George Mansbridge invented the metalized paper capacitor in 1900, and patented it in 1902. The design subsequently proved popular in telephone equipment, where compact size was a consideration. This was because it produced similar capacitance as foil-paper alternatives double that size. We don’t know much about the inventor, but his application is rich in detail.
Core Factors in George Mansbridge’s Patent Application
VARIOUS OPTIONS CONSIDERED
- Paper-tinfoil condensers (capacitors) are expensive and tricky to manufacture
- This proposal replaces many small parts with a single roll of two active materials
- However, the thin sheets of tinfoil available only come in strictly limited lengths
- Using a tin-lead alloy increases both the weight and the length of the product
GEORGE MANSBRIDGE’S METHOD
- There is no difficulty in obtaining a sheet of paper of the required length
- The solution lies in coating one side of the paper with finely-fragmented metal
- The paper then becomes the dielectric, while the coating becomes the plate
- Tinfoil paper is fairly suitable, and is available in large quantities cheaply
- The finely-fragmented version forms into a paste, before coating the paper
- The product then passes under local heat to burnish and consolidate it
George Mansfield explains how the diagram accompanying the application shows ‘the strips forming the capacitor partly unwound and broken off for illustration purposes’.
Practical Drawbacks of Original Design
Conrad Hoffmann (see link at the end of this article) advises the original design proved impractical for mass adoption. Apparently, the largest drawbacks were the ‘non-uniformity of the metal film’, and the paper weakening during rolling. However, the principles were sound, and subsequent developments rendered the concept feasible.
More Information
Experiment to Measure Capacitor Resistance
What is a Capacitor in Simple Terms?
Preview: George Mansfield’s Patent Design
