Oct 14, 2011
Disappearing act: concealment using transparent carbon nanotube sheets
Ali Aliev and coworkers at The University of Texas at Dallas, US, have demonstrated that transparent carbon nanotube sheets, which can have the density of air and the specific strength of steel, can be used to make objects invisible. This invisibility for light oblique to the nanotube sheets is caused by the mirage effect, in which a thermally generated refractive index gradient bends light away from a hidden object.
The extremely low thermal capacitance and high heat-transfer ability of these electrically conducting nanotube sheets, which are drawn from forest-like arrays of carbon nanotubes, enables high frequency modulation of sheet temperature over a wide temperature range, thereby providing a sharp, rapidly changing gradient of refractive index in surrounding liquid or gas.
Using these nanotube sheets, concealment can be realized over the entire optical range and rapidly turned on and off at will, using either electrical heating or a pulse of electromagnetic radiation. However, concealment is easiest to realize underwater, where the high temperature dependence of liquid refractive index can be used.
Ali Aliev and his colleagues Yuri Gartstein and Ray Baughman also use this mirage effect to make photodeflectors for optical applications, like optical scanning. Advantages over prior art technologies for light deflection are low-voltage operation, the absence of an undeflected beam component and mechanical movement, large beam diameter capabilities, and low cost.
The research provides useful insights into the optimization of nanotube sheets as thermoacoustic projectors for loud speaker and sonar applications, where sound is produced by heating using an alternating electrical current.
More information can be found in the journal Nanotechnology.
About the author
The study was conducted by a research team from the University of Texas at Dallas, US. Dr Ali E Aliev is a research scientist at the Alan G MacDiarmid NanoTech Institute and adjunct professor at the physics department. He performed the experimental part of the work. Prof. Yuri N Gartstein at the physics department performed supporting calculations. Ray H Baughman (Robert A Welch Chair in Chemistry and director of the Alan G MacDiarmid NanoTech Institute) contributed to the analysis of results and writing. This research work was supported by Office of Naval Research MURI grant N00014-08-1-0654, NASA Phase II SBIR grant NAS-54C, Air Force Office of Scientific Research grant FA9550-09-1-0537, and Robert A Welch Foundation grant AT-0029.