Molnar, Jena and Xing join national consortium to develop future cellular infrastructure

Alyosha Molar, Huili (Grace) Xing, and Debdeep Jena

https://www.ece.cornell.edu/news/index.cfm?news_id=96488

Imagine a roomful of 1,000 students all simultaneously experiencing an augmented reality lecture and demonstration. Or, how about riding in an autonomous vehicle that can detect, in real time and despite inclement weather, an accident or obstacle miles ahead? For those scenarios to be possible, we need a new, enhanced generation of wireless communication.

And that is the focus of the newly established $27.5 million ComSenTer, a center for converged terahertz communications and sensing. Three Cornell faculty will be part of this consortium of over 18 faculty researchers across 10 institutions with the main center at University of California Santa Barbara (USCB). 

“Our center is simply the next next generation of communication and sensing, something that may become ‘6G’,” said Ali Niknejad, ComSenTer associate director and a UC Berkeley professor of electrical engineering and computer sciences.

The fifth generation (5G) in mobile communications is currently under active investigation by industry, with expected deployments ahead of the 2020 Olympics. This emerging network will employ higher frequency bands, more spatial multiplexing and higher throughputs than those available to consumers today.

ComSenTer’s research will go further, laying the foundation for the next generation by utilizing extremely high frequencies in the range of 100 GHz to 1 Thz. According to the researchers, this will allow for the extreme densification of communications systems, enabling hundreds and even thousands of simultaneous wireless connections, with 10 to 1,000 times higher capacity than the nearer-term 5G systems and network.

Augmented reality and next-level imaging and sensing with a terahertz imaging radar are only some of the potential applications that ComSenTer seeks to make a reality. Other possibilities include chemical sensors and new medical imaging modalities.

ComSenTer is part of the new $200 million, five-year JUMP (Joint University Microelectronics Program), a consortium of industry research participants and the U.S. Defense Advanced Research Projects Agency (DARPA), administered by Semiconductor Research Corporation (SRC). The partnership will fund research centers at six top research university networks that are led by UCSB, Carnegie Mellon University, Purdue University, the University of Virginia, the University of Michigan, the University of Notre Dame. 

Each research center will examine a different challenge that advances microelectronics, a field crucial to the U.S. economy and its national defense capabilities. The centers will collaborate to develop solutions that work together effectively. Each center will also have liaisons from the program’s sponsoring companies, which both aids in research collaboration and a proven model for technology transfer into the sponsors. JUMP sponsors come from both commercial and defense electronics industries.

The UCSB-led center that Cornell is part of will focus on large and scalable mm-wave arrays, which find applications in radar, high-resolution real-time imaging, situational awareness, and for precision navigation. For example, emerging autonomous systems place a huge demand on dependable and robust imaging at mm-wave frequencies, which are relatively transparent in most weather conditions. The team’s work will center around millimeter-wave circuits design with applications in scalable sparse arrays that aim to achieve a relatively high lateral resolution with fewer elements compared to traditional arrays. 

SRC is a world-renowned, high technology-based consortium that serves as a crossroads of collaboration between technology companies, academia, government agencies and SRC’s highly regarded engineers and scientists. For more information, visit www.src.org

Adapted from Jan 18, 2018 press release from SRC/UCSB, Beyond 5G: UCSB is the lead institution for a research center that will explore terahertz-range communications and sensing. https://www.src.org/newsroom/press-release/2018/923/ 

FOCUS ON: Huili (Grace) Xing- Cornell University (XING RESEARCH GROUP)

• Huili (Grace) Xing
• Dept: Electrical and Computer Engineering
• Title: Richard Lunquist Sesquicentennial Professor
• Address: 425 Philips Hall
• Phone: 607 255-0605
• Email: grace.xing@cornell.edu
• https://www.ece.cornell.edu/people/profile.cfm?netid=hgx2

