Shortwave Infrared Imaging for Machine

Vison ApplicationsMartin H. Ettenberg, Ph.D.

PresidentPrinceton Infrared Technologies, Inc.

Outline

• What is Short Wave Infrared?

• Reflective vs Emissive Samples

• Various Applications• Thermal Imaging

• Detection of Water

• Imaging through Silicon

• Hyperspectral Imaging

• Other applications

• Optics/Lighting in SWIR

• Conclusion

What is the SWIR?

• Short Wave Infrared (SWIR) Imaging

• Defined from 1000nm -2600nm

• Near Infrared (NIR) 750-1000nm (what Si can detect)

• InxGa1-xAs, InSb, and

HgCdTe is typically used to

image in this band• Lattice Matched InGaAs,

In.53Ga.47As allows low dark

current and low cost imaging

• Lattice matched InGaAs

allows 0.9 to 1.7um typically

or 0.4 to 1.7um

Ettenberg, M. H., Malchow, D., “ShortWave Infrared (SWIR) Imaging Aids laser Tracking, Detection” Photonic Tech Briefs, April 2007.

SWIR Imagers

• SWIR imagers are in two varieties• Uncooled (Room temperature stabilized) • Cooled to modest temperatures ~-20C to -80C

• Lattice Match InGaAs most common• 900-1700nm detection range• 400-1700nm in extended versions• Highest performing materials (low noise and high sensitivity)

• InSb, HgCdTe, and Non-lattice matched InGaAs• Enable detection to 2600nm down to 400nm or 1000nm depending on the material and

processing• Requires extensive cooling • Noise is significantly higher

• Resolution, Pitch, Speed• 320x256 to 1280x1024 • Pitch varies from 25um to 10um• Frame rates from 100fps at 1280 to ~400fps at small resolution.• Linear arrays available from 256x1 to 2048x1

• Linerates 100+kHz

• Pitches 12.5 to 50um

Reflected Versus Emitted Light

http://www.equinoxsensors.com/products/multispec_faces.html

http://www.oneonta.edu/faculty/baumanpr/geosat2/RS-Introduction/RS-Introduction.html

SWIR Uses Reflected and Emitted Light

• SWIR imagery is typically reflected imagery very similar to visible light

• Samples can be illuminated in the front and reflected light can be used

• Back lighting of samples is also conducted and one can look at the absorption of light.

• Hot samples will emit in the SWIR range and we can measure temperature of objects with the

SWIR.

• Mid-Wave Infrared (MWIR) and Long Wave Infrared (LWIR) cameras use

emitted light from the object itself. No external light source is needed.

• SWIR imaging allows for better resolution because of smaller wavelength

and the fact that it uses reflected light versus emitted light.

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InGaAs Imagers Detect Emitted and Reflected Light

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SWIR OnlySWIR Emission from Soldering

Soldering Iron Dominates

Visible and SWIRRoom lights and Soldering Iron Emission

Room Lights Dominate

• SWIR only image is illumination only by a hot soldering iron.• Visible & SWIR is with fluorescent lights on.• Soldering Iron is emitting light in SWIR band while the person is imaged by

reflected light from the soldering iron and/or fluorescent light source.

Imaging Thermal Emissions Using Glass Optics

• Water heated to 75C

• Thermal emission in SWIR• 90ms integration time• Able to image hot water through

the glass

• SWIR imagers can use glass or plastic optics

• MWIR and LWIR need sapphire or Ge optics which are expensive

http://www.photonics.com/EDU/Handbook.aspx?AID=25134

SWIR Camera Thermal or LWIR Camera

SWIR Can Detect Water Easily

• 4 clear liquids in visible are very different in SWIR band

• Water is very absorbing

• Utilizing specific wavelengths of light can improve contrast versus broadband.

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TCE IsopropanolAcetone Water

TCEIsopropanol

AcetoneWater

Linear Array Showing H20 vs. Acetone

Agricultural Inspection, Water Detection in Fruit

• Bruise on fruit is obvious in SWIR but with visible light it is difficult to image

• Water released from bruise makes it very detectable

• Many other agricultural applications

• Shells from nuts• Leaves from twigs• Dryness of wood

http://www.qualitymag.com/articles/91011-short-wave-infrared-enhances-machine-vision

Many Plastics are Transparent in SWIR

• Water in detergent is absorbing

• Plastic bottle is fairly transparent in SWIR band

• Plastic sorting is also conducted in SWIR band by looking at reflected signals of different plastics at different wavelengths of light

http://www.qualitymag.com/articles/91011-short-wave-infrared-enhances-machine-vision

Plastic Sorting Through Spectroscopy

• Various materials may look the same color wise but are different spectroscopically

• Studying the material by wavelength enables one material to be differentiated from another.

