A. Fleming offered van der Pol the use of the Pender Electrical Laboratory at University College for a study of the heuristics of wireless reception on board ships.

For his thesis he wrote The effect of an ionised gas on electro-magnetic wave propagation and its application to radio, as demonstrated by glow-discharge measurement[2] under the supervision of Willem Henri Julius.

As observed by Hendrik Casimir, "Radio might have remained a field of haphazard empiricism along with wild commercial ventures, but for the influence of men like van der Pol who stressed the need for a more scientific approach.

"[3] The differential equations of coupled electrical systems drew his interest, and he developed the idea of "relaxation oscillations".

[4][5] With J. van der Mark he applied the idea to the heartbeat,[6] which provided one of the earliest quantitative models of the action potential.