Ken Ishino

Realization of compact semi- and fully anechoic chambers using a new developed composite absorber

The shape of a composite absorber consisting of ferrite and dielectric lossy material was investigated to reduce the length of the absorber and improve the reflection coefficient in the low frequency range by effectively changing the cross section of the dielectric lossy materials towards the direction of the length. It was found that the most suitable change of cross section was logarithmic function. Consequently, the length of the absorber could be reduced by 35% of that of the former composite absorber and the size of the anechoic chambers with the newly developed absorber could be reduced by 20%.<<ETX>>

Compact anechoic chamber for immunity test and EMI noise measurement

The distribution of the electromagnetic field in the compact anechoic chamber consisting of four walls, ceiling, and floor with ferrite absorbing materials was investigated. The compact anechoic chamber used for both immunity test and electromagnetic interference (EMI) noise measurement was developed by improved ferrite absorber. The compact chamber was extremely uniform, and the maximum deviation is less than 6 dB in the vertical plane. The site attenuation characteristics in the compact chamber were in good agreement with those in the open-field test site.<<ETX>>

Investigation on convenient measuring method of oblique incident characteristics for absorbing panel in low frequency range (lower than 1 GHz)

The ferrite absorbing panel used for suppressing TV ghost images caused by TV wave reflection from tall buildings and the RF absorber used for an anechoic chamber have been realized for many years. The convenient and accurate measuring method of the reflectivity characteristics of RF absorbers against the oblique incidence in the low frequency range (lower than 1 GHz) is investigated by using a new time domain reflectometer method. The direct wave vector from the transmitting antenna to the receiving antenna and the undesired reflection vector can be eliminated by means of a mathematical treatment or by subtraction of the receiving signal without the target from that signal with the target in advance of time gating in the desired response. By using these new methods, a convenient and efficient evaluation method for an RF absorbing panel and absorber could be realized.

The Shielding Effect of Wave Absorber on Leakage through the Gap of Microwave Oven

Recently many kinds of electronic equipments have been developed. However since the electro-magnetic waves radiate from micro-computer, personal computer, printer or microwave oven. Especially the very high microwave power is used for heating in microwave oven, and a certain type of shielding method must be considered because the microwave oven has a door for putting foods in and it is difficult to shut it completely without any gaps. It is well known that the microwave easily leaks through gaps between the door and the main frame of the microwave oven. If this leaky microwave power is strong, it caused a bad influence upon human health. Therefore, some method should be considered for preventing the microwave leakage. One of the best method is to fill the gaps with the microwave absorbing materials such as rubber ferrite sheet which is already practically used. In this paper, the shielding effect of absorbing materials on the microwave leakage through the gaps of the oven is described. First, theoretical analyses is explained and it was found that the numerical results of shielding effect were in good agreement with experiments for several kinds of absorbing materials. Then, the attenuation constants of absorbing sheet which is inserted into the gaps were theoretically obtained by changing the complex values of material permittivity and.permeability. These results must be very useful for selecting the absorber for designing the safe microwave oven.

Investigation on the Lossy Electro-Magnetic Shielding Materials by Ferrite and Resistive Materials

Lossy electro-magnetic shielding materials were investigated to reduce the radiation noise from electronic equipments. Two types of shielding sheets are proposed here and shielding effects are discussed both theoretically and experimentally. These results are very useful for designing the electronic equipments with small radiation noise.