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A plastic optical fiber (POF) temperature sensor with high sensitivity is experimentally demonstrated in this work. The temperature sensor is realized by a combination of macrobending and an unclad region in the fabrication of its sensor head. The POF sensor is bent into a balloon-like structure in order to introduce the effect of macrobending. For the optimization of the sensor performance, the bending radius of the balloon-like structure is varied. Experimental results suggest that the performance is optimized when the bending radius is fixed at 55 mm. With this amount of bending radius, temperature sensitivity of up to 22.2 × 1 0 − 3 ∘ C − 1 can be achieved in the range from 40°C to 80°C, with linearity of 0.99 and resolution of 0.45°C. This technique is found to improve the POF temperature sensitivity in comparison to previous developments.

The measurement of uric acid based on the optical absorption at visible light spectrum is investigated and tested. Sensing in the visible region was conducted for determination of suitable wavelength that produces high sensitivity and accuracy performance based on the Beer-Lambert law calculation. In this work, the uric acid is detected by detecting sodium urate as a product of chemical reaction between uric acid with sodium hydroxide buffer. The setup has been tested for uric acid concentration ranging from 15 mg/dL to 85 mg/dL. Three wavelengths have been analyzed which are 460 nm, 525 nm and 630 nm. Measured data at 460nm wavelength exhibits the highest sensitivity, which is 0.0012 (mg/dL)-with 86.51% accuracy. Detection of uric acid at visible light spectrum offers a low-cost sensor based on visible LEDs and photodiode is possible to be realized.

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Soil is a medium for plant roots to grow, absorb water and necessary solutes for growth. Soil macronutrient testing is helpful for determining the nutrients content in soil before applying fertilizer for quality and process controls of agricultural produce and soil fertility. Spectroscopy is an emerging technology which is rapid and simple has been widely used in agricultural and food analysis processes. The capability of spectroscopy to characterize material from the transmission or absorbance has been used in this paper to measure nitrogen (N), phosphorus (P) and potassium (K) content in non-agriculture soil. The paper details preliminary characterization of soil spectroscopy with a Deuterium-Halogen light source and Ocean Optic spectrometer to measure the absorbance level of the macronutrients. The extracted nutrients were mixed with the colour reagent and specific colored solution was developed. Two soil samples have been employed for the experimental characterization, which are mud flood and kaolin. The result shows that high absorbance level of N at 450 nm in wavelength, P at 750 nm for both samples.  The absorbance level of K was measured high at 500nm for mud flood and 450nm for kaolin. In addition, the tested macronutrients give similar wavelength of peak absorbance level at 970 nm for both samples. For future works, the optical measurements will be implemented using visible and near infrared LED and the photodetector in order to replace the spectrometer usage for soil spectroscopy. This would lead to achieve the primary objective of this research in developing a simple and low cost spectroscopy uses light-emitting diode (LED).