research

May 2016

Recently published in Lab on a Chip, a journal of the Royal Society of Chemistry, Professor Audrey Bowden and Gennifer Smith, a PhD student in electrical engineering, detail their new low-cost, portable device that would allow patients to get consistently accurate urine test results at home, easing the workload on primary care physicians.

Other do-it-yourself systems are emerging, but Bowden and Smith's approach is inexpensive and reliable, in part because they base their system on the same tried and trusted dipstick used in medical offices.

Their approach uses an easy-to-assemble black box that allows a smartphone camera to capture video that accurately analyzes color changes in a standard paper dipstick.

 

Excerpts from Stanford News, May 16, 2016.

Read full Stanford News article

December 2015

Collaborative efforts of researchers at Stanford, University of California Berkeley, University of Michigan, and Carnegie Mellon University are working toward creating a faster and more efficient computing architecture.

The team describes their approach as 'N3XT, Nano-Engineered Computing Systems Technology.' N3XT will eliminate bottlenecks by integrating processors and memory like floors in a skyscraper and by connecting these components with millions of "vias," which play the role of tiny electronic elevators.

The key is the use of non-silicon materials that can be fabricated at much lower temperatures than silicon, so that processors can be built on top of memory without the new layer damaging the layer below.

N3XT high-rise chips are based on carbon nanotube transistors (CNTs). Transistors are fundamental units of a computer processor, the tiny on-off switches that create digital zeroes and ones. CNTs are faster and more energy-efficient than silicon processors. Moreover, in the N3XT architecture, they can be fabricated and placed over and below other layers of memory.

Mitra and Wong have already demonstrated a working prototype of a high-rise chip. At the International Electron Devices Meeting in December 2014 they unveiled a four-layered chip made up of two layers of RRAM memory sandwiched between two layers of CNTs.

In their N3XT paper they ran simulations showing how their high-rise approach was a thousand times more efficient in carrying out many important and highly demanding industrial software applications.

"When you combine higher speed with lower energy use, N3XT systems outperform conventional approaches by a factor of a thousand," Wong said.

 

Excerpts from the Stanford Report.

November 2015

Professor Arbabian and research professo Khuri-Yakub's research was spurred by a challenge posed by the Defense Advanced Research Projects Agency (DARPA), best known for sponsoring the studies that led to the Internet. DARPA sought to develop a system to detect plastic explosives buried underground – improvised explosive devices (IEDs) – that are currently invisible to metal detectors. The task included one important caveat: The detection device could not touch the surface in question, so as not to trigger an explosion.

Professor Arbabian and research professor Khuri-Yakub detail their latest step toward developing such a device through experiments, which are detailed in Applied Physics Letters and presented at the International Ultrasonics Symposium in Taipei, Taiwan.

The work grows out of research designed to detect buried plastic explosives, but the researchers said the technology could also provide a new way to detect early stage cancers.

"We've been working on this for a little over two years," Khuri-Yakub said. "We're still at an early stage but we're confident that in five to ten to fifteen years, this will become practical and widely available."

 

The research team includes graduate students Hao Nan, Kevin Boyle, Nikhil Apte, Miaad Aliroteh, Anshuman Bhuyan and senior research associate Amin Nikoozadeh.

 

Excerpts from Stanford Report.

October 2015

Recent articles published by EE Professors Eric Pop and H.S. Philip Wong describe advances in memory and data storage using graphene. The three experiments demonstrate post-silicon materials and technologies that store more data per square inch and use a fraction of the energy of today's memory chips.

The unifying thread in all three experiments is graphene, an extraordinary material isolated a decade ago but which had, until now, relatively few practical applications in electronics.

"Graphene is the star of this research," said Eric Pop, associate professor of electrical engineering and a contributor to two of the three memory projects. "With these new storage technologies, it would be conceivable to design a smartphone that could store 10 times as much data, using less battery power, than the memory we use today."

Professor H.-S. Philip Wong and Pop led an international group of collaborators who describe the graphene-centric memory technologies in separate articles in Nature Communications, Nano Letters, and Applied Physics Letters.

"Data storage has become a significant, large-scale consumer of electricity, and new solid-state memory technologies such as these could also transform cloud computing," Wong said.

Pop and Wong agree that these studies show that graphene is far from a laboratory curiosity. The material's unique electrical, thermal and atomically thin properties can be utilized to create more energy-efficient data storage. Such properties do not exist in the silicon world, yet could potentially transform the way we store and access our digital data in the future.

 

Excerpts from the Stanford Report

September 2015

EE Professor Shanhui Fan, research associate Aaswath P. Raman, and doctoral candidate Linxiao Zhu describe their research in the current issue of Proceedings of the National Academy of Sciences.

The group's discovery, tested on a Stanford rooftop, addresses a problem that has long bedeviled the solar industry: The hotter solar cells get, the less efficient they become at converting the photons in light into useful electricity.

Their solution is based on a thin, patterned silica material laid on top of a traditional solar cell. The material is transparent to the visible sunlight that powers solar cells, but captures and emits thermal radiation, or heat, from infrared rays.

"Solar arrays must face the sun to function, even though that heat is detrimental to efficiency," Fan said. "Our thermal overlay allows sunlight to pass through, preserving or even enhancing sunlight absorption, but it also cools the cell by radiating the heat out and improving the cell efficiency."

In 2014, the same trio of inventors developed an ultrathin material that radiated infrared heat directly back toward space without warming the atmosphere. They presented that work in Nature, describing it as "radiative cooling" because it shunted thermal energy directly into the deep, cold void of space.

