Please make me understand this as I’ve been trying to figure it out and it’s been bugging me so much!!
In: Physics
TL DR: Tiny wavelengths such as gamma pass between atoms, Massive wave lengths such as radio diffract between large objects such as houses. Stuff like UV, Light and those around 5G frequency can’t pass.
Because frequency times wavelength is a constant. Or in other words, as frequency goes up, wavelength goes down.
As wavelength changes, it will be more affected by certain mediums and less by others. I guess a generic wall has a construction that particularly affects waves in the 5GHz frequency.
Lower energy means more penetration power, because it is less likely to be absorbed by anything other than an antenna tuned to that frequency. This is the reason why the military used to use ELF (extremely low frequency) radio antennas to communicate with submarines many hundreds or even thousands of miles away. I’m actually not sure if they still do but I know they used to
There is no general trend that high frequency (which is also short wavelength and high energy per photon/light particle) penetrates any less or more than lower frequency (which is also long wavelength and low energy per photon). Your assumption is wrong, and if you consider visible light this can be seen quite easy. Essentially zero visible light will go through dry wall, even a millimeter of it. Depsite it being vastly more energy per photon than either type of wifi.
For electromagnetic radiation / light / radio waves to not go through something, it requires that it is either be absorbed or reflected. To be absorbed or reflected, it needs to first actually collide with the material. And secondly, actually interact with the material. Interact meaning either exciting something (being absorbed, making heat) or having the material respond to push it back (reflection).
To start, what are the actual odds of a collision. This is sometimes called cross section in some physics, as the cross sectional area relates to the odds of a collision. Take your microwave door for example. The short wavelength (a few hundred nanometers) visible light goes through with maybe 70%. The other 30% collides with the grid. It’s got decent odds if going through without even interacting. The long wavelength (a few centimetres) 2.4 GHz microwaves (same as your wifi) however is bounced right back. Why? It’s wavelength is to long, it interacts with the small grid in all cases.
You may think high energy photons penetrate materials well, and they sometimes do. See gamma rays. However, these wavelengths are so small the atoms begin to look like your microwave screen door to them. They can mostly pass by without striking any of them. But that takes very high energy. This does not apply at all to radio waves, nor even infrared, visible light, and UV. Visible light starts to see this with microscopic particles though, see fog. Small drops of water let most of the visible light by simply because it misses them, much like gamma rays to a solid object. But eventually they strike, so it goes from transparent, to translucent (scattered lights through), to opaque depending on how thick.
Also works the other way, if the wave is really long wavelength, it will simply go around small objects by diffraction. If a ocean wave hits a wall, it will crash into it. If it hits a pole, it will calmly pass right by. Long AM radio wavelengths will simply bend around most human scale objects, and even bend with the curvature of the earth going over the horizon. But the time your reach higher frequency FM, this stops and the stations have a lot less range. If you held up your microwave oven door in front of your radio, it will still get a perfectly clean signal. It’s not going through the door, it’s going around it. It doesn’t need exact line of site to the tower.
Now, there’s clearly more to this. Glass is a solid, yet visible light goes through. In fact, UV and IR on either side of visible light don’t go through your standard glass window. Visible light definitely isn’t missing the glass atoms. Glass simply has nothing available to be excited by visible light. If the energy of a visible light photon doesn’t correspond to some atomic motion in the glass, it can’t do anything. It needs to move an electron up an orbital, move some electrons around, vibrate some atoms, spins some molecules, etc. If the energy of these atomic scale motions don’t match the photon energy, the light won’t do anything. These random atomic motions are heat, and if the light can’t trigger them, it can’t be absorbed and make heat. Light will pass right by glass for the most part. Although you’ll note a little minor reflection, and of course a little refraction (bending). This is because the light will temporarily distort the atom’s shape slightly in a non absorbing way as it passes by. This doesn’t excite them leaving heat, it just distorts the light a little. On the other hand, IR and UV happily match some atomic scale motion in glass however, and they get absorbed. Dry wall will happily match some atomic scale motion in visible light, so it gets absorbed pretty much instantly.
Metals conduct electricity, and this makes them reflect everything up to UV. From the longest radio waves the visible light, the electrons will move in direct response to the light, create an opposing wave, and cause a reflection. This is why metals are shinny. Polished at least, if they are rough things bounce every which way. Well, at least for visible light. Radio waves are too large to care about small roughness bumps.
So to the wall. Why does 2.4 GHz penetrate better? Both have centimetre scale wavelengths. Neither is going between the atoms. Neither is going around the whole house with diffraction. They simply don’t interact with drywall very well (very different if the wall was metal) and pass by without fully being absorbed or reflected. Some of it is absorbed and reflected however, the 2.4 GHz a little less so with more passing through. This is the general trend for microwaves with a lot of common materials.
There’s also a lot more in play with the signal quality between the two, from interference, overlapping channels, multiple paths to the same destination with delay from reflections. It’s hard to say really if 2.4 or 5 will have better speeds in a given situation.
Higher energy doesn’t necessarily mean more penetration power. Look at visible light for instance, it is in the THz range, but it has pretty crappy penetrative power.
When talking about radio waves, the lower the frequency, the higher the range. That is why 2.4 ghz has higher range but 5 ghz has lower range.
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