In this paper, a compact and highly sensitive refractive index plasmonic sensor, based on a metal-insulator-metal (MIM) waveguide coupled to double hexagonal ring-shaped resonators in the mid-infrared range, is proposed and analyzed using the finite-difference time-domain (FDTD) method embedded in the commercial simulator R-soft, where it has been found that the transmission peaks and dipspositions can be easily manipulated, by simply adjusting the structural parameters of the proposed design, such as the inner side length and the distance between the centers of the two hexagonal ring resonators. So, these parameters have a key role in the sensor's performances, and it is clearly noticed from the results, where a linear link between the refractive index of the material under testing and its wavelength resonances was established. Furthermore, the maximum achievable linear sensitivity was S = 4074 nm/RIU, with a matching sensing resolution of 2.45 x 10-6 RIU; the temperature sensitivity is around 1.55 nm/°C; and the highest linear sensitivity is S = 3910 nm/RIU in 0-200 g/L glucose concentration, making this proposed sensor an attractive one, to be implemented in high-performance nano and bio-sensing devices.
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