Haosen Chen

Graphene-Based Sandwich Structures for Frequency Selectable Electromagnetic Shielding

Due to substantial development of electronics and telecommunication techniques, materials with electromagnetic interference (EMI) shielding performance are significant in alleviating the interference impacts induced from a remarkable variety of devices. In the work, we propose novel sandwich structures for manipulating the EM wave transport, which holds unique EMI shielding features of frequency selectivity. By employing electrical and magnetic loss spacers, the resultant sandwich structures are endowed with tunable EMI shielding performance, showing substantial improvements in overall shielding effectiveness along with pronounced shielding peak shift. The mechanisms suggest that the multiple interfaces, electromagnetic loss media, and changes of representative EM wavelength could be critical roles in tailoring the EMI shielding performance. The results provide a versatile strategy that could be extended in other frequency ranges and various types of sandwich structures, promising great opportunities for designing and fabricating advanced electromagnetic attenuation materials and devices.

Geometric design of micron-sized crystalline silicon anodes through in situ observation of deformation and fracture behaviors

Large anisotropic volume expansion during lithiation leads to the electrochemical performance degradation and premature fracture of micro-sized silicon electrodes in lithium-ion batteries, which prohibits its practical applications. To date, the failure mechanism of micron-size silicon electrodes has not been fully comprehended due to the lack of convincing experiments. For good understanding of lithiation/delithiation processes in the silicon anodes, in the present contribution, in situ observation of anisotropic volume expansion, crack initiation, penetration, deflection and delamination at the amorphous/crystalline silicon interface has been reported. The observation suggests that novel hollow and anisometric geometric electrodes have shown substantially enhanced capability in improving the fracture behaviors of the crystalline micropillar electrodes, implying that geometric design greatly impacts the strain alleviation and reversible volume change. Due to more favorable mechanical reliability, the anisometric geometric silicon electrode is expected to present essentially enhanced electrochemical performance and structural stability, which promises a novel strategy of designing Li-ion battery electrodes from a geometric perspective.

Constructing Repairable Meta-Structures of Ultra-Broad-Band Electromagnetic Absorption from Three-Dimensional Printed Patterned Shells

Ultra-broad-band electromagnetic absorption materials and structures are increasingly attractive for their critical role in competing with the advanced broad-band electromagnetic detection systems. Mechanically soft and weak wax-based materials composites are known to be insufficient to serve in practical electromagnetic absorption applications. To break through such barriers, here we developed an innovative strategy to enable the wax-based composites to be robust and repairable meta-structures by employing a three-dimensional (3D) printed polymeric patterned shell. Because of the integrated merits from both the dielectric loss wax-based composites and mechanically robust 3D printed shells, the as-fabricated meta-structures enable bear mechanical collision and compression, coupled with ultra-broad-band absorption (7-40 and 75-110 GHz, reflection loss xa0smaller than -10 dB) approaching state-of-the-art electromagnetic absorption materials. With the assistance of experiment and simulation methods, the design advantages and mechanism of employing such 3D printed shells for substantially promoting the electromagnetic absorption performance have been demonstrated. Therefore, such universal strategy that could be widely extended to other categories of wax-based composites highlights a smart stage on which high-performance practical multifunction meta-structures with ultra-broad-band electromagnetic absorption could be envisaged.