Ultrasound is a diagnostic imaging technology. It uses high-
frequency sound waves - well beyond the range of human hearing -
to produce pictures of the inside of the body. Ultrasound has
many medical uses, but it is associated with screening
pregnancies. This is because the technology is widely available
and does not endanger the developing foetus. Ultrasound scanners
use a hand-held device called a transducer to scan the body.
Crystals in the transducer send high-frequency sound waves into
the body and detect the returning echoes. This is called the
piezoelectric effect, which was discovered by Pierre Curie in
1880. A computer processes this information and produces a real-
time moving image of the inside of the body. During the Second
World War the Allies developed sonar technology to detect
underwater German U-boats. This relied on sound pitched within
the range of human hearing. After the war, sound detection
techniques were used for medical diagnosis and therapy. The
higher the frequency of the sound, the