Heinrich Hertz: Building the Foundation for Modern RF Understanding
Heinrich Hertz is credited for his work with electromagnetic radiation, expanding on the works of others, and having the unit of frequency named after him, but how did he get there?
There are many laws and terms in the EE world that directly relate to the people who founded the idea, term, or discovery. One term that appears rather frequently is that of hertz. We know of hertz the unit, but what about the man behind the discovery?
Portrait of Heinrich Hertz. Image used courtesy of the Library of Congress
A famed German physicist and mathematician, Heinrich Rudolf Hertz is credited with the discovery of radio waves—building on James Clerk Maxwell’s revelations on electromagnetic radiation. Equating these energetic waves with light itself, Hertz paved the way for our modern RF understanding. How did he get there?
Early Days and Education
Heinrich Hertz was born in Hamburg, Germany, on February 22nd, 1857. The oldest of five children, he began his educational journey at six years old––spurred onward by his mother, who insisted that he be at the top of his class.
With this push, Hertz excelled while attending Richard Lange's school. Lange himself was a gifted scientist and watchmaker who passed his obsession for precision to his students. His woodworking skills, drawing, and foreign languages soon shone brightly with that teaching instilled within him. He also enjoyed Arabic and technical sketching, in particular, which he studied alongside his formal coursework.
Accordingly, his education was incredibly well-rounded given his age. Since he showed talent and interest in so many areas, he found it difficult to settle. Choosing a university field of study was challenging.
Art and music didn't seem feasible; while the natural sciences were a passion of his, it meant abandoning the practical field of engineering.
Hertz thus pursued the latter—moving to Frankfurt shortly after taking his Abitur examinations in early 1875, where he eventually secured a position in the building industry. In the following year, he dove head-first into his engineering work.
Transitioning to University
Though from an academic background, he struggled with the university's environment and isolation. His experiences helped form his opinion that private study—in comparison to public research—was selfish and unfulfilling.
With the sunk-cost fallacy weighing heavily on his mind, he pressed onward with engineering. This progression kicked off a brief stint at Dresden Polytechnic, followed by a year of military service and continued coursework at Munich's Technische Hochschule.
Hertz's university days proved beyond all doubt that engineering wasn't his calling. Engineering seemed mundane, soulless, and decidedly ordinary. However, his invigorated love for mathematics was a silver lining.
With his father's blessing (and financial backing), he enrolled at the University of Munich and worked towards a research career. It was here where his scholarly mindset flourished alongside his investigative nature. He eagerly branched out and studied numerous topics while honing his mathematical skills in 1877.
Hertz embarked on research into electrical inertia, solving a practical problem and winning the 1879 Philosophy Faculty Prize for his efforts.
After declining a prolonged prize study into Maxwell's theoretical assumptions, he penned On Induction in Revolving Balls, which focused on electromagnetic induction related to magnetic fields. The work explored how a circular disk, turning about its axis of symmetry, behaved within magnetic fields.
Hertz used an alternating-current resistor-inductor-capacitor (RLC) circuit. Image used courtesy of cnxuniphysics and BCcampus
This work became his 1880 doctorate submission and took only three months to complete. He then earned his Ph.D. with distinction from the University of Berlin after passing his oral exams.
Research Career and Notable Accomplishments
Upon becoming Helmholtz's assistant at the Berlin Physical Institute, Hertz began publishing a flurry of 15 papers on assorted topics. He tackled electricity, cathode rays, and new instrumentation.
From 1880 to 1883, Hertz gradually turned away from private lecturing and embraced the burgeoning field of mathematical physics. He set up shop at the University of Kiel—writing three papers on meteorology, electromagnetic units, and the theoretical particulars of Maxwell's findings.
He later returned to Technische Hochschule as a professor in 1885—which would later host his most critical discoveries. In November of 1886, he circled back and took a deep dive into Maxwell's theories.
He was challenged to generate and detect electromagnetic radiation via an instrument, which required a transmitter. It was his job to design and test this apparatus.
A recreation of Hertz's experiment. Image used courtesy of Prerna Gupta and Lesics
This apparatus featured three primary components:
- A high-voltage induction coil
- A condenser, comprised of a capacitor and a Leyden jar
- A spark gap, flanked by small spheres of opposite polarity
Hertz fashioned an experimental circuit using a thin, circular piece of copper wire, a brass sphere, and a pointed wire end. A screw mechanism ensured that the wire could approach the brass sphere very closely.
With the spark gap paired with the copper receiver, the transmitter's goal was to determine how closely the electrical current's oscillation period matched the transmitter's. Sparks traversed the tiny gap between sphere and wire point, thus confirming the presence of electromagnetism.
After that, he discovered that the velocity of this radiation equaled that of light. Its reflection and refraction properties were also identical.
Consequently, the light was a form of electromagnetic radiation—putting to bed a decade's-long debate in the scientific community. The one-cycle-per-second unit of electromagnetic frequency became known as the "hertz," in his honor. These key findings unlocked Marconi's invention of the radio and the birth of the wireless telegraph.
An adjacent discovery was the photoelectric effect—where a material emits electrically charged particles after absorbing electromagnetic radiation. Hertz showed in 1887 that light changes sparking voltages upon hitting two charged metal electrodes. This change in voltage influenced several additional experiments. Ultimately, scientists learned the relationship between electron kinetic energy and the frequency of light waves.
Today, Hertz's findings and those of his successors are applied across many fields. Electrical engineering, physics, and others have significantly benefitted from his inventions and equations on contact mechanics.
Accordingly, he left behind such an unfathomable legacy recognized far and wide. Though he passed in 1894, Heinrich Hertz remains a cornerstone figure to this day, with his teachings becoming the foundations of past, present, and future educations.