Category Archives: Other Materials

Raytek’s Online Spectral Emissivity Guide

Screen Shot of Webpage

Santa Cruz CA, USA — As part of the IR Education section, the Raytek Corporation website contains some useful and well-presented information on Spectral Emissivity, one of the few instrument makers who do so.

Although they just call it plain “emissivity” they then present values for three or four different wavebands, according to the table viewed, “A Rose by any other name…”. There are two pages with disclaimers.

Here’s a summary of the opening statements and links to the actual data pages. Read more

Emissivity of human skin

Novel approach to assess the emissivity of the human skin
J. Biomed. Opt., Vol. 14, 024006 (2009); DOI:10.1117/1.3086612 Published 6 March 2009
by: Francisco J. Sanchez-Marin, Sergio Calixto-Carrera, and Carlos Villaseñor-Mora
Centro de investigaciones en optica, Loma del Bosque 115, Lomas del Campestre, Leon, Guanajuato 37150, Mexico

Abstract:

To study the radiation emitted by the human skin, the emissivity of its surface must be known. We present a new approach to measure the emissivity of the human skin in vivo. Our method is based on the calculation of the difference of two infrared images: one acquired before projecting a CO2 laser beam on the surface of the skin and the other after such projection. The difference image contains the radiation reflected by the skin, which is used to calculate the emissivity, making use of Kirchhoff’s law and the Helmholtz reciprocity relation. With our method, noncontact measurements are achieved, and the determination of the skin temperature is not needed, which has been an inconvenience for other methods. We show that it is possible to make determinations of the emissivity at specific wavelengths. Last, our results confirm that the human skin obeys Lambert’s law of diffuse reflection and that it behaves almost like a blackbody at a wavelength of 10.6 µm.

Editor’s Note: Back in the 1960s there were several serious projects mounted by the US Army Medical Research Laboratory’s BioPhysics Division on determining injury thresholds of laser radiation on human skin analogs. The article THRESHOLD LESIONS INDUCED IN PORCINE SKIN BY CO2 LASER RADIATION” by Brownell, Arnold S. ; Parr, Wordie H. ; Hysell, David K. ; Dedrick, Robert, USAMRL Report No. 7327, June 1967, is available as a pdf download at: http://handle.dtic.mil/100.2/AD659347.

Although not fully described in the article, the measured results compared favorably with a semi-infinite solid model of heat conduction for a surface that was essentially black (10.6 micron spectral absorptivity or emissivity very close to 1.0) or fully absorbing at 10.6 microns. This editor was a member of the USAMRL BioPhysics Division staff at that time and helped with the dosimetry of the experiments described.

Table of Emissivities in Three Popular Spectral Regions

The Table of Emissivity on the INFRAPOINT Messtechnik GmbH website, posted in 2009 (No longer available online) had summary data for a wide variety of materials broken down into three distinct spectral regions for the wavelength regions where the majority of infrared radiation thermometers and Infrared Thermal Imaging cameras operate.

First and second are tables that deal with the narrow spectral bands about 0.9 µm and 1.6 µm, the regions where many Silicon (Si) photovoltaic detectors (peak wavelength response: (0.9 µm) and both Germanium (Ge) and Indium Gallium Arsenide (InGaAs) (nominal wavelength region (0.7 – 1.6 µm) are used.

The third table cover the 8 – 14 µm waveband where most “low” (near ambient) temperature IR thermometers and thermal imaging sensors operate.

It has been reproduced here below in the spirit of Internet openness from our archives. We hope there is no problem in doing so and if any heir or assigns of INFRAPOINT Messtechnik GmbH wishes to keep this information secret, obviously against the original intent of INFRAPOINT, please contact us according to our webpage contact information.


   Table of emissivity        
  The emissivity ? (radiant emittance factor) is the relationship of the radiated intensity of a body to the intensity of a blackbody of the same temperature.
It is the most important factor, in order to determine of an item exactly.

If you want to measure the surface temperature with an infrared thermometer the emissivity must be known and correct adjusted
on the instrument.

