Developing power sources for flexible, stretchable electronics

Dec. 14, 2012 — Electronic devices become smaller, lighter, faster and more powerful with each passing year. Currently, however, electronics such as cell phones, tablets, laptops, etc., are rigid. But what if they could be made bendable or stretchy?

According to the University of Delaware's Bingqing Wei, stretchable electronics are the future of mobile electronics, leading giants such as IBM, Sony and Nokia to incorporate the technology into their products.

Beyond traditional electronics, potential stretchable applications include biomedical, wearable, portable and sensory devices, such as cyber skin for robotic devices and implantable electronics.

"Advances in soft and stretchable substrates and elastomeric materials have given rise to an entirely new field," says Wei, a mechanical engineering professor at UD.

But even if scientists can engineer stretchable electronics -- what about their energy source?

"Rechargeable and stretchable energy storage devices, also known as supercapacitors, are urgently needed to complement advances currently being made in flexible electronics," explains Wei.

Wei's research group at the University is making significant progress in developing scalable, stretchable power sources for this type of application using carbon nanotube macrofilms, polyurethane membranes and organic electrolytes.

This, he says, requires new thinking about materials processing and device manufacturing to maximize energy storage without compromising energy resources.

To reveal a stretchable supercapacitator's true performance, the Wei group examined the system's electrochemical behavior using buckled single-wall nanotube (SWNT) electrodes and an elastomeric separator.

According to Wei, the supercapacitor developed in his lab achieved excellent stability in testing and the results will provide important guidelines for future design and testing of this leading-edge energy storage device.

As they work to refine the technology, Wei has filed a provisional patent to protect his team's research. The work was recently published in Nano Letters, a journal of the American Chemical Society.

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The above story is reprinted from materials provided by University of Delaware. The original article was written by Karen B. Roberts.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Xin Li, Taoli Gu, Bingqing Wei. Dynamic and Galvanic Stability of Stretchable Supercapacitors. Nano Letters, 2012; 12 (12): 6366 DOI: 10.1021/nl303631e

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Scientists discover ways to optimize light sources for vision: Tuning lighting devices could save billions

Nov. 15, 2012 — Vision researchers at Barrow Neurological Institute have made a groundbreaking discovery into the optimization of light sources to human vision. By tuning lighting devices to work more efficiently with the human brain, the researchers believe billions of dollars in energy costs could be saved.

The research was conducted by Stephen Macknik, PhD, of Barrow's Laboratory of Behavioral Neurophysiology, and Susana Martinez-Conde, PhD, of Barrow's Laboratory of Visual Neuroscience. The study is published Proceedings of the National Academy of Sciences. The paper is believed to be the first attempt to tune light-emitting devices to the optimal temporal dynamics of the human visual system.

The discovery concerns the way humans perceive temporal modulations of light. For example, most light-emitting devices, such as light bulbs, video monitors and televisions, flicker. Faster flicker rates result in reduced perception of flicker, which is more comfortable to viewers. In studying this phenomenon in the brain, the researchers discovered that there is a range of flicker dynamics of light that optimizes the perceived brightness of the light without increasing power.

"We found a temporal sweet spot in visual perception that can be exploited to obtain significant savings by redesigning light emitting devices to flicker with optimal dynamics to activate visual system neurons in the human brain," says Dr. Macknik.

The researchers estimate that if every light-emitting device in the U.S. -- from light bulbs to cell phones -- operated at optimal efficiency for the human visual system, it could result in billions of dollars of savings in electricity and power.

To come to their conclusion, the researchers conducted experiments into two contradictory theories of temporal visual perception, or how bright a light appears. Bloch's Law states that the perceived contrast of a visual stimulus increases with its duration, but eventually plateaus at approximately 100 milliseconds. For example, a 5-millisecond flash will appear half as bright as a 10-millisecond flash, but a 200-millisecond flash will be just as bright as one of 400 milliseconds. The Broca-Sulzer Effect, on the other hand, states that perceived contrast increases with duration initially, but then peaks and falls again.

The researchers discovered that the discrepancy between Bloch's Law and the Broca-Sulzer Effect is caused by an intrinsic bias among experiment subjects, leading to dramatically skewed data. By improving their experimental design to overcome this bias, something that has never been before reported or intentionally controlled for, the results demonstrated that temporal vision actually follows the Broca-Sulzer Effect.

"Researchers have been studying temporal vision for more than 125 years, but because ours is the first experiment of its kind to control for all known forms of criteria, it is the first to accurately measure the role of temporal dynamics in brightness perception," says Dr. Macknik. "Thus, the power savings are ripe for the picking because we can adjust our lighting to flicker to take advantage of this peak in perception."

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The above story is reprinted from materials provided by St. Joseph's Hospital and Medical Center.

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Journal Reference:

H. Rieiro, S. Martinez-Conde, A. P. Danielson, J. L. Pardo-Vazquez, N. Srivastava, S. L. Macknik. Optimizing the temporal dynamics of light to human perception. Proceedings of the National Academy of Sciences, 2012; DOI: 10.1073/pnas.1213170109

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Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

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