In 2370, while Starfleet officers Jean-Luc Picard and Beverly Crusher were attempting to escape into Kes territory on Kesprytt III, they were able to use a tricorder to produce a multiphase pulse with a frequency modulation in the upper-harmonic range to open up a gap in the force field separating the Kes territory from the Prytt territory. (TNG: "Attached" )