Shielding efficiency

Electromagnetic interference (EMI) testing has become more prevalent for materials that either emit or are affected by EMI. Shielding efficiency (SE) of materials is deterrnined by measuring electric field strength between a transmitter and receiver with or without the presence of the material under test. Several researchers have suggested a correlation between volume resistivity and SE values (300,301). 

Exposure is minimized by choice of source, by duration of exposure, by distance from source (at 1 m the radiation level is reduced almost 10-fold), and by shielding. The greater the mass per unit area of shield material the greater the shielding efficiency. Whereas a- and fTparticles pose few problems (the former can be absorbed by, e.g., paper and the latter by 1 cm Perspex) y- and X-rays are not completely absorbed by shield material but attenuated exponentially such that radiation emerging from the shield is given by... 

The melting behavior can be extracted from the dynamic viscosity [3,4], The dynamic viscosity also affects the morphology of the char, which may improve the shielding efficiency from the fire by the nanoparticle layer formed on the polymer [5-7],... 

The zinc complex A is probably the reactive [17] species in these conversions, as it activates the imine and tethers the carbonyl group of the ester group in 2-position with the anomeric imine. The Re-side is shielded efficiently and the attack of nucleophiles at the Si-side of the imine is strongly favored. 

The common feature of all black carbon constituents is the strong absorption within the whole solar spectrum. Black carbon particles are particularly toxic as pollutants on the other hand, they share the beneficial aspect of shielding efficiently harmful UV radiation. Although commercial products such as industrially produced carbon black, impure graphite and activated carbon differ chemically and morphologically from emitted organic aerosols, they are usually used as model particles for screening studies [56]. So far,... 

The total shielding efficiency of conducting polymers increases as the thickness of the polymer film increases, with the relative contribution of... 

Figure 8 Thickness dependence of total shielding efficiency (SET) of highly conducting polymers (A) stretched heavily iodine doped Tsukamoto polyacetylene, (B) camphor sulfonic acid doped polyaniline cast from m-cresol solvent, (C) PFg doped polypyrrole.

Figure 19.29 shows the comparative shielding efficiency data for various materials. Rubber filled with lead oxides comes very close in performance to lead and is superior to concrete and aluminum. Exposure of these shields to radiation causes degradation of mechanical properties (hardness, in particular, is increased) but it does not affect shielding efficiency. 

Ahrens (1954) has suggested that the term Sett = 52 //o2 /r, representing the nuclear shielding efficiency of the cation electrons, should be inversely related to the relative stability of metal complexes. 

FIGURE 7.8 (a) Magnitude of diverse 5-parameters and (b) shielding efficiency for the elliptical cavity with 0 = 75°... 

Let us now analyze the more complex shielding application of Figure 7.12(a), which illustrates a rectangular enclosure partitioned by two equal horizontal PEC walls. In the front plane, there is a centered (20 x 5) cm horizontal aperture. The dimensions are a = b = 60 cm, d = 120 cm, / = 70 cm, w = 2 cm, and the excitation is launched by a vertical coaxially fed monopole. Due to the nonstandard operators of (3.43), the domain is discretized into the coarse grid of30 x 60 x 30 cells with Ax = Ay = Az = 2 cm and At = 30.567 ps. In the area of the aperture, spatial derivatives are computed by the fictitious-point technique of Section 2.4.5, whereas the DRP schemes of Section 2.5.3 are also utilized. Figure 7.12(b) displays the shielding efficiency defined as the ratio of the electric field amplitude evaluated in front of... 

FIGURE 7.14 (a) An elliptical waveguide with multiple inclined slots located in a conducting plane, (b) Shielding efficiency versus the number of inclined slots for various 6 angles... 

FIGURE 7.15 Shielding efficiency of the elliptical waveguide for (a) vertical and (b) horizontal slots... 

FIGURE 7.20 Shielding efficiency of two cylindrical cavity-backed apertures with (a) four and (b) two cocentric metal elements... 

Figure 8.1. Thickness dependence of total Shielding Efficiency (SE,) of highly conducting polymers measured at 6.5 GHz (from [23c]) sample A stretched heavily iodine doped Tsukamoto polyacetylene (dotted line is obtained by using calculation of Se, with approximated values of a absorption coefficient and n) sample B unstretched heavily iodine doped Tsukamoto polyacetylene sample C camphor sulphonic acid doped polyaniline in m-cresol solvent sample D PFe doped polypyrrole sample E TSO doped polypyrrole Inset comparison of (microwave conductivity), c, and tan 6, Reprinted from ref. 23c with permission. Copyright American Institute of Physics.

The absolnte confignrations of both the Diels-Alder and the Michael addncts with R = Ph were elncidated by transformation into known compounds. In the case of the D-A reaction, the (2S,3S) enantiomer was formed in excess, indicating that cyclopentadiene attacks from the Si face of the dienophile. Similarly, nucleophilic attack to the enone in the Michael reaction was shown to occur from the Si face. These results suggest that the Re face of the bound substrate is shielded efficiently by the DNA in both reaction classes (Fig. 14). 

Contributions of reflection and absorption to the EM shielding efficiency of a 3 mm thick filled moulding, at a frequency of 100 MHz (from Mobius K. H., Kunststoffe, 78, 31, 1978). 

Comprehensive radiation survey has been carried out to ensure shielding efficiency in the cells having primary radiation components and cover gas system. The measured dose rates have been found to be less than the design values. The average annual collective dose is 2.2 P-mSv. This indicates very low radiation exposure from the plant. 

Burnett, T. H. J., Subsequent. Tests - MTR Shield Efficiency, ORNL CF-March 29, 1950. 

Stefecka, M Kando, M. Matsuo, H. Nakashima, Y. Koyanagi, M Kamiya, T. Cernak, M (2004). Electromagnetic shielding efficiency of plasma treated and electroless metal plated polypropylene nonwoven fabrics.. Mater. Set, Vol. 39, pp. 2215-2217, ISSN 0022-2461. 

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