Construction Of Automatic Measurement System For GMI Effect Based On Virtual Instrumentation

Giant Magneto-Impedance (GMI) effect has been a topic interest in the fields of high sensitive magnetic sensors and magnetic recording heads. Devices based on GMI effect have a great potential application. However, there are still some problems on the measurement system for GMI effect, such as low degree of automation, tedious data processing and so on. In order to study the accurate mechanism of GMI effect, and to develop advanced application system, an automatic measurement system with property of high speed, direct indication and easy operation is designed for GMI effect of amorphous microwires.The analysis of impedance by current intensity and voltage (I-V) based on virtual instrumentation was proposed as the measurement method. PXI system was selected as the hardware platform. Arbitrary waveform generator module card was employed to generate the driving voltage. Digital oscilloscope module card was used for signal acquisition. Programmable DC current source module card was adopted to control the strength of the external DC magnetic field by controlling the current of helmholtz coil. LabVIEW 8.2 was selected as the software platform. Three measurement ways were designed to meet different needs. The first way was scanning of driving voltage frequency (0-10 MHz) on single sample. The second way was scanning of driving voltage amplitude (0-5 V) on single sample. The third way was to measure several samples under the same condition, which would be possible to compare different results directly.After testing the as-cast and treated glass-coated amorphous microwires (Co68Fe5Ni1B14Si12 )made by Taylor-Ulitovsky technique, it was found that the experiment results were consistent with the theoretical analysis. There were many factors influencing the GMI effect, including the frequency and amplitude of driving voltage, the anisotropic magnetic field, the glass-coated layer and so on. The maximum value of GMI effect was high up to 160%. All of above had confirmed the validity of this automatic measurement system.