Tiny transmitter sets frequency record: Revolutionary terahertz transmitter developed

ScienceDaily (Jan. 13, 2012) — A terahertz transmitter developed at the TU Darmstadt has generated the highest frequency ever attained by a microelectronic device. The innovative device is also minuscule and operates at room temperature, which could lead to it paving the way for new applications in, e.g., nondestructive testing or medical diagnostics.

Although terahertz (THz) electromagnetic radiation, which has wavelengths ranging from 0.1 mm and 1 mm, penetrates common materials, such as plastics, paper, fabrics, or ceramics, allows, e.g., nondestructively testing workpieces, analyzing processes occurring in engine combustion chambers while engines are running, inspecting packages and letters for hazardous biological substances without need for opening them, it has yet to establish a reputation for itself in scientific and engineering fields. One of the hindrances involved was that, until now, transmitters and receivers operating at THz?frequencies were bulky and very expensive.

However, that situation might soon be reversed, since a team of physicists and engineers led by Dr. Michael Feiginov at the TU?Darmstadt's Institute for Microwave Technology and Photonics has developed a resonance tunnel diode (RTD) for generating terahertz electromag­netic radiation that takes up less than a square millimeter and may be produced using more or less conventional semiconductor-device fabrication technologies. Furthermore, their innovative transmitter has set a new frequency record, 1.111 THz, for microelectronic devices.

The highest frequency ever generated by an active semiconductor device

Feiginov, a physicist, noted, that, "That is the highest frequency ever generated by an active semiconductor device." He was also able to theoretically prove that a minuscule transmitter, like that developed by his group, should be capable of generating much higher frequencies extending up to 3 THz. As Feiginov, who intends to continue pursuing development work on the transmitter over the coming years until generation of such higher frequencies has been achieved, went on to say, "That was formerly regarded as impossible by those involved in terahertz research." Achieving such higher frequencies would allow attaining better spatial resolutions, i.e., recognizing finer details, employing terahertz electromagnetic radiation in materials testing and analysis than would be possible at lower frequencies.

That the RTD his group has developed operates at room temperature makes it even more attractive for use in engineering applications. He further commented that, "It might, for example, be utilized in spectroscopic analyses of molecules that have transitions falling within the THz?range." According to Feiginov, that would mean that substances that have thus far escaped spectroscopic analysis in the THz?range could be investigated employing that widely practiced, scientific method, which would be of great benefit in various fields, among them medicine, where it might, e.g., allow distinguishing diseased body tissues from healthy body tissues in vivo. Since active semiconductor devices, such as the THz?transmitter developed by the TU?Darmstadt group, represent the heart of modern informatics and telecommunications technologies, as well as all sorts of electronic equipment, Feiginov presumes that the device developed by his group will prove useful in many other application areas that cannot readily be foreseen at this stage. As he put it, "Extracting higher frequencies from the device would lead to new applications, or application areas, in the fields of computers, mobile telephones, and other types of electronic equipment."

In the course of miniaturizing their new device, the group of TU?Darmstadt researchers spent the past few years taking microelectronics close to the limits of the technically feasible. The heart of their RTD is a dual-barrier structure, within which a quantum well (QW) is embedded. A QW is a very thin layer of indium-gallium arsenide semiconductor sandwiched between a pair of ultrathin barrier layers of aluminum-arsenide semiconductor. Every one of those layers is just one nanometer to a few nanometers thin. This dual-barrier structure, plus a quantum-mechanical effect, provides that electromagnetic waves generated within a terahertz oscillator will be repeatedly amplified, rather than attenuated, which means that the oscillator will emit continuous-wave electromagnetic radiation at terahertz frequencies. The group of TU?Darmstadt researchers collaborated with ACST GmbH, a local fabricator of microelectronic circuit components, in producing their diode.

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The above story is reprinted from materials provided by Technische Universit?t Darmstadt, via AlphaGalileo.

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Journal Reference:

Michael Feiginov, Cezary Sydlo, Oleg Cojocari, Peter Meissner. Resonant-tunnelling-diode oscillators operating at frequencies above 1.1?THz. Applied Physics Letters, 2011; 99 (23): 233506 DOI: 10.1063/1.3667191

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Highly efficient method for creating flexible, transparent electrodes developed

ScienceDaily (Nov. 22, 2011) — As the market for liquid crystal displays and other electronics continues to drive up the price of indium -- the material used to make the indium tin oxide (ITO) transparent electrodes in these devices -- scientists have been searching for a less costly and more dynamic alternative, particularly for use in future flexible electronics.

Besides its high price, ITO has several drawbacks. It's brittle, making it impractical for use in flexible displays and solar cells, and there is a lack of availability of indium, which is found primarily in Asia. Further, the production of ITO films is relatively inefficient.

Now, researchers at UCLA report in the journal ACS Nano that they have developed a unique method for producing transparent electrodes that uses silver nanowires in combination with other nanomaterials. The new electrodes are flexible and highly conductive and overcome the limitations associated with ITO.

