Limau madu sweetness measurement using low-frequency capacitor fixture and microwave monopole sensor / Hudaliyana Ghazali

The main objective of the current study was to create a fast, portable and real-time measurement method as well as to develop a non-destructive sensing technique in determining sweetness of Limau Madu. A total number of 100 Limau Madu has been collected from an orchard in Slim River, Perak. Other orchards are not selected for sample collection due to their long distance from the lab in UiTM, Shah Alam. The distance is a significant factor due to the limitation of storage capacity in the lab. The reflection coefficient, S11 of monopole antenna was measured at the feed point of the sensors by a Vector Network Analyzer (VNA). The operating frequency for antenna ranges from 85 MHz to 5 GHz. In contrast, the capacitance method uses a voltage divider circuit to obtain Vout and the capacitance value is then calculated. Following prior studies, the operating frequencies for capacitance method are 10 MHz, 15 MHz, 20 MHz and 25 MHz. The selected range of frequency would yield a different range of results. In addition, the internal qualities such as °Brix, pH, moisture content and acidity are measured destructively using an appropriate instrument. °Brix and acidity are measured using refractometer while pH is measured using pH meter. Limau Madu undergo drying process to obtain the moisture content. Evaluation of S11 and °Brix by using monopole antenna indicate strong correlation at the frequency of 2.4 GHz with the R2 value of 0.8945 which is higher than other frequencies and a relative error of 0.7232 which is lowest than other frequencies. This error can be minimized by adding sample size and ensure calibration is done prior to measurement. However, even with this error, it is possible to predict the sweetness of the Limau Madu. Other measured parameters such as acidity, pH and moisture content also contribute to the stability of frequency at 2.4 GHz. Meanwhile, for the capacitive sensing technique, the correlation with °Brix is strong with an R2 value of 0.6750 at 15 MHz. These results prove that measurement at a specific frequency can provide a better result of the correlation between non-destructive and destructive parameters. Based on the destructive result for °Brix values, the rating can be categorized into poor and average.