Friday, October 29, 2004

"OPTICS: Silicon circuit demonstrates optical switch"
The world's first silicon chip that switches optical wavelengths has been brought to light by Cornell University researchers using nanoscale techniques. "We have demonstrated for the first time a silicon structure that enables one low-power optical beam to switch another one on and off," said Cornell University EE Michal Lipson. Silicon circuits traditionally don't do optics. Because silicon is an indirect-bandgap material � meaning that the bottom of its conduction band is shifted with respect to the top of its valence band � the energy released during electron recombination with a hole is converted primarily into phonons (lattice vibration) instead of the photons you get from a "direct-bandgap" material like gallium arsenide. The key is a ring-shaped nanoscale cavity whose resonant frequency depends on its refractive index, which can be optically switched by virtue of a second light beam controlling free-carrier dispersion. According to Lipson, the technique should eventually enable terahertz switching of signals on silicon chips with integrated ultralow-power, high-modulation-depth picosecond optical switches fabricated alongside conventional silicon circuitry.

Monday, October 25, 2004

"QUANTUM: 'Spin filter' initializes quantum computing"
Purdue University researchers have invented a "spin filter" that can sort charge carriers by their spin state. "This component is essential to future quantum computers, which need to be initialized in a known state," said professor Leonid Rokhinson. "It will also be necessary for the many other 'spintronic' devices that people are working on today." Storing data on the polarized-wave function, or "spin," of a charge carrier- a mobile electron or hole in a semiconductor-holds promise for future single-electron transistors, nanoscale nonvolatile memories, quantum computers and other so-called spintronic devices. But even the simplest components necessary to make spintronics a reality-such as filters-have been lacking. Using the basic physics of a mass spectrometer as his model, Rokhinson fabricated a chip version that can sort particles based on their spin configuration. "Spin filters are one of the most crucial missing ingredients of spintronic devices because they allow you to create spin polarization," he said. The device uses magnetic focusing to enable the spatial separation of trajectories of carriers (in a two-dimensional "hole" gas fabricated from GaAs heterostructures) by virtue of their spin state. Two quantum-point contacts, acting as a monochromatic source of ballistic holes and a narrow detector, respectively, were demonstrated to work as a tunable spin filter.
"MAGNETISM: EEs needed to propel mag-beams"
EEs are desperately needed to help design magnetized-beam plasma propulsion systems that could send future spacecraft to Mars and back in 90 days. The systems would use a mag-beam to accelerate a craft out of Earth's orbit and another to decelerate it in Mars' orbit, eliminating or greatly reducing the need for on-board fuel or engines. Such systems would rejigger the cost and time calculations of manned flights to Mars, which would take more than two years with current propulsion technology. "We want to get the word out to electrical engineers, because this is a field where EEs can make major contributions," said Robert Winglee, an earth- and space-sciences professor at the University of Washington who is leading a multidisciplinary group at the school's Research Institute for Space Exploration. "Mag-beams could make space travel routine, and they are enabled by electrical engineering." NASA's Institute for Advanced Concepts ( has given Winglee's group $75,000 and six months to prove its plasma propulsion system can work. Eleven other teams have received similar funding, and, like Winglee's group, will be eligible for $400,000 of phase two monies.

Monday, October 18, 2004

"OPTICS: Photoluminescent method detects explosives at a distance"
Experience in photoluminescent spectroscopy has helped university researchers bring to light a method by which explosives can be detected at a distance. In contrast, to detect the presence of explosives today, airport and other screeners must swab an object like a suitcase or clothing, use a dog to sniff it, or blast puffs of air across a filter that traps airborne explosive particles. The advantages of the photoluminescence-based explosive detection method are that it can be remotely applied and that it requires neither time-consuming and expensive machines nor trained dogs. All you do is shine a laser on an object and watch for the photoluminescent "signature" distinctive of explosives. Whether it's an approaching ship, a suitcase, a moving car or a pile of trash half a mile up the road, if you can shine a green laser on it, professor Rolf Hummel at the University of Florida (Gainesville) says he can tell you whether it's an explosive device.

Tuesday, October 12, 2004

"BIOSENSOR: slashes time to detect Listeria bacteria"
A fiber-optic biosensor that reduces testing time for a deadly form of the Listeria bacteria from one week to less than 24 hours has been created by two Purdue University microbiologists and a control engineer. Listeriosis kills one in five that it infects and accounts for the highest rate of hospitalization and mortality among foodborne illnesses. Usually, when the (monocytogenes) Listeria bacteria is detected in a food sample, it has already been on store shelves for up to a week, because the detecting sensors are so crude that the food has to be cultured in petri dishes for that long before enough bacteria multiply to trip the alarm. "We still need to culture the food sample with our new biosensor, but for a much shorter time-less than a day," said Arun Bhunia, associate professor of food microbiology. Bhunia developed the sensor with Tao Geng, research associate in the Department of Food Science. Mark Morgan, an engineering professor in Purdue's Food Science Sensors and Controls Laboratory, also participated in the research. "Instead of having to recall food that is already on the shelves, we want test results before it gets delivered to stores," said Bhunia. The researchers are aiming eventually for real-time operation of the biosensor.

