A magnetostrictive sensor is a type of sensor used to measure physical quantities like distance, pressure, or stress based on the principle of magnetostriction. Magnetostriction refers to the phenomenon where certain materials change their shape or dimensions when subjected to a magnetic field.
The working principle of a magnetostrictive sensor involves three main components:
Waveguide: The waveguide is typically a metallic rod made of magnetostrictive material such as nickel or iron. It serves as the core of the sensor and is designed to transmit mechanical waves, usually in the longitudinal direction.
Excitation coil: The excitation coil surrounds the waveguide and generates a magnetic field when an electrical current passes through it. This magnetic field magnetizes the magnetostrictive waveguide.
Sensing coil: The sensing coil is also wound around the waveguide but located at a specific distance from the excitation coil. It serves as a magnetic field sensor and detects the changes in the magnetic field caused by the magnetostrictive effect in the waveguide.
Here's how the sensor operates:
Excitation phase: To start the measurement process, an electrical current is applied to the excitation coil, creating a magnetic field around the waveguide. This magnetic field magnetizes the waveguide.
Mechanical wave generation: When an external force is applied to the waveguide (e.g., due to pressure, stress, or displacement), it undergoes physical changes in length or shape. This leads to the propagation of mechanical waves along the waveguide in both directions, away from the point of excitation.
Arrival of the mechanical wave: The mechanical wavefront travels along the waveguide until it reaches the sensing coil. When the wavefront arrives at the sensing coil, it alters the magnetic field in the region surrounding the coil.
Magnetic field detection: The sensing coil is connected to a sensitive detector that measures the changes in the magnetic field. The detector interprets these changes, which are proportional to the distance or physical quantity applied to the waveguide.
Signal processing: The output from the detector is then processed and converted into meaningful data, providing information about the physical parameter being measured. Depending on the application, the sensor can be designed to provide analog voltage signals, digital signals, or other forms of output.
The key advantage of magnetostrictive sensors is their high accuracy and reliability. They can be used in various applications, including position sensing in industrial machinery, liquid level measurement, and pressure sensing in hydraulics, to name a few. However, they can be relatively expensive compared to other sensor types and may require careful installation to avoid external interferences.