A Ferromagnetic Particle Sensor Based on a Honeycomb Permanent Magnet for High Precision and High Throughput

A multichannel passive ferromagnetic particle inductive sensor is proposed, which is mainly composed of a honeycomb permanent magnet and a set of coils. The honeycomb magnet generates the same high gradient static magnetic field in each channel (a total of seven channels, six surrounding, and one center), which helps improve the sensor's throughput while maintain high precision. An induced voltage model that includes most of the structural design parameters is proposed, which provides theoretical support for sensor optimization. The correctness of this model is verified by finite element simulation and experiments. The experimental results show that the detection performance of each channel is almost the same, which is expected to be further improved by setting a reference channel. Moreover, the sensor can detect 70 \mu \text{m} iron particles in a single channel of diameter 4 mm. The proposed sensor can reduce the influence of magnetic field radial uniformity on the induced signals, improve the detection precision, and achieve high throughput (about a 14-fold increase in throughput compared to our previous work). Its high precision and high throughput favor lots of lube oil detection.