Resonant sub-THz cavities and waveguides for sensing applications

Details

Supervisors

Lederer, Dimitri ; Raskin, Jean-Pierre

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil électricien, à finalité spécialisée

Abstract

enAt sub-terahertz frequencies, electromagnetic waves are highly sensitive to the dielectric properties of the medium they pass through, which makes label-free gas detection possible. This work covers the design, fabrication, and characterization of two D-band (110–170 GHz) structures: a 14-mm WR-6.5 waveguide and a TE101 resonant cavity, both perforated for analyte injection. The devices, designed with CST Studio Suite, were machined from aluminum in a split-block architecture and characterized on a VNA bench with frequency extenders under controlled atmospheres (dry air, N2, O2, H2, and humid air). The cavity, resonating at 155.85 GHz, discriminates between pure gases based on their permittivity, with a sensitivity of the order of −4 × 104 MHz per unit of ε′ and a detection limit of 9 × 10−6 in ε′. The response of the waveguide, meanwhile, remains below the noise floor, as its interaction length is too short: the contrast between the two devices quantifies the contribution of the resonance. Humidity produces the clearest and most reversible response, visible in both the resonant frequency and the quality factor, with an amplitude suggesting a contribution from water in the condensed phase. These results validate the transduction principle and pave the way for the integration of a host material such as porous silicon.