Heinrich Hertz and the Transmission of Electromagnetic Waves

Heinrich Hertz (1857 – 1894)

Heinrich Hertz (18571894)

On November 13, 1886, German physicist Heinrich Hertz succeeded to transmit electromagnetic waves from a sender to a receiver in KarlsruheHertz conclusively proved the existence of the electromagnetic waves theorized by James Clerk Maxwell’s electromagnetic theory of light. The unit of frequencycycle per second – was named the “hertz” in his honor.

Heinrich Hertz studied science and engineering in Dresden, Munich, and Berlin under Gustav R. Kirchhoff and Hermann von Helmholtz. At the University of Berlin Hertz earned his PhD and in 1883 he became lecturer in theoretical physics at the University of Kiel. Two years later, Hertz was appointed full professor at the University of Karlsruhe.

In Karlsruhe, Hertz experimented with Riess spirals and he noticed that discharging a Leyden jar into one of these coils would produce a spark in the other coil. The scientist came up with an idea to build an apparatus and intended to prove Maxwell’s theory. Hertz used a Ruhmkorff coil-driven spark gap and one-meter wire pair as a radiator. Capacity spheres were present at the ends for circuit resonance adjustments. His receiver was a simple half-wave dipole antenna with a micrometer spark gap between the elements. This experiment produced and received what are now called radio waves in the very high frequency range.

The first spark gap oscillator built by Heinrich Hertz around 1886

The first spark gap oscillator built by Heinrich Hertz around 1886

The scientist proceded to conduct a series of experiments between 1886 and 1889, which would prove the effects he was observing were results of Maxwell’s predicted electromagnetic waves. He further discussed his results in his paper On Electromagnetic Effects Produced by Electrical Disturbances in Insulators. Heinrich Hertz sent a series of papers to Helmholtz at the Berlin Academy, including papers in 1888 that showed transverse free space electromagnetic waves traveling at a finite speed over a distance. In his device, the electric and magnetic fields would radiate away from the wires as transverse waves. Hertz had positioned the oscillator about 12 meters from a zinc reflecting plate to produce standing waves. Each wave was about 4 meters long. Using the ring detector, he recorded how the wave’s magnitude and component direction varied. Hertz measured Maxwell’s waves and demonstrated that the velocity of these waves was equal to the velocity of light. He further measured the the electric field intensity, polarity and reflection of the waves. These experiments established that light and these waves were both a form of electromagnetic radiation obeying the Maxwell equations.

His proof of thee xistence of airborne electromagnetic waves led to an explosion of experimentation with this new form of electromagnetic radiation, which was called “Hertzian waves” until around 1910 when the term “radio waves” became current.  Researchers like Oliver Lodge, Ferdinand Braun, and Guglielmo Marconi employed radio waves in the first wireless telegraphy radio communication systems, leading to radio broadcasting, and later television.

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