The flexibility of amorphous Giant Magneto-Impedance (GMI) micro wires makes them easy to use in several magnetic field sensing applications, such as electrical current sensing, where they need to be deformed in order to be aligned with the measured field. The present paper deals with the bending impact, as a parameter of influence of the sensor, on the GMI effect in 100 µm Co-rich amorphous wires. Changes in the values of key parameters associated with the GMI effect have been investigated under bending stress. These parameters included the GMI ratio, the intrinsic sensitivity, and the offset at a given bias field. The experimental results have shown that bending the wire resulted in a reduction of GMI ratio and sensitivity. The bending also induced a net change in the offset for the considered bending curvature and the set of used excitation parameters (1 MHz, 1 mA). Furthermore, the field of the maximum impedance, which is generally related to the anisotropy field of the wire, was increased. The reversibility and the repeatability of the bending effect were also evaluated by applying repetitive bending stresses. The observations have actually shown that the behavior of the wire under the bending stress was roughly reversible and repetitive.

A new concept of a high-frequency amplitude detector and demodulator for Giant-Magneto-Impedance (GMI) sensors is presented. This concept combines a half wave rectifier, with outstanding capabilities and high speed, and a feedback approach that ensures the amplitude detection with easily adjustable gain. The developed detector is capable of measuring high-frequency and very low amplitude signals without the use of diode-based active rectifiers or analog multipliers. The performances of this detector are addressed throughout the paper. The full circuitry of the design is given, together with a comprehensive theoretical study of the concept and experimental validation. The detector has been used for the amplitude measurement of both single frequency and pulsed signals and for the demodulation of amplitude-modulated signals. It has also been successfully integrated in a GMI sensor prototype. Magnetic field and electrical current measurements in open- and closed-loop of this sensor have also been conducted.

A proof-of-concept of the use of a fully digital radiofrequency (RF) electronics for the design of dedicated Nuclear Magnetic Resonance (NMR) systems at low-field (0.1 T) is presented. This digital electronics is based on the use of three key elements: a Direct Digital Synthesizer (DDS) for pulse generation, a Software Defined Radio (SDR) for a digital receiving of NMR signals and a Digital Signal Processor (DSP) for system control and for the generation of the gradient signals (pulse programmer). The SDR includes a direct analog-to-digital conversion and a Digital Down Conversion (digital quadrature demodulation, decimation filtering, processing gain…). The various aspects of the concept and of the realization are addressed with some details. These include both hardware design and software considerations. One of the underlying ideas is to enable such NMR systems to “enjoy” from existing advanced technology that have been realized in other research areas, especially in telecommunication domain. Another goal is to make these systems easy to build and replicate so as to help research groups in realizing dedicated NMR desktops for a large palette of new applications. We also would like to give readers an idea of the current trends in this field. The performances of the developed electronics are discussed throughout the paper. First FID (Free Induction Decay) signals are also presented. Some development perspectives of our work in the area of low-field NMR/MRI will be finally addressed.

Electrical current measurement by a Giant Magneto-Impedance (GMI) sensor may require the sensitive element (amorphous wire) to be aligned with the magnetic field produced by the conductor (toroidal configuration), which involves a bending stress. In this paper, a first study is made to investigate the impact of bending stress on a GMI sensor. For practical GMI sensor implementation, the offset and intrinsic sensitivity are crucial parameters. This is why these quantities have been evaluated in both diagonal and off-diagonal configurations. A Co-rich amorphous wire (from Unitika Ltd.) of 100 μm diameter and 15 cm length was used. The off-diagonal voltage was measured through a pick-up coil. The wire was bent over a cylinder with a radius of 2.5 cm. The excitation frequency was 800 kHz. In the diagonal configuration, the sensitivity at a given bias field, Hbias, was decreased by 50% in the bent position compared to the straight position. The offset also decreased by 25%. In the off-diagonal configuration, the sensitivity around zero decreased by about 28%. The offset stayed quasi-null during the test. These results showed that the off-diagonal configuration seems to be best suited for an application as a current sensor that involves bending. The reversibility and repeatability of the bending effect have been evaluated under 10 successive bending stresses. It was showed that the effect is quite reversible and repetitive.

This paper deals with practical issues and solutions related to the use of the giant magnetoimpedance (GMI) for electrical current measurement. It presents an overview of a full attempt of design and realization of an almost industrial GMI-based current sensor or clamp. The sensor combines dc and ac measurements with the same flexible sensitive element. This paper addresses several practical problems encountered in a real measurement environment. In this context, main attention was paid to the impact of the influence quantities that largely condition the implementation strategies and solutions of the sensor. For the intended industrial application, these influence quantities first include the operating temperature. Its impact on the intrinsic sensor response was investigated in an almost industrial temperature range. Second, bending stress on the sensitive element is another involved influence parameter in the toroidal and flexible structure of the sensor. The effect of this was also characterized. Finally, the third considered influence parameter is the effect of magnetic disturbances. These include the eccentricity of the conductor of interest and the impact of the surrounding magnetic fields such as the earth's field or fields produced by other conductors in close proximity to the sensor. Different strategies of implementation and solutions, taking into account the impact of influence parameters, were proposed and compared. A sensor prototype was realized, and its first performances were given.

In this paper, the torsional stress effect on Giant Magneto-Impedance (GMI) was studied in Co-rich amorphous wires. The study, which was conducted in the context of the development of a current clamp based on GMI, considered torsion as a parameter of the influence of this sensor. Both diagonal, Z₁₁, and off-diagonal, Z₂₁, components of the impedance tensor were investigated. The samples were Co-rich wires with a 100 µ diameter. The wires were twisted positive and negative angles with respect to a reference position. For each component of the impedance, the intrinsic sensitivity and offset were measured as a function of the rotation angle. The results showed that the sensitivity of the diagonal component at a given working point slightly increased for angles between −90° to +90°, whereas the sensitivity was almost constant for the off-diagonal component at zero-field. The intrinsic offset in the diagonal configuration was almost unchanged for the rotation angles considered, whereas this offset increased in the off-diagonal configuration. Furthermore, the GMI ratio of Z₁₁ was also measured as a function of the rotation angle for comparison purposes with known data. The maximum of this ratio was obtained for a rotation angle of about 50°.