A conformal metamaterial absorber with simultaneous optical transparency and broadband absorption is proposed in this paper. The absorptance above 90% over a wide frequency range of 5.3–15 GHz can be achieved through topology optimization combined with a genetic algorithm (GA). The broadband absorption can be kept at incident angles within 45° and 70° for TE mode and TM mode, respectively. In the meantime, by employing transparent substrates, including polyvinyl chloride (PVC) and polyethylene terephthalate (PET), good optical transmittance and flexibility can be obtained simultaneously. The experimental results agree well with the numerical simulations, which further validates the reliability of our design and theoretical analysis. With its visible-wavelength transparency, flexibility, broadband absorption, low profile, excellent angle stability and polarization insensitivity, the proposed absorber is highly favored for practical applications in microwave engineering, such as electromagnetic interference and stealth technology. Moreover, the proposed design method of topology optimization can be extended to design the absorber quickly and efficiently, according to specific engineering requirements.

Coding is an effective method of designing wideband metabsorber, but the resultant metabsorbers are usually associated with complicated shapes that hinders clear physics understanding of the wideband principle behind the scene. This study presents characteristic mode analysis (CMA) of two types of coding metabsorber composed of single-layer and bilateral resonators, respectively, generated by the genetic algorithm optimization methods. Compared with the conventional single-layer design, CMA results illustrate the wideband principle of the bilateral design introducing additional absorption modes. With a fractional bandwidth of 143.5%, the proposed bilateral metabsorber measures an absorption bandwidth of 5.9–35.9 GHz for 90% absorptance. CMA provides a low-threshold method to analyze the metabsorber with complicated resonators, thereby paving the way for the physical-oriented coding optimization improvement.

A micro-cavity based on phase-change material is a very important strategy for the realization of tunable absorption and conversion of terahertz waves. In this work, a tunable terahertz metamaterial absorber based on the phase-change material germanium–antimony–tellurium (GST) is demonstrated. The device features a metal–insulator–metal triple-layer structure, where the dynamic switching of absorption characteristics is achieved via thermally controlled GST phase transition. In the amorphous state, the absorber exhibits a single absorption peak at 7.7 THz. Upon crystallization, the absorption switches to dual peaks at 5.1 THz and 8.3 THz, achieving near-perfect absorption in both states. Full-wave electromagnetic simulations and theoretical analysis based on a multiple-reflection interference model indicate that this performance tuning originates from the GST-phase-transition-induced change in the equivalent optical cavity length. This corresponds to a switch between two resonant modes: coupled inner–outer ring resonance and independent outer ring resonance. These results provide a foundation for developing dynamically tunable terahertz devices with promising applications in terahertz communications, imaging, and sensing.

The development of advanced multispectral stealth technology plays a vital role in enhancing the survivability of combat platforms. In this paper, a novel design of metamaterial structure based on laser-induced graphene (LIG) that enables bi-stealth compatibility in both infrared and radar regions is proposed and experimentally validated. The structure features a layered design, consisting of an infrared shielding layer (IRSL) and a radar absorption layer (RAL). Specifically, the IRSL layer is structured as an array of Indium Tin Oxide (ITO) based square patches, provides low infrared emissivity and high microwave transparency. While, the RAL is fabricated using LIG technology. which provides excellent radar-absorbing properties through its porous, conductive, and tunable electromagnetic characteristics. The proposed design demonstrates exceptional broadband absorption performance, with an absorption rate exceeding 90% in a range of 2.42 ~ 16.2 GHz, and a relative absorption bandwidth of 148%, which aligns well with simulated results. Additionally, the structure with a low infrared emissivity of 0.26 in the infrared range from 8 to 14 μm. By integrating an LIG-based RAL with a low-emissivity IRSL, this design overcomes the limitations of traditional single-mechanism approaches to multispectral detection, offering new perspectives for the further development of multispectral stealth technology.