Biography: I got my Bachelor Degree in Physics from Peking University. After that, I pursued a Master Degree in Material Science and Engineering at Lehigh University. Wanting to work with devices that use wonderful material properties, I went to the University of California at Santa Barbara for my Ph.D. and eventually had my degree in Electrical Engineering. From 2004 to 2014 I was a faculty at the University of Notre Dame. I moved to Cornell in 2015.
Research Interests:
The topics I work on now can be loosely categorized into 4 areas, supported by DoD, NSF, SRC and Doe.1). GaN based devices. The current projects include GaN power diodes and transistors, AlN/GaN ultrascaled high electron mobility transistors for high-speed high power applications, polarization doping for p-type in UV optoelectronic devices, negative differential resistance and plasma based THz sources for biomedical imaging and spectroscopy, wafer fused enabled hybrid structures. 2). nanowire enabled devices, including InGaN nanowires for high efficiency green emission and solar cells, II-VI nanowires for polarization sensitive wide spectrum photodetection etc. 3) 2D crystal materials and devices. We investigate van der Waals epitaxy, carrier electrostatics and transport, optoelectronic responses, p-n junctions and heterostructures, field modulation and tunneling, metamaterials and THz applications, graphene physics and devices. We investigate graphene based metamaterials for THz applications, lateral bandgap engineering in graphene, carrier electrostatics and transport, and optoelectronic responses, p-n junctions, field modulation and tunneling phenomena. 4) steep slope transistors for high-efficiency logic and RF electronics, especially tunnel FETs. We pioneered design, fabrication and characterization of III-V TFETs. Our current focus is 2D-crystal based steep slope transistors: the Thin-TFETs, tunneling field effect transistors for high efficiency logic electronics.

Selected Publications

• Hu, Z., K. Nomoto, B. Song, M. Zhu, M. Qi, M. Pan, X. Gao, V. Protasenko, D. Jena, H G Xing. 2015. "Near unity ideality factor and Shockley-Read-Hall lifetime in GaN-on-GaN p-n diodes with avalanche breakdown." Applied Physics Letters 107 (24): 243501-243501.
• Zhu, M., B. Song, M. Qi, Z. Hu, K. Nomoto, X. Yan, Y. Cao, W. Johnson, E. Kohn, D. Jena, H G Xing. 2015. "1.9-kV AlGaN/GaN Lateral Schottky Barrier Diodes on Silicon." IEEE Electron Device Letters 36 (4): 375-377.
• Jena, D., K. Banerjee, Huili Xing. 2014. "Intimate Contacts." Nature Materials.
• Sensale-Rodriguez, Berardi, Rusen Yan, Michelle Kelly, Tian Fang, Kristof Tahy, Wan Sik Hwang, Debdeep Jena, Lei Liu, Huili Xing. 2012."Broadband graphene THz modulators enabled by intraband transitions." Nature Communications; Featured by NSF at LiveScience 3(780).
• Simon, John, Vladimir Protasenko, Chuanxin Lian, Huili Xing, Debdeep Jena. 2010. "Polarization-induced hole doping in wide-band-gap uniaxial semiconductor heterostructures." Science 327 (60).

Selected Awards and Honors

• Richard E. Lunquist Sesquicentennial Faculty Fellow (Cornell University) 2015
• Young Scientist Award (International Symposium on Compound Semiconductors (ISCS)) 2014
• Featured Notre Dame Faculty at UND-BYU football game 2012
• CARREER Award (National Science Foundation) 2009
• Young Investigator Program Award (Air Force Office of Scientific Research) 2008

Websites

• http://grace.engineering.cornell.edu

Education

• BS (Physics), Peking University, 1996
• MS (Material Science), Lehigh University, 1998
• Ph D (Electrical Engineering), University of California, 2003
• Postdoc (Electrical Engineering), University of California, 2003

Interstellar molecules are branching out: Detection of iso-propyl cyanide with ALMA

