Absorption-dominant Microwave Shielding Properties of Sn0.2Fe2.8O4-Graphite-PVDF Ternary Nanocomposite Films

Absorption-dominant microwave shields are in high demand for mitigating the effect of electromagnetic interference on devices and the environment. In this paper, we describe the development of absorption enhanced ternary nanocomposites and their electromagnetic interference shielding capability. Polymer based shields have been fabricated by dispersing conducting graphite and magnetic spinel ferrite Sn0.2Fe2.8O4 nanoparticles in electroactive polymer PVDF. Shielding effectiveness (SE) values in the expected range of 10 - 30 dB in the X-band region, were achieved with as low as 30 – 50 wt% of pristine graphite and 1 – 10 wt% of Sn0.2Fe2.8O4. The industrial standard of 99% shielding (SE ≥ 20 dB) was obtained with 50 wt% of graphite. The composites exhibit absorption as the dominant mechanism of shielding. The percentage shielding effectiveness due to absorption is about 70% and is tuned upwards by the increase in ferrite concentration. The composites were characterized by XRD and VSM; thermal analysis confirms their stability. The thin, flexible films fabricated by the simple and cost-efficient technique of solution casting will be extremely valuable as wrap-on shields for X-band microwave attenuation.

High Frequency Electromagnetic Shielding by Biochar-Based Composites

We report on the microwave shielding efficiency of non-structural composites, where inclusions of biochar—a cost effective and eco-friendly material—are dispersed in matrices of interest for building construction. We directly measured the complex permittivity of raw materials and composites, in the frequency range 100 MHz–8 GHz. A proper permittivity mixing formula allows obtaining other combinations, to enlarge the case studies. From complex permittivity, finally, we calculated the shielding efficiency, showing that tailoring the content of biochar allows obtaining a desired value of electromagnetic shielding, potentially useful for different applications. This approach represents a quick preliminary evaluation tool to design composites with desired shielding properties starting from physical parameters.

Observation of microwave shielding of ultracold molecules

Harnessing the potential wide-ranging quantum science applications of molecules will require control of their interactions. Here, we used microwave radiation to directly engineer and tune the interaction potentials between ultracold calcium monofluoride (CaF) molecules. By merging two optical tweezers, each containing a single molecule, we probed collisions in three dimensions. The correct combination of microwave frequency and power created an effective repulsive shield, which suppressed the inelastic loss rate by a factor of six, in agreement with theoretical calculations. The demonstrated microwave shielding shows a general route to the creation of long-lived, dense samples of ultracold polar molecules and evaporative cooling.