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Heinrich Hertz – a spark that made history

2021-02-22

Heinrich Hertz

Heinrich Hertz was born on 22 February 1857 in Hamburg. Although he began his education in his hometown, later on he continued his studies throughout the country, at universities that could offer him the best conditions to develop his interests. He first moved to Frankfurt for an internship, and then to Dresden. Hertz also studied in Munich, until he finally found his way to the University of Berlin, where in just a few months he finished his doctoral dissertation and became assistant to Hermann von Helmholtz. Over the years, Hertz also developed a research career in Cologne and Karlsruhe, at the famous Karlsruher Institut für Technologie.

Helmholtz had high hopes for the talented young physicist, believing that with Hertz's help, he could refute James Clerk Maxwell's theory of electromagnetism, which contradicted Helmholtz's own hypotheses. Contrary to these expectations, during his research Hertz experimentally demonstrated the validity of Maxwell's equations. This occurred inadvertently during experiments with Riess spirals. During the research, a spark appeared in a Leiden bottle which was not connected to the spirals. It was clear to the scientist that this had to be a reaction to some then-unknown phenomenon. After this observation, Hertz began intensive research, during which he used devices of his own construction, such as an oscillator and an impulse generator. His research proved the existence and investigated the nature of electromagnetic waves and resulted in the discovery of radio waves. The experiments proved, among other things, that these waves can be refracted or reflected, which in the future contributed to the development of radio and radar techniques. Interestingly, Hertz did not anticipate any practical application of his research and did not realise the significance of his discoveries. He also did not have the opportunity to find out about them, as he died prematurely due to a serious illness.

 Diagram of Hertz's experimental system Diagram of Hertz's experimental system: Rühmkorff coil and a dipole antenna made of two electric wires (12m) with a spark gap between them (7.5mm). The free ends of the dipole wires are connected to 30 cm diameter zinc balls. A metal ring serves as a receiver antenna.

However, the brilliant German physicist has not been forgotten by the world of science. His research was followed, among others, by Oliver Lodge, who based on it as he constructed his coherer. This in turn was used by Marconi to build the first working radio. The photoelectric effect, first noticed and described by Hertz, was explained by Albert Einstein, for which he was awarded the Nobel Prize. Photovoltaic panels and various photoelectric elements owe their widespread popularity thanks to this very discovery. The Nobel Prize was also awarded to Philipp Lenard, Hertz's assistant, who continued his research on cathode rays, which in the future led to the development of medicine and the invention of the X-ray machine.

The German physicist has been commemorated in a number of ways. For example, hertz is the SI unit of frequency. Moreover, a lunar impact crater located on the far side of the Moon is named after him. He also appeared on postage stamps a number of times, e.g. in Germany, San Marino, Czechoslovakia and Mexico. Moreover, Hertz is the patron of numerous schools and scientific institutions.

Today, the echoes of Heinrich Hertz's achievement can be found in many areas of electronics. His work was a cornerstone of the era of wireless communication, the benefits of which we now enjoy on a daily basis. Of course, nowadays radio waves are used mainly to transmit digital data, but the very principle of operation of transmitting and receiving devices remains closely related to the experiments of the German scientist. The most obvious examples seem to be devices using GSM, WIFI and Bluetooth communication, which include mobile phones as well as miniature computers or even building automation components.

However, Hertz's achievements have influenced modern electronics to a much greater extent. GPS signal transmission is worth mentioning here. This system, known to every driver and traveller, thanks to easily available modules, can be used not only in professional projects but also in amateur ones. The same applies to RFID technology, whose operation is comparable to the solutions used in contactless payments. Other universal RF communication modules are currently mass produced and deployed in thousands of applications, from wireless switches to complex control systems. Yet, all of these applications seem quite “niche” when compared to consumer electronics, used by billions of people every day.

Radio transmission methods have required years of improvements and have undergone significant evolution and (along with all electronics) miniaturisation. Over the decades, many types of antennas specialised for narrow applications have been developed. Nowadays, their size sometimes happens to be so tiny that they are almost invisible. Yet, the dipole that Hertz used for his research and demonstration remains a widely applied solution, as well as a model example of an antenna. Cable TV or even satellite installations commonly use coaxial cables with 75Ω impedance. This value is not accidental, because it is an approximate impedance of a simple half-wave dipole. Perhaps this single figure will best make us aware of how modern technologies are closely related to the work of Heinrich Hertz.

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