Non-destructive near-field characterization of deep-groove defects

Abstract A slow-wave structure with a staggered double-grid structure is a critical component in high-frequency traveling-wave tubes, but its performance is often affected by defects induced by deep-groove fabrication. By employing a dual-port quarter-wavelength coaxial resonator, the near-field scanning microwave microscope (NSMM) system achieves strong evanescent coupling, enabling the imaging of electromagnetic parameters in deep-groove structures. Guided by near-field perturbation theory, the introduction of local protrusion defects causes measurable shifts in the resonant frequency, providing a direct electromagnetic signature of structural imperfections. A comparison between optical imaging and near-field scanning images confirms that the defect locations correspond one-to-one. The NSMM successfully identified a protrusion defect with a height of approximately 50 μm within a deep-groove structure of 100 μm depth. It confirms the feasibility of the NSMM for non-destructive characterization of deep-groove defects induced by etching in the field of microelectromechanical systems (MEMS), offering a promising tool for structural integrity assessment in MEMS and vacuum electronic device fabrication.