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A key issue with surface plasmon resonance (SPR) biosensors, which are the focus of many researchers, is improving their sensitivity to detect lower amounts of analyte in a solution. Most SPR developments have focused on the grating-based sensitivity-enhancement approach. In addition to sensitivity, a substantial enhancement of other sensor characteristics such as resolution and signal-to-noise ratio (SNR) is desired for designing a practical sensor. So, in this paper, the characteristics of surface plasmon polaritons sustained by 1D subwavelength metallic gratings on a thin metal slab (under the Krestchmann configuration) have been investigated numerically for the analyte-ligand interactions detection. Effects of different structural parameters, such as grating period, grating depth, metal film thickness, and fill factor have been evaluated on the sensor sensitivity as well as resolution and SNR. Numerical results indicate that the sensor working in the near-infrared wavelength has a better performance than that in the visible one. The result of numerical investigation has been used to design an optimized sensor with the best figure of merit.

Recurrence plot (RP) and recurrence quantification analysis (RQA) have been used for studying the dynamic behaviour of gas-solid fluidised beds. RQA variables (recurrence rate, determinism, laminarity and entropy) were calculated for the bubbling fluidised bed at different superficial gas velocities (ranging 0.1-1.5 m/s) and aspect ratios (1, 1.5 and 2). Patterns within RP changed with these various conditions, and subsequently RQA parameters changed accordingly. These changes can be potentially useful to study the bed hydrodynamic. It was shown that transition from bubbling to turbulent velocity can be determined by the variation of recurrence rate and entropy.

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A metallic subwavelength grating structure built on a thin gold film is studied for surface plasmon resonance (SPR) detection of refractive index variations of biological buffer solutions. By employing finite element analysis as a numerical method, characteristics of the angle interrogated SPR sensor were calculated and discussed in a broad operating wavelength varying from visible to near-infrared (NIR). The effects of grating structural parameters such as grating depth, grating period, and grating fill factor in different operating wavelengths have been evaluated on the sensor performance parameters of sensitivity, full width at half-minimum, minimum reflectance at resonance, and resonance angle. Numerical results indicate that adjusting grating geometrical parameters can enhance the performance parameters of the sensor especially in the NIR wavelengths. The enhanced sensor performance parameters for optimizing grating geometry have been explored in detail for visible and NIR wavelengths of 633 and 984 nm, respectively. These findings are important for developing localized surface plasmon sensors with enhanced performance.