The evolution of the magnetron — a device for generating microwave radiation — from World War II radar systems to the household microwave ovens illustrates how engineers think about “best.”

Learn More: Companion Book
Explore the ideas in this video series further with its companion book: The Things We Make: The Unknown History of Invention from Cathedrals to Soda Cans (ISBN 978-1728215754)
https://www.amazon.com/Things-We-Make...

Other videos in this series
Episode 1: Building a Cathedral without Science or Mathematics: The Engineering Method Explained    • Building a Cathedral without Science ...  
Episode 2: Controlling Turbulence and Evolution: How Engineers Overcome Uncertainty forthcoming    • Controlling Turbulence and Evolution:...  
Episode 3: The Steam Turbine: The Surprising Relationship of Engineering & Science forthcoming    • The Steam Turbine: The Surprising Rel...  

0:00 Titles

0:07 Engineering Notion of “Best”
The video opens by contrasting an absolute notion of “best” — the Renaissance ideal of da Vinici’s Vitruvian man — with an engineering relative notion as illustrated by the work of industrial designer Henry Dreyfuss, who developed drawings of ordinary people with their far-from-ideal proportions. Dreyfuss’s approach demonstrates that an engineering solution can only be judged based on how it handles the constraints unique to its situation — a balance of cultural forces, societal values, availability of material resources, and even urgency. This means that the notion of best changes with time.

1:04 Cavity Magnetron
The cavity magnetron, which powers mobile radar, was created by British scientists in early 1940 in response to fears that Nazi planes would bomb London. This device generates microwave radiation of sufficient power and of the right frequency to detect individual planes.

2:09 First Notion of “Best”
The standard of “best” used by the physicist-engineers who developed this magnetron was simply that it worked — prior to this nothing had sufficient power. The device worked in the laboratory, but now it needed to be mass manufactured to equip thousands of British, American and other allies planes and ships with radar.

2:42 Second Notion of Best
To mass manufacture the magnetron the British turned to Raytheon and their vacuum tube engineer Percy spencer. For engineer spencer, the notion of best changed: now the issue was one of prioritizing speed of production while maintaining reliability.

3:00 Tolerance Central Problem
The slightest deviation in the cavity’s diameter along the length of the cylinder would change the frequency of the radiation and blur the results from the radar. The tolerance was exacting: The diameter of these cylindrical cavities must deviate by at most one ten-thousandth of an inch (about 2.54 microns).

3:36 spencer Magnetron Compared to Prototype
A World War II magnetron, likely used in the Pacific Theater, is compared to the laboratory prototype.

4:16 Laminations
Bill explains how engineer spencer used a time-honored engineering rule of thumb — break complex problems into smaller, more manageable pieces — by creating thin layers, called laminations, which, when assembled, construct a complete magnetron.

5:44 New Notion of Best for Microwave Oven
To reversion the magnetron for an oven the idea of best had to change. At first the goal was to replace the conventional oven and to cook fast.

6:06 1946 Microwave Oven
The first microwave oven, which appeared in 1946, was aimed at restaurants, which is a commercial, not a consumer, use.

6:57 New Notion of Best for Consumer Oven
To become a household item — a consumer oven — needed a new notion of best as seen in the ads of the first successful consumer oven. They now aimed for a standard 115 volt outlet and an oven that fit onto a kitchen counter and into a household budget.

7:27 Evolution of Oven Magnetron
A detailed discussion of the changes from the World War II magnetron to those used in the consumer oven.

9:48 Mythical Story of Microwave Oven Invention
Bill mentions a likely apocryphal story, from a popular magazine, of the oven’s invention after a candy bar melted in spencer’s pocket.

10:14 Problems with Mythical Story
Bill explains how simple stories like a melting candy bar obscure the engineering method and strips away all the richness of how engineers create.

10:47 Review of Video Series
Bill review the engineering creativity discussed in the previous videos in this series.

11:10 Why Understand the Engineering Method
Hiding that creativity dissuades our best and brightest from recognizing engineering as a supremely creative endeavor, which robs us of the next generation of mental firepower, the new wave of engineers, who can help solve the problems our world faces.

11:27 Contact info
Bill can be reached at [email protected] or at 217-689-1461 text/voice (use WhatsApp if outside US)

11:31 End Titles