Last June, I noted research in Singapore which promised a wide-ranging imaging sensor based on graphene. The hyperspectral detection of graphene ranges from ultraviolet to far infrared but there has been a problem with very low sensitivity of the single layer of carbon atoms.
A paper in Nature Nanotechnology, published on March 16 2014, outlines a method devised by researchers at the University of Michigan whereby electrons freed by photons hitting a first layer of graphene tunnel through an insulating barrier layer and into a second graphene layer. This affects current flowing through the second graphene layer and this is what is detected. The result is a dramatic increase in sensitivity as well as IR detectors that perform well at room temperatures. This is all explained in a press release from the University of Michigan. The 'trick' was to look into how the signal could be amplified, rather than making the signal itself stronger. (I haven't read the whole paper but I would ask what noise does this generate.)
"We can make the entire design super-thin," said Zhaohui Zhong, assistant professor of electrical and computer engineering at Michigan, and one of the inventors. "It can be stacked on a contact lens or integrated with a cell phone." This mention of contact lenses led the Register to ask "Want to see at night? Here comes the infrared CONTACT LENS".
A patent, 'Photodetector based on double layer heterostructures', has been applied for.
Showing posts with label hyperspectral. Show all posts
Showing posts with label hyperspectral. Show all posts
Saturday, 5 April 2014
Wednesday, 30 October 2013
Frogs and leaf growth
Back in January I noted research by into infrared reflectance of insects carried out by Michael Mielewczik and others. Michael has contacted me again about two more papers on similar subjects.
The first is Non-Invasive Measurement of Frog Skin Reflectivity in High Spatial Resolution Using a Dual Hyperspectral Approach [1] (on PLOS ONE here with a PDF here).
As before, the team used a camera with filtering that split near-infrared (specifically the red-edge between 675-775 nm) and blue to explore the 'colour' of frog skin. They also used a two further hyperspectral cameras sensitive to visible and near-infrared between 400 and 1000 nm and to SWIR (short wave infrared) between 1000 and 2500 nm. This image is of agalychnis callidryas using the red-edge camera.
I've come across hyperspectral cameras before and they're quite fascinating devices. They produce a multi-dimensional image where each of the pixels in the x and y plane have a complete spectrum recorded in the z axis ... so z records intensity at a range of wavelengths. This means that you can choose which wavelength (or wavelengths) to view the scene after the fact. This multiplies the amount of data dramatically of course.
The second paper uses infrared imaging to help a study of leaf growth. The paper is Diel leaf growth of soybean: a novel method to analyze two-dimensional leaf expansion in high temporal resolution based on a marker tracking approach (Martrack Leaf) [2], available on the Plant Methods web site. This study used dark beads attached to the margins of a leaf and a camera fitted with a 940nm narrow bandpass filter. At this wavelength the leaf is brighter than the beads which makes image analysis easier.
[1] Pinto F, Mielewczik M, Liebisch F, Walter A, Greven H, et al. (2013) PLoS ONE 8(9): e73234. doi:10.1371/journal.pone.0073234
[2] Mielewczik M, Friedli M, Kirchgessner N, Walter A. Plant Methods 2013, 9:30 doi:10.1186/1746-4811-9-30
[Note: corrected information about the hyperspectral camera added 31 October]
The first is Non-Invasive Measurement of Frog Skin Reflectivity in High Spatial Resolution Using a Dual Hyperspectral Approach [1] (on PLOS ONE here with a PDF here).
As before, the team used a camera with filtering that split near-infrared (specifically the red-edge between 675-775 nm) and blue to explore the 'colour' of frog skin. They also used a two further hyperspectral cameras sensitive to visible and near-infrared between 400 and 1000 nm and to SWIR (short wave infrared) between 1000 and 2500 nm. This image is of agalychnis callidryas using the red-edge camera.
I've come across hyperspectral cameras before and they're quite fascinating devices. They produce a multi-dimensional image where each of the pixels in the x and y plane have a complete spectrum recorded in the z axis ... so z records intensity at a range of wavelengths. This means that you can choose which wavelength (or wavelengths) to view the scene after the fact. This multiplies the amount of data dramatically of course.
The second paper uses infrared imaging to help a study of leaf growth. The paper is Diel leaf growth of soybean: a novel method to analyze two-dimensional leaf expansion in high temporal resolution based on a marker tracking approach (Martrack Leaf) [2], available on the Plant Methods web site. This study used dark beads attached to the margins of a leaf and a camera fitted with a 940nm narrow bandpass filter. At this wavelength the leaf is brighter than the beads which makes image analysis easier.
[1] Pinto F, Mielewczik M, Liebisch F, Walter A, Greven H, et al. (2013) PLoS ONE 8(9): e73234. doi:10.1371/journal.pone.0073234
[2] Mielewczik M, Friedli M, Kirchgessner N, Walter A. Plant Methods 2013, 9:30 doi:10.1186/1746-4811-9-30
[Note: corrected information about the hyperspectral camera added 31 October]
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