Archive for Solids & Liquids

Ultra-thin perfect absorber employing a tunable phase change material

New device hides, on cue, from infrared cameras

November 26, 2012

Tunable material developed at Harvard boasts nearly 100% absorption on demand

Cambridge, Mass. – November 26, 2012 – Now you see it, now you don’t.

A new device invented at the Harvard School of Engineering and Applied Sciences (SEAS) can absorb 99.75% of infrared light that shines on it. When activated, it appears black to infrared cameras.

Composed of just a 180-nanometer-thick layer of vanadium dioxide (VO2) on top of a sheet of sapphire, the device reacts to temperature changes by reflecting dramatically more or less infrared light.

Announced today in the journal Applied Physics Letters, and featured on its cover, this perfect absorber is ultrathin, tunable, and exceptionally well suited for use in a range of infrared optical devices.

Perfect absorbers have been created many times before, but not with such versatile properties. In a Fabry-Pérot cavity, for instance, two mirrors sandwich an absorbing material, and light simply reflects light back and forth until it’s mostly all gone. Other devices incorporate surfaces with nanoscale metallic patterns that trap and eventually absorb the light.
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Reflectivity of Mineral Powders

From the Website of Ocean Optics, an applications note for their Jaz Spectrometer

 Figure-3-Experiment-Setup.jpgIt begins:

“Reflectance spectroscopy is a versatile technique than can be used to identify and characterize a range of powdered samples including mineral powders, grains in lunar samples, mining samples, natural deposits, soils and sediment core samples. In this application note, reflectance spectroscopy is used to characterize mineral powder samples.

The Jaz spectrometer was used to acquire reflectance spectra for pure samples and powder mixtures to assess the power of reflectance spectroscopy to characterize mineral powder samples.”

Figure-3-Experiment-Setup.jpg from the Ocean Optics Blog

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Publications of Robert O. Knuteson

Reference online:,%20Robert%20O.&numOfRecs=25&currPage=1.

Sample Entries of the 38 records online at the University of Wisconsin Library:

1. Seemann, Suzanne W.; Borbas, Eva E.; Knuteson, Robert O.; Stephenson, Gordon R. and Huang, Hung-Lung. Development of a global infrared land surface emissivity database for application to clear sky sounding retrievals from multispectral satellite radiance measurements. Reprint # Journal of Applied Meteorology and Climatology, Volume 47, Issue 1, 2008, pp.108-123. Call Number: Reprint # 5663

2. Tobin, David C.; Antonelli, Paolo; Revercomb, Henry E.; Dutcher, Steven; Turner, David D.; Taylor, Joe K.; Knuteson, Robert O. and Vinson, Kenneth. Hyperspectral data noise characterization using principle component analysis: Application to the atmospheric infrared sounder. Reprint # Journal of Applied Remote Sensing, Volume 1, 2007, Doi:10.1117/1.2757707. Call Number: Reprint # 5392…

Emissivity of Human Skin in the Waveband between 2 & 6 micrometers

From a Nature Article of the same title:

By DAVID J. WATMOUGH & R. OLIVER, Department of Radiation Physics, Churchill Hospital, Oxford.
Citation: Nature 219, 622 – 624 (10 August 1968); doi:10.1038


The emissivity of human skin epsilon(lambda) in the range 2micro to 6micro has recently assumed considerable importance because of the increasing medical use of infrared scanners to measure skin temperature (t). Several commercially available scanners utilize indium antimonide detectors which are sensitive in the range 2micro to 5.4micro . Such machines measure the energy (Q) Bactrim radiated by the skin and, being calibrated against a standard black body, changes in Q are represented as variations in skin temperature. Dreyfus1 has shown that Q is related to t by an equation of the form, where k is a constant, and where the index n depends on lambda as lambdamax being the wavelength corresponding to the maximum in the emission curve. The importance of variations in emissivity can be seen by differentiating equation (1) for constant Q. We obtain which simplifies to give for Deltat For a skin temperature of 27° C (t=300° K), n is about 12.5. It follows from equation (2) that if epsilon(lambda) were to vary by as much as 5 per cent over the skin surface, this would be interpreted by the scanner as a temperature variation of about 1° C. A fairly accurate knowledge of epsilon(lambda) is thus necessary, for hot spots with temperature elevations of only 2° C are considered to be of clinical significance.

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Determination of the Infrared Emissivity with Multi-spectral Thermal Infrared Data from Space

A 2004 Amercian Geophysical Union Conference Presentation by:

Schmugge, T ( , USDA/ARS Hydrology and Remote Sensing Lab, Bldg. 007 – BARC West, Beltsville, MD 20705 United States
Ogawa, K ( , Hitachi Ltd., 4-6 Kanda-Surugadai Chiyoda- Ku,, Tokyo, 101-8010 Japan
Ogawa, K ( , Faculty of Engineering,University of Tokyo, University of Tokyo, Tokyo, 113-0033 Japan
Rokugawa, S ( , Faculty of Engineering,University of Tokyo, University of Tokyo, Tokyo, 113-0033 Japan » Read more..