Heinrich BarkhausenBorn 2 Dec 1881; died 20 Feb 1956 at age 74.Heinrich Georg Barkhausen was a German physicist who discovered the Barkhausen effect (1919), a principle concerning changes in the magnetic properties of metal. His work in acoustics and magnetism led to the discovery that magnetization affects whole domains of a ferromagnetic material, rather than individual atoms alone. He discovered that a slow, smooth increase of a magnetic field applied to a piece of ferromagnetic material, such as iron, causes it to become magnetized, not continuously but in minute steps. With Karl Kurz, he developed the Barkhausen- Kurz oscillator (1920) for ultrahigh frequencies (forerunner of the microwave tube), leading to understanding of the principle of velocity modulation. He is also known for experiments on shortwave radio transmissions.