Durham, NC -- A team led by scientists at Duke University's Pratt School of Engineering has demonstrated the first working "invisibility cloak." The cloak deflects microwave beams so they flow around a "hidden" object inside with little distortion, making it appear almost as if nothing were there at all.
Microwave cloaking isn't as shocking as optical cloaking. But it is still very impressive.
Cloaks that render objects essentially invisible to microwaves could have a variety of wireless communications or radar applications, according to the researchers.
The team reported its findings on Thursday, Oct. 19, in Science Express, the advance online publication of the journal Science. The research was funded by the Intelligence Community Postdoctoral Fellowship Program.
The researchers manufactured the cloak using "metamaterials" precisely arranged in a series of concentric circles that confer specific electromagnetic properties. Metamaterials are artificial composites that can be made to interact with electromagnetic waves in ways that natural materials cannot reproduce.
The cloak represents "one of the most elaborate metamaterial structures yet designed and produced," the scientists said. It also represents the most comprehensive approach to invisibility yet realized, with the potential to hide objects of any size or material property, they added.
Earlier scientific approaches to achieving "invisibility" often relied on limiting the reflection of electromagnetic waves. In other schemes, scientists attempted to create cloaks with electromagnetic properties that, in effect, cancel those of the object meant to be hidden. In the latter case, a given cloak would be suitable for hiding only objects with very specific properties.
I figure when the Terminator robots take over and start hunting us down the ability to hide from their microwave search beams will help some of us live longer.
The cloak passes microwaves around it unlike materials in stealth bombers that just absorb microwaves. Prevention of reflection in existing stealth technology is not as impressive as a design that keeps microwaves going on their natural course.
"By incorporating complex material properties, our cloak allows a concealed volume, plus the cloak, to appear to have properties similar to free space when viewed externally," said David R. Smith, Augustine Scholar and professor of electrical and computer engineering at Duke. "The cloak reduces both an object's reflection and its shadow, either of which would enable its detection."
The team produced the cloak according to electromagnetic specifications determined by a new design theory proposed by Sir John Pendry of Imperial College London, in collaboration with the Duke scientists. The scientists reported that theoretical work in Science earlier this year.
Are there non-military applications for this technology? If so, what are they?
Scientists have invented an efficient way to coat cotton cloth with tiny particles of titanium dioxide. These nanoparticles are catalysts that help to break down carbon-based molecules, and require only sunlight to trigger the reaction. The inventors believe that these fabrics could be made into self-cleaning clothes that tackle dirt, environmental pollutants and harmful microorganisms.
Hong Kong Polytechnic University researchers Walid Daoud and John Xin baked 20 nanometer titanium dioxide particles into clothes for 15 minutes to create cloth that can be cleaned by standing in the sunlight. I like efforts to achieve better living through materials science. Not sure if this approach is wise though.
The first potential problem here is that when hit by photons the materials generate oxygen free radicals. Well, do you want to wear clothing that generates oxygen free radicals? It might accelerate the aging of your skin. Also, some of the oxygen radicals may react with O2 to form O3 ozone gas. It would be like walking around in a microenvironment that is like Los Angeles on a bad day (or Bakersfield or Fresno even more often). You wouldn't want to stand still too long since in order to avoid clothing pollution.
The other problem with this approach is that the oxygen radicals would probably damage the cotton fibers. Cotton is made from cellulose which is a polymer of glucose sugar. That polymer can be damaged by free radicals. So the clothing might wear out faster.
Self-cleaning clothes will be developed eventually. Though it is not clear that this approach is the one that will ultimately succeed.
University Park, Pa. -- Penn State engineers have designed 10 concrete mixtures containing industrial by-products that make it possible for concrete bridge decks to last three times longer, or 75 to 100 years.
