Communications: directive radio wave systems and devices (e.g. – Radio wave absorber
Patent
1995-12-14
1998-01-20
Pihulic, Daniel T.
Communications: directive radio wave systems and devices (e.g.,
Radio wave absorber
H01Q 1700
Patent
active
057105642
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a system for the broad band absorption of electromagnetic waves, whereby a plurality of thin surface resistance layers are arranged three dimensionally in a chamber subjected to the electro-magnetic waves and to methods of manufacturing a system for the broad band absorption of electromagnetic waves.
Such absorption systems are principally used as non-reflective linings of chambers for testing electromagnetic tolerance (EMT).
EP-A 018873 discloses an absorption element for electromagnetic waves which comprises a three dimensional hollow body of rectangular cross-section. The four side walls each have a dielectric substrate and an external surface coating whose specific resistance varies from one end to the other end of the side wall in order to be able to absorb electromagnetic waves with a certain band width.
In another known absorber construction, effective absorption of electromagnetic waves over a predetermined frequency range is supposed to be achieved by increasing the layer thickness and by electromagnetic material parameters designed in dependence on frequency. Such resonance absorbers with large layer thicknesses have a correspondingly large weight and result in relatively high costs and complex static structural features. Their broad band characteristics are not adequate for current EMT test chambers despite the high complexity.
DE-B 1254720 described a system in which a plurality of hollow pyramids are arranged on a wall in abutment with one another. The hollow pyramids are coated on their external and internal surfaces with a conductive lacquer. The conductive lacquer layer is either sprayed directly onto the three dimensional carrier body or produced by dipping the three dimensional body.
In the known systems, either the operational characteristics, for instance the band width and the degree of absorption, are inadequate or the manufacture of the absorption system is complex and expensive.
It is therefore the object of the invention to combine a high degree of absorption efficiency over a large band width with the advantages of manufacturing in a simple manner which may be automated.
This object is solved in accordance with the invention by the features of the apparatus and method claims.
As a result of the invention it is possible for the first time to absorb a broad band spectrum of electromagnetic radiation with the aid of lightweight and thin surface resistance layer components which may be economically manufactured. The invention is based on the recognition that thin surface resistance sheets have an absorptive effect on electromagnetic radiation with differing wave lengths, even with a uniform distribution of the surface resistance, if they are arranged in a chamber subjected to the electromagnetic radiation in a predetermined and/or statistical three dimensional geometry. The broad band characteristics are therefore produced by the particular geometrical arrangement of the thin surface resistance layers in the chamber. Both the powder coated or deposited layer of electrically conductive or semi-conductive layer and also the electrically conductive organic layer make a uniform and constant specific surface resistance distribution possible. The absorption characteristics may be adjusted in a reproducible manner. Since the surface resistance layers are very thin, they advantageously have a low weight and are correspondingly economical to manufacture. The ratio of absorption performance/unit weight of the system is particularly high so that the device in accordance with the invention has an ecological tolerance which has not previously been achieved.
An important aspect of the manufacture of the absorber system in accordance with the invention is that any desired number of absorption elements can be produced from a surface resistance sheet. The carrier sheet or the surface resistance sheet produced after the coating can, for instance, have a breadth of 0.8 m and a length of 10,000 m. The finished surface resistance sheet may be rolled up at the end of the sheet prod
REFERENCES:
patent: 5225284 (1993-07-01), Tusch
Enders Achim
Nimtz Gunter
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