research

November 2016

Clarivate Analytics, formerly the Intellectual Property & Science business of Thomson Reuters, announced the publication of its annual Highly Cited Researchers. The list is a citation analysis identifying scientists – as determined by their fellow researchers – whose research has had significant global impact within their respective fields of study.

More than 3,000 researchers, in 21 fields of the sciences and social sciences, were selected based on the number of highly cited papers they produced over an 11-year period from January 2004 to December 2014.

The Stanford EE faculty are

The 2016 Highly Cited Researchers list can be seen in its entirety by visiting: http://hcr.stateofinnovation.thomsonreuters.com

Excerpted from http://www.prnewswire.com/news-releases/clarivate-analytics-names-2016-highly-cited-researchers-300362643.html

November 2016

Sachin Katti and Pengyu Zhang, a postdoctoral researcher in Katti's lab, announced "HitchHike" this week at the ACM SenSys Conference. HitchHike is a tiny, ultra-low-energy wireless radio.

"HitchHike is the first self-sufficient WiFi system that enables data transmission using just micro-watts of energy – almost zero," Zhang said. "Better yet, it can be used as-is with existing WiFi without modification or additional equipment. You can use it right now with a cell phone and your off-the-shelf WiFi router."

HitchHike is so low-power that a small battery could drive it for a decade or more, the researchers say. It even has the potential to harvest energy from existing radio waves and use that electromagnetic energy, plucked from its surroundings, to power itself, perhaps indefinitely.

"HitchHike could lead to widespread adoption in the Internet of Things," Katti said. "Sensors could be deployed anywhere we can put a coin battery that has existing WiFi. The technology could potentially even operate without batteries. That would be a big development in this field."

The researchers say HitchHike could be available to be incorporated into wireless devices in the next three to five years.

The Hitchhike prototype is a processor and radio in one. It measures about the size of a postage stamp, but the engineers believe that they can make it smaller – perhaps even smaller than a grain of rice for use in implanted bio-devices like a wireless heart rate sensor (see video).

"HitchHike opens the doors for widespread deployment of low-power WiFi communication using widely available WiFi infrastructure and, for the first time, truly empower the Internet of Things," Zhang said.

 

 

Excerpted from Stanford Engineering News. Original article by Andrew Myers

 

Jon Fan's research on nanoscale optical devices
November 2016

A field of materials science known as metamaterials has recently captured the imagination of engineers hoping to create nanoscale optical devices. Jonathan Fan, an assistant professor of electrical engineering and director of the ExFab at the Stanford Nanofabrication Facility, is leading the way. He recently won the prestigious 2016 Packard Fellowship in Science and Engineering, which funds the most promising early-career professors in fields ranging from physics and chemistry to engineering. Fan is just the fourth Stanford electrical engineer to win the fellowship since 1988, and the financial support that comes with it will enable him to carry on work that is so innovative that it can otherwise prove difficult to fund through traditional means. We talked to Fan about his visions in metamaterial engineering and about his interdisciplinary collaborations with fellow Stanford professors Allison Okamura and Sean Follmer in projects such as integrating new types of electromagnetic systems with robots.

What are metamaterials?

At its most basic level, we are bringing the idea of an antenna down to the nanoscale. Back in the day before cable and satellite, TVs had metal antennas. If your picture wasn't very good, you would get up and physically reconfigure the antenna geometry to change its performance. Those antennas were designed for radio waves that were centimeters to meters in length. We are working to create nanoscale antennas that would be able to respond to visible light with wavelengths of 400 to 700 nanometers, or infrared light, where wavelengths are on the order of a micron. By configuring the geometry of these antennas individually and in collections, we can engineer systems that can interact with and manipulate light in entirely new ways.

These tiny antennas are many orders of magnitude smaller than a TV antenna. Fortunately, the development of the modern electronic integrated circuit platform over the last half-century has produced mature technological processes that can help us define nanoscale features. We use those same patterning technologies to make these nanoscale antennas. That's the very basic overview.

What is the derivation of the term "meta" in the name metamaterials?

