AbstractIn this study, the propagation characteristics of electromagnetic waves in a parity-time (PT)-symmetrical 1D photonic crystal comprising dispersed silver layers are investigated. Based on the transmission matrix theory, the total reflection and transmission coefficients of the structure are obtained. It was found that, due to the PT-symmetrical structure, the reflections of the left and right incident waves are nonreciprocal. Numerical simulations indicated that the width of the band gap decreases with the increase in the gain and loss factor ρ in the PT medium, and the band gap ultimately disappears when ρ reaches a critical value, i. e., ${\rho }_{PT}$. With the increase in $\rho { >}{\rho }_{PT}$, anomalous transmittance and reflection occur within the original bang gap. As the gain and loss factor ρ continue to increase, the abnormal transmittance and reflectivity exhibit a trend of oscillatory decline, and perfect transmission can be achieved at larger values of ρ.

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We investigate the non-reciprocal transmission properties of a three-layer structure filled with magneto-optical medium and normal medium. Based on the transfer matrix method, we deduce the total transmission coefficient for a one-dimensional (1D) structure with anisotropic mediums. When two-side layers with magneto-optical medium loaded in opposite external magnetic field, the time-reversal symmetry of transmission properties will be broken. Our numerical results show that the non-reciprocal transmission properties are influenced by external magnetic fields, incident angle, and thickness of the normal medium layer. Since the non-reciprocal properties can be easily realized and adjusted by the simple structure, such a design has potential applications in integrated circulators and isolators.

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The aim of this study is to evaluate the cooling effect of a spray fan in an indoor hot environment. An experimental workplace with a thermal environment of high temperature and radiation intensity was set up. The hot environment of the experimental workplace could not meet occupational health requirements when the heat source temperature exceeded 150°C. The effects of air velocity and relative humidity on the natural wet bulb temperature, black globe temperature and wet bulb globe temperature (WBGT) were investigated. The maximum reduction of the WBGT was about 1.7°C, with an air velocity increase by 1 m/s. There was a notable cooling effect on the hot environment for low air velocities (e.g. 0–2 m/s), while the cooling effect only increased slightly for high air velocity (e.g. 2–5 m/s). We also found that the indoor WBGT declined by 0.2–0.8°C when the relative humidity was increased by about 10%. These results may provide guidance for reducing heat stress in industrial hot environment.