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A novel method has been used for accurately measuring low voltage signals (~[10.sup.-4] V) associated with inductance changes of bilayer thin-film sensors under bending stress. In this paper the architecture of the system is first presented, and then the design ideas and key technologies are followed. Initially, the frequency modulated signals were simulated with superimposed noise signals to test the demodulation performance of the written program. From the results, the expected output of the program was confirmed. Following this, the frequency modulation technique was used with actual sensor signals to measure the displacement of a bilayer thin film sensor. The results from the acquisition were compared with a previously developed amplitude modulation based setup, and it proved that the frequency modulation system provided a robust and accurate solution to evaluate magnetostrictive materials and their application in magnetic sensors. Index Terms--Amorphous magnetic films, frequency modulation, magnetic sensors, magnetostriction.

Amorphous magnetic glass-covered wires are of interest for basic research and potential applications. Their specific magnetic behavior originates in their very small diameters and in the high internal stresses induced during preparation. Removal of the glass cover leads to significant changes in their magnetic properties and behavior, thus improving their suitability for sensing applications. A thorough study of the changes produced by the glass removal implies the consideration of the changes produced in the internal stress distribution. We propose a method for the calculation of the residual internal stress distribution in wires obtained after the glass removal, based on the results of the magnetic measurements. The residual internal stress distribution allows us to explain the magnetic behavior of these wires. We also present the advantages of wires obtained after the glass removal from the practical point of view in comparison with those of conventional amorphous wires.

In this paper we report some results concerning the dependence of the pulsed voltage output on the exciting magnetic field and on the bias magnetic field applied at the exciting or receiving point, for [Fe.sub.77.5][Si.sub.7.5][B.sub.15] amorphous wires used as delay lines. The obtained results show a strong dependence of the pulsed voltage output on the values of the magnetic fields. Magnetic fields up to about 2000 A/m applied at the receiving point can be detected. Small magnetic fields applied at the exciting point can be detected using small values of the exciting magnetic field. Using this technique magnetic field sensors with high accuracy and sensitivity and absence of hysteresis can be realized. Such sensors can be formed in integrated arrays measuring the distribution of the magnetic field along the magnetostrictive delay line axis.

In this paper we report some results on the dependence of the pulsed voltage output on the applied torsion or tensile stress in [Fe.sub.77.5][Si.sub.77.5][B.sub.15] amorphous wires used as magnetostrictive delay lines. The obtained results show a not monotonic dependence of the response of the delay line on applied torsion. For applied tensile stress the response could be fitted by a linear curve for as-cast wires and by an exponential curve for annealed wires. The good ratio between minimum and maximum magnetostrictive delay line signals and the absence of hysteresis suggest the possibility to use this technique in load cells and torque sensors.