Diffraction is a curvature effect in the propagation of electromagnetic and acoustic waves. Diffraction causes a deviation from the straight-line propagation of electromagnetic waves and occurs at obstacles, mountains or buildings. However, it can also be a slit or a grating through which the electromagnetic and acoustic waves are diffracted.
- Electromagnetic waves of certain frequencies are subject to diffraction just like light waves. In the case of electromagnetic waves, this effect is known from long waves that bend to the curvature of the earth. According to Huygens' principle (1690), each mass particle seized by a wave motion becomes the starting point of a new spherical wave. Their superposition( interference) results either in the normal rectilinear wave propagation or behind an opening or an obstacle in the appearance of diffraction.
- The effect of diffraction also exists in acoustics, but like reflection, it is strongly frequency dependent. Diffraction of a sound wave, where the sound is not completely shadowed by an obstacle, depends very much on the size and nature of the body causing the diffraction. Diffraction occurs only when the size of the body is not several times larger than the wavelength of the sound frequency. In this case, the sound waves are bent towards the body. Since sound waves have wavelengths between 17 m at 20 Hz and 1.7 cm at 20 kHz, the obstacles must be in this order of magnitude. relation to the wavelength, the stronger the diffraction, which is shown by the fact that the sound waves form a semicircle behind the opening.