In this paper, we show a fast and accurate numerical method for simulating the microwave heating of moving objects, which is still a challenge because of its complicated mathematical model simultaneously coupling electromagnetic field, thermal field, and temperature-dependent moving objects. By contrast with most discrete methods whose dielectric parameters of the heated samples are updated only when they move to a new position or even turn a circle, in our simulations a real-time procedure is added to renew the parameters during the whole heating process. Furthermore, to avoid the mesh-mismatch induced by remeshing the moving objects, we move the cavity instead of samples. To verify the efficiency and accuracy, we compared our method with the arbitrary Lagrangian–Eulerian method, one of the most accurate methods for computing this process until now. For the same computation model, our method helps in decreasing the computing time by about 90% with almost the same accuracy. Moreover, the influence of the rotational speed on the microwave heating is systematically investigated by using this method. The results show the widely used speed in domestic microwave ovens, 5 rpm, is indeed a good choice for improving the temperature uniformity with high energy efficiency.
Core–shell structured Fe/C have been successfully derived from a metal-organic framework for microwave absorbing. Based on the measured electromagnetic parameters, it is found that the maximum reflection loss (RL) of Fe/C reaches [Formula: see text][Formula: see text]dB at 5.8[Formula: see text]GHz with a thickness of 3.0[Formula: see text]mm and the broadest absorption bandwidth ([Formula: see text][Formula: see text]dB) is up to 6.0[Formula: see text]GHz (from 11.2 to 17.2[Formula: see text]GHz) with a thickness of 1.5 mm. The excellent microwave absorption is mainly ascribed to the multiple reflections, good impedance matching, dielectric loss and interface polarization originating from the core–shell structure. It is believed that Fe/C can be a promising microwave absorbing material.
In this paper, we numerically demonstrated a simple metamaterial for wide-angle and polarization-insensitive absorption in the visible region, which simultaneously showed a strongly suppressed absorption in the near-infrared region. Numerical simulations demonstrated that under normal incidence the proposed absorber had a high absorptivity almost over 90% in the wavelength range from 340 nm to 770 nm, while a low absorptivity less than 10% from 1 μm to 2 μm. Because a small unit cell with four-fold symmetry was utilized, the selective absorption of this nanostructure was almost independent of the incident angle and polarization of the incident light. To understand the underlying physical mechanisms, the impedance and the electromagnetic field distributions in a unit cell were analyzed. Moreover, the influence of the structural geometry parameters on the absorption spectrum was systematically studied. Our results may provide a method for using a simple nanostructure to reduce the radiative heat loss for the visible light thermal conversion, or to depress the temperature rise induced by the absorption of below-bandgap photons for photovoltaic solar cells working in the visible region.
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