From the world of nanotechnology we've gotten electronic skin, or e-skin, and electronic eye implants¹ or e-eyes. Now we're on the verge² of electronic whiskers（胡须）. Researchers with Berkeley Lab and the University of California (UC) Berkeley have created tactile³（触觉的） sensors⁴ from composite films of carbon nanotubes and silver nanoparticles similar to the highly sensitive whiskers of cats and rats. These new e-whiskers respond to pressure as slight as a single Pascal, about the pressure exerted on a table surface by a dollar bill. Among their many potential applications is giving robots new abilities to "see" and "feel" their surrounding environment. "Whiskers are hair-like tactile sensors used by certain mammals and insects to monitor wind and navigate⁶ around obstacles in tight spaces," says the leader of this research Ali Javey, a faculty⁷ 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 elastic⁸ fibers⁹ coated with conductive composite films of nanotubes and nanoparticles. In tests, these whiskers were 10 times more sensitive to pressure than all previously¹⁰ reported capacitive or resistive pressure sensors."

 

Javey and his research group have been leaders in the development of e-skin and other flexible electronic devices that can interface¹¹ with the environment. In this latest effort, they used a carbon nanotube paste to form an electrically conductive network matrix with excellent bendability. To this carbon nanotube matrix they loaded 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 tuned¹² by changing the composition ratio of the carbon nanotubes and the silver nanoparticles," Javey says. "The composite can then be painted or printed onto high-aspect-ratio elastic fibers to form e-whiskers that can be integrated with different user-interactive systems."

 

Javey notes that the use of elastic fibers with a small spring constant as the structural¹³ component¹⁴ of the whiskers provides large deflection and therefore high strain in response to the smallest applied¹⁵ pressures. As proof-of-concept, he and his research group successfully used their e-whiskers to demonstrate highly accurate 2D and 3D mapping of wind flow. In the future, e-whiskers could be used to mediate¹⁶ tactile sensing for the spatial¹⁷ 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 sensor⁵ networks for real time monitoring of environmental effects," Javey says. "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 interfaces¹⁸, and biological applications."

 

A paper describing this research has been published in the Proceedings¹⁹ of the National Academy of Sciences. The paper is titled "Highly sensitive electronic whiskers based on patterned carbon nanotube and silver nanoparticle composite films." Javey is the corresponding author. Co-authors are Kuniharu Takei, Zhibin Yu, Maxwell Zheng, Hiroki Ota and Toshitake Takahashi.

 

This research was supported by the Defense²⁰ Advanced Research Projects Agency.

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