It is an acoustic wave or sound wave whose frequency is below the audible spectrum of the human ear (approximately 20 Hz).
Infrasound is used by large animals such as the elephant to communicate over long distances (sounds from 100 to a few kilometers from the course) without any problem. The key that these animals can hear at these distances is the separation of their ears, as this is directly proportional to the frequency of the waves they can catch (as opposed to small-headed animals). Recently, elephants have been shown to record infrasound not only with their ears, but also to feel the vibrations produced by themselves from their legs, as their nails act as conductors for low-frequency sounds.
Infrasound is an advantage of various animals, especially larger ones, such as elephants, who use it to communicate over long distances.
The ability to hear at enormous distances is plausible thanks to the size of their heads and the separation of their ears, which is directly proportional to the frequency they can pick up. It is worth noting that elephants even manage to catch the infrasound when they perceive the vibrations that they produce with the movements of their legs, since their nails act as conductive sensors of sounds that have a low frequency.
The main application of infrasound is object detection. This is done due to the poor absorption of these waves in the medium, unlike ultrasound, as we will see. For example, a 10 Hz plane wave is absorbed four times less than a 1000 Hz wave in water.
The disadvantage is that the objects to be detected must be quite large since, at such frequencies, the wavelength is very large, which limits the minimum diameter of the object. As an example, we will say that a 10 Hz infrasound has a wavelength of 34 m in air, then the objects to be detected must have a minimum size of the order of 20 m in air and 100 m in water.
A curiosity regarding infrasound is that the human body is also capable of producing this type of sound through the movement of the muscles, sliding one over the other, through the ears and even the heart.
