ 6 sq ft Hot air Close proximity Non-contact FOV: ~ 2 sq ft Vibro Close proximity Contact FOV: large Scanning Close proximity Non-contact FOV: large stripe All of these approaches detect the impact damage successfully, but they vary in sensitivity, cost, working distance, coverage area and inspection time.

On-Aircraft Inspection Requirements Performance Area coverage Size / weight Ease-of-use Cost

On-Aircraft Inspection Requirements Performance –Demonstrated for many applications –Some applications require laboratory scale systems Area coverage –Inherent feature of thermography Size / weight Ease-of-use Cost Critical issues

Optical Excitation Noncontact Well-suited to area excitation Pulse heating (xenon flash lamp) –Precise high energy pulse facilitates high performance –Size, weight, cost issues Step Heating (halogen lamp) –Low cost –High power when applied over longer duration –Some applications may be inaccessible

Conventional Optical Heating IR NDT reflector IR camera lamp target emitted IR light

Conventional Optical Heating IR NDT reflector IR camera lamp target emitted IR Visible + IR reflected IR

Spectral Filtering of Lamp Output reflector IR camera halogen lamp (visible + IR) IR filter target emitted IR visible

Halogen Lamp Spectral Distribution

Integtrate Planck Equation Integrating Planck Equation over visible range (4-7 um): temperature efficiency 3000 K 8.1% 3200 K 10.5% 4000 K 20.8% 5000 K 31.6% A typical 1500 W halogen lamp puts out ~ 150 W of visible light! typical Halogen lamps are inefficient generators of visible light!

Spectral Distribution and Efficiency visible visible + IR filter visible + NIR visible INPUTOUTPUT Solving Planck Equation for visible range (4-7 um): temperature efficiency 3000 K 8.1% 3200 K 10.5% 4000 K 20.8% 5000 K 31.6% A typical 1500 W halogen lamp puts out ~ 150 W of visible light! typical Ref: Carl Zeiss

Where Does Blocked Energy Go? Heat applied to one side of the filter passes through to the outer surface This is the same heat conduction mechanism thermography is based on Long wave IR (5-12 um) is emitted from the outer surface Time constant for passage through filter is similar to inspection time scale By blocking NIR, the filter creates a LWIR source. visible visible + NIR visible + LWIR visible +NIR time visible visible + NIR filter t0t0 t1t1 t2t2

Uniformity, Efficiency and Lamp Geometry Reflective optics can achieve excellent uniformity for a point source. Point source Parabolic reflector

Uniformity, Efficiency and Lamp Geometry Actual lamps are not point sources, and may not be at exact focus of reflector. Collimation and uniformity suffer as source becomes larger. With a line source, a simple reflector illuminates a stripe. Diverging components may not hit the target. Can improve line source area uniformity with multiple lamps and reflectors in a reflective cavity, but system becomes larger. Parabolic reflector Line source Diverging Collimated

Conventional Step Heating IR NDT System Poor efficiency –IR component of lamp output is blocked by filter. Net efficiency is approx. 10% Non-uniform heating of target –Linear lamp array with reflecting enclosure required for uniform heating of 2D area. Much of the output of a single linear tube does not hit the target Reflection artifacts –Light passing through raises filter temperature –Black paint may be required for reflective surfaces Transient reflection artifacts –Elevated temperature in reflector heats filter wall –Heat conduction through filter results in delayed temperature increase on outer filter wall Slow onset and decay of heating –Processing methods are based on rectangular step reflector IR camera Halogen lamp (visible + NIR) IR filter target emitted IR visible

Lamp and Focusing Reflector Lamp Focusing Reflector High intensity lamp, e.g. halogen Source element to allow focusing Reflector surface optimized for visible and IR wavelengths Focal Point Visible and IR beam

Direct Visible and IR Onto Surface Reflector Lamp Focusing Reflector Focal Point Visible and IR beam Target

Reflector Motion Reflector rotates between open and closed positions Beam directed away from target Closed position Target

Paint Beam Onto Surface Beam forward direction Beam off-axis Target

VoyageIR PRO TM Patents Pending

VoyageIR PRO TM Precise and efficient excitation Compact, lightweight 12 x 9 field of view Uncooled microbolometer camera Low cost (~ 40 K$) TSR signal processing Integrated touch screen controlLarge area inspection using MOSAIQ ® software Single case transport

Applications: Moisture Ingress

Drill Down Validation of Image Result A320 Rudder TSR Raw

Drill Down Validation of Image Result A320 Rudder water

Patch Identification: Raw IR Result

TSR result

Overlay Result Onto Aircraft

Overlay Result Onto Aircraft

Applications: Polymer FOD Raw IR (video)

Raw IR Result

TSR Result

TSR Result poly insert Hole 1 Hole 2 ABCD Lab flash system – cooled camera VoyageIR Pro with uncooled camera

Boeing 7X7 Al Doubler Disbond Inspection Raw IR result TSR result Boeing disbond cal std

Boeing 7X7 Al Doubler Disbond Inspection TSR result Boeing disbond cal std UT

ProjectIR TM Far-field thermography –Working distance 5 – 50 ft

Summary VoyageIR Pro –Unique approach to excitation removes –Artifact reduction –Advanced signal processing –Apply to wide range of applications –Drill-down confirmation of result