This invention provides a thin microwave absorbing wall member using a ferrite plate of which complex permeability is represented substantially by a formula:
Electromagnetic wave-absorbing wall comprising ferrimagnetic plates arranged at some intervals in the direction of the electric field of the electromagnetic wave said ferrimagnetic plates being plates of ferrite having the following general formula: wherein M is a bivalent metal such as Mn, Ni, Co, Mg, Cu, Zn and Cd, or plates of a mixture of ferrite powders or carbonyl iron with organic high molecular weight compounds, and said plates having a specified thickness according to the interval.
A radio wave absorbent comprises an Ni--Cu--Zn base ferrite having a major composition comprising 49 to less than 50 mol % of Fe.sub.2 O.sub.3, 32 to 35 mol % of ZnO, 3 to 9 mol % of CuO and 9 to 14 mol % of NiO. The radio wave absorbent further contains an additive molybdenum oxide in an amount of greater than 0 to 0.10 wt %, calculated as MoO.sub.3, with the proviso that the total amount of the major composition is 100 wt %. The radio wave absorbent may be used as an exterior or interior material for a building or structure.
Ferrites as an electromagnetic wave absorber have their unique attenuation ranges depending on their compositions. The possibility of controlling attenuation characteristics of ferrite absorber by forming laminates of ferrite is disclosed. This invention provides that the center frequency of laminated ferrites could be changed arbitrarily employing ferrite with different composition and thickness. The method consists of stacking at least two soft ferrite layers (Ni-Zn, Mn-Zn) with various thickness.
A wave absorber comprising a sintered ferrite tile wave absorber as a base substrate lowermost relative to the incident wave, and one or more laminates comprising two layers as one set, with a dielectric layer as a lower layer and a dielectric loss-causing layer as an upper layer, laminated on the base substrate. The wave absorber of the present invention is thin, but is capable of absorbing waves over wide frequency bands of from tens of megahertz to a dozen or so gigahertz. By making the absorber thin, the absorber weighs less and is easy to handle, which in turn leads to fine workability and low construction cost.