In their new paper, the researchers applied their previous work to improve solar array performance when the sun is beating down.

The Stanford team tested their technology on a custom-made solar absorber – a device that mimics the properties of a solar cell without producing electricity – covered with a micron-scale pattern designed to maximize the capability to dump heat, in the form of infrared light, into space. Their experiments showed that the overlay allowed visible light to pass through to the solar cells, but that it also cooled the underlying absorber by as much as 23 degrees Fahrenheit.

 

Excerpts from the Stanford Report.

 

August 2015

The first fully internal method of delivering optogenetics has been established. Miniature implanted devices are being wirelessly powered by a special power source that transmits frequencies that resonate in certain lab mice.

The device dramatically expands the scope of research that can be carried out through optogenetics to include experiments involving mice in enclosed spaces or interacting freely with other animals. The work is published in the Aug. 17 edition of Nature Methods.

Professor Ada Poon states, "This is a new way of delivering wireless power for optogenetics. It's much smaller and the mouse can move around during an experiment." See video.

The device can be assembled and reconfigured for different uses in a lab, and the design of the power source is publicly available. "I think other labs will be able to adapt this for their work," Poon said.

This novel way of delivering power is what allowed the team to create such a small device. And in this case, size is critical. The device is the first attempt at wireless optogenetics that is small enough to be implanted under the skin and may even be able to trigger a signal in muscles or some organs, which were previously not accessible to optogenetics.

The team says the device and the novel powering mechanism open the door to a range of new experiments to better understand and treat mental health disorders, movement disorders and diseases of the internal organs. They have a Stanford Bio-X grant to explore and possibly develop new treatments for chronic pain.


Professor Poon's lab recently sponsored a summer program for local female high school students, providing them a chance to explore several introductory concepts of EE. View article.

Excerpts are from the Stanford Report. View full article

August 2015

Stanford's Global Climate and Energy Project (GCEP) has awarded Professor Shanui Fan's group funding to develop new techniques for cooling buildings.

Fan reported the energy-saving breakthrough in the journal Nature. Using a thermal photonic approach, the material reflects sunlight and emits heat, demonstrating new possibilities for energy efficiency. The photonic radiative cooler consists of seven alternating layers of hafnium dioxide (HfO2) and silicon dioxide (SiO2) of varying thicknesses, on top of 200 nm of silver (Ag), which are all deposited on top of a 200-mm silicon wafer.

This passive energy source, which exploits the large temperature difference between space and Earth, could provide nighttime lighting without batteries or other electrical inputs.

GCEP is an industry partnership that supports innovative research on energy technologies to address the challenge of global climate change by reducing greenhouse gas emissions. The project includes five corporate sponsors: ExxonMobil, GE, Schlumberger, DuPont and Bank of America.

 

View full Stanford Report article.

July 2015

The Innovation Transfer Program at the TomKat Center for Sustainable Energy is providing financial support for 11 new teams trying to put university research to work. The Innovation Transfer Program is in its first year.

Of the 11 teams that have been awarded, three are led by EE faculty advisors.

  • Humblade is an embedded sensor that provides online monitoring of wind power generators, and eventually pipeline, trains, planes and other critical infrastructure. Advisor: Boris Murmann.
  • Spark Thermionics will prototype a device to convert heat to electricity with record-setting efficiency, and is scalable from watts to megawatts. Advisor: Roger Howe.
  • Vorpal (awarded in fall 2014) is developing a handheld device for sterilizing liquids using pulsed electric field technology as an energy-efficient alternative to pasteurization and other means of purification. Advisor: Juan Rivas-Davila.

The Energy Innovation Transfer Program at the TomKat Center for Sustainable Energy provides financial support for clean energy technologies.

 

Read full Stanford Report article.

June 2015

In their Nature Photonics paper, Professor Shanhui Fan, graduate student Yu Shi, and alum Zongfu Yu show that, "when a signal is transmitting through, such isolators are constrained by a reciprocity relation for a class of small-amplitude additional waves and, as a result, cannot provide isolation for arbitrary backward-propagating noise. This result points to an important limitation on the use of nonlinear optical isolators for signal processing and for laser protection."

The Stanford News reports, "In previous works, researchers used a specific method to test whether nonlinear isolators on a chip could keep information flowing in the right direction. They would direct a beam of light in the "forward" direction and verify that the isolator would let the light through. Then they would direct a beam of light in the "backward" direction toward the isolator, and verify that the isolator would block that beam. It was not standard practice to test forward and backward beams at the same time."

This finding is important for designing isolators for optical chips. Engineers will need to look elsewhere for devices that can keep optical information flowing in one direction, but not the other.

Read full Stanford News article.

May 2015

"A new algorithm enables a moment-by-moment analysis of brain activity each time a laboratory monkey reaches this way or that during an experiment. It's like reading the monkey's mind," states the Stanford Report article.

Professor Shenoy and neuroscientist Matthew Kaufman, a previous student of Shenoy's, published the research findings in eLife.

Shenoy's lab focuses on movement control and neural prostheses — such as artificial arms — controlled by the user's brain.

"This basic neuroscience discovery will help create neural prostheses that can withhold moving a prosthetic arm until the user is certain of their decision, thereby averting premature or inopportune movements," Shenoy said.

  

Krishna Shenoy is Professor of Electrical Engineering and Courtesy Professor of Neurobiology.

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