Use of the Cast Amorphous Microwire Witch Natural Ferromagnetic Resonance for High Frequencies Radioabsorbing Materials and Screens

Abstract

The use of high and extra-high frequency (EHF) fields in engineering has led to demands to design a various protective/shielding screens. As there are not the publications on protective screens manufactured on the basis of cast amorphous microwires, we will be limited of the analysis of an opportunity of application of these materials. The radio absorption properties of these cast amorphous microwire (produced by Ulitovsky-Taylor method) appear around the frequency of natural ferromagnetic resonance, in the range of 1-12 GHz ( see in [1][2][3][4][5][6][7][8] ). In that range, dispersion is observed in the real and imaginary components of relative magnetic permeability:The characteristic parameter is the skin-effect penetration depth 6 ( 6 is a skin layer depth). In the high frequency (HF) band [ 9 ] for fo-I10 GHz, c) = 2irfowhere (,u1uo )e is the effective magnetic permeability, c-is the microwire electrical conductivity, d5 is a skin layer depth in non magnetic microwire (S5 -10:5 gm for 1-10 GHz). The resonance permeability /u1(Co) is proportional to 10÷102, and a decreases three times when frequency increases to resonance (from 1 GHz to 10 GHz). Now we know experimental data on absorption of electromagnetic waves only in case [1] r>8 ,where r~3 10 gm is the radius of amorphous metal core of microwire . The existence of natural ferromagnetic resonance in the cast amorphous microwire in the frequency of range of order -I 12 GHz has opened up the possibility of developing of radio absorbing screens.The substantial increase in the absorption can be attributed to the imaginary part of the complex magnetic permeability which is given by p(o)=p'(co)+i ,`(w) or magnetic viscosity proportional to u" (w). (The magnetic viscosity is determined by 13' which depends quasi-linearly in nature on , (c)). For the imaginary part of magnetic permeability we considerwhere Q2 is frequency of natural ferromagnetic resonance, y is absorption factor (g°i s static magnetic permeability).We obtain where F > IQ-cj The absorption function of microwire is proportional to ,up' (co).

Dimensional absorption high-frequency properties of the cast glass coated microwires

“…In general, optimal absorption is obtained with microwires with metallic nucleus of diameter 2r m = 1-3 μm and length L = 1-3 mm. Such pieces of microwires can be taken as dipoles which length, L, is comparable to the half value of the effective wavelengths, Λ eff /2, of the absorbed field in the composite material (i.e., in connection to a geometric resonance) [5][6][7]. Figure 3 also shows the frequency absorption spectra of a screen with Fe 69 C 5 B 16 Si 10 microwires after being monotonically rotated (90° each spectrum) with respective fixing the sample (case 1, 2, 3, 4).…”

“…Different attenuation is seemingly ascribed to the lack of perfect random angular distribution of microwires which length does not always fit within the screen thickness [6,7].…”

“…Parallel theoretical studies suggest that a noticeable absorption fraction can be ascribed to geometrical resonant effect while concentration effect is expected for thinnest microwires as dimensional metamaterials effect. The absorbing characteristic of screen from microwires with natural resonance in the range of frequencies 10-12 GHz [6,7]. (The measurement error was less than 10% for the frequency, while the spread of the attenuation factor was 5-7 dB.…”