Microwave absorber with broadband absorption and thin thickness is one of the main research interests in this field. A flexible ultrathin and broadband microwave absorber comprising multiwall carbon nanotubes, spherical carbonyl iron, and silicone rubber is fabricated in a newly proposed pyramidal spatial periodic structure (SPS). The SPS with equivalent thickness of 3.73 mm covers the $-10\mathrm{dB}$ and $-15\mathrm{dB}$ absorption bandwidth in the frequency range 2–40 GHz and 10–40 GHz, respectively. The excellent absorption performance is achieved by concentration and dissipation of the electromagnetic field inside different parts of the magnetic–dielectric lossy protrusions in different frequency ranges.

A resistive metasurface surface featured by Rossler Chaos reaction-diffusion system patterns is proposed and realized in a wideband electromagnetic absorber. The chaos surface consists of units with both random shapes and dimensions. Simulation results show absorption phenomenon and correlation function analysis indicates new wave-absorbing mode can be generated when correlation of the edges of the chaos patterns matches geometrical size of chaos units. Experimental results indicate unconventional bandwidth ratio with reflectivity lower than -10dB, -15dB, -19dB reaches 96.84%, 80.1% and 56.1%, respectively. High absorption nature makes this structure has application potential in modern anechoic chamber or other electromagnetic wave absorbers.

Broadband sound absorption has consistently been a challenge in designing underwater sound absorption structure (USAS). Most research of USASs achieve broadband sound absorption through structural optimization, which curbs the freedom of designing, and commonly alights it at the expense of increased thickness. In this paper, a method is reported to broaden the frequency band of the USAS by embedding a membrane-type resonator into the cavity, which forming a membrane-type underwater acoustic absorption metamaterial. We demonstrate the mechanism of membrane-type metamaterial by theory, and verify it by simulation and experiment. The experimental results show that the sound absorption coefficient in the frequency range of 2000–10 000 Hz is significantly improved after implanting the membrane-type resonator into the cavity. The average sound absorption coefficient is increased by nearly 17%, and the improvement effect of the sound absorption covers to each frequency point, which is consistent with our expectation. As the case of applying membrane-type metamaterials to the design process of underwater acoustic structures, this research possesses great application potential in acoustic wave communication and device compatibility design technologies.