Sheath width effect on the determination of plasma frequency in the cutoff probe

To analyze the sheath width effect on the determination of the plasma frequency in the cutoff probe, two simulations (a simplified circuit simulation and an E/M simulation) were conducted. Both two simulations showed a consistent result: the cutoff frequency $ωc$⁠, which is selected as a frequency of minimum peak in a transmission microwave frequency (TMF) spectrum, deviates from the plasma frequency $ωp$ while increasing the sheath width on the two probe tips. The physics behind the movement of cutoff frequency in the TMF spectrum deviating from the plasma frequency was analyzed and discussed in this paper. This study can provide not only the basis for the precise measurement of the cutoff probe but also the discernible boundary conditions for the cutoff probe application.