GMI sensor driven by DDS

The design and performances of a Giant Magneto-Impedance (GMI) sensor utilizing a Direct Digital Synthesizer (DDS) is presented. Since the GMI characteristics depend largely on the high frequency source parameters, the DDS, as a highly stable frequency source, could be advantageous for GMI sensors. The DDS technology allows digitally and dynamically programming of the waveform parameters with high accuracy which allows easily optimizing the sensor response. The sensing element is an amorphous (Co-Fe-Si-B) wire driven by a high frequency current delivered by the DDS and its voltage-to-current converter. To measure the voltage variation across the sensing element, a peak detector and a high gain amplifier with zero adjust are used. A DC bias magnetic field is applied to the sensing wire to get an asymmetric GMI effect. The sensor presents a sensitivity of 0.26 V/A/m and good linearity in a dynamic range of ± 25 A/m.