The effects of the surface roughness of thin films and defects on photomasks are investigated in two representative plasmonic lithography systems: thin silver film‐based superlens and multilayer‐based hyperbolic metamaterial (HMM). Superlens can replicate arbitrary patterns because of its broad evanescent wave passband, which also makes it inherently vulnerable to the roughness of the thin film and imperfections of the mask. On the other hand, the HMM system has spatial frequency filtering characteristics and its pattern formation is based on interference, producing uniform and stable periodic patterns. In this work, we show that the HMM system is more immune to such imperfections due to its function of spatial frequency selection. The analyses are further verified by an interference lithography system incorporating the photoresist layer as an optical waveguide to improve the aspect ratio of the pattern. It is concluded that a system capable of spatial frequency selection is a powerful method to produce deep‐subwavelength periodic patterns with high degree of uniformity and fidelity.

Borehole radar (BHR) is one of the most important types of ground-penetrating radar and has very strict requirements for antenna. Considering the detection resolution and the limited borehole size, the BHR antenna should be both wideband and compact. In this article, a compact nonsymmetric wideband dipole (NSWD) antenna is proposed. One arm of the NSWD antenna consists of several patches with different lengths, and the other one is a hollow metal tube. The combination of patches which are resistively loaded at the ends is used for increasing antenna bandwidth and frequency reconstruction. In addition, a three-section binomial matching transformer is designed for impedances match between antenna ( 120 Ω) and coaxial cable ( 50 Ω). Matching transformer and other radar system devices are housed in the hollow metal tube, which makes the BHR system much compact. The central frequency of the antenna is set to 86 MHz for long-range detection. The proposed antenna is fabricated and measured. The measurement results show that the proposed antenna has the advantages of wide bandwidth (~41.8% from 68 to 104 MHz) and high radiation efficiency (~65%). Finally, the antenna (including electronics) is assembled into a polyvinyl chloride pipe to form a BHR prototype, and we used it to conduct a field test in a water-filled borehole. The experimental results show that the NSWD antenna can work well with the BHR system inside borehole.

In this paper, a compact wideband semi-elliptical dipole antenna for boat-borne ground penetrating radar (GPR) is presented. The antenna is a semi-elliptical dipole for obtaining wideband performance. In addition, to reduce the size of the antenna, a V-shaped slot structure was applied. Furthermore, resistors are loaded between the slot of the V-shaped structure to improve the time-domain performance of the antenna. The compact wideband semi-elliptical dipole antenna is fabricated and measured. The measurement results show that the reflection coefficient (|S ₁₁ |) of the proposed antenna in the range of 170 - 247.6 MHz is less than -10 dB. The realized gain of the proposed antenna is 0.98 dBi in the center frequency. Finally, the field experiments are carried out and the boat-borne GPR with the proposed antenna can clearly map the bottom of the river.

Healthy coasts have a high ecological service value. However, many coastal areas are faced with oil spill risks. The Synthetic Aperture Radar (SAR) remote sensing technique has become an effective tool for monitoring the oil spill risk in coastal areas. In this study, taking Jiaozhou Bay in China as the study area, an innovative oil spill monitoring framework was established based on Polarimetric SAR (PolSAR) images and deep learning theory. Specifically, a DeepLabv3+-based semantic segmentation model was trained using 35 Sentinel-1 satellite images of oil films on the sea surface from maritime sectors in different regions all over the world, which not only considered the information from the PolSAR images but also meteorological conditions; then, the well-trained framework was deployed to identify the oil films in the Sentinel-1 images of Jiaozhou Bay from 2017 to 2019. The experimental results show that the detection accuracies of the proposed oil spill detection model were higher than 0.95. It was found that the oil films in Jiaozhou Bay were mainly concentrated in the vicinity of the waterways and coastal port terminals, that the occurrence frequency of oil spills in Jiaozhou Bay decreased from 2017 to 2019, and that more than 80 percent of the oil spill events occurred at night, mainly coming from the illegal discharge of waste oil from ships. These data indicate that, in the future, the PolSAR technique will play a more important role in oil spill monitoring for Jiaozhou Bay due to its capability to capture images at night.