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.

What the Heck is (Spectral) Emissivity?

Part One of Two from the mind of FLIR
It health partners pharmacies starts:

Fill two soda cans with hot water and wrap one with scotch tape. Which one will radiate more heat?

You might be surprised at the answer

(It has all to do with Spectral Emissivity, although this video continues the illusion that it's really simple "Emissivity" at work! The concept of Emissivity is simple and easy to grasp as the video shows. The understanding is a bit more difficult and begins when one realizes that it is really Spectral Emissivity.)

But looking beyond that technical fine point, the video illustrates two other things:

ASTM E307 - 72(2008) Standard Test Method for Normal Spectral Emittance

At Elevated Temperatures
Developed by ASTM Subcommittee: E21.04, on Space Simulation Test Methods, and in the Annual Book of ASTM Standards, Volume 15.0 Space Simulation; Aerospace and Aircraft; Composite Materials

Quoting from the standard's Scope:

1. Scope

1.1 This test method describes a highly accurate technique for measuring the normal spectral emittance of electrically conducting materials or materials with electrically conducting substrates, in the temperature range from 600 to 1400 K, and at wavelengths from 1 to 35 ?m.

1.2 The test method requires expensive equipment and rather elaborate precautions, but produces data that are accurate to within a few percent. It is suitable for research laboratories where the highest precision and accuracy are desired, but is not recommended for routine production or acceptance testing. However, because of its high accuracy this test method can be used as a referee method to be applied to production and acceptance testing in cases of dispute...

Obtaining directly from ASTM International has two options:

1. Buy Standard (PDF): 6 pages $ 37.00 US (In PDF format, this active standard is the most current version published by ASTM. You will download the file after you check out of the ASTM Store.)

2. Buy Standard (Print): 6 pages $ 37.00 US (In printed format, this active standard is the most current version published by ASTM. After you place your order, ASTM will print this standard and deliver it to your ship-to address by common carrier.)

Ordering Options Outside of the United State. has many more: Click here: (http://www.astm.org/IMAGES03/InterNatDist.pdf)

Electro Optical Industries BB Emissivity Coatings

Electro Optical Industries (EOI) uses one of two high emissivity coatings on the surface of its blackbodies.

The EOI mid-temperature coating is used on both cavity and flat plate blackbodies that have a maximum operating temperatures of up to 210 °C.



Read the rest by visiting their webpage at: www.electro-optical.com/eoi_page.asp?h=What%20Is%20Emissivity?

Blackbody Emissivity Primer

From the Electro-Optical Industries website:

"Effective emissivity is the ratio of the total amount of energy exiting a blackbody to that which is predicted by Planck’s law. This is the value most frequently referred to as "emissivity".

Effective emissivity of a cavity type blackbody will normally be much higher than the surface emissivity due to the multiple energy bounces inside the body cavity."

You can read the rest on this useful and informative webpage: www.electro-optical.com/html/bb_rad/emissivity/emisivty.asp