Friday, October 08, 2004

"OPTICAL: NEMS tunes the 'most sensitive' accelerometer"
By coupling a nanoscale etched diffraction grating to an optical sensor, Sandia National Laboratories researchers have demonstrated an accelerometer that they say is the most sensitive in the world. The nanoelectromechanical system (NEMS) could measure vibrations as low as 10 nano-G's, compared with the 100 milli-G vibrations measurable with today's accelerometers, by making mechanical motions as small as 10 nanometers visible to the naked eye. "Because the wavelength of light from our laser is much smaller than the dimensions of our [diffraction] grating, very very small motions have a disproportionate effect," said Sandia researcher Dustin Carr. Team member Bianca Keeler will describe the work later this month at the SPIE Optics East convention in Philadelphia. Today's best integrated accelerometers, such as those that trigger automotive air bags, can detect hundreds of milli-G's. But many unfulfilled apps need more-sensitive accelerometers, such as those that can anticipate earthquakes or sense a skid where the back end of a car is moving in a different direction than the front end.
"ANTITERROR: EEs seek way to ID triggers of Iraq's IEDs"
One of the United States' largest electromagnetic-emission "shielding" labs has switched roles to help armed-services personnel detect bombs. The University of Missouri at Rolla's Electromagnetic Compatibility Laboratory is trying to sense, rather than shield, emissions from the triggering mechanisms in improvised explosive devices (IEDs), which could alert troops to unexploded munitions. EE professor Todd Hubing and assistant professor Daryl Beetner said they saw the benefit of reorienting their work when visiting nearby Fort Leonard Wood, Mo., where they viewed IED training tapes. They saw that the emissions from many command-initiated IEDs, which are normally placed at the side of a road, were sufficient to be sensed from a distance. Hubing and Beetner immediately began thinking that it would be possible to detect the signature of electronically triggered IEDs, even when they are not transmitting, but merely "waiting" beside a road in Iraq to receive a detonation signal. "We started looking at unintended electromagnetic emission from improvised explosive devices and found that if we shifted their frequency to the audio range, almost anyone could recognize their distinctive 'signature' sound," Beetner said. "And if you can hear the difference, then there has got to be a way to build a device for soldiers to use that detects radio-controlled IEDs from a distance." That's the opposite of the lab's typical practice. "At our lab we try to shield devices, so we know just how very difficult it is to make an electronic device not emit electromagnetic energy � even when it's just a receiver," Beetner said. According to the engineers, sophisticated electronic devices like cell phones cannot be completely turned off � there is always active circuitry inside

Wednesday, October 06, 2004

"METAMATERIAL: Demo takes subwavelength focusing to visible light "
Engineers at Purdue University claim to have conjured a mathematical model for metamaterials that designers can use to improve the resolution of lenses below the wavelength of light. Subwavelength focusing, for instance, could enable semiconductor lithography to plumb the nanoscale without having to use ultrashort-wavelength extreme-ultraviolet or X-rays. Others have already demonstrated metamaterials with subwavelength focusing for microwaves and acoustic waves. Now, engineers at Purdue and elsewhere are working toward photonic metamaterials that provide subwavelength focusing for visible light. Professor Kevin Webb, a EE at Purdue performed the work with his EE assistant Ming-Chuan Yang and MIT professor Keith Nelson, assisted by one of his doctoral candidates, David Ward. Metamaterials put macroscopic objects sized for a desired subwavelength into a giant-sized crystalline lattice, which interacts in the opposite way from natural materials.

Friday, October 01, 2004

"MATERIALS: Darpa funds work on rigid shape-shifting materials"
A new world of applications for shape-changing materials might become available if man-made rigid structures � like an airplane wing, which derives its strength from being "fixed" � could adopt the abilities of rigid structures that can change shape, like a flower stem that twists to follow the sun. Airplane wings imbued with such ability might, for example, self-trim as they sensed the plane's speed, or prepare for an imminent landing by cupping the air as a bird's wing does. The Defense Advanced Research Projects Agency has granted four contracts under its Nastic Materials Program ( to explore these possibilities. One includes a 17-month, $2.1 million effort at the Virginia Polytechnic Institute and State University in Blacksburg, Va. "We will use the concept of nastic biological transport to create a synthetic template for making shape-changing materials," said Virginia Tech professor Don Leo, leader of a team that will develop a class of materials that mimic plant protein structures.
"QUANTUM: encryption milestone reached"
A prototype quantum-key distribution system may move from lab to commercial systems as early as next year, NEC Corp. reports. Company researchers have completed the prototype, NEC said, and the needed software is now being written. NEC described its progress to the 30th European Conference on Optical Communication ( At the conference, held last month in Stockholm, Sweden, NEC described how it overcame previously reported obstacles. It said researchers had successfully encoded, modulated and added a clock signal to their single-photon transmissions, achieving a sustained quantum-key distribution (QKD) rate of 100 kbits/second over a distance of about 25 miles. The researchers predicted that NEC will likely begin delivering commercial QKD systems based on their prototype by the end of 2005.