The Van der Pol oscillator was originally proposed by the Dutch electrical
engineer and physicist Balthasar van der Pol while he was working at
Philips. Van der Pol found stable oscillations, which he subsequently
called relaxation-oscillations and are now known as a type of limit cycle in
electrical circuits employing vacuum tubes. When these circuits were driven
near the limit cycle, they become entrained, i.e. the driving signal pulls the
current along with it. Van der Pol and his colleague, van der Mark, reported in
the September 1927 issue of Nature  that at certain drive frequencies an
irregular noise was deterministic chaos.

The Van der Pol equation has a long history of being used in both the physical
and biological sciences. For instance, in biology, Fitzhugh and Nagumo
extended the equation in a planar field as a model for action potentials of
neurons. The equation has also been utilised in seismology to model the two
plates in a geological fault, and in studies of phonation to model the right
and left vocal fold oscillators.

## References

* Wikipedia:
  [Van der Pol oscillator](https://en.wikipedia.org/wiki/Van_der_Pol_oscillator)