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BIT Makes Progress in Reverse Design of Chemical Power Sources and Systems

release date :2019-12-03 02:28:00  |   [ close window ]ViewCount:


  Beijing Institute of Technology, Nov 27th, 2019:After the academic team of Academician Fang Daining reported the electrochemical-mechanical-optical coupling bionic discoloration device for reverse design of chemical power system on Advanced Functional Materials (2018, 1806383.) on November 17, 2018, the international top comprehensive journal Advanced Science, (2019, 1902162, Journal IF = "15.804) reported online results of the research team’s latest reverse design of the chemical power system: Ionic" Conductive Gels for Optically Manipulatable Microwave Stealth Structure (second class conductor) on November 27.


  Transmission structure and the action window of the light have attracted the attention of the industry because of their unique functions and their wide application in industry. The pursuit of smart technology, smart structures and smart windows can present unique variables as the external environment changes. The application of 5G communication technology (band I: 0.45–6 GHz; band II: 24.25–40 GHz or higher) proposes higher requirements on electromagnetic protection. Microwave stealth structures integrated with intelligent control functions have a high value in research and application, also, the realization of microwave absorption and light wave transmission has become a key challenge for intelligent microwave stealth structures. Usually, the first class of conductor (electronic conductor) is mainly used to design the stealth structure with adjustable transmittance. The second class of conductor (ionic conductor) is more commonly used in chemical power electrolytes, and its intrinsic excellent ion polarization and ion conductivity characteristics, can present the gel effective polarization loss and conductivity loss, and little attention is paid by researchers in the design of electromagnetic structures.


  Figure 1 Design, preparation and characterization of optically transparent gels and transparent multilayer structures: (a) optically transparent multilayer stealth structure at room temperature; (b) transmission spectrum of different gels in the range of ultraviolet visible; (c) preparation ratio of different gels; (d) viscosity test of different gels; (e) real part of permittivity of different gels; (f) real part of permittivity of different gels;


  Based on the second class of optically transparent conductor, ionic conductors as polarization and loss media, for the first time, the research team applies water-soluble polyvinyl alcohol as the absorbing material. Study of the microwave absorption mechanism of aqueous polyvinyl alcohol-based gels shows that highly polar water molecules play a key role in the attenuation of electromagnetic waves in terms of dielectric loss (shown as in Fig.1). Also, the polyvinyl alcohol polymer with hydroxyl functional groups and phosphoric acid molecules is added to make the water molecules have a certain fluidity in the form of a crosslinked hydrogen bond network. When the temperature drops below zero, the gel in the polyvinyl alcohol aqueous solution becomes polycrystalline, thereby forming an opaque gel with the ability to scatter light waves. This optical property is changed due to the temperature-dependent crystal-transformation ability of the water-soluble polyvinyl alcohol-based gel. Studies of complex dielectric constants have shown that liquid and solid phase polyvinyl alcohol-based gel polar molecules have different sensitivities to electromagnetic waves, in which the liquid phase is more sensitive to electromagnetic waves and thus generates more dielectric loss. With more solid hydrogen bond network structure in the semi-solid gel phase, the degree of polarization will be suppressed in the electromagnetic field, and the electromagnetic parameters can be adjusted.


  Figure 2 Design of a 300 X 300mm2 multilayer structure based on an optically switchable transparent gel and measurement with the bow method: design of power loss density distribution of multilayer structure based on (a) single layer gel and (b) double layer gel based on optimal gel; optimization of multi-layer stealth structure with (c) single-layer gel and (d) dual-layer gel; (e) measure the multi-layer transparent stealth structure by bow method; (f) comparison of simulation design results and actual results of bow method.


  By screening the gel with the best performance, by screening the gel with the best performance, a highly transparent electromagnetic stealth structure based on ionic conductor hydrogel was designed with the multilayer transparent structure. Through modeling simulation and parameter iterative optimization, a multilayer structure with broadband stealth characteristics is obtained (Figure 1). Based on the optimized design results, a broadband stealth structure with multiple layers of optical transparency is established. The comparison between the actual measurement and the simulation results of the bow method proves that the designed electromagnetic stealth structure has excellent broadband electromagnetic stealth characteristics. At the same time, the temperature-controllable hydrogen bond network realizes the switching of light transparency and opacity (Figure 3), and can maintain excellent ionic conductivity over a wide temperature range, and can maintain gel conductivity loss in a stable range of temperature. While the light transmittance is switched, the effective stealth frequency range of the structure (15-40 GHz) can cover the band II part of the 5G communication band, not only a new breakthrough is achieved by expanding the second class of transparent conductors, by integrating new optical structures with microwave absorption and light transmission functions, but also it provides new ideas for the development of new adjustable microwave stealth structures and intelligent optical structures.


  Figure 3 Performance measurement of multilayer stealth structures under different light transmission conditions: (a) Optically transparent multilayer stealth structures at room temperature; (b) optically opaque multilayer stealth structure at -20 degrees Celsius; (c) measurement of electromagnetic stealth performance at room temperature and transparent state using a single layer gel multilayer stealth structure; (d) measure the electromagnetic stealth performance in a non-light-transmitting state at -20 degrees Celsius using a multilayer stealth structure with a single layer of gel; (e) measure the electromagnetic stealth performance under the normal temperature and transparent state of the multilayer stealth structure with double-layer gel; (f) Measure the electromagnetic stealth performance in a non-light-transmitting state at -20 degrees Celsius using a multilayer stealth structure with double-layer gel; (g) verification by temperature-controlled light transmission experiments; (h) ionic conductivity of the gel at −20-30 ° C.


  The research was carried out by associate professor Chen Mingji, associate professor Chen Haosen, associate professor Lei Hongshuai, and associate professor Song Weili (first author) under the guidance of Academician Fang Daining, chief scientist of the Institute of Advanced Structure Technology. Relevant institutions include the Institute of Advanced Structure Technology, Beijing Institute of Technology (the primary institute) and the Technology and Engineering Center for Space Utilization, Chinese Academy of Sciences.


Editor: News Agency of BIT

Translation: News Agency of BIT


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