The goal of this technical note was to compare experimentally and via simulation of eight substrate-integrated hollow waveguide (iHWG) designs, and to predict promising future iHWG structures in lieu of experiments. The iHWGs differed in their geometry (i.e., inlet funnel cross-section and inner channel cross-section), as well as in their material properties (i.e., type of metal, polish of inner channel). Experimentally, calibration functions of isobutane as a model analyte were determined, and the analytical figures of merit, i.e., signal-to-noise ratio, limit of detection, were evaluated for each iHWG. Evaluation of the amount of radiation incident at the real-world and simulated detector revealed that experiment and simulation were in excellent agreement. While material and quality of the inner channel wall did not have a significant influence on the performance, the iHWG geometry profoundly affected the performance in terms of light throughput: Increasing the inlet funnel dimensions and the inner channel cross-section benefits light throughout, and thus, the analytical signal. Based on these results, simulations of not yet fabricated iHWGs were performed and promising new iHWG structures were suggested.
From Light Pipes to Substrate-Integrated Hollow Waveguides for Gas Sensing: A Review
