In this paper, the design, simulation, fabrication, and measurement of an ultrathin and broadband microwave metamaterial absorber (MMA) based on a double-layer structure are presented. Compared with the prior work, our structure is simple and polarization insensitive. The broadband MMA presents good absorption above 90% between 8.85  GHz and 14.17 GHz, with a full width at half maximum (FWHM) absorption bandwidth of 6.77 GHz and a relative FWHM absorption bandwidth of 57.3%. Moreover, the structure has a thickness of 1.60 mm (only λ/20 at the lowest frequencies). The experimental results show excellent absorption rates which are in good correspondence with the simulated results. The broadband absorber is promising candidates as absorbing elements in scientific and technical applications because of its broadband absorption and polarization insensitive.

In this paper, the design, simulation, fabrication, and measurement of the five-band metamaterial absorber (MMA) based on Chinese ancient coin-shaped structure are proposed. Simulation results show that the proposed absorber has five distinctive absorption peaks at frequencies of 2.538 GHz, 7.092 GHz, 9.702 GHz, 13.302 GHz, and 15.588 GHz with the absorptivity of 0.99, 0.99, 0.99, 0.98, and 0.99, respectively. Experiment results matches well with the simulation. Both simulation and experiment results exhibit that the MMA sample is polarization insensitive for transverse electric and transverse magnetic incident wave. It also shows that high absorption for wide angle of incidence is up to 60°. Finally, the current distribution for the MMA is presented to gain an insight into the physics behind the multiple absorption mechanism. The five-band absorber is promising candidates as absorbing elements in scientific and technical applications because of its multiband absorption, polarization insensitive, and wide angle incidence.

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Heating and cooling time directly influence the response speed of a shape memory alloy (SMA) wire actuator. An SMA wire is heated quickly by electric current, however quickly cooling it to a given temperature is difficult. In this study, we proposed a pipeline-type active air convection cooling scheme, which uses compressed air as cooling airflow to achieve rapid active cooling of SMA wire actuators. We designed an SMA wire linear actuator consisting of SMA wires, a compressed air tank, an air valve, an Outlet Pipeline, an SMA Cooling Pipeline, and some other additional accessories. We established theoretical models of heat transfer under natural cooling and active convection cooling of an SMA wire. In addition, we carried out theoretical simulation and experiments on a NiTi alloy SMA wire with a diameter of 1 mm and compared the accuracy of simulation with test results. The SMA wire actuators are used for deflectable morphing winglets of aircraft wing. We designed three-dimensional numerical models of the morphing winglets that can be deflected within ±20° and the experimental models are machined and assembled. Final test results show that active cooling time is reduced by more than 70% compared with natural cooling and the response speed is improved significantly.

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