This paper presents a broadband polarization insensitive prefect metamaterial absorber based on fractal structures. Through the combination of fractal and circular structure, the bandwidth is extended without increasing the size of the unit cell. A simple equivalent circuit model has been proposed describing the absorption phenomenon to predict the frequency of absorption of the proposed absorber. The simulated result shows that the absorber's full width half maximum is 18.5%. With rotational symmetry structures, the absorber is insensitive to the polarization. The incident angles at which the metamaterial absorber can maintain 50% of the absorbance are up to 50°. With the geometrical scalability, the absorber can be extended to any frequencies. This absorber is fabricated and measured at X-band, and the experimental results coincide well with the simulation results.

In this paper, an ultra-wideband flexible absorber is proposed. Based on a summary of the absorption mechanism, using lossless air to replace the heavy lossy dielectric layer will not substantially impact the absorption. The dielectric layer is only a thin layer of polyimide. The proposed absorber is a sandwich structure. The surface is a layer of copper metal ring and wire, and it is loaded with chip resistors to expand the absorber bandwidth. Simulated results show that the bandwidth of the proposed absorber, with an absorptivity of more than 90%, is 2.55–10.07 GHz, with a relative bandwidth over 119.2%. When the electromagnetic wave has a wide incident angle, the absorber still maintains a high absorption. This absorber has been fabricated by FPC (flexible printed circuit) technology. The proposed absorber was attached to the cylinder and measured. The measurement results are roughly the same as the simulation results. The fabricated absorber is easy to carry and flexible, such that it can easily be conformed to irregular objects. The proposed absorber is polarization-insensitive, low profile, thin, and portable, so it is easier to apply in a variety of practical fields.

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