A Multi-Parameter Microfluidic Particle Sensor Based on Permalloy for High Sensitivity

Abstract

Technologies for particle detection in lubricating or hydraulic oil are essential in mechanical industries to avoid constant machinery failure. The existing technologies utilize offline or online methods. Some of the online methods either have weak sensitivity or can only detect one type of particle. This article presents a highly sensitive, multi-parameter sensor for detecting various particles in hydraulic oil. This design takes advantage of high magnetic permeability and shielding efficiency of permalloy, placed behind dual opposite planar coils with a straight microchannel structure to improve the sensitivity of the sensor. The design includes both an inductive mode sensor, which can detect and distinguish ferromagnetic and nonferromagnetic metallic particles, and a capacitive mode sensor, which can detect and distinguish air bubbles and water droplets. Comparative COMSOL simulation and experiment were used to investigate the effect of permalloy and the results show that the sensor with permalloy has higher sensitivity compared to the sensor without permalloy. The sensor with permalloy successfully detected 15-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> iron particle, 55-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> copper particle, 75-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> water droplet, and 95-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> air bubble. This research shows the application of permalloy in the sensitivity improvement of microfluidic sensors.