Monitoring of Repeatedly Heated Cooking Oil Quality using Different Types of Optical Fiber Sensors

Abstract

In recent times, optical fiber sensors have seen widespread utilization in diverse sensing applications, marking a notable trend. These applications encompass the detection of changes in refractive indices, temperatures, pressures, and even biological compositions. Hence, the primary aim of this study is to evaluate the quality of cooking oil that undergoes repetitive heating using a variety of optical fiber sensors, including optical fiber tip, d-shaped optical fibers, and fiber Bragg gratings (FBGs). Several types of cooking oil, exposed to different cooking cycles, were meticulously prepared and subjected to analysis using these three distinct optical fiber sensor types, employing both dip-coating and drop-casting techniques. In the drop-casting method, an amplified spontaneous emission (ASE) source is utilized to transmit light through the D-shaped optical fiber to an optical spectrum analyser (OSA). On the contrary, the tip-coating approach involves an optical fiber circulator to split optical signals that travel in opposing directions. The obtained findings demonstrate a progressive reduction in optical power levels and shifts in wavelengths as the cooking cycles progress. These wavelength shifts serve as indicators of the refractive index changes in the cooking oil, suggesting that the cooking oil that undergoes repeated heating shows enhanced light absorption. This observation supports the conclusion that the D-shaped optical fiber sensor, FBG, and optical fiber tip are capable of distinguishing cooking oil quality. It can be observed that the sensitivity of the D-shaped optical fiber sensor is 0.9 dBm per unit of cooking oil cycles which is 9 times better than the optical fiber tip sensor. This is due to the exposed area of the D-shaped sensor being larger than the optical fiber tip sensor. In addition, the D-shaped sensor demonstrated higher levels of sensitivity and consistency when detecting cooking oil quality. In fact, greater light absorption might be linked to more pronounced degradation, implying a decline in oil quality. Thus, cooking oils exhibiting lower refractive indices (RIs) are indicative of superior oil quality.