The image shows dust and molecules in the central region of our galaxy. The background image shows the dust emission in a combination of data obtained with the APEX telescope and the Planck space observatory at a wavelength around 860 micrometers. The organic molecule iso-propyl cyanide with a branched carbon backbone (i-C3H7CN, left) as well as its straight-chain isomer normal-propyl cyanide (n-C3H7CN, right) were both detected with the Atacama large millimeter/submillimeter array in the star-forming region Sgr B2, about 300 light years away from the Galactic center Sgr A*. Credit: MPIfR/A. Weiss (background image), University of Cologne/M. Koerber (molecular models), MPIfR/A. Belloche (montage)
:
http://phys.org/news/2014-09-interstellar-molecules-iso-propyl-cyanide-alma.html#jCp

Scientists from the Max Planck Institute for Radio Astronomy, Cornell University, and the University of Cologne have for the first time detected a carbon-bearing molecule with a "branched" structure in interstellar space. The molecule, iso-propyl cyanide (i-C3H7CN), was discovered in a giant gas cloud called Sagittarius B2, a region of ongoing star formation close to the center of our galaxy that is a hot-spot for molecule-hunting astronomers. The branched structure of the carbon atoms within the iso-propyl cyanide molecule is unlike the straight-chain carbon backbone of other molecules that have been detected so far, including its sister molecule normal-propyl cyanide. The discovery of iso-propyl cyanide opens a new frontier in the complexity of molecules found in regions of star formation, and bodes well for the presence of amino acids, for which this branched structure is a key characteristic. The results are published in this week's issue of Science.

While various types of molecules have been detected in space, the kind of hydrogen-rich, carbon-bearing (organic) molecules that are most closely related to the ones necessary for life on Earth appear to be most plentiful in the gas clouds from which new stars are being formed. "Understanding the production of organic material at the early stages of star formation is critical to piecing together the gradual progression from simple molecules to potentially life-bearing chemistry," says Arnaud Belloche from the Max Planck Institute for Radio Astronomy, the lead author of the paper.

The search for molecules in interstellar space began in the 1960's, and around 180 different molecular species have been discovered so far. Each type of molecule emits light at particular wavelengths, in its own characteristic pattern, or spectrum, acting like a fingerprint that allows it to be detected in space using radio telescopes.

Until now, the organic molecules discovered in star-forming regions have shared one major structural characteristic: they each consist of a "backbone" of carbon atoms that are arranged in a single and more or less straight chain. The new molecule discovered by the team, iso-propyl cyanide, is unique in that its underlying carbon structure branches off in a separate strand. "This is the first ever interstellar detection of a molecule with a branched carbon backbone," says Holger Müller, a spectroscopist at the University of Cologne and co-author on the paper, who measured the spectral fingerprint of the molecule in the laboratory, allowing it to be detected in space.

But it is not just the structure of the molecule that surprised the team - it is also plentiful, at almost half the abundance of its straight-chain sister molecule, normal-propyl cyanide (n-C3H7CN), which the team had already detected using the single-dish radio telescope of the Institut de Radioastronomie Millimétrique (IRAM) a few years ago. "The enormous abundance of iso-propyl cyanide suggests that branched molecules may in fact be the rule, rather than the exception, in the interstellar medium," says Robin Garrod, an astrochemist at Cornell University and a co-author of the paper.

The central region of the Milky Way above the antennas of the ALMA observatory. The direction to the Galactic center is halfway between Antares, the brightest star visible in the picture and the tip of an ALMA antenna in the foreground (second from right). Credit: Y. Beletsky (LCO)/ESO

The team used the Atacama Large Millimeter/submillimeter Array (ALMA), in Chile, to probe the molecular content of the star-forming region Sagittarius B2 (Sgr B2). This region is located close to the Galactic Center, at a distance of about 27,000 light years from the Sun, and is uniquely rich in emission from complex interstellar organic molecules. "Thanks to the new capabilities offered by ALMA, we were able to perform a full spectral survey toward Sgr B2 at wavelengths between 2.7 and 3.6 mm, with sensitivity and spatial resolution ten times greater than our previous survey," explains Belloche. "But this took only a tenth of the time." The team used this spectral survey to search systematically for the fingerprints of new interstellar molecules. "By employing predictions from the Cologne Database for Molecular Spectroscopy, we could identify emission features from both varieties of propyl cyanide," says Müller. As many as 50 individual features for i-propyl cyanide and even 120 for n-propyl cyanide were unambiguously identified in the ALMA spectrum of Sgr B2. The two molecules, each consisting of 12 atoms, are also the joint-largest molecules yet detected in any star-forming region.

