4.7 Article

Single-Layer Evanescent Wave Absorbers in Rectangular Waveguides Based on Evanescent Mode Coupling and Attenuation

Journal

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION
Volume 71, Issue 5, Pages 4394-4405

Publisher

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TAP.2023.3248448

Keywords

Probes; Cutoff frequency; Noise measurement; Absorption; Conductors; Electromagnetic interference; Rectangular waveguides; Electromagnetic interference (EMI); evanescent wave (EW); metasurface; microwave absorber; rectangular waveguide (RWG)

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A microwave absorber is proposed to absorb waves below the cutoff frequency of a rectangular waveguide (RWG). The absorber utilizes a lossy capacitive metasurface to couple with and attenuate the waves below the cutoff frequency, effectively absorbing the evanescent waves (EWs). Three samples made of indium tin oxide (ITO) thin films were designed, fabricated, and tested, showing good agreement between experimental and theoretical results, with a maximum measured absorptance of 97%. Compared to conventional plane-wave absorbers, the proposed absorber has a distinct working mechanism, design principle, and application scenario, requiring only a single-layer conductor.
A microwave absorber for absorbing waves below the cutoff frequency of a rectangular waveguide (RWG) is proposed in this study. By loading an ideal lossy capacitive metasurface (LCMS) in the cross Section of an RWG close to the radiation source, the LCMS exhibits the ability to couple with and attenuate the waves below the cutoff frequency of the RWG, that is, absorb the evanescent waves (EWs). The operating mechanism is analyzed with several parametric studies based on the momentum-matching principle, and a systematic design procedure for a practical EW absorber is concluded. Three samples made of indium tin oxide (ITO) thin films are designed, fabricated, and tested, and the experimental results agree well with the theoretical results. The maximum measured absorptance reaches up to 97%. Compared with conventional plane-wave absorbers with multilayer conductors, the proposed EW absorber only requires a single-layer conductor and has a distinct working mechanism, design principle, and application scenario. In the examples considered in this study, the samples can serve as the specific matching component for calibrating the RWG below the cutoff frequency. Notably, our EW absorption technique provides a feasible approach to suppress the electromagnetic interference (EMI) dominated by the evanescent mode in the electrically small metallic cavity packages and near field (NF) of integrated circuits (ICs).

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