research

June 2017

If electric cars could recharge while driving down a highway, it would virtually eliminate concerns about their range and lower their cost, perhaps making electricity the standard fuel for vehicles.

Now Stanford University scientists have overcome a major hurdle to such a future by wirelessly transmitting electricity to a nearby moving object. Their results are published in the June 15 edition of Nature.

"In addition to advancing the wireless charging of vehicles and personal devices like cellphones, our new technology may untether robotics in manufacturing, which also are on the move," said Shanhui Fan, a professor of electrical engineering and senior author of the study. "We still need to significantly increase the amount of electricity being transferred to charge electric cars, but we may not need to push the distance too much more."

The group built on existing technology developed in 2007 at MIT for transmitting electricity wirelessly over a distance of a few feet to a stationary object. In the new work, the team transmitted electricity wirelessly to a moving LED lightbulb. That demonstration only involved a 1-milliwatt charge, whereas electric cars often require tens of kilowatts to operate. The team is now working on greatly increasing the amount of electricity that can be transferred, and tweaking the system to extend the transfer distance and improve efficiency.

"We can rethink how to deliver electricity not only to our cars, but to smaller devices on or in our bodies," Fan said. "For anything that could benefit from dynamic, wireless charging, this is potentially very important."

The study was also co-authored by former Stanford research associate Xiaofang Yu. Part of the work was supported by the TomKat Center for Sustainable Energy at Stanford.

 

Excerpted from Stanford News, "Wireless charging of moving electric vehicles overcomes major hurdle in new Stanford research," June 14, 2017.

May 2017

A research team led by EE professor Jelena Vuckovic, has spent the past several years working toward the development of nanoscale lasers and quantum technologies that might someday enable conventional computers to communicate faster and more securely using light instead of electricity. Vuckovic and her team, including Kevin Fischer, a doctoral candidate and lead author of a paper describing the project, believe that a modified nanoscale laser can be used to efficiently generate quantum light for fully protected quantum communication. "Quantum networks have the potential for secure end-to-end communication wherein the information channel is secured by the laws of quantum physics," states PhD candidate Kevin Fischer.

Signal processing is helping the IoT and other network technologies to operate faster, more efficiently, and very reliably. Advanced research also promises to open new opportunities in key areas, such as highly secure communication and various types of wireless networks.

The biggest challenge the researchers have faced so far is dealing with the fact that quantum light is far weaker than the rest of the light emitted by a modified laser, making it difficult to detect. Addressing this obstacle, the team developed a method to filter out the unwanted light, enabling the quantum signal to be read much better. "Some of the light coming back from the modified laser is like noise, preventing us from seeing the quantum light," Fischer says. "We canceled it out to reveal and emphasize the quantum signal hidden beneath."

Despite being a promising demonstration of revealing the quantum light, the technique is not yet ready for large-scale deployment. The Vuckovic group is working on scaling the technique for reliable application in a quantum network.

 

Excerpted from "A Networking Revolution Powered by Signal Processing," IEEE Signal Processing Magazine, January 2017.
Read full article (opens PDF)

May 2017

"Quantum computing is ideal for studying biological systems, doing cryptography or data mining – in fact, solving any problem with many variables," states Professor Jelena Vuckovic"When people talk about finding a needle in a haystack, that's where quantum computing comes in."

 In her own studies of nearly 20 years,  Vuckovic has focused on one aspect of the challenge: creating new types of quantum computer chips that would become the building blocks of future systems.

"To fully realize the promise of quantum computing we will have to develop technologies that can operate in normal environments," she said. "The materials we are exploring bring us closer toward finding tomorrow's quantum processor."

The challenge for Vuckovic's team is developing materials that can trap a single, isolated electron. Working with collaborators worldwide, they have recently tested three different approaches to the problem, one of which can operate at room temperature – a critical step if quantum computing is going to become a practical tool.

In all three cases the group started with semiconductor crystals, material with a regular atomic lattice like the girders of a skyscraper. By slightly altering this lattice, they sought to create a structure in which the atomic forces exerted by the material could confine a spinning electron.

"We are trying to develop the basic working unit of a quantum chip, the equivalent of the transistor on a silicon chip," states Vuckovic. "We don't know yet which approach is best, so we continue to experiment."

 

 

 

Excerpted from the Stanford News, "Stanford team brings quantum computing closer to reality with new materials".

