High Sensitivity Differential Giant Magnetoresistance (GMR) Based Sensor for Non-Contacting DC/AC Current Measurement

Abstract

This paper presents the design and implementation of a high sensitivity giant magnetoresistance (GMR) based current sensor with a broad range of applications. The novelty of our approach consists in using a double differential measurement system, based on commercial GMR sensors, with an adjustable biasing system used to linearize the field response of the system. The work aims to act as a fully-operational proof of concept application, with an emphasis on the mode of operation and methods to improve the sensitivity and linearity of the measurement system. The implemented system has a broad current measurement range from as low as 75 mA in DC and 150 mA in AC up to 4 A by using a single setup. The sensor system is also very low power, consuming only 6.4 mW. Due to the way the sensors are polarized and positioned above the U-shaped conductive band through which the current to be measured is flowing, the differential setup offers a sensitivity of about between 0.0272 to 0.0307 V/A (signal from sensors with no amplifications), a high immunity to external magnetic fields, low hysteresis effects of 40 mA, and a temperature drift of the offset of about −2.59×10−4 A/°C. The system provides a high flexibility in designing applications where local fields with very low amplitudes must be detected. This setup can be redesigned for a wide range of applications, thus allowing further specific optimizations, which would provide an even greater accuracy and a significantly extended operation range.

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

“…In this way, equivalent currents down to 100 μA can be measured. Typical current sensors include the AC/DC current transformers [ 2 , 3 , 4 ], fluxgate magnetometers [ 5 , 6 ], Hall effect sensors [ 3 , 7 ], anisotropic magnetoresistive (AMR) [ 3 , 8 ], giant magnetoresistance (GMR) [ 2 , 3 , 9 , 10 ] and tunnelling magneto-resistance (TMR) sensors [ 2 , 11 ].…”

“…Also, it should be mentioned that for MR sensors the response characteristics like sensitivity, linearity, saturation field, noise, etc., are strongly affected by the magnetic properties of the utilized materials, the structure of their underlying multilayered and the layout of the microfabricated sensor. A short review of MR effects, underlying the physical origin of AMR, GMR and TMR, and the specific field behavior was presented in [ 10 ].…”

“…The GMR effect occurs in multilayered magnetic structures of the type FM/NM/FM coupled by exchange interaction; here FM denotes magnetic layers like Ni 80 Fe 20 , Co, CoFeB, etc., and NM denotes a nanometer thick conductive nonmagnetic layer as Cu, Ag. If the NM is a dielectric of the type Al 2 O 3 or MgO 2 we talk about a TMR structure [ 10 , 11 ]. In GMR effect the resistance changes according to the angle between the directions of the magnetization of adjacent layers.…”

“…Usually, one of the ferromagnetic layers is pinned by an anti-ferromagnetic (AFM) layer of FeMn or IrMn while the second FM layer has the magnetization free to rotate under the action of an external magnetic field. Such that, a GMR structure is of the type substrate/buffer layer (Ta)/FM(free layer)/NM/FM(pinned layer)/AFM/Cap layer [ 10 ].…”

“…Compared with AMR based sensors, the GMR sensors offer higher field sensitivity, wide frequency range, and do not require an internal coil (for example, of type KMZ51) or external controlled magnetic field to be used to reset the magnetization to the initial orientation [ 8 ]. However, most of the GMR sensors have a nonlinear behaviour around zero field and the output is unipolar which limits the application for bipolar and AC fields [ 9 , 10 ]. Until now, several methods of improving the response of a GMR sensor have been used.…”