Every day we use our sense of touch to guide our way through life without giving it a second thought. Engineers have long sought to replicate the complex sense of touch in electronic components

to give robots and, eventually, prosthetic limbs the same ability to interact with the surrounding world. A group of electrical engineers at UC Berkeley have made a significant breakthrough in the pursuit of producing a sensor similar to human skin in its ability to detect pressure. Professor Ali Javey and his team fabricated a seven square centimeter sensor array using inorganic semiconductors called nanowires mounted onto flexible, pressure-sensitive rubber. Previous electronic skins used flexible organic components that were 50 times smaller in area and required a large battery to provide the voltage needed to operate them. Javey’s group instead opted to use nanowires that require smaller volt-ages. “Previous research using nanowires was limited to using single nanowire transistors on a very small scale,” says Dr. Kuniharu Takei, a postdoctoral scholar in Javey’s group and lead author of the paper. The sensor makes use of an innovative contact printing technique pioneered by the team to mount hundreds of nanowires onto the sensor. The electronic skin is durable, making it ideal for future applications, which Javey explains can range, “from robotics, to giving gas pipelines the ability to self diagnose the formation of cracks, and one day even interfac- ing with prosthetic limbs.”

-Mohan Ganesh

-Monica Smith

Although scientists often want to look at very tiny things, it is theo-retically impossible to see something smaller than the wavelength of the radiation used to image it. In order to observe even smaller

objects, one could either use a shorter wavelength, for instance a beam of X-rays instead of light, or play a number of tricks to get around

this limit. The same principles that restrict the ability to resolve details in optical imaging also hold true for methods that use

soundwaves like ultrasound. Jie Zhu, a postdoctoral fellow in Professor Xiang Zhang’s lab at UC Berkeley, and colleagues

recently engineered a device capable of imaging objects smaller than the wavelength of sound used to create the

acoustic image. The device has very small, square holes drilled through a block that act as perfect lenses for

transmitting sound waves. When waves with the proper wavelength hit an object on one side of

the block, information contained in standing waves that only exist very close to the object

is faithfully transferred through the device. A microphone placed close to the output of the “holey”

material can detect features up to 50 times smaller than the wavelength emitted by the source, seven times better

than the best resolution previously available. This technology could spawn the next generation of probes for medical sonography

and the non-destructive evaluation of materials.

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Spring 2011 5Berkeley Science Review

In many developing countries like India, running water is scarce and only intermittently available. To tackle this challenge, UC Berkeley graduate students Thejo Kote, Emily Kumpel, and Ari

Olmos, launched a social enterprise called NextDrop in the fall of 2009, with advice from Assistant Professor Tapan Parikh of the School of Information. NextDrop aims to address the problem of unreliable piped water in India by exploiting the ubiquity of cell phones in the country. “Mobile phones are everywhere,” explains Kumpel.

“They’re a very easy way to get information to people.” Local families participate by sending a text message to NextDrop as soon as water becomes available. As an incentive, the first set of callers receives a micropayment. NextDrop then verifies the accuracy of the water delivery update and immediately sends a text to all its subscribers in the same neighborhood. Since its modest beginnings as a class project, NextDrop has gone on to win UC Berkeley’s 2010 Big Ideas competition and grants from the Gates Foundation and the Clinton Global Initiative. In July 2010 they began their first pilot program in the southern Indian town of Hubli, with 200 families as well as the local water utility board participating. In the future, NextDrop hopes to use delivery data accumulated over time to predict when water will arrive in a particular locality, thereby empowering consumers to actively participate in improving a vital utility.

-Sharmistha Majumdar

-Molly Sharlach

When you think of the Napa and Sonoma Valleys, you probably imagine rolling hills adorned with row upon row of succulent grapes vine-ripening in the sun. However, beneath this idyllic exterior the bacterium Xylella fastidiosa is wreaking havoc on California’s wine grapes. By cutting off water transport through the plants, Xylella causes leaves to wither and fall off, ultimately killing entire

vines. In an effort to better understand the mechanism of this disease, Associate Specialist Clelia Baccari and Professor Steven Lindow of the Department of Plant and Microbial Biology are studying the movement of the bacteria through the tissues of resistant and susceptible grape varieties. They use a strain that expresses green fluorescent protein, making the bacterial cells easy to visualize under a microscope. The plant’s ray cells appear red, and between them are xylem vessels—water-transporting vascular tissue. The bright yellow-green areas on the walls of the xylem are full of bacteria. Dr. Baccari found that susceptible varieties, such as Cabernet Sauvignon on the left, had about five times as many infected xylem vessels as the Tampa grape, on the right, which is relatively resistant to the disease. Current hypotheses as to why some grape varieties are more resistant include differences in sap composition and the production of tyloses—outgrowths of cells surrounding xylem vessels, which may block bacterial movement through the plant.

Wireless water

Winey pests

Cabernet Sauvignon (10x) Tampa (10x)