Vanadium dioxide (VO2) is a representative thermochromic material because of its unique first-order metal–insulator transition (MIT) at 68 °C. However, reducing the MIT temperature and clarifying the modulation relationship between Zr doping concentration and the MIT temperature of VO2 are extremely challenging. Here, we combine first-principles calculations and thermodynamic models to modulate the phase transition behavior of VO2 nanofilms by coupling Zr doping and the thickness-dependent band gap. It is observed that Zr doping causes changes in the structural stability and electronic and optical properties of VO2, which lead to a decrease in the MIT temperature. Comparing the calculated results with the experimental results, we clarify that the Zr doping concentration and MIT temperature of VO2 have a linear modulation relationship. These findings provide a concept for modulating the phase transition of VO2 nanomaterials.
Abstract Respiration monitoring of a large population is important in containing the spread of viral respiratory infections such as the coronavirus disease 2019 (COVID‐19). Current technologies, however, lack the ability in respiration monitoring of multiple human subjects in a long‐term, robust, and low‐cost manner. Herein, wireless respiration monitoring of multiple human subjects using facemask‐integrated flexible meta‐antennas is demonstrated. The flexible meta‐antenna has an architecture of multi‐layered anisotropic hole‐array, which is optimized by theory and simulations to achieve high performances including good antenna gain, robustness against body interferences, and high air permeability favorable for facemask integration. A person's respiration patterns and respiration rates are wirelessly obtained by the meta‐antenna integrated with a temperature‐sensor‐embedded chip. Respiration monitoring of multiple subjects in long range and long term during daily activities is simultaneously demonstrated. In addition, a real‐time data processing system is introduced in which a local server, a cloud server, and an application layer are implemented for the real‐time display of respiration patterns and automatic recognition of abnormal status. The design of flexible meta‐antennas may lead to a distinct class of physiological sensors over a large population for applications in pandemic control and personalized healthcare.
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