A magnetoresistive sensor, also known as a magnetoresistor or magnetic field sensor, is a device used to measure the strength and direction of a magnetic field. It relies on the magnetoresistive effect, which is the change in electrical resistance of certain materials in response to an applied magnetic field. This effect allows the sensor to convert the magnetic field's intensity into an electrical signal that can be measured and analyzed.
The fundamental principle behind the operation of a magnetoresistive sensor is based on the fact that when a magnetic field is applied to a magnetoresistive material, the electrons' motion within the material is affected. This, in turn, leads to a change in the material's electrical resistance. There are two main types of magnetoresistive effects used in sensors:
Anisotropic Magnetoresistance (AMR): In AMR sensors, a thin film of a magnetoresistive material, often a ferromagnetic material like nickel-iron alloys, is used. The electrical resistance of the material changes depending on the angle between the direction of the current flowing through it and the direction of the applied magnetic field. When the field is parallel to the current, the resistance is lower (minimum), and when perpendicular, the resistance is higher (maximum).
Giant Magnetoresistance (GMR): GMR sensors use multiple thin layers of ferromagnetic and non-magnetic materials. The electrical resistance in GMR sensors is highly sensitive to the relative orientation of the magnetic moments in these layers. When a magnetic field is applied, it causes a significant change in resistance, enabling precise magnetic field measurements.
The sensor's output is typically processed by electronic circuits to convert the resistance variation into a voltage signal that can be further calibrated and converted to meaningful magnetic field values. The output can be in the form of an analog voltage, a digital signal, or a communication protocol like I2C or SPI, depending on the sensor's design and application.
Magnetoresistive sensors find applications in various fields, such as magnetic compasses, position and motion sensing, current measurements, automotive applications, and magnetic storage devices (e.g., hard disk drives). Their advantages include high sensitivity, low power consumption, and compact size, making them valuable tools for accurately measuring magnetic fields in a wide range of applications.