Infrared is an electromagnetic wave at nearly Light wave,
electromagnetic wave propagation characteristics with relevant wavelength, In generally long wavelengthtransfer above the ground. medium wave along the surface of the earth, shortwave is reflected by the ionosphere propagation, ultra short wave(FM) and microwave are sight propagation.Rectilinear propagation,lights will be totally reflected when encounter an obstacle, so the infrared communication Similar visible light is unable to penetrate the specifically obstacles, but the glass and the transparent barrier is unaffected,Impedance of red glass blocked is also very small.Let me summarize just by saying that frequency ever more low, diffraction capability of longer wavelength is strong,when attenuation is low; the frequency ever more high, the shorter the wavelength penetration ability ever more strong, may make a higher the attenuation easier.