Why is it that high frequency signals don’t pass through walls easily but you need a block of lead to block the radiation (for Gamma)?
In: Physics
There is no global all encompassing rule that high or low frequency pass through materials better. For example, “high frequency” visible light goes through some solid walls really easily. We call those walls windows. “Low frequency” radio waves are stopped by a thin sheet of aluminum foil.
There’s a variety of different ways that light can interact with matter. Moving free changes, rotating molecules, polarizing the material, exciting valence electrons between energy levels, ionizing electrons from valence to core, causing all sorts of qausi particles, interacting with the nucleus, etc. List goes on. Some of these methods work for low frequency, some work for high frequency, some work for both. Not all materials interact with light with all these methods, nor to the same strength, nor at the same frequencies. Basically saying materials are coloured, but to a much wider sense that the visible spectrum.
Additional, size comes into play. If the light is high frequency, low wavelength, it can be too small and miss and pass right by. Look at your microwave door. Visible light is small and has no issues going through the holes in the mesh. Some hits the mesh, some goes right through the holes. The mesh isn’t transparent to visible light, it’s size just has holes for it. The larger microwaves however can’t fit through the holes, the mesh blocks it all. On the hand, if the object is too small relative to the wavelength, the light can just bend right around it as if it wasn’t even there. If you look at an ocean wave, a pole (like for a dock) doesn’t leave a “shadow” where the wave is blocked. Pole is skinny, wavelength is large, the wave just bends right around it as soon agter passing it is as if the pole wasn’t even there.
Shape and structure also comes into it to. Antennas have very intentional shapes, so beyond material and size shape can help absorb too. If you look at water and ice, you’ll note they can be clear or white. Snow versus a nice ice cube. Still water versus a turbulent wave or a mist. They are always clear, but a bunch of small disorder causes too much random scattering and it ends up white and opaque rather than clear.
Lead shielding of x-rays and gamma rays basically comes down to this size issue. Basically, solid materials are your microwave mesh door to x-rays and gamma rays. The atoms will interact with them, they aren’t transparent to them. However, even a solid is far to full of holes. The rays are very small wavelength, so can miss the electrons of most solids. Similar to how visible light mostly passes through most all gasses uninhibited. Lead has a lot of electrons, and the atoms are bound tightly, so it’s basically just playing the odds and increasing the chance of a collision to absorb or scatter.
The “high frequency penetrates less” basically is just rough rule of thumb high frequency radiowaves and microwaves with some common materials and objects. Yes, it is true that your 5 GHz wifi does tend to penetrate your house walls less than your 2.4 GHz wifi giving it inferior range.
Gamma is so high frequency that it has a *really* short wavelength and *really* high energy per photon. The gamma wavelengths are less than the diameter of an atom, in a rough sense they can literally shoot through the empty space between atoms. That’s why you need big heavy nucleuses to stop them, like lead.
What we think of as “high frequency” signals, like WiFi, has a wavelength of several centimeters. Compared to gamma, or compared to atoms, it’s HUGE, and far lower energy per photon.
Low frequencies go through individual atoms because the waves are really big, and each atom doesn’t see the whole wave so it doesn’t know to reflect it. They *can* be reflected, but mostly only by conductive materials that allow the electrons to move large distances to affect the wave.
Medium frequencies bounce off the atoms and get reflected.
High frequencies go through the gaps between the atoms.
Latest Answers