When you think of a conventional lens, you think of glass – the material, right? The glass in your camera or your eyeglasses bends light in very predictable ways based on the intrinsic material response of glass. A lens made of a metamaterial will respond to light in ways that are no longer solely based on the properties of the material itself, but largely on the design and layout of these optical antennas. So the concept of "meta" comes from our ability to engineer artificial materials, consisting of a composite of nanoscale structures, which can respond to light in entirely new ways. It's kind of neat to see an example in the case of a metal like gold. We usually think of gold as a bulk material that is reflective, yellowish and shiny. Even when you go down to the nanoscale, gold is still gold. But by specifying the geometry of nanoscale gold, we can change the color of gold from yellow to green or red, and it can support many other types of optical properties that we don't associate with bulk gold. Those are properties engineers can use to make new devices.

What do metamaterials allow us to do that we couldn't before?

Metamaterials are promising for a couple reasons. First, they enable the extreme miniaturization of existing optical devices. For example, we can take an eyeglass lens and we can make it 100 times thinner than a strand of hair. This allows us to translate traditionally bulky optical systems to extremely small form factors. Second, they can be customized to support novel properties that currently are not accessible with existing optical hardware, leading to entirely new optical systems.

What's an example of a potential metamaterial device?

A major opportunity today arises from the fact that high-resolution cameras have miniaturized to sizes that can fit onto cellphones, making them accessible to audiences a million times larger than before. Part of my larger research question is: Is there something more we can do with imaging systems with form factors of a cellphone camera? There is so much information in the incoming light field that is not currently captured by a cellphone camera, but that could be captured with imaging systems that include metamaterials. Access to this additional information could change how we use the images we take. For example, if you have a skin condition, a great deal more optical information of the skin could be extracted from a simple cellphone image and used to better assess your condition.

What excites you about metamaterials?

Metamaterials lead us to a completely different set of questions – metaquestions, if you will. For instance, are these nanoantennas even the best way to go about doing what we want to do? At this point in time, even that's not clear. In addition, you get to the big questions of applications for these materials and devices. It's just wide open. That's why this is exciting to me.

Any early impressions to share as a new faculty member?

Stanford is a really special place. The people are top-notch and the environment is highly collaborative, not siloed. As an example, I have recently expanded into robotics, where I have been looking to apply concepts in radio frequency waves to create smarter soft robotic systems. In this effort, I've started a collaboration with Allison Okamura and Sean Follmer, who are mechanical engineers. It's been fantastic so far, and I've been learning so much. People here are very open-minded and are inspired to do exciting interdisciplinary research to identify and solve big problems. I'm thrilled to be a part of that.

By Andrew Myers
Source: Stanford School of Engineering News

 

 

Related News:

Fan awarded the Presidential Early Career Awards for Scientists and Engineers, January 2017

Jonathan Fan awarded 2016 Packard Fellowship for Science and Engineering, October 2016

Jonathan's EE Spotlight

November 2016

Professor Andrea Goldsmith and post-doc fellow Nariman Farsad are currently looking into how chemical communication could advance nanotechnology.

Goldsmith and Farsad's research aims to create a system that uses chemicals to transmit messages. Instead of zeros and ones, their system uses an acid-base combination. The complications of this type of system are largely due to the fact that it's completely new. Goldsmith has spent her entire career working in wireless communication. Chemical messaging offers a new twist on familiar problems.

One potential of chemical-based data exchange is that it could be self-powered, traveling throughout the body harmlessly – and undetectable by outside devices. "This is one of the most important potential applications for this type of project," Farsad said. "It could enable the emergence of these tiny devices that are working together, talking together and doing useful things."

While working to improve their current chemical texting system, Goldsmith and Farsad are also collaborating with two bioengineering groups at Stanford to make human body-friendly chemical messaging a reality.

 

Excerpted from Stanford News. Full article.

