Theoretical verification of photonic crystals sensor for biodiesel detection and sensing

Among the two past decades, the biodiesel fuels received a significant attention due to its lower hydrocarbon emissions and low sulfur diesel. However, the incomplete transesterification represents the main problem for the possibility of wider use. Thus, we present in this research a new method for detecting and measuring of methyl ester biodiesel fuel based on its optical characteristics. The proposed sensor is designed using the well-known one dimensional photonic crystals. The cornerstone of our idea is mainly based on two sides. First, the inclusion of methyl ester as a defect layer inside the one dimensional photonic crystals gives rise to the formation of a resonant peak within the photonic band gap. Second, the concentration of the converted methyl ester due to the transesterification reaction of soybean oil is closely related to its refractive index. Therefore, the sensing and detection procedure is essentially based on the dependence of the characteristics of the resonant peak on the concentration of the biodiesel fuel. The parameters that refer to the performance of our sensor such as, the sensitivity, figure of merit and the detection limit are investigated. Moreover, the effect of the defect layer thickness and the angle of incidence on the performance of our sensor is demonstrated. The numerical results show that our design could provide high sensitivity of 136 nm RIU(-1)and figure of merit 2240 RIU-1. In addition to that, it could differentiate between the different biodiesel fuels despite the very limited difference between their indices of refraction.