Heinrich Rudolf Hertz (22 February 1857 – 1 January 1894) was a German physicist who clarified and expanded James Clerk Maxwell's electromagnetic theory of light, which was first demonstrated by David Edward Hughes using non-rigorous trial and error procedures. Hertz is distinguished from Maxwell and Hughes because he was the first to conclusively prove the existence of electromagnetic waves by engineering instruments to transmit and receive radio pulses using experimental procedures that ruled out all other known wireless phenomena. The scientific unit of frequency – cycles per second – was named the "hertz" in his honor.
He was born in 1857 in Hamburg, then a sovereign state of the German Confederation, into a prosperous and cultured Hanseatic family. His father Gustav Ferdinand Hertz (de) (originally named David Gustav Hertz) (1827–1914) was a barrister and later a senator. His mother was Anna Elisabeth Pfefferkorn. While studying at the Gelehrtenschule des Johanneums in Hamburg, Heinrich Rudolf Hertz showed an aptitude for sciences as well as languages, learning Arabic and Sanskrit. He studied sciences and engineering in the German cities of Dresden, Munich and Berlin, where he studied under Gustav R. Kirchhoff and Hermann von Helmholtz.
In 1880, Hertz obtained his PhD from the University of Berlin, and remained for post-doctoral study under Hermann von Helmholtz. In 1883, Hertz took a post as a lecturer in theoretical physics at the University of Kiel. In 1885, Hertz became a full professor at the University of Karlsruhe, where he discovered electromagnetic waves.
The first successful radio transmission was made by David Edward Hughes in 1879, but it would not be conclusively proven to have been electromagnetic waves until the experiments of Hertz in 1886. For the Hertz radio wave transmitter, he used a high-voltage induction coil, a condenser (capacitor, Leyden jar) and a spark gap—whose poles on either side are formed by spheres of 2 cm radius—to cause a spark discharge between the spark gap’s poles oscillating at a frequency determined by the values of the capacitor and the induction coil.
To prove there really was radiation emitted, it had to be detected. Hertz used a piece of copper wire, 1 mm thick, bent into a circle of a diameter of 7.5 cm, with a small brass sphere on one end, and the other end of the wire was pointed, with the point near the sphere. He bought a screw mechanism so that the point could be moved very close to the sphere in a controlled fashion. This "receiver" was designed so that current oscillating back and forth in the wire would have a natural period close to that of the "transmitter" described above. The presence of oscillating charge in the receiver would be signaled by sparks across the (tiny) gap between the point and the sphere (typically, this gap was hundredths of a millimeter).
In more advanced experiments, Hertz measured the velocity of electromagnetic radiation and found it to be the same as light’s velocity. He also showed that the nature of radio waves’ reflection and refraction was the same as those of light and established beyond any doubt that light is a form of electromagnetic radiation obeying the Maxwell equations. Hertz's experiments triggered broad interest in radio research that eventually produced commercially successful wireless telegraph, audio radio, and later television. In 1930 the International Electrotechnical Commission (IEC) honored Hertz by naming the unit of frequency—one cycle per second—the "hertz"
In 1886, Hertz developed the Hertz antenna receiver. This is a set of terminals which is not electrically grounded for its operation. He also developed a transmitting type of dipole antenna, which was a center-fed driven element for transmitting UHF radio waves. These antennas are the simplest practical antennas from a theoretical point of view.
In 1887, Hertz experimented with radio waves in his laboratory. Hertz altered Maxwell's equations to take this view into account for electromagnetism. Hertz published his work in a book titled: Electric waves: being researches on the propagation of electric action with finite velocity through space. Through experimentation, he proved that transverse free space electromagnetic waves can travel over some distance, as predicted by James Clerk Maxwell and Michael Faraday. He found that radio waves could be transmitted through different types of materials, and were reflected by others, leading in the distant future to radar.
Hertz helped establish the photoelectric effect (which was later explained by Albert Einstein) when he noticed that a charged object loses its charge more readily when illuminated by ultraviolet light. His discoveries would later be more fully understood by others and be part of the new "wireless age". In bulk, Hertz's experiments explain reflection, refraction, polarization, interference, and velocity of electric waves.
In 1892, Hertz began experimenting and demonstrated that cathode rays could penetrate very thin metal foil (such as aluminium). He postulated a dispersion theory before Röntgen made his discovery and announcement.
In 1892, an infection was diagnosed (after a bout of severe migraines) and Hertz underwent some operations to correct the illness. He died of Wegener's granulomatosis at the age of 36 in Bonn, Germany in 1894, and was buried in the main Protestant Ohlsdorf Cemetery in Hamburg.
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