research

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.
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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.

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.

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