research

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.

March 2015

The university that pioneered research collaborations between academia and industry has expanded from a device-driven to a systems-level view of how to ignite innovation.

The shift involves a change in name and philosophy at what had been the Stanford Center for Integrated Systems (CIS).

Since the late 1970s, CIS had enabled Stanford researchers to work with industry counterparts to improve semiconductors, software, computers and other technologies. CIS helped create the global networks and mobile devices that put technology in our pockets.

Now, SystemX researchers are working on the next killer applications – the data center of tomorrow, the self-driving car, the smartphones with artificial intelligence built in and next-generation biomedical devices, among others.

Bringing these applications to fruition will require new materials and power sources, novel hardware and software, and coordination of these technologies through reliable control networks.

Stanford President John Hennessy, whose research helped revolutionize computing during the 1980s, describes this systems-level approach as the "technology stack."

"For 30 years, CIS was the model of industry-university partnership to support advanced research in microelectronics," Hennessy said. "SystemX is updating that model to spur innovation in what we call the technology stack and open up new possibilities for sensing, communication and computing technologies."

To highlight this change Stanford has rechristened CIS as the SystemX Alliance.

 

Read the full Stanford Report article

image of Assistant Professor Jonathan Fan
January 2015

The Air Force Office of Scientific Research (AFOSR) has announced the Young Investigator Research program (YIP) grant recipients. EE Assistant Professor Jonathan Fan's winning proposal will investigate Neuromorphic Infrared Nano-Optical Systems.

"The YIP is open to scientists and engineers at research institutions across the United States who received Ph.D. or equivalent degrees in the last five years and who show exceptional ability and promise for conducting basic research."

The AFOSR news article continues, "This year AFOSR received over 200 proposals in response to the AFOSR broad agency announcement solicitation in major areas of interest to the Air Force. These areas include: Dynamical Systems and Control, Quantum and Non-Equilibrium Processes, Information, Decision and Complex Networks, Complex Materials and Devices, and Energy, Power and Propulsion. AFOSR officials select proposals based on the evaluation criteria listed in the broad agency announcement. Those selected will receive the grants over a 3-year period."

Read the entire article

Wetzstein's research featuredScientific American’s features Assistant Professor Wetzstein’s Research as a World-Changing Idea as a world-changing idea
December 2014

In an article titled, "Smartphone Screens Correct for Your Vision Flaws," the December issue of Scientific American features Wetzstein's research with colleagues from MIT and University of California, Berkeley. The articles states, "Informal tests on a handful of users have shown that the technology works, Wetzstein says, but large-scale studies are needed to further refine it. In the process, the researchers also plan on developing a slider that can be used to manually adjust the focus of the screen. Wetzstein says that the technology could be a boon for people in developing countries who have easier access to mobile devices than prescription eyewear."

Gordon Wetzstein's research addresses challenges in computational imaging and display and in computational light transport. He received his PhD in computer science from the University of British Columbia in 2011, then worked at MIT's Media Lab as a research scientist and postdoctoral associate before joining the Stanford faculty.

 

Read the complete article from Scientific American.

Professors Wong and Mitra's CNT chips revealed at IEDM conference
December 2014

Professor H.-S. Philip Wong and Associate Professor Subhasish Mitra's research team has built a four-layer high-rise chip using carbon nanotubes (CNT) and resistive random access memory (RRAM). The new materials required a new method of connecting them, which were created by EE grad students, Max Shulaker and Tony Wu.

"This research is at an early stage, but our design and fabrication techniques are scalable," Mitra said. "With further development this architecture could lead to computing performance that is much, much greater than anything available today."

Wong said the prototype chip to be unveiled at IEDM shows how to put logic and memory together into three-dimensional structures that can be mass-produced.

"Paradigm shift is an overused concept, but here it is appropriate," Wong said. "With this new architecture, electronics manufacturers could put the power of a supercomputer in your hand."

 

Read the full article in the Stanford Report. 

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