6.1. Outside Reflectors and Absorbers Shielding is an effective way to reduce the cross section X- (10) which defines the power dissipated in the interior space. Measures to accomplish this are as follows. Utilize natural obstructions (e.g., tree grove). Use high-reflectance surfaces for the outer shell (metal sidings) especially towards the south. Shade apertures with metal awnings or cover them with wire mesh. The insertion loss of wire mesh in copper or steel at 2.45 GHz is: Lp dB 44 51 58 Size, meshes/cm 7x7 9x9 11x11. Cover apertures with resistive sheet material or embed absorbing cord around the edges where the highest electric coupling field strength occurs (see Figure 2). Keep unnecessary openings (slots, cracks, etc.) away from the exposed side or keep them below 2 cm in size (then < 0.1). 6.2. Inside Absorbers Field uniformity is the desired objective for anechoic chambers and has been studied extensively (Appel-Hansen, 1973; Crawford, 1974; Emerson, 1973; Donaldson et al., 1978). In these applications, it is-attempted to keep the free-field SWR below + 0.5 dB (see Table 5). In the case of habitable space, one could lessen the SWR tolerance. The application of nonreflecting absorbers to exposed metal surfaces should be an effective measure to mitigate potential hot spots. Absorbers provide nearly reflection-free surfaces by matching their impedance Z to the free-space value ZQ (4). They come in three basic types: 1. Broad band absorbers are typical in anechoic chambers. To be effective under all angles of incidence, they have to be shaped (e.g., cones) and mounted in thick layers (d > lOx). Different absorber materials can be staggereu to reduce the thickness and improve matching.
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