Digital electronic conditioning approach for the high-sensitivity off-diagonal GMI sensors

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In this paper, the design and performance of a novel digital electronic conditioning for the off-diagonal Giant Magneto-Impedance (GMI) sensors are presented. The concepts and functions of this digital conditioning were implemented using Field-Programmable-Gate-Array (FPGA) reconfigurable circuits. This implementation consists of a Direct Digital Synthesizer (DDS) for the excitation of the GMI sensitive element and of a real-time quadrature digital demodulation of the voltage across the GMI element. This digital demodulation, which includes digital mixing and decimation, allows preserving important intrinsic characteristics of the off-diagonal configuration of the GMI sensors. In the case of GMI wires with transverse anisotropy as the Co-rich wire used in this study, these characteristics include the intrinsic asymmetric (odd) and the almost linear response of the off-diagonal component of the impedance near the zero-field, without the use of bias magnetic field and without employing additional offset canceling devices in the sensor chain. These features are important for the implementation of a number of linear sensors and magnetometers. The main rules for the implementation of this reconfigurable electronics for such GMI sensors are developed and explained throughout the paper. The first results and performance, in terms of response, sensitivity, equivalent magnetic noise, dynamic range, linearity and slew rate of the developed sensor, are presented and discussed.