November 2016

A team led by Jim Harris and Thomas Jaramillo, an associate professor of chemical engineering and of photon science, has made a significant improvement to the efficiency of solar energy. In work published in Nature Communications, they were able to capture and store 30 percent of the energy captured from sunlight into stored hydrogen, beating the prior record of 24.4 percent.

Solar energy has the potential to provide abundant power, but only if scientists solve two key issues: storing the energy for use at all hours, particularly at night, and making the technology more cost effective. The interdisciplinary team has made significant strides toward solving the storage issue, demonstrating the most efficient means yet of storing electricity captured from sunlight in the form of chemical bonds. If the team can find a way of lowering the cost of their technology, they say it would be a huge step toward making solar power a viable alternative to current, more polluting energy sources.

The basic science behind the team's approach is well understood: Use the electricity captured from sunlight to split water molecules into hydrogen and oxygen gas. That stored energy can be recovered later in different ways: by recombining the hydrogen and oxygen into water to release electricity again, or by burning the hydrogen gas in an internal combustion engine, similar to those running on petroleum products today.

"It took specialists in different fields to do what none of us could have done alone," Harris said. "That's one of the lessons of this result: There is no single fix. How everything links together is the key."

 

Jim Harris is the James and Elenor Chesebrough Professor in the School of Engineering, professor, by courtesy, of applied physics and of materials science and engineering, a member of Stanford Bio-X and of the Stanford Neurosciences Institute, and an affiliate of the Precourt Institute for Energy and the Stanford Woods Institute for the Environment. Jamarillo is also an affiliate of the Precourt Institute for Energy.

 

This article is adapted from the Stanford Report. Read full article

September 2016

For years, the net neutrality debate has been at an impasse: either the internet is open or preferences are allowed. But professors Nick McKeown and Sachin Katti, and EE PhD Yiannis Yiakoumis ­– say their new technology, called Network Cookies, makes it possible to have preferential delivery and an open internet. Network Cookies allow users to choose which home or mobile traffic should get favored delivery, while putting network operators and content providers on a level playing field in catering to such user-signaled preferences.

"So far, net neutrality has been promoted as the best possible defense for users," Katti said. "But treating all traffic the same isn't necessarily the best way to protect users. It often restricts their options and this is why so-called exceptions from neutrality often come up. We think the best way to ensure that ISPs and content providers don't make decisions that conflict with the interests of users is to let users decide how to configure their own traffic."

McKeown said Network Cookies implement user-directed preferences in ways that are consistent with the principles of net neutrality.

"First, they're simple to use and powerful," McKeown said. "They enable you to fast-lane or zero-rate traffic from any application or website you want, not just the few, very popular applications. This is particularly important for smaller content providers – and their users – who can't afford to establish relationships with ISPs. Second, they're practical to deploy. They don't overwhelm the user or bog down user devices and network operators and they function with a variety of protocols. Finally, they can be a very practical tool for regulators, as they can help them design simple and clear policies and then audit how well different parties adhere to them."

 


This article is adapted from Stanford Engineering News. Read full article.

September 2016

Technology developed by Stanford Bio-X scientists Krishna Shenoy (EE) and postdoctoral fellow Paul Nuyujukian, directly reads brain signals to drive a cursor moving over a keyboard. In an experiment conducted with monkeys, the animals were able to transcribe passages from the New York Times and Hamlet at a rate of up to 12 words per minute.

Earlier versions of the technology have already been tested successfully in people with paralysis, but the typing was slow and imprecise. This latest work tests improvements to the speed and accuracy of the technology that interprets brain signals and drives the cursor.

"Our results demonstrate that this interface may have great promise for use in people," said Nuyujukian, who will join Stanford faculty as an assistant professor of bioengineering in 2017. "It enables a typing rate sufficient for a meaningful conversation."

The technology developed by the Stanford team involves a multi-electrode array implanted in the brain to directly read signals from a region that ordinarily directs hand and arm movements used to move a computer mouse.

It's the algorithms for translating those signals and making letter selections that the team members have been improving. They had tested individual components of the updated technology in prior monkey studies but had never demonstrated the combined improvements in typing speed and accuracy.