• Nylon versus Polypropylene versus Acrylic is very different in the SWIR band

Data and Graph from Ocean Optics Application note on Sorting Plastics https://oceanoptics.com/wp-content/uploads/App-Note-Sorting-Plastic-Resins-Using-NIR-Spectroscopy2.pdf

Coffee Beans Versus Contaminants at 1400nm

• Black Background• Most of the objects are brown in visible making sorting difficult• Rocks and pieces of wood are unreflective in SWIR• Coffee beans highly reflective in SWIR

SWIR Visible

wood rocks

rock

Coffee Beans

wood rocks

Oil and Water on Steel

water

Motor oil

Note how oil and water don’t mix, very visible in SWIR band

Broadband SWIR Visible Light0

2000

4000

6000

8000

10000

350 450 550 650 750Si

gnal

(C

ou

nts

)

Pixel Number

water

oilsteel

Human’s have different reflective characteristics in SWIR band

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• Hair is highly reflective

• Skin is very absorbing (water content)

• Clothing is reflective, some is transparent

http://www.upcscavenger.com/wiki/infrared/#page=wiki

SWIR Images through Silicon

Silicon Wafer is transparent to SWIR light but not in visible• Allows for detection of defects in processing• Enables raw material inspection

Solar Cell Inspection

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From Sensors Unlimited, Inc. websitehttp://www.sensorsinc.com/applications/photovoltaics/electroluminescence-for-pv-cells

Solar cell Inspection is conducted two different ways:• Inspection through the silicon to look for defects, cracks, voids, saw error• Electroluminescence and/or photoluminescence by activating the cells

through light or electricity to find defects(seen above)

Underdrawings In Paintings

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• Many paints are transparent in SWIR enabling users to see charcoal underdrawings.

• We see many things that are unseen.

Advanced Imaging, Len Yencharis, “Scientific Imaging Extends IR Value” April 2004.

Household Paints Transparent to SWIR Light

Sugar versus Salt

1400nm light

Sugar

Salt

Visible Camera

5000

7000

9000

11000

13000

15000

17000

400 500 600 700 800 900

Sign

al (

Co

un

ts)

Pixel Number

Pixel 450

Pixel 800

Sugar has different reflective properties from Salt in the SWIR band,yet they look the same in the visible band.

Epoxies Absorb Differently

SWIR Broadband Visible Light

Epoxies, caulk, and silicone on AluminumReflective properties very different from one another

Multi- or Hyper-spectral Imaging in SWIR

• Materials have different structures and these structures results in different absorption and reflection of light in SWIR band.

• Looking at multiple colors of light enables one to differentiate item A from item B

• Imaging cubes are created by looking at multiple colors simultaneously

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Molero, J. et al, J. Appl. Remote Sens. 6(1), “Anomaly detection based on a parallel kernel RX algorithm for multicore platforms” May 10, 2012.

Various Lens Options

• Glass Optics can be used• Visible optics can be used with degraded performance

• Chromatic aberrations

• Transmission losses

• Fine for single wavelength imaging

• Various Vendors for commercial SWIR optics• Edmund Optics

• Optec

• Stingray optics

• Navitar

• Many Others

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Conclusion

• Short Wave Infrared provides a unique option for identifying various components and compounds that can’t be differentiated in the visible band

• Reflective characteristics in visible sometimes have little to no relationship to what happens in the SWIR band

• Various camera and optic manufacturers to help solve your imaging needs

• Cameras are more expensive solution but maybe an easier deployment because signal to noise makes for simpler processing for sorting

Contact Information

Martin H. Ettenberg, Ph.D.President

Princeton Infrared Technologies, Inc.9 Deerpark Dr.

Suite J-5

Monmouth Jct. NJ, 08852

USA

+1 609 917-3380

martin.ettenberg@princetonirtech.com

www.princetonirtech.com

Visit us at Booth 2463