Compare the concept of <i>Frequency Selective Surfaces</i> (FSS) (blocks and/or reflects some frequencies, lets others through) to the concept of <i>Impedance</i> (blocks and/or reflects some types of electrical signal, lets others through) in Electrical Engineering:<p><a href="https://en.wikipedia.org/wiki/Electrical_impedance" rel="nofollow">https://en.wikipedia.org/wiki/Electrical_impedance</a><p>...<p>Related:<p><a href="https://en.wikipedia.org/wiki/Frequency_selective_surface" rel="nofollow">https://en.wikipedia.org/wiki/Frequency_selective_surface</a><p>Frequency Selective Surfaces: A Review:<p><a href="https://www.mdpi.com/2076-3417/8/9/1689" rel="nofollow">https://www.mdpi.com/2076-3417/8/9/1689</a><p>Google image search, "Frequency Selective Surface":<p><a href="https://www.google.com/search?q=frequency+selective+surface&udm=2" rel="nofollow">https://www.google.com/search?q=frequency+selective+surface&...</a><p>"Frequency Selective Surface" books:<p><a href="https://www.amazon.com/s?k=frequency+selective+surface" rel="nofollow">https://www.amazon.com/s?k=frequency+selective+surface</a>