The team constructed computational models that simulate the chemistry of formation of the molecules detected in Sgr B2. In common with many other complex organics, both forms of propyl cyanide were found to be efficiently formed on the surfaces of interstellar dust grains. "But," says Garrod, "the models indicate that for molecules large enough to produce branched side-chain structure, these may be the prevalent forms. The detection of the next member of the alkyl cyanide series, n-butyl cyanide (n-C4H9CN), and its three branched isomers would allow us to test this idea".

"Amino acids identified in meteorites have a composition that suggests they originate in the interstellar medium," adds Belloche. "Although no interstellar amino acids have yet been found, interstellar chemistry may be responsible for the production of a wide range of important complex molecules that eventually find their way to planetary surfaces."

"The detection of iso-propyl cyanide tells us that amino acids could indeed be present in the interstellar medium because the side-chain structure is a key characteristic of these molecules", says Karl Menten, director at MPIfR and head of its Millimeter and Submillimeter Astronomy research department. "Amino acids have already been identified in meteorites and we hope to detect them in the interstellar medium in the future", he concludes.

 Explore further: Probing hydrogen catalyst assembly

More information: "Detection of a branched alkyl molecule in the interstellar medium: i-propyl cyanide," by A. Belloche et al. Science, www.sciencemag.org/lookup/doi/… 1126/science.1256678

Journal reference: Science  

Presentation Dr. Ehsan Afshari, "“Terahertz: The Last Untapped Spectrum”

Dr. Ehsan Afshari

http://www.ece.utah.edu/terahertz-the-last-untapped-spectrum/

Cornell University

When: Monday, October 21, 2013 at 3:05 p.m.

Where: Warnock 1250- University of Utah

Abstract

There is an increasing interest in low cost THz systems for medical imaging, spectroscopy, and high data rate communication. Recent results in the lower THz frequencies (<600 GHz) suggests that a standard CMOS process can compete with compound semiconductors for some applications. In this talk, after a brief introduction to our research group at Cornell, we present a few “real” applications for the CMOS THz systems as well as a few “fake” ones. Next, we discuss major challenges in realizing these systems in CMOS. Moreover, we show several novel methods to overcome these challenges to generate mW-level powers at 300-500 GHz with relatively low noise using oscillators, amplifiers, and frequency multipliers.

Speaker Biography

Ehsan Afshari received the B.Sc. degree in Electronics Engineering from the Sharif University of Technology, Tehran, Iran and the M.S. and Ph.D. degree in electrical engineering from the California Institute of Technology, Pasadena, in 2003, and 2006, respectively. In August 2006, he joined the faculty in Electrical and Computer Engineering at Cornell University.

He was awarded National Science Foundation CAREER award in 2010, Cornell College of Engineering Michael Tien excellence in teaching award in 2010, Defense Advanced Research Projects Agency (DARPA) Young Faculty Award in 2008, and Iran’s Best Engineering Student award by the President of Iran in 2001. He is also the recipient of the best paper award in the Custom Integrated Circuits Conference (CICC), September 2003, and the first place at Stanford-Berkeley-Caltech Inventors Challenge, March 2005.