"The exact life expectancy of bridges constructed with these mixtures will not be known for many years," said Paul J. Tikalsky, associate professor of civil and environmental engineering, who led the study. "However, in full-scale trials, each of the mixtures optimizes the ingredients to produce concrete with substantially lower permeability, higher electrical resistivity and lower cracking potential than the standard bridge deck concrete used in Pennsylvania for the past 30 years."
He added, "The cost of bridges constructed with these mixtures is nearly identical to the previous generation of bridges. With life expectancies at least three times as long, the life-cycle cost savings will be more than $35 million annually in Pennsylvania with the added benefit of using environmentally friendly materials to contribute to a more sustainable future for the highway infrastructure."
Concrete is used in many other types of structures and so it seems likely these materials will be useful in lengthening the useful life expectancies of other types of structures as well.
The materials used are cheap because they are waste products of existing industrial processes.
"Fly ash, silica fume and slag are all industrial waste products that have been used previously in some types of construction,” Tikalsky noted. “These additives reduce the permeability of concrete and deter salts from entering. The additives also increase electrical resistance. So, in 40 or 50 years when water and salt eventually reach the steel reinforcement rods in the bridge deck, corrosion won't progress as rapidly."
Materials advances will continue to contribute to lengthening lives of all manner of human-built structures. Better materials will lenghten the lives of roads, bridges, buildings, vehicles, ships, and countless other structures and manufactured products. One result of increased durability is that obsolescence rather than decay will be the major reason old structures and old products are torn down and thrown away. Therefore as we develop the ability for most structures to last for centuries we need to ask how to build structures in ways that make them easier to upgrade in order to avoid (or at least delay) future obsolescence.
Future advances in materials science will yield cheap materials that will last for centuries. Humans built some structures centuries ago that are still in use today. But most of those structures require on-going maintenance and most structures that were built in previous centuries are not still around. Given that a much larger fraction of all structures will be long-lasting what should we do differently in designing and choosing the locations for such structures?
ALBUQUERQUE, N.M. — Researchers at the Department of Energy’s Sandia National Laboratories have developed a new lightweight material to withstand ultra-high temperatures on hypersonic vehicles, such as the space shuttle.
The ultra-high-temperature ceramics (UHTCs), created in Sandia’s Advanced Materials Laboratory, can withstand up to 2000ºC (about 3,800ºF).
Ron Loehman, a senior scientist in Sandia’s Ceramic Materials, said results from the first seven months of the project have exceeded his expectations.
“We plan to have demonstrated successful performance at the lab scale in another year with scale-up the next year,” Loehman said.
Thermal insulation materials for sharp leading edges on hypersonic vehicles must be stable at very high temperatures (near 2000ºC). The materials must resist evaporation, erosion, and oxidation, and should exhibit low thermal diffusivity to limit heat transfer to support structures.
Composite materials UHTCs are composed of zirconium diboride (ZrB2) and hafnium diboride (HfB2), and composites of those ceramics with silicon carbide (SiC). These ceramics are extremely hard and have high melting temperatures (3245ºC for ZrB2 and 3380ºC for HfB2). When combined, the material forms protective, oxidation-resistant coatings, and has low vapor pressures at potential use temperatures.
“However, in their present state of development, UHTCs have exhibited poor strength and thermal shock behavior, a deficiency that has been attributed to inability to make them as fully dense ceramics with good microstructures,” Loehman said.
Loehman said the initial evaluation of UHTC specimens provided by the NASA Thermal Protection Branch about a year ago suggests that the poor properties were due to agglomerates, inhomogeneities, and grain boundary impurities, all of which could be traced to errors in ceramic processing.
During the first seven months, the researchers made UHTCs in both the ZrB2 and HfB2 systems that are 100 percent dense or nearly so. They have favorable microstructures, as indicated by preliminary electron microscopic examination. In addition, the researchers have hot pressed UHTCs with a much wider range of SiC contents than ever before. Availability of a range of compositions and microstructures will give system engineers added flexibility in optimizing their designs.
