Fiber Bragg grating has embraced the area of fiber optics since the early days of its discovery, and most fiber optic sensor systems today make use of fiber Bragg grating technology. Researchers have gained enormous attention in the field of fiber Bragg grating (FBG)-based sensing due to its inherent advantages, such as small size, fast response, distributed sensing, and immunity to the electromagnetic field. Fiber Bragg grating technology is popularly used in measurements of various physical parameters, such as pressure, temperature, and strain for civil engineering, industrial engineering, military, maritime, and aerospace applications. Nowadays, strong emphasis is given to structure health monitoring of various engineering and civil structures, which can be easily achieved with FBG-based sensors. Depending on the type of grating, FBG can be uniform, long, chirped, tilted or phase shifted having periodic perturbation of refractive index inside core of the optical fiber. Basic fundamentals of FBG and recent progress of fiber Bragg grating-based sensors used in various applications for temperature, pressure, liquid level, strain, and refractive index sensing have been reviewed. A major problem of temperature cross sensitivity that occurs in FBG-based sensing requires temperature compensation technique that has also been discussed in this paper.
In this study, the authors present three different metamaterial absorbers (MMAs) namely, T, split‐I (SI) and split‐Jerusalem cross (SJC) with different dimensions and geometrical configurations. The absorption rates of T‐, SI‐ and SJC‐shaped absorbers are studied at microwave frequencies. T‐shaped absorber demonstrates perfect absorption at 10.19 GHz, making it suitable for single band operation, whereas SI‐shaped absorber exhibits two perfect absorption peaks at 9.32 and 10.75 GHz finding its application in dual band operation. However, novel SJC‐shaped absorber demonstrates multiple absorption peaks at 9.92, 10.42, 10.93, 11.75 and 13.25 GHz with absorption of 99.5, 91, 99.9, 91.8 and 99.6%, respectively, making it suitable for X‐ and Ku‐band operations. The proposed MMAs have a thickness of around 0.8 mm (i.e. <λ/37) with respect to the lowest frequency of operation. Furthermore, the absorbers are analysed for different angles of polarisation and incidence for transverse electric polarised wave with a step size of 15°. The proposed absorbers have been fabricated and experimentally demonstrated at X‐band verifying the results obtained from simulations and implementing an equivalent circuit method. Further, SJC‐shaped absorber is demonstrated for multi‐and wide‐band terahertz applications exhibiting four perfect absorption peaks at 2.76, 2.89, 3.02 and 3.31 THz.
We present a high-performance bilayer graphene (BLG) and mercury cadmium telluride (Hg1−xCdx=0.1867Te) heterojunction based very long wavelength infrared (VLWIR) conductive photodetector.
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