Architecture Cracks Terahertz Power Generation And Tuning

http://mwrf.com/active-components/architecture-cracks-terahertz-power-generation-and-tuning
My Note: I came across this article yesterday on the Virginia Diodes Facebook page

Nancy Friedric

CMOS circuits have been proven suitable for sub-millimeter-wave and terahertz frequencies from 300 GHz to 3 THz. To realize a complete terahertz system, however, a challenge still remains in the high-power, tunable signal source. When using LC-resonator-based voltage-controlled oscillators (VCOs), performance begins to degrade beyond 100 GHz. While frequency multipliers solve some of these problems, they require a high-power external source—something undesirable in a fully integrated terahertz source. One alternative could lie in a VCO architecture based on coupled oscillators in a loop configuration, which has been created by Yahya M. Tousi and Ehsan Afshari from Cornell University and Omeed Momeni from the University of California at Davis.

To realize a high-power VCO at the sub-millimeter-wave and terahertz band, three requirements must be met. First, the signal source should be able to generate high harmonic power above the device f_max. The generated power also should be efficiently delivered to the output load. Finally, a frequency-tuning mechanism is needed that will not adversely affect the first two requirements.

In this approach, multiple core oscillators are coupled to generate, combine, and deliver their harmonic power to the output node without using varactor diodes. Leveraging the theory of nonlinear dynamics, the researchers are able to control the coupling between the cores. In doing so, they can set their phase shift and frequency.

Because of the new architecture’s approach to frequency control, the tradeoff between frequency tuning and power generation in conventional VCOs is largely resolved. Frequency tuning can therefore be achieved while maintaining high output power in the sub-millimeter-wave frequency range. The engineers’ approach also provides an effective way to generate and combine the harmonics of the fundamental frequency from multiple core oscillators.

The researchers fabricated two high-power terahertz VCOs in a 65-nm low-power (LP) bulk process. According to measurements, the first one provides 0.76 mW output power at 290 GHz with a 4.5% tuning range. The second VCO puts out 0.46 mW at 320 GHz with a 2.6% tuning range. See “A Novel CMOS High-Power Terahertz VCO Based on Coupled Oscillators: Theory and Implementation,” IEEE Journal Of Solid-State Circuits, Dec. 2012, p. 3032.

Semi-OT The electronic origin of photoinduced strain

http://phys.org/news/2013-02-electronic-photoinduced-strain.html#jCp

(Phys.org)—Multiferroics are in a class of materials that exhibits more than one ferroic order simultaneously. One of the prototypical multiferroics is BiFeO3, an important material because it is one of a few materials that exhibit both ferroelectricity and magnetism at room temperature. The interaction of BiFeO3 with light has attracted great attention because optical control of either magnetism, ferroelectricity, or both has implications for future electronic devices.

The origin of a large photoexcited structural change in BiFeO3 was not well understood because of the lack of direct experimental evidence, preventing a rational design for future optomechanical and optoelectrical applications using ferroelectric and multiferroic materials. 

Now, a team of researchers led by Argonne scientists at the Advanced Photon Source (APS) and Center for Nanoscale Materials (CNM), along with colleagues from the University of Wisconsin-Madison, Cornell University, Northwestern University, Sandia National Laboratories, and Kavli Institute at Cornell for Nanoscale Science, has revealed the electronic origin of the interaction between optical light using a nanometer-thick layer of BFO at the atomic level and ultrafast time scales. Their work was recently published in Physical Review Letters. 

Under illumination with light, these multiferroic respond by creating a large electric current, termed a photocurrent, and can also change their atomic structure, both of which are potentially useful in applications.

 "One of the central problems is how the physical processes associated with the absorption of light in multiferroics leads to these potentially useful properties," said Paul Evans, an article co-author and professor at the University of Wisconsin-Madison. 

Utilizing state-of-art tools readily available at Argonne, a new approach was employed to study what happens after BiFeO3 is excited by an intense pulse of light. Structural studies were conducted using the X-ray Science Division (XSD) 7-ID-C ultrafast x-ray diffraction beamline at the APS. These structural results were compared with the electronic response measured at the ultrafast spectroscopy lab led by Richard Schaller at the CNM.

