After our last blog entry, “5 Things to Know About Pulse Power” in which we covered some of the origins of pulse power, I received some feedback from the corner office. Our CEO brought up a few interesting history lessons on the subject that I thought would be worth exploring a little further in regard to the history of pulse power.
If we really want to get down to the origins of scientifically exploring a pulsed discharge, one could argue that Ben Franklin was the first, since he “captured” lightning. In fact, lightning is in essence a form of pulse power as it is a high-energy capacitive discharge, with charges separated between the clouds and ground. In fact, the lightning “pulse” is thoroughly characterized by multiple standards, including MIL-STD-464C, which we partially covered in our blog “INCREASED EMP THREATS LEAD TO CHANGING TESTING STANDARDS- Part 2: Understanding the Standards”, but neglected to mention lightning.
However, most give credit to Heinrich Hertz as a progenitor of pulse power, given his demonstration of electromagnetic waves using spark gaps. This experiment was done to essentially prove the correctness of Maxwell’s equations and happened all the way back in 1887! Hertz utilized an induction coil and Leyden Jar (the first capacitor) to generate electromagnetic waves via a dipole antenna and used a spark gap between two brass spheres to detect them.
Figure 1 Heinrick Hertz’s radio transmitting and recieving apparatus (Source: Wikipedia)
Coincidentally, Hertz’s original transmitting apparatus is not so different than APELC’s RF Suitcase system, which similarly uses a pulse-charged capacitance discharged through a spark gap into a dipole antenna. While things like power supplies, capacitors and insulating materials have become much more advanced in the last hundred years, the basis technology for much of pulse power has remained fairly similar.
Figure 2 APELC’s RFSC-400 RF Suitcase System
The invention of RADAR in 1940 essentially helped the Allies win WWII, and kicked off the development of pulse power as we know it today. In 1939, John Randall and Henry Boot, physicists at the University of Birmingham, in England, began work on design of the magnetron as a means of detecting aircraft and protecting Britain from German bombers. While there was a prior RADAR system, it used lower frequencies and was ground-based- making it unpractical for detecting most aircraft. The magnetron brought the ability to generate 10cm wavelengths that could detect much smaller objects. Moreover, the relatively compact size of the magnetron meant that the source could be deployed on both planes and ships. The British sent the device over to the MIT Radiation Lab to share the technology with the US in hopes of further development to win the war effort.
Figure 3 The Cavity Magnetron (Source: IEEE Spectrum)
The work done at MIT also heralded the design of more mature pulsed systems to drive these radars. The work from the MIT lab can now be found in the MIT Rad Lab book series dating from about 1948. Volume 5 of this series is called “Pulse Generators” and is thought to be the real start of modern pulse power. This work was the electrical genesis of things like Pulse Forming Networks (PFNs) and high-power electron-tube switches such as the thyratron, which APELC and others still use today.
- Glasoe, G. Norris, and Jean Victor Lebacqz. “Pulse generators.” (No Title)(1948).