Free Newsletters - Space - Defense - Environment - Energy - Solar - Nuclear
..
. Space Industry and Business News .




TECH SPACE
Mystifying materials
by Staff Writers
Chicago IL (SPX) May 28, 2012


These metamaterials may enable new applications, including the development of new protective mechanical devices and actuators (a type of assembly for operating or controlling a system), and the enhancement of microelectromechanical systems.

It's not magic, but new materials designed by two Northwestern University researchers seem to exhibit magical properties. Some contract when they should expand, and others expand when they should contract.

When tensioned, ordinary materials expand along the direction of the applied force. The new metamaterials (artificial materials engineered to have properties that may not be found in nature) do the opposite when tensioned - they contract. Other materials designed by the researchers expand when compressed.

"Materials are networks of connected constituents, and when you apply tension or pressure, they can respond in surprising ways," said Adilson E. Motter, the Harold H. and Virginia Anderson Professor of Physics and Astronomy at Northwestern's Weinberg College of Arts and Sciences.

"Think of a piece of rod that you tension by pulling its ends with your fingers," he said. "It would normally get longer, but for these materials it will get shorter."

Motter and Zachary G. Nicolaou applied network concepts to design the new materials, all of which exhibit negative compressibility transitions. Their results are published this week in Nature Materials. Nicolaou, an undergraduate physics student at Northwestern when the work was done, now is a first-year graduate student at Caltech.

Different types of metamaterials already have led to interesting applications such as superlenses, visibility cloaks and acoustic shields. But no existing material or metamaterial was previously shown to exhibit negative compressibility transitions.

These metamaterials may enable new applications, including the development of new protective mechanical devices and actuators (a type of assembly for operating or controlling a system), and the enhancement of microelectromechanical systems.

The materials also exhibit force amplification, a phenomenon in which a small increase in deformation leads to an abrupt increase in the response force. The latter can be useful for the design of micro-mechanical controls, ratchets and force amplifiers.

All known materials deform along the direction of a constant applied force by expanding when they are tensioned and contracting when they are compressed. Owing to stability considerations, such contraction of a material in the same direction of an applied tension (in response to tension) cannot occur continuously.

Possibly because of this, most people would intuitively expect that contraction in response to tension would be impossible.

The important point of the Northwestern study is that such a counterintuitive response can occur discontinuously, namely, through something known by physicists as a phase transition. A familiar form of phase transition is the transformation of water into ice or vapor. Phase transitions allow for abrupt changes in the physical properties of a material. Yet, all conventional materials are such that phase transitions will lead to ordinary compressibility.

"This research shows that new materials, in fact, can be created to exhibit a phase transition during which the material undergoes contraction when tensioned or expansion when pressured," Motter said. "We refer to such transformations as 'negative compressibility transitions.'"

Materials with such properties have not been discovered in nature, but they can be constructed as metamaterials. Metamaterials are engineered materials that gain their properties from structure rather than composition. The relevant building blocks of such materials are not necessarily microscopic, atomic-sized objects, but may in fact be composed of a large number of atoms and hence be mesoscopic or macroscopic in size.

A key step for the discovery of the materials in this study was the representation of the material as a network of interacting particles.

"We were inspired by the observation that the realized equilibrium is not necessarily optimal in a decentralized network," Motter said. "A conceptual precedent to this is the now 45-year-old insight from German mathematician Dietrich Braess that adding a road to a traffic network may increase rather than decrease the average travel time."

Analogous effects also have been identified in physical networks, including an increase of current upon the removal of an intermediate conductor in electric networks. These are examples in which the equilibrium realized by the system can be brought closer to the optimum by constraining the structure of the network.

"Our materials are devised such that an analogous phenomenon occurs spontaneously, in response to a change in the external force rather than in the structure of the network," Motter said.

The article, "Mechanical Metamaterials With Negative Compressibility Transitions," is available here

.


Related Links
Northwestern University
Space Technology News - Applications and Research






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





TECH SPACE
Thousands of invisibility cloaks trap a rainbow
Washington DC (SPX) May 28, 2012
Many people anticipating the creation of an invisibility cloak might be surprised to learn that a group of American researchers has created 25 000 individual cloaks. But before you rush to buy one from your local shop, the cloaks are just 30 micrometres in diameter and are laid out together on a 25 millimetre gold sheet. This array of invisibility cloaks is the first of its kind and has be ... read more


TECH SPACE
Mystifying materials

Just How Green is Google

'Metamaterials,' quantum dots show promise for new technologies

Thousands of invisibility cloaks trap a rainbow

TECH SPACE
Researchers Improve Fast-Moving Mobile Networks

Second AEHF Military Communications Satellite Launched

Fourth Boeing-built WGS Satellite Accepted by USAF

Raytheon to Continue Supporting Coalition Forces' Information-Sharing Computer Network

TECH SPACE
SpaceX capsule has 'new car' smell, astronauts say

SpaceX makes final approach to space station

SpaceX's Dragon makes historic space station dock

SpaceX Launches NASA Demonstration Mission to ISS

TECH SPACE
Spirent Launches New Entry-Level Multi-GNSS Simulator

Beidou navigation system installed on more Chinese fishing boats

Scientists design indoor navigation system for blind

Chinese navigation system to cover Asia-Pacific this year

TECH SPACE
EADS head says helicopter cracks not comparable to A380 woes

India may bar Europe carriers in climate tax row

Boeing to Modernize Flight Deck and Avionics for US and NATO AWACS Fleets

Northrop Grumman's Joint STARS Completes Flight Testing of JT-8D Engines

TECH SPACE
Japan's Renesas ups chip outsourcing to Taiwan giant

New silicon memory chip developed

Return of the vacuum tube

Performance boost for microchips

TECH SPACE
Nea Kameni volcano movement captured by Envisat

My American Landscape Contest: A Space Chronicle of Change

City's population is counted from space

Unparalleled Views of Earth's Coast With HREP-HICO

TECH SPACE
Fears as Latin America's largest trash dump closes

Ship's captain jailed over New Zealand oil spill

Germany, India in talks over treating Bhopal waste

Italy ditches plan for rubbish dump near Hadrian's villa




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement