A Multiband Microwave Sensor Designed to Sense the Shelf Life of Raw Fresh Milk

The nutritional benefits of milk and its widespread consumption make drinking only fresh and healthy milk important. Safely consuming milk necessitates differentiating between fresh and spoiled milk, which can lead to stomach disturbance and food-borne illness. Researchers and the food industry work hard to maintain milk quality by devising techniques to impede spoilage and determine the duration for how long milk remains fresh. In this study, three different split-ring microstrip resonators (multi-SRRs) with passive elements were planned and fabricated on printed circuit boards (PCD). Each resonator operated at a separate resonant frequency: 3, 4, and 5 GHz with amplitudes of −10.91, −11.53, and −26.26 dB, respectively. The simulation and experimental results were identical when the sensor was tested by placing a Petri dish covering its upper surface. To better understand the lifespan of fresh buffalo milk, we investigated it in a controlled setting. This sensor was used to study how long fresh milk remains suitable for use. For 14 h, we analyzed the resonant amplitude variations (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta $ </tex-math></inline-formula>Amplitude) and monitored pH levels to estimate shelf life. The maximum rate of resonant amplitude change was found by calculating the slope of the linear model representing shelf life during the initial 8 h. The calculated values were 0.588, 0.361, and 0.159 dB/h, respectively, each with high coefficients of determination. The instrument can discern between fresh milk with a pH of 6.85–6.57 and spoiling milk (pH 6.57–5.46). Our results showed that the sensor had high-resolution and nondestructive monitoring capabilities, with results that closely agreed with pH meter readings and microscopic images.