A magnetostrictive pressure sensor is a type of transducer that measures pressure by utilizing the magnetostrictive effect, which refers to the phenomenon where certain materials change their shape when exposed to a magnetic field. This effect occurs in materials that exhibit magnetostriction, a property where their dimensions change in response to variations in magnetic fields.
The working principle of a magnetostrictive pressure sensor can be explained in the following steps:
Construction: The sensor is typically composed of a magnetostrictive element, a sensing element, and an external magnetic field generation system. The magnetostrictive element is a wire or rod made of a magnetostrictive material, usually an alloy containing elements like Terfenol-D (terbium, dysprosium, and iron). The sensing element is a tube or diaphragm that experiences the applied pressure. The external magnetic field generation system generates a magnetic field around the magnetostrictive element.
Magnetic field application: The external magnetic field generation system applies a steady magnetic field to the magnetostrictive element.
Pressure application: When pressure is applied to the sensing element (tube or diaphragm), it causes the sensing element to deform slightly.
Magnetostriction effect: Due to the magnetostrictive property of the material, the application of pressure causes a change in the shape and dimensions of the magnetostrictive element. This change in shape causes the propagation of torsional stress waves along the length of the element.
Propagation of torsional waves: The torsional stress waves travel along the magnetostrictive element at a constant speed.
Time of flight measurement: The sensor detects the torsional waves at two points along the magnetostrictive element. One point acts as a transmitter, generating the waves, and the other point acts as a receiver, sensing the waves. The time it takes for the torsional waves to travel between these two points is measured.
Pressure determination: The time difference in the wave propagation between the two points is directly related to the distance traveled by the waves, which, in turn, is influenced by the length of the magnetostrictive element. Since the length of the element changes with the applied pressure, the time difference can be used to calculate the pressure applied to the sensing element.
Output and calibration: The pressure sensor provides an output signal (usually electrical) that corresponds to the measured pressure. Calibration is performed to convert the output signal into meaningful pressure values using a calibration curve or equation.
In summary, a magnetostrictive pressure sensor measures pressure by detecting the time of flight of torsional stress waves generated in a magnetostrictive element due to the pressure-induced changes in its shape. The measured time difference is then converted into pressure readings using calibration. This type of sensor is known for its accuracy and durability in industrial and harsh environments.