A high sensitive multi-parameter micro sensor for the detection of multi-contamination in hydraulic oil

A high sensitive multi-parameter micro sensor consisted of a microfluidic chip and a sensing unit is presented. The sensing unit, which composed of a dual-coil and two silicon steel sheets, is embedded in the simple microfluidic chip with a straight microchannel structure. The micro sensor can be used not only as an inductive sensor to distinguish between ferromagnetic and non-ferromagnetic metal particles, but also as a capacitive sensor to distinguish between water droplets and bubbles in hydraulic oil. The simulation results show that both the magnetic field and the electric field of the sensing unit are enhanced under the effect of the silicon steel sheets. In the experiments, the number of turns of the coil was optimized first, and then the comparative experimental results show that the detection amplitudes of both iron and copper particles were increased about four times compare with the sensing unit without silicon steel sheets, which verified the simulation results. Using the simple micro sensor, without any complicated external circuits, in the inductance detection experiments, we demonstrate the successful detection of 33 μm iron particles and 90 μm copper particles in hydraulic oil; and in the capacitance detection experiments, we can detect 100 μm water droplets and 180 μm bubbles in hydraulic oil. For both the inductance and capacitance detection, the results of particles with different sizes were in good agreement with the simulation results.