Photo credit: Amanda Law

EE PhD admit poster session winners
March 2017

The 2017 EE Admit Weekend welcomed nearly 80 newly admitted PhD graduate students. The 2-day event connected admitted students with current students, faculty and staff. Bringing everyone together, the event encourages exploration of the department and current research. Friday concludes with a PhD student research poster session and social reception. Admits enthusiastically engaged with presenters to discuss their research and various aspects of graduate life at Stanford.

The research posters present topics from EE's core research areas. In addition to meeting incoming PhD students, it is an opportunity for current grad students to present their work and hone their presentation skills. The posters are competitively judged, based on oral presentation, visual quality, and clarity of presenting their research within a one minute timeframe. The judges include staff, faculty and students. A winner from each core research area are selected based on their score in the judging criteria.

The well-deserved awards went to:

  • Leighton Barnes (pictured below second from left) winner in Information Systems and Science for poster titled "Geometry and the Relay Channel,” 
  • Adrian Alabi (pictured below, center) in Hardware/Software Systems for poster titled "915 MHz FSK Detection for Wireless Ultrasonic Imaging Data Reception,” 
  • Max Wang (pictured below second from right) in Physical Technology and Science for poster titled "Minimally Invasive Ultrasonically Powered Implants for Next-Generation Therapies and Neuromodulation” 

The winning researchers were awarded a gift card and certificate, presented by Daisy Chavez (pictured below, left), Graduate Admissions Specialist and Student Life Coordinator and Professor Andrea Goldsmith (pictured below, right), Chair of the EE Student Life Committee.

Congratulations and thanks to everyone for participating in the 2017 EE Admit Weekend and research poster session. Additional thanks to the EE Admissions, GSEE, and the EE Student Life Committee for sponsoring the poster contest and generous prizes.

March 2017

Kwabena Boahen's research on building brain-like computers, or neuromorphic computers, is moving toward creating physical devices that are more energy efficient and robust. Kwabena envisions this technology would be most useful in embedded systems that have extremely tight energy requirements, such as very low-power neural implants or on-board computers in autonomous drones.

While others have built brain-inspired computers, he and his collaborators have developed a five-point prospectus for how to build neuromorphic computers that directly mimic in silicon what the brain does in flesh and blood.

The first two points of the prospectus concern neurons themselves, which unlike computers operate in a mix of digital and analog mode. In their digital mode, neurons send discrete, all-or-nothing signals in the form of electrical spikes, akin to the ones and zeros of digital computers. But they process incoming signals by adding them all up and firing only once a threshold is reached – more akin to a dial than a switch.

That observation led Kwabena to try using transistors in a mixed digital-analog mode. Doing so, it turns out, makes chips both more energy efficient and more robust when the components do fail, as about 4 percent of the smallest transistors are expected to do.

From there, Kwabena builds on neurons' hierarchical organization, distributed computation and feedback loops to create a vision of an even more energy efficient, powerful and robust neuromorphic computer.

Over the last 30 years, Kwabena's lab has actually implemented most of their ideas in physical devices, including Neurogrid, one of the first truly neuromorphic computers. In another two or three years, Boahen said, he expects they will have designed and built computers implementing all of the prospectus's five points.

He states that neuromorphic computers will not replace current computers. The two are complementary.

An additional challenge is getting others, especially chip manufacturers, on board. Kwabena is not the only one thinking about what to do about the end of Moore's law or looking to the brain for ideas. IBM's TrueNorth, for example, takes cues from neural networks to produce a radically more efficient computer architecture. On the other hand, it remains fully digital, and, Kwabena said, 20 times less efficient than Neurogrid would be had it been built with TrueNorth's 28-nanometer transistors.

Professor Kwabena Boahen is also a member of Stanford SystemX and the Stanford Computer Forum. His work was supported by a Director's Pioneer Award and a Transformative Research Award from the U.S. National Institutes of Health and a Long Range Science and Technology Grant from the U.S. Office of Naval Research.

 

Below, Professor Kwabena Boahen shares his research with Electrical Engineering undergraduates who are in the REU program (Research Experience for Undergrads).

Boahen shares his research with EE undergrads who are in the REU program

 


 

Excerpted from Stanford News, "As Moore's law nears its physical limits, a new generation of brain-like computers comes of age in a Stanford lab"

Image credit (top): Linda A. Cicero / Stanford News Service

 

March 2017

At the IEEE International Electron Devices Meeting, researchers presented work they say shows that molybdenum disulfide not only makes for superlative single transistors, but can be made into complex circuits using realistic manufacturing methods.

