Method for making a low diffuse scatter, anechoic chamber absorber
An electromagnetic chamber absorber provided improved absorption across a wideband and both lower diffuse and specular scatter and a method for constructing the same. An exemplary device can compromise a periodic arrangement of disconnected electromagnetically lossy elements where the periodicity of the lattice is adjusted to suppress all or most grating lobe scattering. Because the electromagnetically lossy elements are disconnected, scalable manufacturing approaches are enabled. The lossy elements can be easily fabricated via shaping, which includes rolling, folding and cutting resistive and/or magnetic sheet materials. The lossy elements can be repeatably placed in a periodic lattice using low density scaffolding approaches and/or other alignment mechanisms. The absorption at the lower frequency part of the electromagnetic bands (below 1-2 GHz) can be improved via the addition of parallel lossy sheets into the low-density scaffolding.
1. A method of making an anechoic chamber absorber comprising placing a periodic arrangement of disconnected, electromagnetically lossy elements on a lattice described by two non-coincident lattice directions, where the electromagnetically lossy elements are free-standing tubular structures having a first section extending from the lattice at a proximal end and a second section extending from a distal end of the first section to a distal end of that electromagnetically lossy element, where a cross-sectional shape of the tubular structure is constant along an axial length of the first section and is tapered along an axial length of the second section, where the second section is tapered along a plane that extends from one side of the tubular structure at the distal end of the first section to an opposite side of the tubular structure at the distal end of that electromagnetically lossy element, where no structures are disposed between adjacent first sections and between adjacent second sections of adjacent electromagnetically lossy elements extending from the lattice in the periodic arrangement.
2. The method of claim 1 where the electromagnetically lossy elements are formed by rolling resistively coated sheets into tubes.
3. The method of claim 1 where the electromagnetically lossy elements are formed by rolling magnetic ram sheets into tubes.
4. The method of claim 1 where the electromagnetically lossy elements are formed by folding electromagnetically lossy sheets into tubes.
5. The method of claim 1 where the electromagnetically lossy elements are formed by cutting and placing shaped pieces of electromagnetically lossy materials onto low density carriers.
6. The method of claim 1 where the electromagnetically lossy elements are formed from window tint materials.
7. The method of claim 1 where the electromagnetically lossy elements are physically tapered by shaping the ends.
8. The method of claim 1 where the electromagnetically lossy elements are formed from coincident tubes made from resistively coated sheets and magram sheets.
9. The method of claim 1 where the electromagnetically lossy elements are tapered by geometrically grading the material properties of the elements.
10. The method of claim 1 where the lattice directions are orthogonal forming a rectangular array.
11. The method of claim 1 where the lattice directions are separated by 60 degrees forming a hexagonal lattice, wherein electromagnetically lossy elements immediately adjacent to one of the electromagnetically lossy elements are spaced at 60 degree intervals thereby forming the hexagonal lattice.
12. The method of claim 1 where the anechoic chamber absorber is configured to absorb electromagnetic waves in a frequency range having an upper frequency with a wavelength, wherein the periodic arrangement has a lattice spacing of the disconnected, electromagnetically lossy elements that is equal to or less than one-half of the wavelength of the upper frequency.
13. The method of claim 1 where the electromagnetically lossy elements are placed perpendicular to the lattice.