Wednesday, February 22, 2012

Hz

Today Google reminded us of the importance of Heinrich Rudolf Hertz. Today was his 155th Birthday. Hertz (Hz) are defined in the International System of Units (SI)  as a frequency measured as the number of cycles per second of a periodic phenomenon. They are named, for Heinrich Rudolf Hertz...



Despite all the times I've written about past developments in radio and electromagnetic research, and made a reference to Hertz, I've never written of Hertz directly, and that's a damn shame. Today I correct that oversight.

He came from a family of means and attended private school and in 1875 at the age of 18 he decided to pursue engineering. He backed out within a year and left Dresden Polytechnic to join the military. He returned and then enrolled in the University of Munich with a more research focused path. A Professor Hermann Helmholtz took an interest in hertz and steered him toward physics. His doctorate thesis was "Über die Induction in rotirenden Kugeln" a paper on electromagnetic induction. Upon graduation in 1880 he became an assistant to Helmholtz. More here.

In 1885 Hertz became a professor at Karlsruhe Institute of Technology. It was there that he made real history. He did an experiment that related back to his doctorate. He used an open circuit to demonstrate to his students a condenser discharge. This was a simple spark gap circuit with a single coil a battery and a Leyden jar (an early capacitor). While opening and closing the circuit to make sparks he found that A nearby loop responded to the action with it's own sympathetic sparks across an air gap. This was a primitive spark gap transmitter and a very simple proof of the reception of that signal. He is widely believed to be the first person to send and receive radio waves. More here.

In 1873  James Clerk Maxwell's had theorizedan equivalence between light and electromagnetic propagation. Hertz made that connection, proving that electromagnetic waves could be transmitted and received as waves. He was just 28 years old. His findings were first published in the journal Annalen der Physik in 1887. He died of vasculitis at the age of 36 in 1894, the same year Marconi finally began his own experiments.