GMI magnetic sensor operating with a Direct Digital Synthesizer (DDS)

This paper presents the design and performances of a Giant Magneto-Impedance (GMI) magnetic sensor utilizing a Direct Digital Synthesizer (DDS) as a highly stable frequency source. This DDS technology can be advantageously used for GMI sensors since the GMI characteristics depend largely on the parameters (frequency, amplitude, mean value) of the high frequency driving current. With the DDS technology, these parameters could be digitally and dynamically programmed with high accuracy so as to allow for an ease of optimization of the sensor response. The developed sensor consists of an amorphous (Co-Fe-Si-B) wire as a GMI sensing element which is driven by a high frequency current delivered by the DDS and its voltage-to-current converter. A peak detector and a high gain amplifier with zero adjust ensure the measurement of the variation of the voltage across the sensing element. To get an asymmetric GMI effect, a DC bias magnetic field is applied to the sensing wire. The sensor presents a sensitivity of 0.26 V/A/m and good linearity in a dynamic range of ± 30 A/m.