Maria Neagu

Bio: Maria Neagu is an academic researcher from Alexandru Ioan Cuza University. The author has contributed to research in topics: Amorphous solid & Magnetostriction. The author has an hindex of 10, co-authored 71 publications receiving 409 citations.

Non-destructive evaluation distribution sensors based on magnetostrictive delay lines

Abstract: In this paper, we present a non-destructive evaluation sensor able to perform distribution measurements on metallic surfaces. The sensing principle is based on the magnetostrictive delay line (MDL) technique. The pulsed MDL excitation field generates eddy currents on the test surface, which are balanced when no cracks are present. In case of cracks, these eddy currents are summed up around the inhomogeneity, thus causing microstrain generation in the region of the MDL close to the crack. The amplitude and time delay of the detected pulsed voltage signals corresponding to those additional microstrains caused by the eddy currents, are the indication of the size and the position of the defect on the test surface. In this paper, we present the sensing principle as well as the first results in such kind of measurements.

Ni–Ag thin films as strain-sensitive materials for piezoresistive sensors

Abstract: Some results concerning the electrical, electromechanical and structural properties of Nix–Ag1−x (for x values between 0.35 and 0.50) thin films in view of their utilization for manufacturing pressure and force sensors are presented. As compared to the well known Ni–Cu (constantan) alloys, which are widely used for these type of sensors, Nix–Ag1−x thin films exhibit gauge factor values of the same order of magnitude, but they are much more corrosion resistant and adherent to the substrate. The influence of composition and post-deposition annealing on the electrical resistance, temperature coefficient of resistance and gauge factor of Nix–Ag1−x thin films is discussed.

Sound velocity in magnetostrictive amorphous ribbons and wires

Abstract: In this paper we present results on the dependence of the longitudinal sound velocity of amorphous magnetostrictive ribbons and wires, tested either in the as-cast stage or after stress relief on the magnetic field along the anisotropy axis. Results show a variation of the sound velocity that is in good agreement with results concerning the triangle E/E effect. Results are also given concerning the change in sound velocity for magnetostrictive ribbons and wires before and after annealing. These results can be used to decide the kind of treatment and biasing field of such materials when they are to be used as magnetostrictive delay lines.

A new magnetic field sensor based on magnetostrictive delay lines

Abstract: A magnetic field sensor based on the dependence of the magnetostrictive delay line (MDL) response on its biasing magnetic field is presented in this paper. Such a sensor can be formed in an integrated array measuring the distribution of field along the MDL axis. Experimental results are reported for amorphous FeSiB wire MDL's, showing that high sensitivity and nonhysteresis are two advantages of this type of sensor.

Wafer-Scale Synthesis and Transfer of Graphene Films

Abstract: We developed means to produce wafer scale, high-quality graphene films as large as 3 in. wafer size on Ni and Cu films under ambient pressure and transfer them onto arbitrary substrates through instantaneous etching of metal layers. We also demonstrated the applications of the large-area graphene films for the batch fabrication of field-effect transistor (FET) arrays and stretchable strain gauges showing extraordinary performances. Transistors showed the hole and electron mobilities of the device of 1100 ± 70 and 550 ± 50 cm2/(V s) at drain bias of −0.75 V, respectively. The piezo-resistance gauge factor of strain sensor was ∼6.1. These methods represent a significant step toward the realization of graphene devices in wafer scale as well as application in optoelectronics, flexible and stretchable electronics.

A soft magnetic wire for sensor applications

Abstract: The main magnetic characteristics regarding the domain structure and magnetization processes (axial, circular and Matteucci and inverse Wiedemann effects) of amorphous wires and glass-coated microwires are analysed. Magnetic bistability, spontaneously observed in samples with large enough ratio magneto-elastic anisotropy with axial easy axis to shape anisotropy, is the main source for a number of sensor applications in pulse generators, position and field sensors, encoded security tags, rotational counters, magnetostrictive delay lines, and so on. The relevant perspectives of the novel giant magneto-impedance effect recently reported and observed in non-magnetostrictive samples are also introduced.