We report the fabrication of graphene-encapsulated nanoballs with copper nanoparticle (Cu NP) cores whose size range from 40 nm to 1 μm using a solid carbon source of poly(methyl methacrylate) (PMMA). The Cu NPs were prone to agglomerate during the annealing process at high temperatures of 800 to 900 °C when gas carbon source such as methane was used for the growth of graphene. On the contrary, the morphologies of the Cu NPs were unchanged during the growth of graphene at the same temperature range when PMMA coating was used. The solid source of PMMA was first converted to amorphous carbon layers through a pyrolysis process at the temperature regime of 400 °C, which prevented the Cu NPs from agglomeration, and they were converted to few-layered graphene (FLG) at the elevated temperatures. Raman and transmission electron microscope analyses confirmed the synthesis of FLG with thickness of approximately 3 nm directly on the surface of the Cu NPs. X-ray diffraction and X-ray photoelectron spectroscopy analyses, along with electrical resistance measurement according to temperature changes showed that the FLG-encapsulated Cu NPs were highly resistant to oxidation even after exposure to severe oxidation conditions.

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On-board data reduction is a major concern in designing of a spaceborne synthetic aperture radar (SAR) system since the volume of acquired SAR data is generally much higher than the downlink capability to the ground-station. The dechirp-on-receive (DoR) method is considered the state-of-the-art SAR data reduction technique. If there is deramping hardware in the SAR instrument, DoR is an effective method to reduce the volume of images for high resolution modes. In this paper, we use a digital signal processing method which applies a modified discrete Fourier transform (MDFT) filter bank for SAR data reduction. We call this method MDFT band selection filter (MDFT-BSF). This paper presents a quantitative analysis of the MDFT-BSF on data reduction performance. In addition, we provide a relationship between the data reduction performance and the number of sub-bands (M), and show that there is an optimal value of M that minimizes the volume of on-board SAR data. An evaluation of MDFT-BSF including a comparison with the DoR method presents that MDFT-BSF has an advantage for SAR data reduction. We show that MDFT-BSF can be implemented and operated on commercial space-grade FPGAs by the development of a spaceborne SAR digital receiver.INDEX TERMS dechirp-on-receive, field programmable gate array, modified discrete Fourier transform filter bank, satellite electronics, synthetic aperture radar