What is Difference Between Ultrasonics and Infrasonic

Ultrasonics:
The study of sound aves with high frequencies beyond the upper limit of human hearing or 20 thousand Hz. This technique is employed to locate a tumour, to scan a pregnant woman’s abdomen in order to produce a picture of foetus or to treat certain neurotically disorders.

Infrasonic:

These are the sound waves which have the frequencies lowest than the lowest limits of human hearing or 20 Hz.