Sensitivity improvement of GMI magnetic and pressure transducers for biomedical measurements

Abstract

This work presents an experimental study aiming the sensitivity optimization of Giant Magnetoimpedance (GMI) sensors, by means of properly choosing the values of their conditioning parameters. The optimized GMI sensors, together with the development of improved transduction electronic circuits, can lead to the sensitivity enhancement of GMI biomedical, pressure and magnetic transducer prototypes, previously developed by the research group at LaBioMet, PUC-Rio. Those prototypes are, respectively, aimed at the measurement of arterial pulse waves and the localization of magnetic foreign bodies inserted in the human body. Thus, the experimental characterization of GMI ribbon-shaped samples (Co 70 Fe 5 Si 15 B 10 ) was performed, as a function of the external magnetic field, including the experimental evaluation of the asymmetric GMI effect (AGMI). The parameters that affect the behavior of the GMI samples were experimentally analyzed, such as the DC level (0 mA to 100 mA) and frequency (100 kHz to 10 MHz) of the excitation current, as well as the samples length (1 cm, 3 cm, 5 cm and 15 cm). The conditioning parameters, experimentally identified, that optimize the GMI samples sensitivity lead to a maximum specific sensitivity of 0.84 W·Oe -1 ·cm -1 (8400 Ω ·T -1 ·cm -1 ). A new electronic circuit was developed for conditioning and reading of the GMI samples, which directly contributed to the performance enhancement of both transducers. The electronic circuits developed were evaluated supposing the operation of the GMI samples in their most sensitive region. Comparing to previously developed prototypes, the optimum sensitivity achieved for the new configuration of the GMI magnetic transducer increased about 9 times (from 0.12 mV/nT to 1.08 mV/nT), and the sensitivity of the modified pressure transducer increased approximately 7 times (from 1 mV/Pa to 7 mV/Pa).