Experimental Research on Improvement of the Orientation Characteristics of a Slit Ferrite Plate in the RF Magnetic Field: Superposition of a Slit Carbon Plate Over a Slit Ferrite Plate

摘要

As part of the basic research for the improvement of the electromagnetic environment, the present study has developed a ferrite plate having orientation characteristics. To exhibit the orientation characteristics of a plane wave, a slit was cut on the surface of the ferrite plate. The values of the radio frequency (RF) magnetic shielding degree $SD_{rm HH}$ when holding the slit horizontal to the ground, in the frequency region of 1 MHz (43 dB) to 200 MHz (8 dB), decreased with frequency. The value of RF magnetic shielding degree $SD_{rm HP}$ when holding the slit perpendicular indicated an average value of 20 dB in this frequency region. Namely, the values of the difference, $SD_{rm HH}-SD_{rm HP}$, indicated an average value of 13 dB as the orientation characteristics. The orientation characteristics of the ferrite plate, however, displayed no orientation characteristics in the frequency region of 200 MHz to 3 GHz. Therefore, in order to improve the orientation characteristics in this frequency region, a compound plate was formed by the superposition of a slit carbon plate over the slit ferrite plate. The values of the difference, $SD_{rm HH}-SD_{rm HP}$, for the compound plate were then improved by approximately 35 dB in the frequency region from 1 MHz to 3 GHz. Experimental results revealed several orientation characteristics of the compound, slit ferrite and carbon plates.