Radar absorption

The B-2 stealth bomber in Figure 1-38 is made by Northrop Grumman. Virtually all external parts are made of various composite materials because of their radar-absorption characteristics and/or their capability to be formed to shapes that naturally lower the radar cross section of the plane. However, the details are not publicly available, nor are they for the Lockheed Martin F-117A stealth fighter. 

Polyaniline exhibits properties which supplement those of polypyrrole and polyalkylthiophenes. It represents an adequate candidate for radar absorption purposes. The most significant properties of this conducting polymer... 

Laser sources that emit in the mid-ir region of the spectmm (2—5 -lm) are useful for detection of trace gases because many molecules have strong absorption bands in that region. Other appHcations include remote sensing and laser radar. Semiconductor lead—salt (IV—VI) lasers that operate CW at a temperature of 200 K and emission wavelength of 4 p.m are commercially available however, they have relatively low output powers (<1 mW) (120). 

LIDAR An instrument that uses a laser-radar to study the concentration and location of particulate matter by the reflection or absorption of a laser beam. 

At Novartis, so-called BioavailabiUty Radar Plots [44] are used to visually display the oral absorption potential of molecules. On these plots five important calculated descriptors (log P, molecular weight, PSA, number of rotatable bonds and water solubility score [45]) are displayed on the axes of a pentagonal radar plot and compared with predefined property limits (green area) which were determined by the analysis of marketed oral drugs. These plots provide an intuitive tool that displays multiple parameters as a single chart in a straightforward but informative way, providing visual feedback about the molecule s bioavailabiUty potential (Fig. 5.5). 

The reflection spectrum of the atmosphere is a measure of the albedo of the planet (Figure 10.4) and, despite the strong methane absorption in the red, Titan s disc looks orange principally due to scatter from the surface of dense methane-hydrocarbon clouds. Scatter from aerosol particles within the thick clouds obscures the surface of the moon although the radar analysis reveals considerable Chapman layer structure within the atmosphere and some interesting surface features. 

Figure 16. A differential absorption THz radar for detecting atmospheric species...

Surface acoustic wave Semiconductor Target Radiation Radar Surface acoustic wave Electrophoresis Electrochemical Paramagnetic Chemi/bioluminescence Tunable diode laser absorption... 

Polyatomic molecules have more complex microwave spectra, but the basic principle is the same any molecule with a dipole moment can absorb microwave radiation. This means, for example, that the only important absorber of microwaves in the air is water (as scientists discovered while developing radar systems during World War II). In fact, microwave spectroscopy became a major field of research after that war, because military requirements had dramatically improved the available technology for microwave generation and detection. A more prosaic use of microwave absorption of water is the microwave oven it works by exciting water rotations, and the tumbling then heats all other components of food. 

Either IR or mass spectrometry may be used for individual hydrocarbon determination. Laser-induced Doppler absorption radar (LIDAR) can be used to remotely measure chemical concentrations in the atmosphere. Two different laser wavelengths are selected so that the molecule of interest absorbs one of the wavelengths, whereas the other wavelength is selected to be in a region of minimal interference. The difference in intensity of the two returned laser signals is then used to determine the concentration (see Figure 3.16, which illustrates the concept for IR signals). 

The absorption of radiation (for NMR, in the radio wave range, 10-80 MHz, or in the radar range, up to 1 GHz for EPR, in the microwave range, 3-100 GHz) depends on the relative population of the ground, or lower (1) state and first excited, or upper (u) state, that is, it depends on a Boltzmann factor of the type Nu/N exp (—AE/kBT), where AE is the relevant energy difference. 

The powders produced from the above method are very fine. TEM observation in Figure 3.29 shows that the typical powder is composed of equiaxed particles and has a size in the range of 50 to 80 nm. Experimental results reveal that the chemical composition of the powders depends weakly on processing conditions. The main chemical compositions of the powders are 50% wt of Si, 28% wt of C, 16% wt of N, while there is a small amount of O and H, 4% wt and 2% wt respectively. Selected area electron diffraction (SAED) also reveals the existence of a partial crystalline phase in the amorphous structure, this being a unique material feature which cannot normally be obtained using other manufacturing techniques. This feature makes it possible for the powders to be used as good functional materials, such as radar wave absorption materials. 

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