Behind the buzz and beyond the hype:
Our Nanowerk-exclusive feature articles
Posted: Jan 30, 2015
Nanotechnology and nanomaterials for camouflage and stealth applications (page 2 of 5)
Basic Concepts of Stealth Technology
Under the threat perception, enemy's detection capabilities through surveillance, reconnaissance or guided weapon system, signatures suppression by way of hiding, blending, and deception i.e. creating false signature of real targets are essential to enhance their survivability.
The development of stealth technology is mostly in reference to combat aircrafts in USA as represented in Fig. 1. The Stealth technology and materials developed for air combat systems are applicable to ground and naval equipment as well, with modifications, to suit their functional and environmental requirements.
In stealth technology the minimization of electromagnetic signature can be realized in several ways which include stealth shaping design, radar absorbing material (RAM), and radar absorbing structures (RAS). Stealth can be passive or active2.
Fig. 1: Evolution of aircraft stealth technology.2
Shape Design Aspect
Stealth shaping design involves the scattering of the incident electromagnetic wave from a radar to other directions thereby minimizing the reflective electromagnetic wave to the radar.
Following are the approaches by which military targets can be camouflaged in multispectral wavelength regions:
Shaped so that it reflects away radar signals
Covered by materials (RAM) that absorb radar signals
Constructed so as to reduce its infrared radiation
Constructed so as to reduce its visual detection
However, stealth shaping design deteriorates the aerodynamic properties of aircrafts and is not useful against bistatic radars.
Stealth materials that are used as military objects are specially designed with reduced or tailored reflectivity, emissivity or absorbance and can either be used in the structure of the object or as surface coatings. RAM absorbs the incident electromagnetic wave or cancels it by interference and ohmic loss. However, RAM has maintenance problems. Radar absorbing structures is a load bearing concept based on RAM. It is resistant to high temperature and humidity. So, RAS has less problems of maintenance.
In either way, stealth materials help to defeat sensors that detect objects by capturing the emitted or reflected electromagnetic radiation from the surface of the object. The basic crux of stealth technology is thus to divert away the observer by reducing the amplitude and/or altering the frequency response with the aid of carefully selected materials of different electromagnetic properties (refractive index, permittivity, permeability etc.).
It is not that stealth measures in microwaves are important but as per law of balanced observables, it is required in all the segments of EM spectrum including visible region. An example3 of visual stealth on F-16 is illustrated in Fig. 2. Here it is to emphasize that along with materials in the form of coatings, the terrain specific camouflage pattern paintings make the object to blend effectively with the background.
Fig. 2: Pattern painting of F-16 aircraft for visual stealth3 (Image: HyperStealth Biotechnology Corp.,Canada)