Application of an array laser–cantilever–magnet measurement sensor incorporated with digital shearography in a Lorentz force particle analyzer

A Lorentz force particle analyzer (LFPA) is a contactless measuring apparatus used to detect inclusions or defects within metallic materials. A laser–cantilever–magnet (LCM) sensor is a reliable method to measure the variations of Lorentz force caused by inclusions in LFPA. In this paper, digital shearography technology, whose displacement resolution is up to 30 nm, is involved in an array LCM measurement sensor to acquire the displacement distribution of the array cantilever. The experimental setup is constructed, and the three-step phase-shifting method is selected to calculate the displacement of cantilevers. The array LCM sensor is arranged in a staggered two-row configuration, and the interval of each sensor is set as 2 mm to avoid mutual disturbance through the numerical method. In the measuring experiment, a pre-experiment, which generates periodic deformation of the cantilever using a piezoelectric ceramic actuator, is first conducted to verify the reliability of the system. Then, dynamic measurement experiments under three different conditions are conducted, and the displacement distributions of the array cantilever are obtained by the phase difference map. The dynamic experimental results show that the displacement of the cantilevers is in the order of μm. Meanwhile, the variation of the Lorentz force and the deformation of the cantilever caused by defects in three different conditions are calculated by numerical simulation. Finally, the results of the experiments and numerical simulations under various conditions are compared. The displacements of the cantilevers are very close in all cases, indicating that the array LCM sensor incorporated with digital shearography technology is robust and reliable to measure the minute force changes in LFPA.