Cu‐Co Hybrid Crystals Assembled on Hollow Microsphere: Temperature‐Dependent Top‐Down Synthesis and Aggregation‐Induced Conversion from Microwave Shielding to Absorption

Abstract

The construction of hollow metallic microspheres with rationally designed building blocks of the metal shell is a promising way to achieve low density and functionality control, but the microengineering of the metallic structures on a micrometer spherical surface is a great challenge. In the present work, a novel and simple calcination‐induced aggregation strategy is developed to realize the distribution status and microstructure control of Co‐Cu bimetal building blocks assembled on a hollow glass microsphere support, and thus a series of low‐density (0.58 g cm−3) dual shell composite hollow microspheres are constructed with gradient in electromagnetic property depending on the calcination temperature (CT). The optimized microwave shielding performance can be achieved at a CT of 500 °C, while further increasing CT to 700 °C leads to an interesting conversion from microwave shielding to absorption with an optimized effective absorption bandwidth of 4.64 GHz at a low matching thickness of 1.33 mm. The mechanism underlying the CT‐dependent metallic shell structure variation and further the decisive effect of the shell structure on the microwave response behavior are proposed based on a series of contrast experiments.

High-Performance Transparent Ultrabroadband Electromagnetic Radiation Shielding from Microwave toward Terahertz

“…Following the booming progress in high-frequency electronics, electromagnetic interference (EMI) shielding has become a critical requirement. − This shielding can protect sensitive electronic devices from severe electromagnetic radiation and provide an efficient solution for electronic security issues. − In view of the growing interest in next-generation wireless communications and burgeoning wide-area Internet-of-Things technologies in recent years, a great challenge for EMI shielding materials has been set to ensure that they operate across diverse frequency ranges ranging from microwave toward terahertz (THz) frequencies. − Specifically, commercial fifth-generation network frequencies’ range span from ∼450 MHz to ∼52.6 GHz; − accordingly, electronic components are required to operate properly in this broad microwave range. Furthermore, in a regime that spans 3 orders of magnitude higher than microwave frequencies, THz technology has attracted extensive attention owing to its potential applications in security screening, biological/medical imaging, nondestructive detection, and electro-optic sensors. − Correspondingly, THz electronics and devices are challenged to operate normally in a broad THz region. , In addition, recent advances in wearable devices and miniaturized electronics call for high-performance transparent EMI shielding coatings with excellent mechanical flexibility and minimal thickness and can be adapted to cover special geometric shapes. − …”