Capacitive Droplet Sensing for Milk Quality Analysis

Milk is an essential food item for all age groups. It contains nutrients like fat, protein, carbohydrates, Vitamin and minerals. Unfortunately, adulteration in milk is a very common practice. Milk adulterants pose serious health problems. In developing countries like India, a significant percentage of total production is handled by unorganized sectors like milkmen, local vendors and middlemen. Various conventional milk quality testing techniques require huge sample sizes and are expensive hence only suitable for industrial applications. Capacitive sensing has the potential to test the quality of milk using a very small sample size. In this work, our motivation was to develop a compact, cost-effective and drop-based non-contact capacitive sensor for milk quality testing. This paper presents the fabrication of a parallel plate capacitive sensor using copper-cladded PCB for milk quality testing. Experiments are conducted on packaged full-fat and skimmed milk after adulteration with different volumes of tap water. The change in capacitance values due to the interaction of sample droplets with a uniform electric field between electrodes is recorded using the AD7150 Evaluation board. This system detects adulteration in terms of capacitance peaks. The shift in capacitance values obtained for pure full-fat milk, pure skimmed milk and pure water are 20.238 fF, 20.33 fF and 40 fF respectively. For each adulterated test sample, the shift in peaks lying between pure milk and pure water shows an increasing trend with an increase in the percentage of water adulterant.