Money spent to fund basic research in materials science does more to advance the cause of space exploration and space travel than money spent operating the Space Shuttle and International Space Station. The development of new materials will eventually help enable the development of much more advanced launch vehicles and spacecraft. Also, nanotech advances promise eventually to enable the construction of a space elevator. Far too much government money is spent doing things in space in the short term that would be better spent pursuing scientific and technological advances that would enable us to do orders of magnitude more in the long term.
A ceramic material reinforced with carbon nanotubes has been made by materials scientists at UC Davis. The new material is far tougher than conventional ceramics, conducts electricity and can both conduct heat and act as a thermal barrier, depending on the orientation of the nanotubes.
Ceramic materials are very hard and resistant to heat and chemical attack, making them useful for applications such as coating turbine blades, said Amiya Mukherjee, professor of chemical engineering and materials science at UC Davis, who leads the research group. But they are also very brittle.
The researchers mixed powdered alumina (aluminum oxide) with 5 to 10 percent carbon nanotubes and a further 5 percent finely milled niobium. Carbon nanotubes are sheets of carbon atoms rolled up into tiny hollow cylinders. With diameters measured in nanometers -- billionths of an inch -- they have unusual structural and conducting properties.
The researchers (postdoctoral scholar Guodong Zhan, graduate students Joshua Kuntz and Javier Garay, and Mukherjee) treated the mixture with an electrical pulse in a process called spark-plasma sintering. This process consolidates ceramic powders more quickly and at lower temperatures than conventional processes.
The new material has up to five times the fracture toughness -- resistance to cracking under stress -- of conventional alumina.
"It's a lot more forgiving under service application when you have a dynamic load," said Mukherjee.
The material shows electrical conductivity ten trillion times greater than pure alumina, and seven times that of previous ceramics made with nanotubes. It also has interesting thermal properties, conducting heat in one direction, along the alignment of the nanotubes, but reflecting heat at right angles to the nanotubes, making it an attractive material for thermal barrier coatings, Mukherjee said.
The work is published in the August issue of Applied Physics Letters.
Certainly newer and better materials can be expected to lower the costs of building or operating a variety of types of equipment, structures, and means of transportation. But seems more exciting to this commentator is the question of what structures and new ground, air, or space vehicles each new materials advance might make possible. Can carbon nanotubes make ceramics and other materials strong enough to make hypersonic scramjet space launch vehicles feasible some day? They are tougher and better at conducting and reflecting heat. Perhaps they will help.
By using carbon particles which are more than an order of magntude smaller than what is typically used to add to steel of researchers at the National Institute for Materials Science in Tsukuba Japan have produced a much stronger steel
By adding just 0.002% carbon to martensitic steel that already contains 9% chromium, Sawada and colleagues were able to increase the time-to-rupture at 923 Kelvin by a factor of 100 over the strongest creep-resistant steel currently available (which contains about 0.08% carbon).
Under constant low-stress loading, and over extended time periods, many materials undergo creep, a permanent deformation that is particularly marked at elevated temperatures. Incorporation of fine particles into metals and alloys, also called dispersion strengthening, is used to impart creep-resistance at high temperatures. A team from Japan's National Institute for Materials Science, Tsukuba, has developed a dispersion strengthening technique that incorporates nanometre-scale carbonitride particles into a martensitic stainless steel (a chromium-containing steel hardened by heat treatment) for improved creep performance.
Nanotechnology researchers at the University of Texas at Dallas and at Trinity College in Dublin Ireland have developed nanotube fibers that are stronger and tougher than any known synthetic or natural fiber.
The nanotube threads, created by Ray Baughman and colleagues at the University of Texas, Dallas, and Trinity College, Dublin, have a toughness of 570 Joules per gram. This is three times greater than the toughest natural material, spider silk.
These fibers are 20 times tougher than steel and 17 times tougher than Kevlar.
Now the researchers report they have spun nanotubes into fibers more than 300 feet long; the fibers have the strength of spider silk and more than three times its shock-absorbing toughness. That makes the fibers more than 17 times tougher than the Kevlar used in military flak jackets.
