I wanted to learn more about Faraday cages and one thing that caught my attention is the relationship between the wave frequency and the hole in the cage. Why is that the higher the frequency of the wave the smaller the holes it can penetrate? The frequency is supposed to correlate the number waves and time so how does this all fit together?
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2 Answers
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The size of any holes need to be significantly smaller than the wavelength of light you want to block.
If you go to high enough frequencies then the wavelength becomes small enough for the waves to diffract through your cage.
If you look at What is the relationship between Faraday cage mesh size and attenuation of cell phone reception signals? you will see that, for a rectangular mesh, the critical thing is that the mesh width should be smaller than $\lambda/2$. Below this, the signal amplitude will be attenuated exponentially, on a length of $\sim \lambda/2\pi$, so ideally your mesh would be thicker than this.
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$\begingroup$ would covering the holes with aluminum foil solve the problem? $\endgroup$– TreyCommented Apr 24, 2020 at 18:18
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$\begingroup$ Yes. Aluminium is highly reflective and also attenuates any electromagnetic radiation that penetrates the surface. @Trey $\endgroup$– ProfRobCommented Apr 24, 2020 at 18:20
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$\begingroup$ is there a way to calculate the size of the hole based on the frequency of the wave? $\endgroup$– TreyCommented Apr 24, 2020 at 18:21
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1$\begingroup$ The optimum hole size depends on the compromise you seek between screening effect and accessibility through the holes. The thickness and electrical and magnetic properties of the material you make the holes through are also significant. Aluminum foil is a cost-effective screen but it is not a high-quality one. It gets complicated. As a rule of thumb, a hole size of less than one-tenth of the wavelength is a good starting point. $\endgroup$ Commented Apr 24, 2020 at 21:01
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microwave ovens work at a wavelength of about 10 cm. If you measure the hole diameters in the screen that sits in front of the window in the door of the oven, you'll have your answer.
answered Apr 24, 2020 at 20:17
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1$\begingroup$ The holes in microwave doors are made so small as much for visibility as anything. Bigger holed would mean bigger areas of metal in between, which would obscure the food inside. $\endgroup$ Commented Apr 24, 2020 at 20:54