Ultrasound is a sound pressure with a frequency greater than the limit of human hearing. This limit varies from person to person, it is around 20 kilohertz in young adults. 20 kHz is a useful lower limit in describing ultrasound. The making of ultrasound is used in many different fields , a property also used by animals such as bats for hunting. The most well known application of ultrasound is its use in sonography to produce pictures of foetuses in the woman's womb. Ultrasound is also used for more as well. It is a fact that children can hear some high-pitched sounds that older adults cannot hear, because in humans the highest limit pitch of hearing tends to become lower with age. A mobile phone company has used this to create ring signals supposedly only able to be heard by younger humans; but many older people are able to hear it, this is probably due to the variation of age-related deterioration in the upper hearing. Some animals e.g. dogs, cats, dolphins, bats, and mice — have an upper frequency limit that is greater than the human ear and can hear ultrasound. This is how a dog whistle works.
Ultrasound imaging or sonography, involves exposing part of the body to high-frequency sound waves to produce pictures of the inside of the body. ultrasound images are captured in real-time, they can show the structure and movement of the body's internal organs, as well as blood flowing through blood vessels. Ultrasound imaging helps physicians diagnose and treat medical conditions. Ultrasound is a useful way of examining many of the body's internal organs
This Picture is using Sonography to look at the kidneys.