3D-printed metal-dielectric quasi-BIC metasurface.

A 3D-printed metal-dielectric microwave metasurface supporting high-Q quasi-bound-state-in-the-continuum (quasi-BIC) resonance is proposed and experimentally demonstrated. The metasurface is realized by combining a resin framework with a surface copper coating, which decouples structural support from electromagnetic functionality. Longitudinal symmetry breaking is introduced through a height difference between adjacent resonant pillars, enabling the conversion of a symmetry-protected BIC into an externally excitable quasi-BIC mode. The proposed structure exhibits an ultranarrow resonance at 7.51~GHz with a simulated Q factor of 45,038. Experimental results show a near-perfect absorption of 99.51% at 7.5~GHz. Multipole decomposition confirms that the resonance is dominated by an electric quadrupole response. The metasurface also achieves a refractive-index sensitivity of 352.7~MHz/RIU and a figure of merit greater than 1856. The proposed design provides a low-cost and practical approach for realizing high-performance microwave absorbers and sensing devices.