Materials Engineering

Dribbling past the radar

Shielding makes military aircraft imperceptible to detection and eliminates electromagnetic interference

MIGUEL BOYAYANAt the CTA, a chamber for testing radiation absorbing materialMIGUEL BOYAYAN

Within a short time, making aircraft that are invisible to radar will no longer be exclusive to countries that have advanced knowledge in the military area. The Aeronautics and Space Institute of the Technical Aerospace Center (IAE/CTA), of São José dos Campos, is developing several kinds of a product called Radar Absorbing Material (RAM). This is the same material used in painting the aircraft of the Air Force of the United States, like the F-117 and B-2, known for making themselves imperceptible to radar. The technique is based on the absorption, by the material, of the electromagnetic energy given off by the radar, which is transformed into thermal energy, easily dissipated, and thus preventing the signals reflection and subsequent detection. Although RAM has military ends, because it was requested by the Ministry of Defense, there is great potential for its use in civilian applications.

In the aeronautical industry, the product can be employed in the internal shielding of civilian aircraft, in the insulation of electrical cables, and in cockpit sealing, preventing interference with the aircraft’s instrumentation, like that caused by mobile telephones. In the same way, radio transmission antennas can be given absorbent rings to eliminate undesirable electromagnetic waves that interfere with communication systems. Antennas for transmission and reception and mobile telephony handsets themselves can be coated with this material, to absorb electromagnetic energy.Other examples of uses for RAM lie in the internal coating of microwave ovens, with the aim of preventing the leakage of radiation, and in the electromagnetic shielding of pacemakers. In scientific research and in industry, it is useful in the insulation of anechoic chambers, used for testing the reflection of electromagnetic waves. Insulation from this kind of radiation can also be used in the building industry, using the material to coat rooms or buildings that have electronic material sensitive to interference.

At the moment, the material that carries tasks similar to RAM is still imported in Brazil. But it can be analyzed and characterized at the CTA itself, which has a laboratory that is appropriate for tests. Since the beginning of research with RAM, the IAE has now received five Brazilian prizes, applied for nine patents with the National Institute of Intellectual Property (INPI), and has awoken the interest of companies in producing the material, although no contract has been closed yet.

Rubber and foam
Under the coordination of researcher Mirabel Cerqueira Rezende, head of the Composites Subdivision of the Materials Division of the IAE, RAM is being developed in the form of paints and of rubber and foam mantles that get high capacity absorbents, such as ferrites, carbonaceous materials, and, more recently, microwave conducting polymers, which are lighter and ideal for painting aircraft. For the military aviation sector, the product is strategic, and can be employed in coating aircraft, armaments and antennas. Besides making stealth planes, the absorbing material will assist in the ridding of electromagnetic radiation harmful to these devices

The technology for this absorbent material is used by the United States, Russia and the United Kingdom in aircraft, ships, submarines, platforms and land vehicles, and is now also under development in Israel, Spain and France. According to Mirabel, Brazil is the first to invest in this kind of research in Latin America. Up until today, the country has imported absorbent material, particularly the foam-based kind, which is applied, for example, in the shielding of anechoic chambers. Something bolder, such as is being developed at the IAE, has never even been imported, being a strategic technology related to the issue of national sovereignty by the companies that have it. To understand this aspect, it has to be appreciated that radar captures the waves reflected by an aircraft and detects not only its type, but even its country of origin. When covered with absorbent material, the radiation that hits the target is absorbed, making the signal weak and preventing the radar’s data systems from identifying it.

The RAM technology under development at the IAE/CTA is effective at frequencies over 2 (GHz), though it does not prevent aircraft being detected by older radar equipment, which operates, for example, in the range of 500 megahertz (MHz). However, its effectiveness consists of the fact that nowadays about 90% of the world’s radars work at frequencies over 1 GHz or even, preferably, from 8 GHz to 12 GHz, in the so-called broadband. “We are trying to develop the material using a combination of additives that increase the absorption of radiation in a broad range of frequencies, like conducting polymers, increasing its quality and efficiency”, Mirabel reckons.

For the researcher, the challenge at the moment is to carry out the measurements using prototypes coated with RAM in the open field, emitting, catching and interpreting signals from radar equipment. “This is very important, because, although the development of RAM involves a rigid control, measurements have to be made in natural surroundings, controlling the material’s humidity and temperature, since these parameters can alter the permeability of the system and, consequently, its behavior in absorbing microwaves”, Mirabel explains. “That is why we are starting a complete measurement system for the material, before we paint the aircraft, because the potential of the absorbents of electromagnetic radiation will only be fully known if taken in conjunction with other factors, like the geometry of the aircraft.”In 2004, it is planned to set up a reactor for the production of RAM on a larger scale, making field tests viable, should the Financier of Studies and Projects (Finep) approve a project with R$ 2.2 million in funds. At this stage, an agreement will also be signed with a company from the aeronautical sector, for the materials produced on a pilot scale to be used by the private sector.

No secrets
For the researcher, the great victory of RAM lies not only in mastering the technology for making aircraft in visible to radar, but in technological qualification. “As we are not working in secret, but in partnership with universities and development agencies, we are training researchers in this area, which is a differential for the country.” Besides six scholarships for master’s, doctor’s and postdoctoral degrees, the CTA’s Electromagnetic Characterization Laboratory has been refurbished with finance from FAPESP.

During the research, the IAE formed partnerships with the Federal University of São Carlos (UFSCar), the Federal University of Campina Grande (UFCG), the Federal University of Goiás (UFG), the State University of Maringá (UEM) and the State University of (Unicamp), besides an international agreement with the Moscow Power Engineering Institute, in Russia, in the area of absorbent materials, to include interchange between researchers.