"The interface we tested is exactly what a human would use," Nuyujukian said. "What we had never quantified before was the typing rate that could be achieved." Using these high-performing algorithms developed by Nuyujukian and his colleagues, the animals could type more than three times faster than with earlier approaches.

 

This article is adapted from the Stanford Report. Read full article.

 

Related News:

Krishna Shenoy's translation device; turning thought into movement, March 2017.

Krishna Shenoy receives Inaugural Professorship, February 2017.


 

September 2016

As the breathalyzer does for alcohol, this experimental 'potalyzer' could provide a practical field test for determining whether a driver might be impaired from smoking marijuana.

This November, several states will vote whether to legalize marijuana use, joining more than 20 states that already allow some form of cannabis use. This has prompted a need for effective tools for police to determine on the spot whether people are driving under the influence.

Shan Wang and team have devised a potential solution, applying magnetic nanotechnology (GMR), previously used as a cancer screen, to create what could be the first practical roadside test for marijuana intoxication.

"To the best of our knowledge, this is the first demonstration that GMR biosensors are capable of detecting small molecules," Wang wrote in a paper describing the device, published in Analytical Chemistry.

Professor Shan Wang and team created a mobile device that uses magnetic biosensors to detect tiny THC molecules in saliva. Officers could collect a spit sample with a cotton swab and read the results on a smartphone or laptop in as little as three minutes.

Wang's device can detect concentrations of THC in the range of 0 to 50 nanograms per milliliter of saliva. While there's still no consensus on how much THC in a driver's system is too much, previous studies have suggested a cutoff between 2 and 25 ng/mL, well within the capability of Wang's device.

 

The co-authors of the Analytical Chemistry paper are Jung-Rok Lee (ME PhD'15), Joohong Choi (EE PhD'15), and Tyler O. Shultz (Biology BS'13).

 

This article is adapted from the Stanford Report.

September 2016

Shanhui Fan and research team are developing a material that cools by letting perspiration evaporate through the material – something ordinary fabrics already do. But the Stanford material provides a second, revolutionary cooling mechanism: allowing heat that the body emits as infrared radiation to pass through the plastic textile.

"Forty to 60 percent of our body heat is dissipated as infrared radiation when we are sitting in an office," states Shanhui Fan, who specializes in photonics. "But until now there has been little or no research on designing the thermal radiation characteristics of textiles."

To develop their cooling textile, the Stanford researchers blended nanotechnology, photonics and chemistry to give polyethylene – the clear, clingy plastic we use as kitchen wrap – a number of characteristics desirable in clothing material: It allows thermal radiation, air and water vapor to pass right through, and it is opaque to visible light.

Eventually, the research culminated in a single-sheet material that met their three basic criteria for a cooling fabric. To make this thin material more fabric-like, they created a three-ply version: two sheets of treated polyethylene separated by a cotton mesh for strength and thickness.

"Wearing anything traps some heat and makes the skin warmer," Fan said. "If dissipating thermal radiation were our only concern, then it would be best to wear nothing."

Comparing the new fabric with cotton fabric, showed cotton making the skin surface 3.6 F warmer than their cooling textile. The researchers said this difference means that a person dressed in their new material might feel less inclined to turn on a fan or air conditioner.

Fan believes that this research opens up new avenues of inquiry to cool or heat things, passively, without the use of outside energy, by tuning materials to dissipate or trap infrared radiation.

 

 

This article is adapted from the Stanford Report.
Read full article

May 2016

Early results show that the quality of optical materials grown from diamondoid seeds is consistently high, says Stanford's Jelena Vuckovic, a professor of electrical engineering who is leading this part of the research with Steven Chu, professor of physics and of molecular and cellular physiology.

"Developing a reliable way of growing the nanodiamonds is critical," says Vuckovic, who is also a member of Stanford Bio-X and SystemX. "And it's really great to have that source and the grower right here at Stanford. Our collaborators grow the material, we characterize it and we give them feedback right away. They can change whatever we want them to change."

 

Excerpted from Stanford News. Read full article.

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