The Fresnel equations of reflectivity of electromagnetic wavelengths in the range of 100nm to 1000nm were adopted in this work, and a simulation program was constructed using MATLAB b2018 based on the transfer matrix for a three-layer system. The layers are FD60_Dense flint prism, brass variable thickness layer (10 - 80) nm with step changes 10nm, and water layer, for improving the sensitivity of (SPR) sensor based Kretschmann’s configuration. Numerical results have demonstrated that there is no surface plasmon resonance sensor within the range of wavelengths (100 – 500) nm, while it appears weak in visible region and well in (IR) region at wavelengths (900 and 1000) nm. The phenomenon of SPR begins to gradually weaken with the increasing brass layer thickness. Also, the Full width at Half Maximum (FWHM) is decrease with increased brass layer thickness and SPR dip length (H). While the best values obtained for sensitivity were in the visible region at the wavelength of 700nm, where it was almost stable with an increase in the thickness of the brass layer from 20nm to 50nm and with values higher than 115 deg/RIU. But in the infrared region, the sensitivity was between (100 to 103) deg/RIU and almost stable for brass layer thicknesses from about 20nm to 60nm. No previous study has examined this wide range of wavelengths. Through the simulation, we were able to determine the best range of wavelengths that can be used for the purpose of designing an aqueous or biological sensor based on the brass layer with a thickness between 40 nm to 50 nm.
