Nano Paint Could Make Airplanes Invisible to Radar
A nanotube coating would allow a plane to absorb a radar beam, making it undetectable.
A new nanostructured coating could be used to make paints for stealth aircraft that can’t be seen at night and that are undetectable by radar at any time of day. The coating, made of carbon nanotubes, can be used to cloak an object in utter darkness, making it indistinguishable from the night sky.
Carbon nanotubes have many superlative properties, including excellent strength and electrical conductivity. They are also the blackest known material. The long straws of pure carbon, each just a few nanometers in diameter, absorb a broad spectrum of light—from radio waves through visible light through the ultraviolet—almost perfectly. Researchers are taking advantage of this perfect absorbance in highly sensitive imaging sensors and other prototype devices.
L. Jay Guo, professor of electrical engineering and computer science at the University of Michigan, realized it could be useful as a kind of camouflage. Stealth aircraft, he notes, are often painted black or dark blue to hide them from view.
Guo’s group grew sparse forests of vertical carbon nanotubes on the surface of various three-dimensional objects, including a silicon wafer patterned with the shape of a tiny tank. The nanotubes make the objects appear completely flat and black, and they disappear against a black background. The nanotube-coated objects neither reflect nor scatter light.
This effect works, Guo says, because the nanotubes are perfectly absorbing, and because when they are grown with some space between them, as in his experiments, their index of refraction is nearly identical to that of the surrounding air. This means that light won’t scatter out of the nanotubes without being absorbed. The work is described in the journal
Applied Physics Letters.
Guo says if an airplane painted with the nanotube coating were hit with a radar beam, nothing at all would bounce back, and it would appear as if nothing were there.
“This type of cloaking is very interesting, especially since they have demonstrated operation in air,” says
Ray Baughman, director of the MacDiarmid NanoTech Institute at the University of Texas at Dallas. Baughman recently demonstrated that nanotubes can form an invisibility cloak when they’re heated up under water. The heat from a sheet of nanotubes affects the optical properties of the surrounding water, creating the illusion of invisibility.
Invisibility cloaks shield objects by manipulating incident light so that it simply flows around them. Materials that can achieve this must be made very painstakingly and typically only work with a very narrow spectrum of light—say, microwaves, or red or green light. Nanotubes are relatively easy to make, and work across a broad spectrum.
However, it’s not yet practical to grow forests of nanotubes on the surface of an airplane directly—growing such forests is a high-temperature, high-pressure process done in chambers much smaller than an airplane. But
Guo says it should be possible to grow the nanotubes on the surface of tiny particles which can then be suspended in paint.
Nano Paint Could Make Airplanes Invisible to Radar | MIT Technology Review
Stealth Paint to Make Airplane Invisible
Radar detection has always been the nightmare of military aircrafts. Once spotted in the radar zone, it is easy to destroy the aircraft in mid air by using anti-aircraft missiles. Defense personnel’s across the world are investing billions to develop better stealth equipped aircrafts that will easily escape from radar eyes. The concept of stealth is applied on an aircraft by making changes in the aircraft design such that it deflects the radar beams instead of reflecting them. The aircraft design is such that there are no perpendicular sections in the body of the plane, so the radar beam never reflects back to the receiver. While making a stealth aircraft we have to compromise with one of its main factor – the engine power. Though reducing the engine power can reduce the heat signature, the speed of the aircraft will also be compromised. What if we could develop a better stealth technology without compromising the aircrafts’ speed? We are talking about a technology that will make any aircraft invisible for radars.
Researchers have invented a special nano tube paint to make any object ultra black. This concept is also used for making aircrafts invisible to radars.
Engineers of NASA developed carbon nano tubes, being the ‘blackest ‘known material for their space missions. Carbon nano tubes will absorb 99 percent of any light- ultraviolet, visible or infrared that strikes on it. The material is also known for its excellent electrical conductivity and high strength .Carbon nano tubes are tiny yet long tubular structures made of pure carbon. A professor from Michigan University L J Guo first realized that by applying the nano paint or the nano tube coating, the aircraft could absorb the radar waves there by making it virtually invisible.
The researchers implanted large volumes of nano tubes into various substances like silicon wafer. Nano tubes have to be planted in a particular manner to make its reflective index similar to surrounding air. After implantation, the light is absorbed without being scattered. A practical method to implant nano tubes on the surface of aircrafts has not been developed until now. Perfect results were obtained only when nano tubes were implanted in tiny particles under the influence of high temperature and pressure. Guo suggested that first, the nano tubes has to be implanted in tiny particles and then suspended in the paint for stealth aircrafts. Earlier, to prevent absorption and radioactive properties, a metallic mixture was added to black paint and then coated on the aircraft.
However, this would add excess weight to the machine. Since nano tube has ultra black property and is denser, there is no need of any additives.
