Sub-THz EM characterization of coated material

The electromagnetic characterization of coating materials is fundamental to build a reliableimpedance model of any accelerator. In particular, since the CLIC (Compact LInear Collider)necessitates bunches with short longitudinal length, a full electromagnetic characterization of thecoating material surface impedance is needed at high frequencies in the millimetric wave length andbeyond. The goal of this paper is to develop a measurement method to characterize the coatingmaterials in the sub-THz frequency range. The electromagneticcharacterization ofthe material is performed using a time domain coherent THz spectrometer. Themethod is based on the attenuation measurement of the signal passing through a waveguide specificallydesigned, having a very thin central layer where the coating material is deposited on bothsides. The guide is equipped with two "horn" antennas integrated on both sides of the device toenhance the electromagnetic signal collection. This noveltechnique is tested on slabs coated with a Non-Evaporable Getter (NEG) and allows evaluatingthesurface impedance in the frequency range from 0.1 to 0.3 THz.