A resonant short-circuit plunger as part of tunable waveguide-dielectric and waveguide-coaxial resonators built around cylindrical evanescent waveguides

Subject and Purpose. Tunable resonant structures make numerous microwave devices, among which are waveguide-dielectric and waveguide-coaxial resonators (WDR and WCR) built around cylindrical evanescent waveguides and involving a resonant short-circuit (RSC) plunger for tuning purposes. The present paper seeks to study specific features of the RSC-plunger operation in the evanescent waveguide and estimate the RSC-plunger efficiency. Method and Methodology. The RSC-plunger efficiency is approximately estimated in terms of the transmission line theory. Comparative experimental verification of the Q-factor increase is provided by an example of a 3 cm WDR resonator equipped with a RSC-plunger. Results. It has been shown that relevant formulae of the transmission line theory can be extended for the RSC-plunger efficiency estimation on the TEM and H11 oscillations. A possibility has been studied of the TEM type transformation to the H11 oscillation and back when the spurious resonance of the RSC-plunger falls within the WDR (WCR) tuning range. Conclusion. Insignificance of the effect that small deviations from the numerically predicted dimensions of the RSC-plunger exert on the RSC-plunger operation efficiency has been demonstrated. The RSC-plunger efficiency and a possibility to remove the spurious resonances from the resonator tuning range have been experimentally confirmed.

Surface Functionalization of SU-8 Vertical Waveguide for Biomedical Sensing: Bacteria Diagnosis

In this paper, we present an SU-8 based evanescent waveguide with a vertical structure as a biomedical sensor. The waveguide is designed vertically to generate evanescent waves on both left and right surfaces for sensing. It is fabricated by E-beam lithography with only one-step process which has the advantage of a better surface quality compared with commonly used dry etching methods. Furthermore, fabrication time and cost is cut down greatly. The surface of the designed waveguide can be functionalized with antibodies to immobilize specific bacteria on it. After surface functionalization and incubation with E. coli solutions of different concentrations, the waveguides absorption was measured. The results demonstrate that the waveguide is sensitive to E. coli concentration changes. In addition, tapers were designed and added to the waveguide to relieve the alignment tolerance for the aim of making a plug-and-play bedside diagnostic system.