 "The large, optically induced strain decays within several billionths of a second, which turned out to be the same rate as the excited electrons return to their initial state," said Haidan Wen, the lead author of the paper and an assistant physicist with XSD. This key insight showed that the structural rearrangements after optical excitation were largely driven by electronic processes.

 Faster data storage devices with lower power consumption can result from optical control of electronic and structural properties. This understanding of how that light can induce simultaneous structural and electronic effects now enables optical control of ferroelectric and multiferroic materials without requiring electrical contacts. 

According to John Freeland, a co-author and a physicist in XSD, "The large optically induced strain opens a new route for ultrafast strain engineering of multifunctional complex oxides and new opportunities for manipulation of magnetism for spintronic applications." 

The researchers also believe that the technique can be applied to many other complex material systems and can be helped dramatically by the APS Upgrade. The development over the next five years of a short-pulse x-ray source at the APS will shorten the x-ray pulse by about a factor of 50.

 "Then we will see more detail of the electrons and atoms in action, and probe physics that is out of reach now, especially these occurring in the material right after the excitation by the laser pulse," said Yuelin Li, an XSD physicist and the paper's corresponding author. 

More information: Wen, H. et al. Electronic Origin of Ultrafast Photoinduced Strain in BiFeO3, Phys. Rev. Lett. 110, 037601 (2013). DOI: 10.1103/PhysRevLett.110.037601

Abstract-Low-cost Terahertz Signals on Silicon Chips

MY NOTE: This is not new information to readers of this blog, but it was just posted in this format and it's certainly worthy of posting here. 
http://www.flintbox.com/public/project/22315/

Posted:Nov 9, 2012 1:58 PM

A mathematical model was developed to generate and process signals in the terahertz range at 10,000 times more power that previously possible, and all this with the inexpensive CMOS microchip technology used in many everyday electronic devices.
A mathematical model was developed to generate and process signals in the terahertz range at 10,000 times more power that previously possible, and all this with the inexpensive CMOS microchip technology used in many everyday electronic devices. Terahertz radiation, used in airport body scanners, promises a wide range of applications in communications as well as science and medicine, from detecting cancer and tooth decay to inspection food through its packaging. Such applications require a portable, low-power radiation source, but most terahertz sources are still bulky and expensive -- usually involving lasers and vacuum tubes, or more recently, compound semiconductors at lower terahertz frequencies -- none of which are cost-effective or suitable for integration of different digital blocks on the same chip.

The Cornell invention was demonstrated using CMOS technology, which offers low-cost, reliable fabrication of the entire analog/digital system. Remarkably, it can also be applied to other semiconductor processes and materials, with the same benefit of optimizing the output of virtually any circuit topology.               Potential Applications: Medical imaging, e.g. to detect tooth decay, skin cancer, cornea hydration, etc. Radar, e.g. UWB and compact range Communications, including short range, high data rate, broadband wireless access, etc. Remote sensing                                Advantages Maximizes signal power and frequency of circuit elements Compatible with virtually all semiconductor processes and materials (Si, GaN, etc.) Enables cost-effective, compact and portable terahertz radiation sources

  Researchers:   

Omeed Momeni

Ehsan Afshari

Additional Information

Momeni, O.; Afshari, E.; , "High Power Terahertz and Millimeter-Wave Oscillator Design: A Systematic Approach," Solid-State Circuits, IEEE Journal of , vol.46, no.3, pp.583-597, March 2011

Licensing Contact

Martin Teschl
mt439@cornell.edu
(607) 254-4454

Researchers Develop Method for Making Atomic Electronics

My Note: A nice introduction to the work being done with graphene at the nanolevel, and with patterned regrowth, coming soon to your THz scanner or device.

Mike Wheatley | http://siliconangle.com/blog/2012/08/30/researchers-develop-method-for-making-atomic-electronics/

inShare0

Electrical engineers have already achieved some pretty amazing feats. The integrated circuits used in everything from computers to coffee makers are incredibly slim these days, allowing us to develop a new breed of electronic gadgets that includes everything from every day smartphones, to more minuscule devices like the Picotux (the world’s smallest PC, measuring just 35mm×19mm×19mm) and even fuel cells measuring just 3mm long.

