From the automobiles we drive and the factories that power our economy to the smartphones in our pockets and the medical devices that save lives, magnetic sensors are crucial components used to sense position, speed, and current. However, with the increasing demands of emerging applications, standard magnetic sensors have reached their limits. To achieve greater accuracy, lower power consumption, and improved reliability, an improved type of sensor is required. This article explores the principles of tunnel magnetoresistance, sensors that use this phenomenon, as well as performance benefits over previous magnetic sensing technologies. The evolution of magnetic sensing Hall effect sensors, which have been widely used for decades, operate on the effect discovered by Edwin Hall in 1879, which states that whenever a current-carrying conductor is placed in a magnetic field, it produces a voltage difference that is perpendicular to the current and magnetic field. While hall effect sensors are cost-effective components, their sensitivity is typically limited, making them unsuited for applications that demand high precision and the ability to detect weak magnetic signals.
Anisotropic magnetoresistance (AMR) sensors, another common technology, exploits the anisotropic magnetoresistance effect to achieve higher sensitivity compared to Hall effect types. In AMR sensors, the electrical resistance of a ferromagnetic material varies, based on the angle between the current flow and magnetization direction. While AMR sensors have higher sensitivity compared to Hall effect types, they typically have a lower signal-to-noise ratio (SNR). These sensors can also consume more power than Hall effect sensors, which can limit their suitability for low-power applications. Giant magnetoresistance (GMR) sensors, a more recent development, comprise multiple layers of ferromagnetic materials separated by thin non-magnetic layers. The resistance of this sensor changes significantly when exposed to an external magnetic field, allowing for higher sensitivity and improving the signal-to-noise ratio compared to hall effect and AMR sensors. GMR sensors have been applied in various products, including hard disk drives, automobiles, and biosensors. On the downside, however, depending on the application GMR sensors consume more power and are susceptible to external interfering magnetic fields.
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