Materials Science

Feeling the Strain

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Science  26 Oct 2012:
Vol. 338, Issue 6106, pp. 445
DOI: 10.1126/science.338.6106.445-b
CREDIT: M. HEMPEL ET AL., NANO LETT. (1 OCTOBER 2012) © 2012 AMERICAN CHEMICAL SOCIETY

Traditional strain gauges use a patterned metallic foil, in which the change in shape on deformation translates into a change in electrical conductivity. These devices typically have a gauge factor of 2 to 5; thus, for measuring smaller deformations, silicon gauges are used, which have a gauge factor closer to 100 but are more sensitive to temperature changes and mechanical deformation. Hempel et al. have developed a scalable deposition method for making strain gauges based on graphene, in which the sensitivity of the device can be tuned by varying the deposition conditions. Solutions containing graphene flakes were spray-coated onto a substrate to make a percolating network as the active part of the sensor. Thicker films had less electrical resistance but lower transparency, and it was shown that the gauge factor could be correlated to the initial resistance of the films. Unlike metal gauges, in which the metal itself deforms during strain, in these sensors the graphene flakes don't deform. Rather, the layers slide past each other, and it is the reduction in flake overlap that changes the electrical conductivity. Gauge factors between 10 and 150 were demonstrated, but in theory much higher values could be obtained. In addition, the sensors can be deposited onto existing surfaces, including curved ones such as light bulbs.

Nano Lett. 10.1021/nl302959a (2012).

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