2010 年 35 巻 4 号 p. 913-916
As one of the basic areas of research for improving the electromagnetic environment, the present authors have developed a slit carbon plate, as a natural resource, that displays orientation characteristics in a radio frequency (RF) magnetic field. When the slit was held perpendicularly to the ground, the value of RF magnetic shielding degree SDHP increased with frequency in the region of 1 MHz (7 dB) to 3 GHz (70 dB). When the slit was held horizontally to it, the values of RF magnetic shielding degree SDHH indicated an average value of approximately 10 dB over this frequency region. The difference in the values, SDHP-SDHH, indicated the orientation characteristics. The slit carbon plate was particularly effective with respect to the orientation characteristics at frequencies above 70 MHz. However, the values of SDHP-SDHH below 70 MHz, having an average value of approximately 15 dB, were not significant enough to display orientation characteristics. Accordingly, the present research improved the orientation characteristics by construction of a slit carbon plate sandwiched between two slit ferrite plates; termed the slit sandwich plate. The value of SDHP-SDHH for the slit sandwich plate improved by an average value of 40 dB in the frequency region from 1 MHz to 70 MHz. The above results confirmed that an important criterion was developed for the fabrication of a slit sandwich plate having highly reliable orientation characteristics.
