EFFECT OF ANOMALOUSLY STRONG ABSORPTION OF ELECTROMAGNETIC RADIATION IN FINE CONDUCTIVE FIBERS

Abstract

Subject and Purpose. The effect of abnormally strong interaction of electromagnetic radiation with fine conductive fibers is сonsidered. Metal, semiconductor, or graphite fibers can heavily absorb electromagnetic radiation provided the fiber diameter is several hundred times smaller than the radiation wavelength. For the most effective transfer of radiation energy, a proper ratio of the radiation wavelength, fiber refractive index, and fiber diameter is sought. Methods and Methodology. The diffraction problem of a cylinder whose diameter is much smaller than the incident wavelength is treated. The formulas to compute the radiation absorption efficiency have a series appearance. The series coefficients depend on the diameter of the cylinder, its refractive index, and the wavelength. With the cylinder diameter much smaller than the wavelength, these coefficients can be series expanded in the small parameter, and it should suffice to take into account only the first term. The findings are experimentally verified by measurements of the microwave radiation energy transmitted to a fine graphite fiber. Results. Relationships have been determined of the fiber diameter, fiber conductivity, and wavelength when the effect of the electromagnetic radiation absorption was at its strongest. The experiment showed that even unfocused, an 8 mm wave beam transmitted more than 10% of the energy to a graphite fiber of a 12 μm diameter. The size of the fiber area struck by the beam was 300 times smaller than the beam cross-section. Conclusions. Conductive fibers of a cross-sectional diameter much smaller than the incident radiation wavelength strongly absorb this radiation. The absorption is at its strongest when the radiation wavelength in the fiber substance is approximately 10 times larger than the cross-sectional diameter of the fiber. The effect of the anomalously strong absorption of electromagnetic radiation can be used to transfer the electromagnetic radiation energy to fine-fiber targets no matter whether the radiation beam is focused or not. Also, this effect can be of use for making protective screens in the microwave region.

Keywords

• diffraction
• scattering
• absorption
• fine fiber