Low Field Optimization of a Non-Contacting High-Sensitivity GMR-Based DC/AC Current Sensor

Abstract

Many applications require galvanic isolation between the circuit where the current is flowing and the measurement device. While for AC, the current transformer is the method of choice, in DC and, especially for low currents, other sensing methods must be used. This paper aims to provide a practical method of improving the sensitivity and linearity of a giant magnetoresistance (GMR)-based current sensor by adapting a set of design rules and methods easy to be implemented. Our approach utilizes a multi-trace current trace and a double differential GMR based detection system. This essentially constitutes a planar coil which would effectively increase the usable magnetic field detected by the GMR sensor. An analytical model is developed for calculating the magnetic field generated by the current in the GMR sensing area which showed a significant increase in sensitivity up to 13 times compared with a single biased sensor. The experimental setup can measure both DC and AC currents between 2–300 mA, with a sensitivity between 15.62 to 23.19 mV/mA, for biasing fields between 4 to 8 Oe with a detection limit of 100 μA in DC and 100 to 300 μA in AC from 10 Hz to 50 kHz. Because of the double differential setup, the detection system has a high immunity to external magnetic fields and a temperature drift of the offset of about −2.59 × 10−4 A/°C. Finally, this setup was adapted for detection of magnetic nanoparticles (MNPs) which can be used to label biomolecules in lab-on-a-chip applications and preliminary results are reported.

A voltage-pulse-modulated giant magnetoresistance switch with four flexible sensing ranges

“…In contrast, after applying a voltage pulse of +8 kV cm −1 , a slanted and slim loop was obtained, as shown in figure 3(b). The easy axis of the free layer was rotated to the [1][2][3][4][5][6][7][8][9][10] direction by applying a large H eff induced by the nonvolatile strain through a +8 kV cm −1 pulse. Since the direction of the testing field was fixed, the modulated easy axis to the [1-10] direction means the GMR effect was achieved in the orthogonal configuration between the free and pinned layers.…”

“…Accordingly, low and high MR states can be obtained to generate the switching properties. This is the operation process of the GMR switch to obtain on and off switching states [7][8][9]. Normally, the pinned field of the FM2/AFM is set to Nanotechnology Nanotechnology 32 (2021) 505504 (6pp) https://doi.org/10.1088/1361-6528/ac2392 be much larger than the operating range.…”

Current Progress of Magnetoresistance Sensors

“…Magnetic sensors (including MR sensors) have been widely applied in position sensing, current sensing, and non-destructive monitoring (Figure 11) [140][141][142][143][144][145][146][147][148][149][150]. In these applications, magnetic sensors are applied to detect the magnetic fields generated by the targets.…”

Integrated Magnetics and Magnetoelectrics for Sensing, Power, RF, and Microwave Electronics

“…Although the GMR/TMR effect offers great potential in sensing application thanks to their large MR change under external magnetic field, it has some major drawbacks including the non-linear response and hysteresis characteristic. Typically, a DC magnetic bias generated by the Helmholtz coils or permanent magnet can mitigate the issue [157]. Differential [114] and bridge [115] sensor configurations have also been adopted to improve the sensitivity and diminish the noise.…”