AMR Sensors (Magnetic Sensors)Fundamentals of magnetic sensors: what is an AMR (magnetic) sensor?

Basic characteristics of AMR sensors

What is AMR?

AMR is an abbreviation for Anisotropic Magneto Resistance. These are elements that have a function where the resistance decreases when a magnetic field is applied, and this function is dependent on the direction of the magnetic force lines applied to the element (anisotropic).

Material of the AMR element is ferromagnetic metal

The material of the AMR element is a ferromagnetic metal that is an alloy of nickel, iron, and other metals.
Because the positive and negative sides have symmetric characteristics, the same operation is performed even if the north and south poles of the magnet are reversed. This characteristic is used to enable the gathering of high-accuracy, high-reliability data without making contact. Also, the capability of detecting without contact can be used in a wide range of applications such as open/close detection, rotation detection, and position detection.

Output type

Digital output

Murata's sensors are built on the same PCB as the ICs and AMR elements. An IC is used to perform digital processing of the analog signals from the AMR element, and the output is converted to Hi and Lo level digital output so that no signal processing is required by the customer.

What is the AMR (magnetic) sensor sensitivity?


The sensitivity of the AMR sensor is the strength of the magnetic force that turns on (or off) the AMR sensor. The ON sensitivity (Hon) is the magnetic force that turns on the AMR sensor which was off with no or weak magnetic field, and the OFF sensitivity (Hoff) is the magnetic force that turns off the AMR sensor which was on with a strong magnetic field. The sensitivity of the AMR sensor varies by AMR sensor, and the Hon and Hoff in the datasheet indicate the specific range for that product.

For example, the sensitivity standards for the MRMS501A-001 are "Hoff: 0.5mT to Hon: 2.5mT".

What are the advantages of AMR sensors?

Lineup with wide range of sensitivities and sizes

Our product lineup features a wide range of sensitivities, responsiveness, and current consumptions so that you can choose the optimal product for your application.
*For a list of our products, check the Selection Guide.

Supports flexible placement and design

The operation of AMR (magnetic) sensors does not change even when the north and south poles of the magnet are reversed.
In this way, the characteristics of compact and high-accuracy AMR sensors enable a wider sensitivity area than Hall effect sensors, and so this allows more flexible placement of magnets and sensors for reducing mounting discrepancies in the casing and at installation.
Also, because they are not mechanical components like reed switches, they have a compact size and high reliability.
For details, see "Fundamentals: Differences from Reed Switches".

Advantages of magnetic sensors

Magnetic force lines are invisible. Magnetic force lines are not absorbed by plastic and other non-magnetic bodies and pass through to the opposite side. Magnetic sensors use these features to enable detection.
For example, the advantages can be easily utilized in the following usage situations.

Compact size, switch location is not visible

Notebook computer open/close detection and security device activation settings

Optimal for structures where sealing is important

Gas, water, and other rotation detection

Easily adaptable into a waterproof structure

Power switches of wearable devices

*Sensor unit requires current