For some time, silver nanowire (AgNW) networks have been seen as promising candidates to replace ITO because they are flexible and each wire is highly conductive. But complicated treatments have often been required to fuse crossed AgNWs to achieve low resistance and good substrate adhesion. To address this, the UCLA researchers demonstrated that by fusing AgNWs with metal-oxide nanoparticles and organic polymers, they could efficiently produce highly transparent conductors.

The team of researchers represents a collaboration between the department of materials science and engineering at the UCLA Henry Samueli School of Engineering and Applied Science; the department of chemistry and biochemistry in the UCLA College of Letters and Science; and the California NanoSystems Institute (CNSI) at UCLA.

The team was led by Yang Yang, a professor of materials science and engineering, and Paul Weiss, director of the CNSI and a professor of materials science and engineering and of chemistry and biochemistry.

"In this work, we demonstrate a simple and effective solution method to achieve highly conductive AgNW composite films with excellent optical transparency and mechanical properties," said Yang who also directs the Nano Renewable Energy Center at the CNSI. "This is by far the best solution: a processed, transparent electrode that is compatible with a wide variety of substrate choices."

Scientists can easily spray a surface with the nanowires to make a transparent mat, but the challenge is to make the silver nanowires adhere to the surface more securely without the use of extreme temperatures (200° C) or high pressures, steps that make the nanomaterials less compatible with the sensitive organic materials typically used to make flexible electronics.

To meet this challenge, Rui Zhu, the paper's first author, developed a low-temperature method to make high-performance transparent electrodes from silver nanowires using spray coating of a unique combination of nanomaterials.

First, researchers sprayed a solution of commercially available silver nanowires onto a surface. They then treated the nanowires with a solution of titanium dioxide nanoparticles to create a hybrid film. As the film dries, capillary forces pull the nanowires together, improving the film's conductivity. The scientists then coated the film with a layer of conductive polymer to increase the wires' adhesion to the surface.

The AgNW composite meshes are highly conductive, with excellent optical transparency and mechanical properties. The research team also built solar cells using the new electrodes and found that their performance was comparable to that of solar cells made with indium tin oxide.

The research received support from the Office of Naval Research and the Kavli Foundation.

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The above story is reprinted from materials provided by University of California - Los Angeles. The original article was written by Jennifer Marcus.

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Journal Reference:

Rui Zhu, Choong-Heui Chung, Kitty C. Cha, Wenbing Yang, Yue Bing Zheng, Huanping Zhou, Tze-Bin Song, Chun-Chao Chen, Paul S. Weiss, Gang Li, Yang Yang. Fused Silver Nanowires with Metal Oxide Nanoparticles and Organic Polymers for Highly Transparent Conductors. ACS Nano, 2011; : 111104125342002 DOI: 10.1021/nn203576v

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Algorithm developed to improve remote electrocardiography

ScienceDaily (Aug. 23, 2011) — Today someone in a remote village in India is able to run an electrocardiogram (ECG) via their smart phone on a loved one having a potential heart attack and send to a doctor in New Delhi for analysis.

Mobile technology is already bringing health care to places it has never been able to reach. However, there is still room for error that can lead to misdiagnosis.

Xiaopeng Zhao, assistant professor in the Department of Mechanical, Aerospace and Biomedical Engineering at the University of Tennessee, Knoxville, is working to eliminate these errors. Zhao and his team of graduate and undergraduate students and physicians have developed an award-winning algorithm that improves the effectiveness of ECGs.

The ECG is the most commonly performed screening tool for a variety of cardiac abnormalities. However, it is estimated that about 4 percent of all ECGs are taken with misplaced electrodes, leading to faulty diagnoses and mistreatments.

Zhao's algorithm examines interferences that result from electrode misplacement and disturbances, including patient motion and electromagnetic noise. Unlike conventional algorithms used to evaluate ECGs, Zhao's algorithm is more reliable because it is based on a matrix which simultaneously tests for irregular patterns caused by such interferences. Therefore, instead of a typical "yes-no" type of classification result, Zhao's produces a more accurate A-F letter grade of the ECG -- indicating specific weaknesses in the test. The algorithm also makes recommendations as to where to accurately place the electrodes.

Zhao's team has implemented the algorithm in a java program, which can be installed and operated on a smart phone. The program takes only a split second to execute on a smart phone and assess a 10-second ECG. The speed is key in situations where a second can mean the difference between life and death.

The goal is for users in remote areas to be able to know which ECGs are accurate to decrease misdiagnoses and ultimately save lives. The algorithm is also helpful in intensive care units where medical staff may be overworked, as well as for novice health professionals.

"There is a large population that does not receive good health care because they live in rural communities," said Zhao. "This algorithm helps to bring the doctor to their home through the help of mobile phone technology. We hope our invention brings their health care quality more in line with that of the developed world by reducing errors and improving the quality of ECGs."

The algorithm recently won the top spots in Physionet Challenge 2011 -- first, first and third places. Sponsored by the National Institutes for Health, Physionet and the annual Computing in Cardiology conference jointly host a series of challenge problems that are either unsolved or not well-solved. Starting in 2000, a new challenge topic is announced each year, aiming to stimulate work on important clinical problems and to foster rapid progress towards their solution.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Tennessee at Knoxville, via EurekAlert!, a service of AAAS.

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