The fibres have twice the stiffness and strength and 20 times the toughness of the same weight and length of steel wire.
The current methods for producing nanotubes still cost many orders of magnitude more than existing materials and the method used to make these fibers is slow and costly as well.
They placed single-walled nanotubes in a rotating bath of aqueous polyvinyl alcohol, yielding gelatinous fibres, which were then coagulated, washed in an acetone bath, dried and reeled up.
This result does far more to demonstrate the performance potential of nanotubes than it does to lower costs. What is most needed to advance the use of nanotubes in materials applications are better methods for making them much more cheaply. While their process may scale well for converting nanotubes to fibers their process does not make the expensive nanotubes that are one of the materials which the process uses.
"We are currently making our fibres on the laboratory scale, producing hundreds of metres of fibre per run," added Baughman. "This basic fibre-spinning process is amenable to upscaling, which will involve increasing the spinning rate and going from single filament to multifilament spinning."
So far, the biggest hurdle to sewing futuristic nanotube clothes is the $500-per-gram cost of the nanotubes.
The ability of the fibers to function as sensors, electronic circuits, and even energy storage devices creates all sorts of possibilities for unusual clothing.
Or, pushing the envelope of imagination, think of a bulletproof shirt that plays MP3's and receives cellphone calls. (A more realistic potential application would be lightweight body armor that would also provide electrical power for a soldier's radio and other equipment.)
Frankly, I do not see what Kenneth Chang of The New York Times finds so unrealistic about clothing that would play music and take phone calls. Once the costs come down far enough one can easily imagine while people would want to wear clothes that provided so many capabilities. Here's another one: how about embedded temperature sensors that would respond to the change in outside and skin temperature to open and close openings in the cloth to change the level of insulation that one's clothes provide?
Baughman and his coworkers have already fashioned the fibers into electricity-storage devices called supercapacitors, which they incorporated into ordinary cloth.
It is likely that the energy storage density of this material is not high enough to get very excited about or they would have more strongly emphasised that part of their results. The discovery of much higher capacity electrical storage materials would enable the widespread use of electric-powered cars and also address the demand for much greater storage capacity for portable electronic devices.
Baughman and coworkers propose a number of applications for the tough fibrous materials, including safety harnesses and explosion-proof blankets for aircraft cargo areas. In addition, the combination of electronic and mechanical properties may be used to make textiles that serve as sensors, electronic interconnects, and electromagnetic shielding.
Aeorspace, automotive, buildings, bridges, and countless other areas would benefit from much stronger materials. Once nanotubes can be manufactured cheaply they are going to replace existing materials in a large variety of uses and will enable the design of many products that can only be imagined today.
Spacecraft design could be completely revolutionized by advances in nanotechnology. Of course greater strength in materials would allow a reduction in the amount of materials used. But nanomaterials holds out the promise of further weight reduction thru their ability to be structural materials while simultaneously functioning as sensors, electronic circuits, mechanical actuators and other mechanical devices.
Beyond merely being strong, nanotubes will likely be important for another part of the spacecraft weight-loss plan: materials that can serve more than just one function. "We used to build structures that were just dumb, dead-weight holders for active parts such as sensors, processors, and instruments," Marzwell explains. "Now we don't need that. The holder can be an integral, active part of the system."
Imagine that the body of a spacecraft could also store power, removing the need for heavy batteries. Or that surfaces could bend themselves, doing away with separate actuators. Or that circuitry could be embedded directly into the body of the spacecraft. When materials can be designed on the molecular scale, such holistic structures become possible.
Advances in nanotech fabrication techniques will do more to advance the state of the art in aerospace design and manufacture than anything else happening in the aerospace industry today.
John Joannopoulos and his photonic crystal research group at MIT have discovered that a shock wave travelling thru a crystal will cause light to reflect off the location of the wave and that this can be used to shift the frequency of light up or down as the light moves thru the crystal.
