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A three-band tunable polarization-insensitive metamaterial absorber is proposed in this paper. The unit cell of the absorber is composed of a dielectric substrate, a metal patch, and four varactor diodes welded on the top layer. A simple metal via bias network is designed to facilitate the absorption frequency tuning of the absorber. The simulation results show that when there is no bias voltage (0 V), the proposed absorber has three absorption peaks of 88%, 99.5%, and 99.8% under normal incidence at 7.27, 10.93, and 15.84 GHz, respectively. Furthermore, by adjusting the reverse bias voltage (0-19 V) of the varactor, the first absorption peak of the absorber can be tuned from 7.27 to 8.2 GHz and the second absorption peak tuned from 10.93 to 11.4 GHz.Meanwhile, the tuning range for the third absorption peak is 15.84-16.1 GHz. Furthermore, the three-band absorption and frequency tunable characteristics of the absorber are confirmed by experimental tests.

As the coastal region is the most developed region in China, an increasing number of engineering projects are under construction in it in recent years. However, the quality of these projects is significantly affected by groundwater, which is influenced by tidal variations. Therefore, the regional groundwater dynamic characteristics under tidal impact and the spatiotemporal evolution of the seepage field must be considered in the construction of the projects. Then, Boussinesq function was introduced into the research to deduce the seepage equation under tidal influence for the coastal area. To determine the spatiotemporal evolution of the deep foundation pit seepage field and the coastal seepage field evolution model, numerical calculations based on changes in the tidal water level and seepage equation were performed using MATLAB. According to the developed model, the influence of the seepage field on the foundation pit supporting structure in the excavation process was analyzed through numerical simulations. The results of this research could be considered in design and engineering practice.

Many materials combine a refractive boundary and a participating media on the interior. If the material has a low opacity, single scattering effects dominate in its appearance. Refraction at the boundary concentrates the incoming light, resulting in an important phenomenon called volume caustics. This phenomenon is hard to simulate. Previous methods used point-based light transport, but attributed point samples inefficiently, resulting in long computation time. In this paper, we use frequency analysis of light transport to allocate point samples efficiently. Our method works in two steps: in the first step, we compute volume samples along with their covariance matrices, encoding the illumination frequency content in a compact way. In the rendering step, we use the covariance matrices to compute the kernel size for each volume sample: small kernel for high-frequency single scattering, large kernel for lower frequencies.Our algorithm computes volume caustics with fewer volume samples, with no loss of quality. Our method is both faster and uses less memory than the original method. It is roughly twice as fast and uses one fifth of the memory. The extra cost of computing covariance matrices for frequency information is negligible.

A wideband multilayer filter with frequency tunable characteristics is proposed using active frequency selective surface (AFSS). The proposed AFSS includes three metal layers, while the top and bottom metal layers are embedded with varactors. The metal layers are separated by dielectric layers. By simultaneously adjusting the bias voltage loaded on both ends of the varactor diode, the working bandwidth of the AFSS can be continuously tuned. The operating mechanism is studied using an equivalent circuit, which is composed of an LC series resonance circuit and a parallel resonance circuit. The simulation results prove that the proposed AFSS performs wideband filtering in the frequency range of 3.55 to 4.43 GHz without a bias voltage. With a bias voltage of À19 V, the AFSS working passband is tuned to 4.43 to 5.53 GHz. Simulation and experimental results show that the AFSS has wideband filtering characteristics and good tunable performance.