A novel sensing chip with dual-coil inductance for determining raw milk quality

• A novel inspection method with dual-coil inductance has developed for evaluating the quality of raw milk.
• The device principally contains a silicon-based chip with two co-planar coils.
• Using the phase variation between both coils, the somatic cell count of the raw milk was evaluated.
• The measurement sensitivity in terms of SCC is 3°/log(SCC) at an excitation frequency of 9 MHz.

This paper presents a novel inspection method that uses dual-coil inductance to evaluate the quality of raw milk. The device principally contains a silicon-based chip with two co-planar coils, which is fabricated using a simple microelectroplating process. When the coils are entirely immersed in raw milk and a specific alternating electrical signal is applied to one of the coils, the other coil induces a phase-shifted electrical signal because of the effect of eddy currents. Using the phase variation between both coils, the quality of the raw milk, in terms of the somatic cell count (SCC), can be evaluated, because the milk from a cow that suffers from mastitis is a better conductor of electric current. In this study, the characteristics of the magnetic inductance for a specified coil design and its sensing performance are simulated and evaluated using COMSOL software and by experiment. The experimental results show that higher SSCs cause larger phase shifts. This shift increases as the excitation frequency is increased. For a typical fabrication result, using a sensing coil with 25 loops, the measurement sensitivity in terms of SCC is 3°/log(SCC) at an excitation frequency of 9 MHz. The proposed dual-coil chip reduces size and cost and has a rapid response, which allows efficient quality inspection of raw milk.