The researchers are part of Eric Pop's team. They showed transistors made from large sheets of MoS2 can be used to make transistors with 10-nanometer-long, gate having electronic properties that approach the material's theoretical limits. The devices displayed traits close to ballistic conduction, a state of very low electrical resistance that allows the unimpeded flow of charge over relatively long distances—a phenomenon that should lead to speedy circuits.

Most of the work on molybdenum disulfide so far has been what professor Eric Pop calls "Powerpoint devices." These one-off devices, made by hand in the lab, have terrific performance that looks great in a slide. This step is an important one, says Pop, but the 2D material is now maturing.

Pop Lab's transistors are not as small as the record-breaking ones demonstrated in October. What's significant is that these latest transistors maintained similar performance even though they were made using more industrial-type techniques. Instead of using Scotch tape to peel off a layer of molybdenum disulfide from a rock of the material, then carefully placing it down and crafting one transistor at a time, Pop's grad student started by growing a large sheet of the material on a wafer of silicon.

At these relatively small dimensions, the molybdenum disulfide transistors approach their ultimate electrical limit, a state called ballistic conduction. When a device is small enough (or at low enough temperature), electrons will travel through the conducting medium without scattering because of collisions with the atoms that make up the material. Transistors operating ballistically should switch very fast and enable high-performance processors. Pop estimates that about 1 in 5 electrons moves though the rusty transistors ballistically. By further improving the quality of the material (or making the transistors smaller), he expects that ratio to improve. The important thing, he says, is the way they achieved this: using methods that could translate to larger scales. "We have all the ingredients we need to scale this up," says Pop.

Eric Pop and graduate students talking during an informal lunchtime Q and A session in the Packard building.


 

Excerpted from IEEE Spectrum, "Molybdenum-Disulfide 2D Transistors Go Ballistic"

March 2017

Kristen Lurie (PhD '16) and Audrey Bowden authored a paper published in Biomedical Optics Express that presents a computational method to reconstruct and visualize a 3D model of organs from an endoscopic video that captures the shape and surface appearance of the organ.

Although the team developed the technique for the bladder, it could be applied to other hollow organs where doctors routinely perform endoscopy, including the stomach or colon.

"We were the first group to achieve complete 3D bladder models using standard clinical equipment, which makes this research ripe for rapid translation to clinical practice," states Kristen Lurie (EE PhD, '16), lead author on the paper.

"The beauty of this project is that we can take data that doctors are already collecting," states Audrey.

One of the technique's advantages is that doctors don't have to buy new hardware or modify their techniques significantly. Through the use of advanced computer vision algorithms, the team reconstructed the shape and internal appearance of a bladder using the video footage from a routine cystoscopy, which would ordinarily have been discarded or not recorded in the first place.

"In endoscopy, we generate a lot of data, but currently they're just tossed away," said Joseph Liao, professor of Urology and co-author. According to Liao, these three-dimensional images could help doctors prepare for surgery. Lesions, tumors and scars in the bladder are hard to find, both initially and during surgery.

This technique is the first of its kind and still has room for improvement, the researchers said. Primarily, the three-dimensional models tend to flatten out bumps on the bladder wall, including tumors. With the model alone, this may make tumors harder to spot. The team is now working to advance the realism, in shape and detail, of the models.

Future directions, according to the researchers, include using the algorithm for disease and cancer monitoring within the bladder over time to detect subtle changes, as well as combining it with other imaging technologies.

 

Read Paper

 

 

Excerpted from Stanford News, "Stanford scientists create three-dimensional bladder reconstruction"

 

March 2017

EE's Krishna Shenoy and neurosurgeon Jaimie Henderson are co-senior authors on a clinical research paper, which demonstrated that a brain-to-computer hookup can enable people with paralysis to type via direct brain control at the highest speeds and accuracy levels reported to date.

Their paper involved three study participants with severe limb weakness — two from amyotrophic lateral sclerosis, also called Lou Gehrig's disease, and one from a spinal cord injury. They each had one or two baby-aspirin-sized electrode arrays placed in their brains to record signals from the motor cortex, a region controlling muscle movement. These signals were transmitted to a computer via a cable and translated by algorithms into point-and-click commands guiding a cursor to characters on an onscreen keyboard.

