Exploring the Feasibility of a Magnetic-Based Probe for Detecting Ferromagnetic Contaminants in Water

In this work, the feasibility of a sensing device to be employed for the real-time measurement of ferromagnetic contaminants in water is shown. Ferromagnetic materials, characterized by a high magnetic permeability, belong to the broader family of heavy metals, whose contribution in water pollution is well known. To measure their presence in water, a novel prototype of probe structure is designed and implemented. The probe integrates a Tunneling Magnetoresistance (TMR) sensor and a permanent magnet positioned at a fixed distance: the presence of the ferromagnetic materials in water is detected by the probe once it is inserted in water, by measuring the variation in the magnetic field generated by the permanent magnet by means the TMR sensors. The voltage output of the TMR sensor is then acquired and made available through an ad-hoc conditioning electronic and a microcontroller unit. To demonstrate the effectiveness of the proposed approach, tests were performed in the laboratory using ultrapure water in which increasing quantities of the three ferromagnetic elements present in nature (i.e., iron, cobalt and nickel) are added. The results of the tests demonstrate a linear relationship among the ferromagnetic materials concentrations in water and the TMR sensor output, demonstrating the feasibility of the proposed approach and the usability of the designed probe also for real-time, in-situ measurements.