Context:

• An electronic skin (e-skin) that simultaneously senses pressure and strain has been fabricated using a PVC-free pencil eraser that has been sliced into a thin layer and deposited with multi-walled carbon nanotubes on either side. The carbon nanotubes are the main sensing elements of the device.
• The low-cost, easily scalable sensor fabricated by a two-member team led by the Indian Institute of Technology (IIT) Hyderabad may find applications in flexible electronics and medical diagnostics.
• The device can be used for human motion monitoring in the case of elderly and infants. The e-skin is sensitive… it can sense even a gentle touch.
• The signal from the device can be interfaced with a microcontroller and the signal can be taken from the sensor to a smartphone using wireless technology.

Making of the sensor:

• The PVC-free pencil eraser is sliced and cut to optimal dimensions and optimised amount of multi-walled carbon nanotubes are pressed on the layer using a rolling pin and a pre-compaction mechanical press. The rolling pin is used to get a uniform thin film with carbon nanotubes deposited on the film to get a desired initial resistance. The film is further pressed using a mechanical press.
• Both the sides of the eraser are patterned with carbon nanotubes so that the film together with the carbon nanotubes acts as a capacitor. Silver paste is applied to make a metal contact to draw the signal from the device.
• When pressure is applied the thickness of the film decreases and the distance between the two carbon nanotube layers that behave like metal plates gets reduced. This increases the capacitance.
• When the e-skin is stretched the distance between carbon nanotubes increases and therefore the resistance increases. But when the e-skin is compressed the distance between carbon nanotubes decreases and so the resistance reduces. “Basically the e-skin acts as a resistance sensor when subjected to strain and capacitive sensor when subjected to pressure.

Source:TH