The thickness of a metal grid represents a significant factor in electromagnetic interference shielding effectiveness (SE), and the skin depth of the uniform metal surface does not represent the critical thickness of the metal grid. In this study, the influence of Cu grid thickness on the electromagnetic interference SE and critical thickness was assessed using a theoretical model, followed by simulation analysis. According to the equivalent circuit model theory, the skin depth in the equivalent resistance was replaced by the actual thickness of the grid, and the equivalent reactance was corrected by changing the coefficient. A physical field model was established, considering the effects of different grid structures on the SE, using the finite element method. The Cu grids were fabricated in line with the simulation results, and we found that the tested electromagnetic interference SE values of the Cu grids with different thicknesses were generally consistent with the equivalent circuit model when the thickness was less than the critical thickness. The simulation demonstrated that the critical thickness of the Cu grid was constant for different periods and line widths, and the critical thickness of the Cu grid was approximately 170 nm at 1–12 GHz. When the thickness of the Cu grid was 170 nm, the average electromagnetic interference SE was 24.8 dB at 1–12 GHz. In engineering applications, grid thickness greater than the critical thickness should be preferentially designed, and the period or line width should be optimized to further improve the electromagnetic interference SE of the target frequency band. In addition, the electromagnetic interference SE of a metal grid can be quickly estimated by the equivalent circuit model, thus guiding future design work.

Cu/Sn-9Zn-30Cu/Cu 3D packaging solder joints were prepared by transient liquid phase (TLP) bonding. The effect of bonding time on microstructure, shear strength, and fracture surfaces of the solder joints was studied. The results show that the interface reaction zone of Cu/Sn-9Zn-30Cu/Cu solder joints consisted of Cu6(Sn, Zn)5 phase and Cu3Sn phase at a bonding time of 15 min. With increasing bonding time, the scallop-type Cu6(Sn, Zn)5 phase gradually transformed into the layer-type Cu3Sn phase, and the thickness of the interfacial intermetallic compound (IMC) layer gradually increased. The interfacial reaction zone entirely consisted of the layer-type Cu3Sn after bonding for 60 min. The in situ reaction zone of Cu/Sn-9Zn-30Cu/Cu solder joint consisted of Cu6(Sn, Zn)5, Cu3Sn, Cu particles, and Zn-rich phase at a bonding time of 15 min. The Cu6(Sn, Zn)5 increased content and evenly distributed in the in situ reaction zone at 30 min, resulting the microstructure gradually refined. The Zn-rich phase disappeared in the in situ reaction zone after bonding 90 min, and the in situ microstructure gradually coarsened and cracks initiated as bonding time increased. The shear strength of solder joints first increased and then declined with increasing bonding time, and the maximum shear strength reached 22.25 MPa at a bonding time of 60 min. The fracture location of the solder joint shifted from the in situ reaction zone to the interface reaction zone with increasing bonding time, and the fracture mechanism of the solder joints always exhibited brittle fracture.

The application range of polyacrylonitrile fiber (PANF) in concrete engineering in alpine regions was clarified by performing six sets of mechanical tests of PANF-reinforced concrete (PANFRC) by outdoor curing. The results show that PANF can enhance the performance of concrete mainly in terms of the tensile performance. The splitting strength and flexural strength increased by 15.69% and 8.54% after 150 days, and the dosage used in the alpine region should be controlled between 1.2-1.5 kg/m3. Finally, based on the experimental results, the multi-linear regression prediction model (MLR) and multi-layer perceptron neural networks model (MLP) were used to predict the compressive strength (fcu), splitting strength (fsp), flexural strength (fts), tensile-compression ratio (fsp/fcu), ratio of flexural strength to compressive strength (fts/fcu), and ratio of flexural strength to splitting strength (fts/fsp) of each group of PANFRC specimens. The prediction model was constructed based on the fiber content (W), curing age (D), dynamic elastic modulus (E), and surface rebound hardness (R). The results of the model test show that MLR and MLP are reasonable for predicting the mechanical properties of PANFRC, and the prediction error of the latter is smaller. Moreover, R has a strong dependence on the mechanical evaluation index, the sensitivity coefficient Qik is 0.37, PANF has the least influence, and Qik is only 0.16. This study has reference significance for the application of PANFRC in alpine regions and provides useful ideas for the efficient and intelligent development of the construction industry in alpine regions.