Because the shock wave is moving through the crystal, the light gets Doppler shifted each time it bounces off it. If the shock wave is travelling in the opposite direction to the light, the light¹s frequency will get higher with each bounce, while if it travelling in the same direction, the frequency drops.
After 10,000 or so reflections, taking a total of around 0.1 nanoseconds, the light can shift dramatically in frequency from red up to blue, for example, or from visible light down to infrared.
It will eventually be possible to use non-destructive acoustic shockwaves in microelectromechanical systems (MEMS) devices to build crystals that will shift the frequency of light. It will also become possible to build devices that will take light that is spread over a wide range of frequencies and shift it to a narrower range.
One application of the ability to shift frequencies in this manner could be to increase the efficiency of photovoltaics. Many photovoltaic materials absorb only a narrow subset of the range of frequencies in natural light. If a photonic crystal could shift the natural light into a frequency band that the photovoltaics materials could convert to electricity then the same amount of photovoltaic material could generate more electricity.
A preprint of the article is available in PDF format. If you have Apple Quicktime installed an animation of the phenomenon is available for viewing.
A group of Japanese materials science researchers at Toyota Central Research and Development Laboratories in Nagakute, Japan have used computers to search thru large numbers of combinations of elements to discover alloys with qualities that exceed that of all known alloys.
While any other metal bends or breaks when experiencing forces well below theorized strength limits because of defects in their crystal structure, these new metals approach their ideal strength limits.
"You could not find this alloy just by mixing things and testing. It's just too many combinations -- millions of combinations," Shiflet said.
They have discovered titanium alloys which expand very little over a large temperature range and have other valuable qualities.
The alloys are strong yet unusually elastic, so they can deform more than other alloys and still return to their original shape. Engineers can also readily mold or bend the materials at room temperature into various shapes, a property called superplasticity.
The most interesting thing about this work is that it shows how the pace of material science research is going to accelerate. The ability to use computers in place of lab experiments is made possible by the continuing increase in speed of computers. Computers are getting fast enough to allow complex physical processes to be simulated. This allows the computer modelling of experiments. This ability to simulate physical experiments has the potential to accelerate many fields of science by orders of magnitude.
Diode lights will reduce energy costs and provide greater control over lighting color and lighting locations. Aside from the obvious expected benefits their ability to light up faster will reduce car accidents.
Buses, trucks and autos have diodes in brake lights and interior lighting. Styling and maintenance benefits are driving the trend, but there are safety benefits, too. Because the diodes light up fractions of a second faster than do incandescent lights when a driver hits the brakes, anyone trailing a vehicle at 65 miles an hour is able to stop about 19 feet sooner, according to a study at the University of Michigan Transportation Research Institute.
Mechanical Engineering magazine has an interesting survey of a large variety of smart materials. The article covers such diverse materials as magneto-rheological fluids which become more viscous when a magnetic field is applied and piezoelectric materials that will be able to generate electricity from normal equipment vibrations. The article describes an electroactive flexible polymer one of whose neater applications is to translate the mechanical energy of a shoe hitting the ground into enough electrical energy to power a cell phone.
The system also can be used to generate electricity, by applying mechanical energy to the polymer. The film can be made to push the positive charge away from the negative, raising the voltage between the two electrodes, Pelrine said. SRI had one project to put such a device in the heel of a shoe, to generate power when a person is walking. Von Guggenberg estimated that enough electricity could be generated to power a cell phone—about one to two watts of power per step.
Another cool application under development is a biodegradable shape memory polymer that could be used to form a suture when doing endoscopic surgery.
Researchers have produced an organic light-emitting diode (LED) that is about 25 times more efficient than the best quantum-dot LEDs to date. The structure contains a single layer of cadmium-selenium quantum dots sandwiched between two organic thin films. Seth Coe and colleagues at the Massachusetts Institute of Technology believe that their approach could be used to fabricate other hybrid organic-inorganic devices (S Coe et al. 2002 Nature 420 800).
