The 2007 Nobel Prize in Physics can be understood as a global recognition to the rapid development of the Giant Magnetoresistance (GMR), from both the physics and engineering points of view. Behind the utilization of GMR structures as read heads for massive storage magnetic hard disks, important applications as solid state magnetic sensors have emerged. Low cost, compatibility with standard CMOS technologies and high sensitivity are common advantages of these sensors. This way, they have been successfully applied in a lot different environments. In this work, we are trying to collect the Spanish contributions to the progress of the research related to the GMR based sensors covering, among other subjects, the applications, the sensor design, the modelling and the electronic interfaces, focusing on electrical current sensing applications.

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Magnetic Field Sensors Based on Giant Magnetoresistance (GMR) Technology: Applications in Electrical Current Sensing.

Advanced sensing and measurement techniques are key technologies to realize a smart grid. The giant magnetoresistance (GMR) effect has revolutionized the fields of data storage and magnetic measurement. In this work, a design of a GMR current sensor based on a commercial analog GMR chip for applications in a smart grid is presented and discussed. Static, dynamic and thermal properties of the sensor were characterized. The characterizations showed that in the operation range from 0 to ±5 A, the sensor had a sensitivity of 28 mV·A−1, linearity of 99.97%, maximum deviation of 2.717%, frequency response of −1.5 dB at 10 kHz current measurement, and maximum change of the amplitude response of 0.0335%·°C−1 with thermal compensation. In the distributed real-time measurement and monitoring of a smart grid system, the GMR current sensor shows excellent performance and is cost effective, making it suitable for applications such as steady-state and transient-state monitoring. With the advantages of having a high sensitivity, high linearity, small volume, low cost, and simple structure, the GMR current sensor is promising for the measurement and monitoring of smart grids.

A current sensor based on the giant magnetoresistance effect: design and potential smart grid applications.

Smart living is a trending and connected lifestyle that envisions efficient and sustainable energy utilization, stable and reliable power supply, intelligent and coordinated transportation and mobility, and personalized and cost-effective healthcare. Its realization needs the Internet of Things (IoT). IoT is a compelling platform connecting trillions of sensors and collecting data for connectivity and analytics. It is more advanced than traditional monitoring systems where limited sensors and wired communication can merely collect fragmented data in the application domains. Spintronic sensors with the superb measuring ability and multiple unique advantages can be one of the critical sensing devices supporting the IoT and enabling smart living. In this paper, we review successful applications of individual spintronic sensors in electrical current sensing, transmission and distribution lines monitoring, vehicle detection, and biodetection that can help to fulfill the promises of smart living in energy management, power delivery, transport, and healthcare. The wireless spintronic sensor networks (WSSNs) working at the massive interconnected network level are proposed and illustrated to provide pervasive monitoring systems, which facilitate the intelligent surveillance and management over building, power grid, transport, and healthcare. The database of collected information will be of great use to policy making in public services and city planning. This paper provides insights for realizing smart living through the integration of IoT with spintronic sensor technology.

Overview of Spintronic Sensors With Internet of Things for Smart Living

A compensation method for the sensitivity drift of a magnetoresistive (MR) Wheatstone bridge current sensor is proposed. The technique was carried out by placing a ruthenium temperature sensor and the MR sensor to be compensated inside a generalized impedance converter circuit (GIC). No internal modification of the sensor bridge arms is required so that the circuit is capable of compensating practical industrial sensors. The method is based on the temperature modulation of the current supplied to the bridge, which improves previous solutions based on constant current compensation. Experimental results are shown using a microfabricated spin-valve MR current sensor. The temperature compensation has been solved in the interval from 0 °C to 70 °C measuring currents from −10 A to +10 A.

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A non-invasive thermal drift compensation technique applied to a spin-valve magnetoresistive current sensor.

This paper proposes a low-cost technique to compensate for the temperature dependence of piezoresistive pressure sensors configured in a Wheatstone bridge. The sensor is treated as a resistive circuit and three equivalent resistances are measured by setting appropriately the bridge terminals. One of these equivalent resistances depends on temperature but not on pressure and, hence, it can be used to compensate for the temperature dependence of the output parameter. In such a way, neither data of a previous temperature calibration nor additional components are required to compensate for the temperature dependence. The proposed technique is applied to a commercial pressure sensor, which is measured by means of a direct sensor-to- microcontroller interface circuit. Experimental results show that temperature effects on the pressure measurement decrease more than ten times when the proposed technique is applied.

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Novel and low-cost temperature compensation technique for piezoresistive pressure sensors

A compensation method of the sensitivity drift of the Wheatstone bridge sensor is proposed. The technique was carried out by placing a temperature sensor and the bridge to be compensated inside a generalized impedance converter with input reference current. No internal modification of the bridge arms is required so that the circuit is capable to compensate practical industrial sensors. The method is based on the temperature modulation of the current supplied to the bridge, which improves previous solutions based on constant current compensation. Experimental results are shown using a commercial magnetoresistive bridge sensor.

Temperature compensation of Wheatstone bridge magnetoresistive sensors based on generalized impedance converter with input reference current

In this article a differential temperature-to-time converter is presented using two thermistors in a generalized impedance converter, polarized in direct current. The voltage drop in one of the thermistors depends on the differential temperature at which both thermistors are exposed. Such voltage drop is compared to a signal which changes exponentially by obtaining a time interval which depends on the differential temperature. The results of the experimental tests support the theorethical analysis performed and at the same time offer a new possibility of application of the generalized impedance converter as a signal conditioning circuit.

Enrique Castro Montero

Papers

Temperature compensation of Wheatstone bridge magnetoresistive sensors based on generalized impedance converter with input reference current

Signal conditioning for differential temperature measurement with thermistors using a generalized impedance converter.