A model of thermal stress in double-layer optical dielectric films on circular substrates was established based on the theory of double-layer composite beams. Here, considering the boundary conditions including force balance and bending moment balance, the distribution of stress and strain in the double-layer film-substrate system was analyzed following equivalence manipulation to determine a detailed formula for calculating the thermal stress in the equivalent film and substrate. The derived formula was not only effective in analyzing the stress and strain of the double-layer film-substrate system but was also applicable for predicting the distribution of thermal stress in the periodic elastic multilayer film-substrate system. According to the actual radius of curvature of the substrate measured via a profilometer before and after the deposition of the HfO $$_2$$ /SiO $$_2$$ double-layer films, the obtained residual stress of the film was − 79.33 MPa, whereas the thermal stress of the film was calculated to be −52.59 MPa using the theoretical formula. The calculations of the theoretical model were similar to the experimental results when the smaller intrinsic stresses were neglected and the double-layer film was only of nanometer thickness, thus verifying the effectiveness of the double-layer film-substrate model.

The work aims to study the effect of deposition temperature on optical properties and residual stresses in Lanthanum titanate (H4) films. The LaTiO3 films were deposited by electron-beam thermal evaporation technique. The residual stress of LaTiO3 films on fused silica was characterized macroscopically and microscopically, using laser interferometry and AFM. The residual stresses and surface profile shape change were simulated using finite element analysis methods. It was confirmed that the deposition temperature did not affect the optical properties of the films, but did for residual stresses. The residual stress of LaTiO3 films changes from decreasing tensile stress to compressive stress as the deposition temperature increases. The deposition temperature is used to modulate the magnitude and transition of the residual stress in the films. There is a strong dependence between the residual stresses and the densities of surface columnar structures in LaTiO3 films. The effect of density of surface columnar structures is found as follows: the film with the lower density of surface columnar structures generally shows a tensile and high density easily transform into compress stress. This conclusion is also verified by the increase of the corresponding refractive index. The simulated surface profiles are basically overlapping with the measured data. The proposed model is validated for the simulation of residual stresses in monolayers.

Photolithography mask and thermal evaporation deposition technology were used to fabricate a thin film devices compatible with electromagnetic shielding infrared window, which could realize the device to possess the efficient anti-reflection of infrared signals in the band of 3-5 pm and shield electromagnetic signals in the frequency band of 12 similar to 18 GHz. The cross-sectional symmetric metal grid microstructures which met requirements were prepared on the double-sided polished Si substrate by photolithography mask and vacuum thermal evaporation deposition technology, the highly efficient anti-reflection infrared in the 3 similar to 5 tun band was prepared by ion beam assisted electron beam thermal evaporation deposition technology. In order to improve the transmittance of the metal grid further, an infrared anti-reflection film was deposited on the metal grid coating with a cycle g of 550 um and different line widths. Results show that the peak transmittance of the infrared anti-reflection film at 3-5 tim is 99.8% and the average transmittance is 99.3% through the measurement of vacuum Fourier infrared spectrometer. The electromagnetic shielding effectiveness in the 12 similar to 18 GHz frequency band of the metal grid was measured by vector network analyzer, and obtained the overall electromagnetic shielding efficiency of the compatible electromagnetic shielding infrared window thin film device in the 12 similar to 18 GHz band is better than 27 dB, the peak transmittance in the 3 similar to-5 mu m infrared band is 86.3%, and the average transmittance is 861%. On the premise of ensuring the electromagnetic shielding efficiency is unchanged (>= 527 dB), the transmittance of the metal grid films has increased by 37.6% ( the grid cycle g is 550 mu m, line width 2a is 30 mu m). The improvement of shielding efficiency can be achieved either by adjusting the cycle and line width of the grid, or selecting a substrate material with lower resistivity.