In a separate story about the race of many companies to bring organic LED products to market Nobel Laureate Alan Heeger sees organic LEDs revolutionizing light fixture technology.
Heeger, whose discoveries in polymer conductivity earned him and two colleagues a Nobel prize in 2000, said the innovations in lighting could be more dramatic than those in consumer electronics.
OLEDs, coupled with mature inorganic LED technology that already brightens traffic signals and auto taillights, could replace incandescent and fluorescent light bulbs with wallpaper that changes lighting patterns and colors, sheets of radiant film that could be cut to size or light cords that accent walls, handrails or steps, Heeger said.
No need for light bulbs. Though I suppose if some of your wallpaper stopped glowing you might need to re-wallpaper part of a wall to get it glowing again.
By sandwiching tiny but super-tough carbon nanotubes between layers of polymer, researchers have created a revolutionary material that is six times stronger than conventional carbon-fibre composites and as hard as some ultrahard ceramic materials used in engineering.
An international team led by Nicholas Kotov of Oklahoma State University in Stillwater say their new material could be used in space engineering or for long-lasting medical implants.
WEST LAFAYETTE, Ind. — Using a more complex system of atoms than carbon nanotubes, scientists at Purdue University have devised a tunable approach to nanotube creation that allows them to build application-specific varieties. Called "rosette nanotubes" and built from a combination of carbon, nitrogen, hydrogen and oxygen, the new structures offer unique physical, chemical and electrical properties, the researchers said.
Duke University researchers may have found a way to fabricate nanotubes with enough consistency for use as electronic circuitry: (same artlcle also here as well)
DURHAM, N.C. -- Duke University chemists report they have made a significant advance toward producing tiny hollow tubes of carbon atoms, called "nanotubes," with electronic properties reliable enough to use in molecular-sized circuits.
In a report posted Oct. 28, 2002, in the online version of the Journal of the American Chemical Society, the Duke group described a method to synthesize starting catalytic "nanocluster" particles of identical size that, in turn, can foster the growth of carbon nanotubes that vary in size far less than those produced previously.
"This is really a first step toward a big future," said Jie Liu, a Duke associate professor of chemistry and the group's leader, of the unprecedented nanotube uniformity they achieved using this process.
Sometimes called "buckytubes," carbon nanotubes' properties were first studied by Japanese researchers in the early 1990s. The nanotubes, measuring just billionths of a meter in diameter (nano means "billionths"), were found to be lightweight but exceptionally strong, with unusual electronic properties.
Depending upon their atomic arrangements, nanotubes can act like conducting metals or like semiconductors, Liu said.
Since microelectronic devices such as computer chips use both semiconductors and metals, researchers foresee nanotubes as the building blocks for even smaller electronic circuitry than the millionths-of-a-meter scale resolutions of today's microchips.
However, "controlling the electronic properties of the nanotubes is becoming the biggest bottleneck that limits the development of nanotube research," Liu said in an interview.
The control problem arises because those electronic properties vary with the way nanotubes' atoms are arranged. And how their atoms are arranged is directly tied to the nanotubes' diameters -- which, until the fabrication advance by Liu and his colleagues, could vary considerably.
LED light sources will make it possible to dial the up your preferred color mix. Want to wake up to a reddish tinge? No problem. If the cost trend for LED light sources continues then the days of incandescent and flourescent bulbs are numbered:
The best white LEDs on the market emit 25 lm/W, which is almost twice as efficient as an equivalent tungsten-filament light bulb, but barely a third as good as a fluorescent tube. To become competitive, the devices need to reach 80 lm/W. To rule the world, 150 lm/W is probably required. If progress continues at the rate of the past 30 years, this will be reached by 2010. That is a big if, but the efficiency of blue and UVLEDs should improve dramatically as better ways are found to build them.