               
   Material  Emissivity     Material  Emissivity  
  Metals Wavelength
0.9 µm 
Wavelength
1.6 µm 
  Non metals Wavelength
8 – 14 µm  
 
               
  Aluminium, bright 0.05 – 0.25  0.05 – 0.25    Asphalt  0.95   
  Aluminium, anodized 0.2 – 0.4  0.1 – 0.4    Concrete 0.95  
  Chrom, bright 0.28 – 0.32  0.25 – 0.3    Gypsum 0.85 – 0.95   
  Iron, oxidised 0.4 – 0.8 0.5 – 0.9    Graphite  0.75 – 0.92   
  Iron, not oxidised 0.35 0.1 – 0.3    Glass*, pane  0.80   
  Gold, bright 0.02 0.02    Rubber 0.85 – 0.95   
  Copper, bright 0.06 – 0.20 0.06 – 0.20    Wood, natural 0.8 – 0.95   
  Copper, oxidised  0.5 – 0.8  0.7 – 0.85    Chalk 0.98   
  Magnesium 0.03 – 0.8  0.05 – 0.3    Ceramics 0.85 – 0.95   
  Brass, bright  0.8 – 0.95  0.01 – 0.05    Plastics 0.85 – 0.95   
  Brass, oxidised  0.65 – 0.75  0.65 – 0.75    Masonry 0.85 – 0.95   
  Nickel, oxidised  0.8 – 0.9  0.4 – 0.7    Human skin 0.98   
  Platinum, black  -  0,95    Oil paints 0.85 – 0.95   
  Silver  0.02  0.02    Paper  0.85 – 0.95   
  Steel, melted 0.30  0.20 – 0.25    Porcelain 0.85 – 0.95   
  Steel, oxidised  0.8 – 0.9  0.8 – 0.9    Quartz  0.8   
  Steel, bright 0.40 - 0.45  0.30 – 0.4    Carbon black 0.95   
  Titanium, bright 0.5 – 0.75  0.3 – 0.5    Chamotte  0.85 – 0.95   
  Titanium, oxidised  -  0.6 – 0.8    Textile, Drapery 0.85 – 0.95   
  Zinc, bright 0.6  0.4 – 0.6    Tone 0.95   
  Zinc, oxidised  0.5  0.05    Water 0.95  
  Tin 0.25  0.1 – 0.3    Cement  0.9   
* The emissivity of glass (0.95 – 0.97 µm) is in the range of 4.5 – 7 µm particularly high.
Glass has there an absorption band (spectral range, where materials absorb radiation).
To measure glass surface temperatures, the best wavelength is at 5.14 µm, because
the measurement at this range is not affected by absorption bands such as carbon or hydrogen.

Spectral emissivity of skin and pericardium

Spectral emissivity of skin and pericardium by J Steketee 1973 Phys. Med. Biol. 18 686-694 doi: 10.1088/0031-9155/18/5/307 Help

J Steketee, Department of Biological and Medical Physics, Erasmus University, Rotterdam, The Netherlands

Abstract.

A monochromator was modified to measure the emissivity, ?(?), of living tissue in the infrared region between 1 and 14 ?m. The infrared radiation from the tissue was compared with blackbody radiation and in this way ?(?) has been determined for white skin, black skin, burnt skin and pericardium.

A compensating skin thermometer was constructed to measure the temperature of the surface of the tissue. The temperature difference before and after contact between a gold ring and the surface was made as small as possible (0.05 K). A reference radiator with the same spectral radiance (experimentally determined) mas used in compensating for the environment.

It appeared that ?(?) for skin is independent of the wavelength and equal to 0.98+-0.01. These results contradict those of Elam, Goodwin and Lloyd Williams, but are in good agreement with those of Hardy and Watmough and Oliver.

In addition there was no difference between ?(?) for normal skin and burnt skin. Epicardium values were found to lie between 0.83 (fresh heart) and 0.90 (after 7 h and after 9 d).

Print publication: Issue 5 (September 1973)
PDF (504 KB)

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