Báo Cáo Developments of new em wave absorbers

Developments of new em wave absorbersThis paper presents some recently developed EM wave absorbers. The research on the development
of new materials and binders for EM wave absorbers has been carried out, where sheet-type absorbers
for mobile phone, ship’s radar, and the complex type absorber for an anechoic chamber designed. Soft
ferrite and hard ferrite are well-known as the materials for EM wave absorbers. Soft ferrite such as
MnZn ferrite and NiZn ferrite, are useful materials for EM wave absorbers, but the magnetic loss of
them decreases quickly in the GHz range. Since, however, hard ferrites such as Ba ferrite and Sr ferrite,
show high magnetic loss in the GHz range, they are useful materials for EM wave absorbers in the
GHz range. Thus the sheet type EM wave absorbers were fabricated with Ba ferrites, Sr ferrites,
Sendust, and Alnico magnet. The sheet-type absorber using Sendust is useful for mobile phone the
frequency of which is from 1.2 GHz to 2 GHz, and they are useful for preventing unwanted EM waves
in the C-band and X-band radar. Especially, the effects of EM wave absorption ability have been
shown by field test. On the other hand, the complex type absorber for an anechoic chamber has been
designed which has the thickness of 178.3 mm and showed absorption ability over 20 dB in the
frequency band from 30 MHz to more than 20 GHz.