A High Sensitivity Micro Impedance Sensor Based on Magnetic Focusing for Oil Condition Monitoring

A high sensitivity micro impedance sensor is presented for oil condition monitoring. The sensor consists of a microfluidic chip and a sensing unit. The sensing unit contains two solenoid coils and eight silicon steel tips, which can generate a highly focusing magnetic field. The micro impedance sensor can not only distinguish between ferromagnetic and non-ferromagnetic metal particles, but also water droplets and air bubbles in oil. The simulation results show that the magnetic induction is significantly improved due to the silicon steel tips, and the electric field intensity is also slightly enhanced. In the inductance experiments, the sensitivity is extremely improved based on magnetic focusing by silicon steel tips, iron particles with diameters down to 18\mu m and copper particles with diameters down to 75 \mu \text{m} have been successfully detected by using the simple high sensitivity micro impedance sensor. In the capacitance experiments, the signal to noise ratio (SNR) of the micro impedance sensor with silicon steel tips is slightly improved; water droplets with diameters down to 100 \mu \text{m} and air bubbles with diameters down to 200 \mu \text{m} have been detected. The high sensitivity micro impedance sensor has been demonstrated to achieve the precise measurement of particle sizes and the accurate counting of microparticles.