Behind those results lie years of efforts by an interdisciplinary team of neurosurgeons, neuroscientists and engineers who brought different scientific vantages together to solve challenges that would have stumped any single discipline. Institutional support was another key ingredient in this long-term effort aimed at ultimately helping people with paralysis affect the world around them using only their minds.

Though more work lies ahead, this ongoing research shows that new engineering and neuroscience techniques can be directly applied to human patients. The milestone is heartening for Krishna Shenoy, who has led the effort to create brain-controlled prosthetic devices since he came to Stanford in 2001. Integral to that success has been his 12-year partnership with Jaimie Henderson, which he describes as a professional marriage of engineering, science and medicine.

"When you have a clear vision, you involve yourself in as many details as possible and you work with absolute mutual respect, as coequals, it's pretty interesting what you can do over a couple decades," Krishna said.

The study's results are the culmination of a long-running collaboration between Henderson and Shenoy and a multi-institutional consortium called BrainGate. Leigh Hochberg, MD, PhD, a neurologist and neuroscientist at Massachusetts General Hospital, Brown University and the VA Rehabilitation Research and Development Center for Neurorestoration and Neurotechnology in Providence, Rhode Island, directs the pilot clinical trial of the BrainGate system and is a study co-author.

 

 

Excerpted from Stanford Medicine News Centers "Brain-computer interface advance allows fast, accurate typing by people with paralysis" and "Listening in on the brain: A 15-year odyssey".

February 2017

In an article titled, "Graphene-Girded Interconnects Could Enable Next-Gen Chips," work by EE PhD candidate Ling Li, a Nanoelectronics Lab researcher, provides insight to the possible future of copper and graphene.

At the IEEE International Electron Devices Meeting in San Francisco in December, researchers described the coming problems for copper interconnects, and debated ways of getting around them. One approach studied by H.-S. Philip Wong's Nanoelectronics Lab, is to bolster copper with graphene. The research group found that the nanomaterial can alleviate a major problem facing copper, called electron migration.

Copper wires are getting so thin, and must carry so much current, that the atoms in the wire can literally get blown out of place. "The electron wind can physically move the copper atoms and create a void," says Wong. Growing graphene around copper wires prevents this, according to research Wong's group presented at the meeting. It also seems to bring down the resistance of the copper wires.

The Stanford group worked with Lam Research, which makes chip manufacturing tools, as well as researchers from Zhejiang University, in China, to make and test the composite interconnects. The materials are a good pair: graphene is often made by growing it on copper. Lam Research has developed a proprietary process for doing this at temperatures that won't damage the rest of the chip—below 400 °C. Compared to copper alone, the composite improved electromigration by a factor of 10. And the composite wires had half the electrical resistance.

Wong says the interconnect problem can no longer be dismissed. "Before, most of the time we were hearing about transistors," he says. "Now it's not just transistors but wires, memory—many other things that were previously not a problem are beginning to be a problem."

 

Excerpted from IEEE Spectrum, 6 January 2017.

January 2017

SPF is a place to use and share expertise; nurture innovation and learning; build efficient, specialized electronics; and reduce researchers' burden of developing electronics without expertise.

Located in the Allen Building, the newly renovated space sports glass-topped walls, surrounded by sleek workstations. Inside the SPF, workbenches and collaborative areas provide organized space for system design, building, and testing.

"The SPF's mission is to support electronic sub-system design for cutting-edge research across our campus," states Professor Boris Murmann, lead SPF faculty. "We are currently working on projects with Principal Investigators in the departments of Physics, Applied Physics, Electrical Engineering, Psychology, Psychiatry and Behavioral Sciences and Bioengineering, looking to enable new possibilities in a wide range of disciplines."

Professor Murmann is also pleased that SPF – together with ExFab (Experimental Fabrication lab) – provides a complete spectrum of device development from creation to software interfacing. Similar to ExFab, SPF usage will help inform the design of future system prototyping facilities on campus.

The SPF welcomes researchers from any department on campus, accommodating project needs with a tiered service and support structure. The tiered structure is based on how much expertise is needed – from independently using the tools to requesting a turnkey solution. Stanford researchers are able to design and build a system themselves, or collaborate with SPF's electrical engineers.

 

SPF is made possible by funding from SLAC and School of Engineering.

Interested in SPF? Please email lab director, Angelo Dragone: dragone@slac.stanford.edu

Pictured above: SPF faculty director, Professor Boris Murmann speaks with Professor Marty Breidenbach, Dr. Angelo Dragone,  Professor Chi-Chang Kao and Sawson Taheri.

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