Delta wave

A delta wave is a form of brainwave associated with sleep. Delta wave augmenters were devices used to aid sleep. (DW: Kinda)

Certain species have specific delta wave frequencies, for example the Daleks who posessed a higher frequency than normal.

A delta wave could also refer to a wave of Van Cassadyne energy that is strong enough to fry the brains of all sentient life within a given radius, although these could be calibrated to be species-specific. The Doctor constructed a delta wave generator on the Game Station to destroy the Daleks, but was unable to bring himself to use it as there was not enough time to allow him to calibrate it for Daleks alone. (DW: The Parting of the Ways)