Stealth Paint to Make Airplane Invisible - Black Bullets
Limitations
There is no one optimum stealth design, but rather each mission requirement generates an appropriate mix of techniques. Implementation of stealth is not without penalties. Some of the materials used require special and costly maintenance. The maneuverability of an aircraft can be compromised by the introduction of stealth design features. As was the case with the F-117A, each B-2 bomber will have its own covered maintenance facility, since the B-2's low observable features require frequent performance of structural and maintenance activities.
Stealth requires not only design compromises, it also imposes operational compromises. Sensors to locate targets pose a particular problem for stealth aircraft. The large radars used by conventional aircraft would obviously compromise the position of a stealth aircraft. Air-to-air combat would rely on passive detection of transmissions by hostile aircraft, as well as infrared tracking. However, these techniques are of marginal effectiveness against other stealth aircraft, explaining the limited application of stealth to the Advanced Tactical Fighter.
Aircraft for attacking targets on the ground face a similar problem. FLIR can be used for precise aiming at targets whose general location is known, but they are poorly suited for searching for targets over a wide area. A radar on the aircraft to scan for potential targets would compromise its position. In order to locate targets, stealth aircraft may rely on an airborne laser radar, although such a sensor may prove of limited utility in poor weather. A more promising approach would be to use data from reconnaissance satellites, either transmitted directly from the satellite or relayed through communications satellites from processing centers in the United States.
There are limits to the utility of stealth techniques. Since the radar cross-section of an aircraft depends on the angle from which it is viewed, an aircraft will typically have a much smaller RCS when viewed from the front or rear than when viewed from the side or from above. In general stealth aircraft are designed to minimize their frontal RCS. But it is not possible to contour the surface of an aircraft to reduce the RCS equally in all directions, and reductions in the frontal RCS may lead to a larger RCS from above. Thus while a stealth aircraft may be difficult to track when it is flying toward a ground-based radar or another aircraft at the same altitude, a high-altitude airborne radar or a space-based radar may have an easier time tracking it.
Another limitation of stealth aircraft is their vulnerability to detection by bi-static radars. The contouring of a stealth aircraft is designed to avoid reflecting a radar signal directly back in the direction of the radar transmitter. But the transmitter and receiver of a bi-static radar are in separate locations — indeed, a single transmitter may be used by radar receivers scattered over a wide area. This greatly increases the odds that at least one of these receivers will pickup a reflected signal. The prospects for detection of stealth aircraft by bi-static radar are further improved if the radar transmitter is space-based, and thus viewing the aircraft from above, the direction of its largest radar cross section.
Several analysts claim stealth aircraft such as the ATF will be vulnerable to detection by infrared search and track systems (IRST). The natural heating of an aircraft's surface makes it visible to this type of system. The faster and aircraft flies, the warmer it gets, and thus, the easier to detect through infrared means. One expert asserts "if an aircraft deviates from its surroundings by only one degree centigrade, you will be able to detect it at militarily useful ranges." In fact, both the Russian MiG-29 and Su-27 carry IRST devices, which indicates that the Russians have long targeted this as a potential stealth weakness.
Stealth aircraft are even more vulnerable to multiple sensors used in tandem. By using an IRST to track the target and a Ladar (laser radar), or a narrow beam, high-power radar to paint the target superior data is provided.
The most basic potential limitation of stealth, is its vulnerability to visual detection. Since the ATF is 25-30 percent larger than the F-15 and 40 percent larger than the F-18, for example, it will be much easier to detect visually from ranges on the order of 10 miles. When one considers that stealth characteristics will drastically reduce the effectiveness of several types of guided air-to-air missiles, fighter engagements will probably move back to the visual range arena. In this context, the cumbersome F-22 would be at a distinct disadvantage.
Another potential "limitation" of stealth technology has little to do with its capabilities. Rather, some question the effect the pursuit of such hi tech aircraft will have on the US aerospace industry as a whole. These aircraft would not be available for foreign export until well into the next century. During that time, competitors such as the Gripen, Rafale and EFA will be peddled aggressively by European exporters. One analyst estimated that US foreign sales saved the Pentagon "about $2.8 billion through surcharges to recover part of their development costs and perhaps another $4 billion through the learning curve effect of higher production runs." Thus, America's stealth success could actually backfire, on its larger aerospace industry by causing it to forfeit sales to a new generation of top-of-the-line, although less formidable, European fighter aircraft.
Stealth Technology > ENGINEERING.com
Radar-absorbent material, or
RAM, is a class of materials used in
stealth technology to disguise a vehicle or structure from
radar detection. A material's absorbency at a given frequency of radar wave depends upon its composition. RAM cannot perfectly absorb radar at any frequency, but any given composition does have greater absorbency at some frequencies than others; there is no one RAM that is suited to absorption of all radar frequencies.
A common misunderstanding is that RAM makes an object invisible to radar. A radar-absorbent material can significantly reduce an object's
radar cross-section in specific radar frequencies, but it does not result in "invisibility" on any frequency. Bad weather may contribute to deficiencies in stealth capability.
Radar-absorbent material - Wikipedia, the free encyclopedia
