We present a theoretical and experimental realization of a thin multi-unit metasurface with multi-order sound absorption that exhibits a continuous near-perfect absorption spectrum in the broadband range of 450 Hz–1360 Hz. The metasurface unit is a perforated composite Helmholtz-resonator (PCHR) that is constructed by inserting one or more separating plates with a small hole into the interior of a Helmholtz resonator (HR). The multi-order sound absorption mechanism can be achieved so that with the original absorption peak and the structural size unchanged, multiple near-perfect peaks are obtained in higher frequencies by a PCHR unit. This extraordinary multi-peak performance is the result of the upgraded multi-degree-of-freedom system with the separating plates, which is explained well by the equivalent acoustic circuit. The specific absorption properties of the PCHR unit are investigated thoroughly with a theoretical approach similar to the plane wave expansion method, and verified via the finite element simulations. On this basis, by precisely balancing the parameters of each unit, the absorption bandwidth of the subwavelength 8-unit metasurface is dramatically broadened about 65% by the proposed mechanism. This work would offer a new guidance for the achievement of the wider absorption band and has great potential in engineering applications.

Fusarium head blight (FHB), a globally significant agricultural disaster, causes annual losses of dozens of millions of tons of wheat toxins produced by FHB, such as deoxyroscyliaceol, further pose serious threats to human and livestock health. Consequently, rapid and non-destructive determination of FHB severity is crucial for implementing timely and precise scientific control measures, thereby ensuring wheat supply security. Therefore, this study adopts hyperspectral imaging (HSI) combined with a lightweight deep learning model. Firstly, the wheat ears were inoculated with Fusarium fungi at the spike’s midpoint, and HSI data were acquired, yielding 1660 samples representing varying disease severities. Through the integration of multiplicative scatter correction (MSC) and uninformative variable elimination (UVE) methods, features are extracted from spectral data in a manner that optimizes the reduction of feature dimensionality while preserving elevated classification accuracy. Finally, a lightweight FHB severity discrimination model based on MobileNetV2 was developed and deployed as an easy-to-use analysis system. Analysis revealed that UVE-selected characteristic bands for FHB severity predominantly fell within 590–680 nm (chlorophyll degradation related), 930–1043 nm (water stress related) and 738 nm (cell wall polysaccharide decomposition related). This distribution aligns with the synergistic effect of rapid chlorophyll degradation and structural damage accompanying disease progression. The resulting MobileNetV2 model achieved a mean average precision (mAP) of 99.93% on the training set and 98.26% on the independent test set. Crucially, it maintains an 8.50 MB parameter size, it processes data 2.36 times faster, significantly enhancing its suitability for field-deployed equipment by optimally balancing accuracy and operational efficiency. This advancement empowers agricultural workers to implement timely control measures, dramatically improving precision alongside optimized field deployment.

To realize optical coupling between various nanostructured elements and nanoscale field confinement, a fundamental model of the near-field diffraction from a subwavelength hole pair within a conducting thin film is derived theoretically. Coupling effects between these two holes are investigated in detail using the near-field optical thin microcavity theory and the coupled-mode method, and the results are then verified via finite element simulations. Some extraordinary diffraction phenomena are found and are attributed to the following two coupling mechanisms: (1) the edge effect from the thin microcavity theory that occurs at each hole edge when an incident electric field illuminates the upper surface of the thin film; and (2) the enhanced in-plane electromagnetic waves that propagate along the two film surfaces and interact with each other in the vicinity of the holes. Analysis of the effects of the structural parameters on the transmittance shows that the coupling effect can be enhanced or attenuated by the interference conditions, depending on the incident wavelength and the phase difference determined by the hole–hole distance. The extraordinary diffraction effects presented here have potential for applications in near-field optical devices.

Lanthanum-doped strontium titanate (LST) perovskite is regarded as a promising candidate for high-temperature solid oxide fuel cells (HT-SOFCs) interconnect material. In this paper, dense LST membranes were deposited on YSZ and steel substrates at the deposition temperature of ~500°C by atmospheric plasma spraying (APS). The effects of particle size of LST powders on the chemical composition, phase composition, and electrical conductivity of LST deposits were studied due to the preferential evaporation of Sr during plasma spraying. When the LST particle size is 30 μm, the evaporation loss of Sr was greatly reduced. The electrical conductivity of APS-sprayed LST deposits after treatment in the reducing atmosphere reached 29.4-25.9 S/cm and 12.6-9.4 S/cm at 600-850°C in hydrogen and nitrogen atmosphere respectively. The LST coatings exhibited excellent phase and dimension stability in both reducing and oxidizing atmospheres during the test period at 900°C.

Stripe rust is one of the most common diseases challenging the safe production of wheat. Rapid identification and analysis of urediospores, responsible for disease transmission, are the key to preventing and controlling stripe rust. The current spore detection is time-consuming and requires auxiliary equipment, but many optical detection methods and sensors with high efficiency, sensitivity, and detection ability have been developed and widely used. Thus, the investigation of optical parameters is the prerequisite for optical sensitive detection and is detailed in this study. Firstly, the microscopic images and surface elements of wheat stripe rust urediospores were obtained using a high-resolution electron microscope and an energy spectrum analyzer. The reflectivity and absorptivity spectra in the near-infrared band of active/inactivate urediospores were measured. Further, the optical parameters, such as reflection phase shift, complex refractive index, and dielectric constant, of the urediospores were analyzed based on electromagnetic theory and Kramers–Kronig relation. The results revealed that the urediospores have a strong tolerance to near-infrared light, and the real part of the complex refractive index n was between 1.0 and 1.4. These observations indicate that whether the spores are active or not has little effect on the real part and dielectric constant of the complex refractive index but has a significant impact on the imaginary part and extinction coefficient of the complex refractive index, and the corresponding relationship between the optical properties of urediospores and biological components was established. These findings were verified with HPLC-MS and Near-Infrared Spectroscopy Analysis Technology and lay a theoretical foundation for detecting urediospores of wheat stripe rust by using optical sensors. The study provides a reference for the analysis of optical characteristics of other biological samples.