The theory formed the basis of most transmission-line type microwave filters for at least the next thirty-five years and the design technique is still in use today.
[3] Richards' transformation, introduced in this work, is still found in modern textbooks on radio frequency filter design.
[5] Between 1947 and 1952 he was a physicist at the Brookhaven National Laboratory helping to develop the magnetic time-of-flight mass spectrometer with Earl E. Hays and Samuel Goudsmit.
From 1952 to 1954 he was director of research at Transistor Products Inc. From 1954 to 1968 he was senior physicist with Technical Operations Inc.[1] In 1956, while at Technical Operations, Richards produced a paper "Shock waves on the highway", one of the earliest theoretical models of traffic waves (there was another paper on this the previous year by Lighthill and Whitham in the UK, but Richards was apparently not aware of it and his work is independent).
[1] Richards was on the publications committee of the Society for Industrial and Applied Mathematics and was an editor of SIAM Review.