Cats’ whiskers inspire nanotube sensors

Researchers have created tactile sensors from composite films of carbon nanotubes and silver nanoparticles that are claimed to be similar to whiskers of cats and rats.

These so-called e-whiskers, developed by researchers at Berkeley Lab and the University of California (UC) Berkeley, are said to respond to pressure as slight as a single Pascal. Potential applications include giving robots new abilities to manoeuvre within their surrounding environment.

‘Whiskers are hair-like tactile sensors used by certain mammals and insects to monitor wind and navigate around obstacles in tight spaces,’ said the research leader Ali Javey, a faculty scientist in Berkeley Lab’s Materials Sciences Division and a UC Berkeley professor of electrical engineering and computer science. ‘Our electronic whiskers consist of high-aspect-ratio elastic fibres coated with conductive composite films of nanotubes and nanoparticles. In tests, these whiskers were 10 times more sensitive to pressure than all previously reported capacitive or resistive pressure sensors.’

For this project, Javey and his research group used a carbon nanotube paste to form a bendable electrically conductive network matrix. They then loaded the carbon nanotube matrix with a thin film of silver nanoparticles that endowed the matrix with high sensitivity to mechanical strain.

‘The strain sensitivity and electrical resistivity of our composite film is readily tuned by changing the composition ratio of the carbon nanotubes and the silver nanoparticles,’ Javey said in a statement. ‘The composite can then be painted or printed onto high-aspect-ratio elastic fibres to form e-whiskers that can be integrated with different user-interactive systems.’

Javey noted that the use of elastic fibres with a small spring constant as the structural component of the whiskers provides large deflection and therefore high strain in response to the smallest applied pressures.

As proof-of-concept, he and his research group used their e-whiskers to demonstrate 2D and 3D mapping of wind flow. In the future, e-whiskers could be used to mediate tactile sensing for the spatial mapping of nearby objects, and could also lead to wearable sensors for measuring heartbeat and pulse rate.

‘Our e-whiskers represent a new type of highly responsive tactile sensor networks for real time monitoring of environmental effects,’ Javey said. ‘The ease of fabrication, light weight and excellent performance of our e-whiskers should have a wide range of applications for advanced robotics, human-machine user interfaces, and biological applications.’

A paper describing the work – Highly sensitive electronic whiskers based on patterned carbon nanotube and silver nanoparticle composite films – has been published in the Proceedings of the National Academy of Sciences.

This research was supported by the US Defense Advanced Research Projects Agency.