Brief History of Ultrasound

--  Natural: Bats, ...
--  Piezoelectric effect:
    Pierre Curie and Jacques Curie (1880)
--  Titanic sank in 1912:
    Underwater detection systems
--  WWI & II:
    SONAR (SOund Navigation And Ranging), Radar, ...
--  1930's: Metal flaw detectors in industry, ...
--  1940's: Medical applications, ...
--  More detail developments: