Design, fabrication, and characterization of giant magnetoresistance (GMR) based open-loop current sensor with U-shaped current carrying conductor

In this work, an open-loop current sensor based on giant magnetoresistance (GMR) effect in magnetic multilayered systems was designed and developed. The whole design of the current sensor consisting of a magnetic field sensing element, a current-carrying conductor, a permanent magnet, and a magnetic shield was conceptualized through FEM analyses. The simulated model was then replicated into a prototype device and the output characteristics were investigated thoroughly under different ambient conditions. It was observed that in an analog mode, the sensor output was linear in the current range of± 50 A over the temperature range of − 40 °C to 125 °C and showed a − 3 dB frequency response at 7.5 kHz. A thermal drift and offset were observed at the analog output which further compensated through a commercial mixed-signal conditioner. The compensated output showed a total error less than 1% F.S. over the operating temperature range of − 25 °C to 105 °C

A novel AMR based angle sensor with reduced harmonic errors for automotive applications

The paper presents the development of a novel anisotropic magnetoresistive sensor for measurement of angle in the interval 0° to 180°. A sensor is comprised of two Wheatstone bridges arranged at 45° to each other. A unique design is proposed wherein each resistive element of the Wheatstone bridge was formed with strips of varying widths. It results in a substantial reduction in harmonics errors due to the dispersion of the shape anisotropy field values within each element. The reduced harmonic errors also lead to a drastic reduction of hysteresis error (60%) and offer better accuracy with a signal amplitude of 18 mV/V even in weak fields of ≤80 G. Further, the sensor was employed in the development of a pedal position sensor. The preliminary results of the development are presented, indicating the usability for industrial and automotive applications

Evolution of magnetoresistance behaviour at low temperatures in naturally oxidised specular spin valve systems

The temperature dependent magnetoresistive behaviour of field cooled naturally oxidised specular spin valve systems has been studied in the temperature range of 300–10 K. Inconsistent to the non-specular spin valve system, an anomalous behaviour was evolved with large exchange bias and higher coercivity, below 200 K. The structural investigations inferred the formation of magnetic oxides with higher density gradient in the pinned layer, and the observed anomalous behaviour at low temperatures was correlated with the antiferromagnetic ordering of these oxides in spin glass state. The uncompensated interfacial magnetism of the nano-oxide layer was further confirmed by comparing with low temperature magnetoresistive behaviour of non-magnetic oxide based specular spin valve systems

MgO based specular spin valve with reversible minor loop and higher exchange bias for futuristic linear magnetic field sensor

Specular spin valves (SVs) containing ultrathin MgO, structured as substrate/seed/AF/PL1/MgO/PL2/Cu/FL/MgO/cap, have been fabricated. Both structural and magnetic characterizations of MgO based specular spin valve (SSV) have been performed and compared them with the measured data on naturally oxidized (NO) and conventional spin valves (CSV), grown under optimised condition. Reversible minor loop characteristics, highest exchange bias of 625 G and 10% magnetoresistive (MR) ratio were important observations in MgO based system. Zero hysteresis behavior was confirmed due to the reduction of grain growth of the stacks above the fine-textured MgO layer, through X-ray diffraction measurements. Interestingly, at 10 K, above 100% enhancement in MR ratio was observed in MgO based system with marginal increase in coercivity of the order 1 G. On the other hand, NO based structure has 10% MR, minor loop hysteresis of 2 G and exchange bias of 560 G at room temperature; however at 10 K, only 75% enhancement in MR ratio with large anomalies in magnetic measurements attributes due to the AFM nature of oxide materials. The above studies reflects the superior performance of MgO based SSV over a wide range of temperature in comparison to other SV structures and may lead to futuristic linear magnetic field sensor applications

Design and development of GMR based low range pressure sensor for medical ventilator application.

In this report, we present a thermally compensated low range magnetic pressure sensor. The fabricated sensor consists of a corrugated stainless steel (SS) diaphragm, a permanent magnet, a giant magnetoresistance (GMR) sensor, and a signal conditioning unit. The diaphragm with a permanent magnet produces a magnetic field which changes under the exposure of external pressure. The GMR sensor is placed asymmetrically with reference to the cylindrical axis of a magnet, which results in an output voltage proportional to external pressure. Simulations were performed to optimize the design having a linear output with higher sensitivity of the order of 14.97 μV/V/mbar, which is close to the experimentally measured value of 13 μV/V/mbar at room temperature. The sensor prototypes were fabricated in pressure ranges: ± 30 and ± 70 mbar. The fabricated pressure sensor prototypes were tested in different temperature ranges and calibrated for offset, linearity, and thermal variations using a commercial sensor signal conditioner. The performance of the calibrated sensors was evaluated at different temperatures and over an extended period. Furthermore, the performance of the sensor was experimentally evaluated in an indigenously developed medical ventilator, and compared with an existing commercial MEMS pressure sensor for a longer duration. The performance of the prototype sensor was found to be equivalent with an accuracy of ±0.1 mbar for an operation in the range of ± 30 mbar