Infrasounds .

can be used to view internal organs
are sounds with frequencies below 20 Hz
are sounds with frequencies above 20,000 Hz
travel in transverse waves

Infra sounds are sounds with frequencies below 20 Hz.The popular concept that infra sounds are in audible holds false

Explanation:

Some example of Infrasounds  are- some animals such as whales, elephants and giraffes which  communicate with each other  using infrasound over long distances. Various natural phenomenon such as Avalanches, volcanoes, earthquakes, ocean waves, water falls and meteors also generate infrasonic wavesInfrasound, is sound that is lower in frequency than 20 Hz or cycles per second.Even the human body can generate mechanical vibrations at very low frequencies, which are known as the  infrasonic waves. Such low-frequency vibrations/infrasonic waves  are produced by physiological processes—such as heartbeats, respiratory movements, blood flow in vessels, and other processes.