But these achievements haven’t stopped researchers from Cornell University from thinking they can take ‘slim’ to a whole new level – an atomic level to be precise.

Using substances called graphene (a semi-conductor) and hexagonal boron nitride (an insulator), which are basically one atom-thick sheets of repeating atoms, researchers led by Jiwoong Park have opened a new frontier in nano-scale electronics.

Their technique, which they’ve termed patterned regrowth, involves the precise placement of atoms on these sheets in order to manipulate their electronic properties, and could possibly lead to the development of next-generation electronic circuits – transparent circuit boards that are so thin they could easily float on the surface of water, or even on air, while maintaining both their rigidity and a high level of efficiency.

Graphene and boron nitride are grown using a process known as photolithography, which ensures that the sheets are perfectly smooth and flat, with no creases or bumps, making them ideal substances for an atomically thin circuit.

Park likened the technique for making his circuits to that of stenciling; firstly, the graphene was grown on a copper base; next, selected areas of the copper underneath the graphene were exposed, in order to create a ‘pattern’ for their circuit. These exposed areas were then filled in with boron nitride, which also grows well on copper and fills all of these ‘gaps’ perfectly.
The end result is a microscopically thin ‘film’ that can easily be peeled off its copper base and used as an electronic circuit, with the graphene atoms acting as the ‘wire’ and the boron nitride assuming the role of the circuit board.
Cool stuff to be sure, but the best thing about it is that researchers believe that the process for making atomic circuit boards may soon commercially viable. The researchers are already highly-skilled in growing graphene, and the photolithography technique is widely used in the production of integrated circuits on flat silicone. With a little refinement, a future of genuinely transparent electronics might not be that far off.

CMOS provides new way to generate terahertz radiation

Enlarge

http://phys.org/news/2012-07-terahertz.html
By Bill Steele
(Phys.org) -- Cornell researchers have developed a new method of generating terahertz signals on an inexpensive silicon chip, offering possible applications in medical imaging, security scanning and wireless data transfer.

Terahertz radiation, the portion of the electromagnetic spectrum between microwaves and infrared light, penetrates cloth and leather and just a few millimeters into the skin, but without the potentially damaging effects of X-rays. Terahertz scanning can identify skin cancers too small to see with the naked eye. Many of the complex organic chemicals used in explosives absorb terahertz radiation at particular frequencies, creating a "signature" that detectors can read. And because higher frequencies can carry more bandwidth, terahertz signals could make a sort of super-Bluetooth that could transfer an entire high-definition movie wirelessly in a few seconds.

Current methods of generating terahertz radiation involve lasers, vacuum tubes and special circuits cooled near absolute zero, often in room-sized apparatus costing thousands of dollars. Ehsan Afshari, assistant professor of electrical and computer engineering, has developed a new method using the familiar and inexpensive CMOSchip technology, generating power levels high enough for some medical applications. With further research, higher power will be possible, Afshari said, enabling such devices as handheld scanners for law enforcement.

Afshari and graduate students Yahya Tousi and Vahnood Pourahma describe the new approach in the June 8 issue of the journal Physical Review Letters.

Enlarge

Schematic of a ring of oscillators (gray circles) coupled to generate terahertz frequencies. Coupling circuits (blue triangles) shift the phase of the oscillations to reinforce the fourth harmonic. (Ehsan Afshari)

The ability of solid-state devices to generate high frequencies is limited by the characteristics of the material -- basically, how fast electrons can move back and forth in a transistor. So circuit designers make use of harmonics -- signals that naturally appear at multiples of the fundamental frequency of an oscillator. That fundamental frequency is usually set by a circuit that uses a variable capacitor called a varactor, but at terahertz frequencies varactors don't tune sharply. Afshari has come up with a new way of tuning by coupling several oscillators in a ring, producing what engineers call a high-quality signal, where all the power goes into a very narrow frequency band.