How do signals go through solid objects?

Question

So many types of signals pass, or seem to pass I don't know, through solid objects. How do they do this?

Answer 1

Your question is really broad. As correctly pointed out by @John Rennie there can be so many signals that can pass from the solids. It must be noted that even if the signal can pass through solid it will experience certain losses.

Mechanical waves such as sound took advantage of elasticity of the material. The sound oscillations are transferred through metal. The reason behind this effect is that the frequency of the sound waves is too small and the atoms can oscillate during this time to effectively couple the waves from one portion to another.

For the case of electromagnetic radiation the radiation may pass from a medium if it do not get absorbed or it do not get scattered by the medium.

Usually the electromagnetic radiation feels a high degree of absorption in metallic objects due to the presence of free electrons. Free electrons oscillate in light wave and collide with neighboring atoms/ions thereby absorbing the light efficiently in metal. Some energy is also reflected back as these electrons also radiate at same frequency when they oscillate. This effect is much smaller for x rays and gamma rays as their frequency is much higher and the electrons could not respond at such high frequency. In this frequency range the photoelectric effect, Compton effect and then pair production start to take over (as we go towards higher frequency i.e. higher energy radiation). These effect start to absorb the energy of the electromagnetic radiation within the material. However the transparency of materials is generally increased for higher energy electromagnetic radiation (in x ray and gamma ray regime).

Now come to insulators. Lower frequency radio waves can pass from solid walls as wall do not have substantial free electrons which can absorb the radio waves and radio wave photons are too weak to ionize the bound electrons. A detailed discussion centered on visible light is given here. The bricks have size much smaller than the wavelength of the radio waves hence the radio waves do not see bricks as separate entities. However for light the wall appears as a dielectric medium but with too many boundaries hence it get scattered very easily from the wall.

For the case of optical transmission such as in glass the light is propagated through it for the reason explained above but the glass has no boundaries/grains inside. However, the light can be scattered from crushed ice and broken glass and hence the material become translucent.

Now comes the transmission of heat. Some information about the system is also transmitted by heat. Heat is also transmitted by the electron energy transfer and mostly the heat conductivity follows the electrical conductivity (however diamond is an exception).

I hope you will get some answer to your query.