Saturday, August 22, 2009

TINY 'MEMS' DEVICES TO FILTER, AMPLIFY ELECTRONIC SIGNALS

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Researchers are developing a new class of tiny mechanical devices containing vibrating, hair-thin structures that could be used to filter electronic signals in cell phones and for other more exotic applications.

Because the devices, called resonators, vibrate in specific patterns, they are able to cancel out signals having certain frequencies and allow others to pass. The result is a new type of "band-pass" filter, a component commonly used in electronics to permit some signals to pass through a cell phone's circuitry while blocking others, said Jeffrey Rhoads, an assistant professor of mechanical engineering at Purdue University.

Such filters are critical for cell phones and other portable electronics because they allow devices to process signals with minimal interference and maximum transmission efficiency. The new technology represents a potential way to further miniaturize band-pass filters while improving their performance and reducing power use, Rhoads said.

The device is an example of a microelectromechanical system, or a MEMS, which contain tiny moving parts. Incoming signals generate voltage that produces an electrostatic force, causing the MEMS filters to vibrate.

Researchers have proposed linking tiny beams in straight chains, but Rhoads has pursued a different approach, arranging the structures in rings and other shapes, or "non-traditional coupling arrangements." One prototype, which resembles spokes attached to a wheel's hub, is about 160 microns in diameter, or comparable in size to a grain of sand.

Findings are detailed in a research paper to be presented on Sept. 2 during a meeting of the American Society of Mechanical Engineers' Third International Conference on Micro and Nano Systems. The conference runs from Aug. 30 to Sept. 2 in San Diego. The paper was written by Rhoads and mechanical engineering graduate student Venkata Bharadwaj Chivukula.

In addition to their use as future cell phone filters, such resonators also could be used for advanced chemical and biological sensors in medical and homeland-defense applications and possibly for a new type of "mechanical memory element" that harnesses vibration patterns to store information.

"The potential computer-memory application is the most long term and challenging," Rhoads said. "We are talking about the possibility of creating complex behaviors out of relatively simple substructures, similar to how in cellular biology you can have a relatively complex behavior by combining hundreds or thousands of simple cells."

The band-pass filter design promises higher performance than previous MEMS technology because it more sharply defines which frequencies can pass and which are rejected. The new design also might be more robust than the traditional linear arrangement, meaning devices could contain manufacturing flaws and still perform well.

The devices are made of silicon and are manufactured using a "silicon-on-insulator" procedure commonly used in the electronics industry to make computer chips and electronic circuits. The small, vibrating mechanical structures contain beams about 10 microns in diameter, which is roughly one-tenth the width of a human hair. The beams can be connected mechanically, like tiny springs, or they can be linked using electric fields and magnetic attractions.

"We are in the process of making a second prototype," said Rhoads, who has used simulations and also conducted experiments with the devices to demonstrate that the concept works.

(Photo: Purdue News Service/Andrew Hancock)

Purdue University

EXPLORING THE STANDARD MODEL OF PHYSICS WITHOUT THE HIGH-ENERGY COLLIDER

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Scientists at the University of California, Berkeley, and Lawrence Berkeley National Laboratory in the US, have performed sophisticated laser measurements to detect the subtle effects of one of nature's most elusive forces - the "weak interaction". Their work, which reveals the largest effect of the weak interaction ever observed in an atom, is reported in Physical Review Letters and highlighted in the August 10th issue of APS's on-line journal Physics (physics.aps.org).

Along with gravity, electromagnetism and the strong interaction that holds protons and neutrons together in the nucleus, the weak interaction is one of the four known fundamental forces. It is the force that allows the radioactive decay of a neutron into a proton - the basis of carbon dating – to occur. However, because it acts over such a short range – about a tenth of a percent the diameter of the proton – it is almost impossible to study its effect without large, high-energy particle accelerators.

Theorists had predicted that the weak interaction between an atom's electrons and its nucleus could be quite large in Ytterbium (element 70 in the periodic table). To actually see this interaction, though, Dmitry Budker and his group at UC Berkeley had to carefully perform delicate measurements based on fundamental quantum mechanical effects and systematically eliminate other spurious signals.

The effect Budker and his colleagues see in Ytterbium is about 100 times bigger than what has been seen in Cesium, the atom in which most experiments in this field have been performed so far. The finding of such a large effect in Ytterbium poses an exciting opportunity to use tabletop atomic physics techniques as part of sensitive searches for new physics that complement ongoing efforts at the world's high-energy colliders.

(Photo: American Physical Society/Carin Cain)

American Physical Society

UNIVERSITY OF TORONTO ARCHAEOLOGISTS FIND CACHE OF CUNEIFORM TABLETS IN 2,700-YEAR OLD TURKISH TEMPLE

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Excavations led by a University of Toronto archaeologist at the site of a recently discovered temple in southeastern Turkey have uncovered a cache of cuneiform tablets dating back to the Iron Age period between 1200 and 600 BCE. Found in the temple’s cella, or ‘holy of holies’, the tablets are part of a possible archive that may provide insights into Assyrian imperial aspirations.

The assemblage appears to represent a Neo-Assyrian renovation of an older Neo-Hittite temple complex, providing a rare glimpse into the religious dimension of Assyrian imperial ideology,” says Timothy Harrison, professor of near eastern archaeology in the Department of Near & Middle Eastern Civilizations and director of U of T’s Tayinat Archaeological Project (TAP). “The tablets, and the information they contain, may possibly highlight the imperial ambitions of one of the great powers of the ancient world, and its lasting influence on the political culture of the Middle East.” The cella also contained gold, bronze and iron implements, libation vessels and ornately decorated ritual objects.

Partially uncovered in 2008 at Tell Tayinat, capital of the Neo-Hittite Kingdom of Palastin, the structure of the building where the tablets were found preserves the classic plan of a Neo-Hittite temple. It formed part of a sacred precinct that once included monumental stelae carved in Luwian (an extinct Anatolian language once spoken in Turkey) hieroglyphic script, but which were found by the expedition smashed into tiny shard-like fragments.

“Tayinat was destroyed by the Assyrian king Tiglath-pileser III in 738 BCE, and then transformed into an Assyrian provincial capital, equipped with its own governor and imperial administration,” says Harrison. “Scholars have long speculated that the reference to Calneh in Isaiah’s oracle against Assyria alludes to Tiglath-pileser’s devastation of Kunulua – ie, Tayinat. The destruction of the Luwian monuments and conversion of the sacred precinct into an Assyrian religious complex may represent the physical manifestation of this historic event.”

The temple was later burned in an intense fire and found filled with heavily charred brick and wood which, ironically, contributed to the preservation of the finds recovered from its inner chambers. “While those responsible for this later destruction are not yet known, the remarkable discoveries preserved in the Tayinat temple clearly record a pivotal moment in its history,” says Harrison. “They promise a richly textured view of the cultural and ethnic contest that has long characterized the turbulent history of this region.”

(Photo: J. Jackson)

University of Toronto

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