Investigation of a Magnetic Levitation Density Measurement System

Magnetic levitation systems are widely used for density measurements in biomedical research and sensor technologies. These systems consist of pairs of magnets with like poles facing each other, creating a repulsive magnetic field. Levitation occurs as diamagnetic particles are suspended in a paramagnetic fluid between the magnets. The force acting on the particles is proportional to the product of the magnetic field and its gradient, while the concentration of the paramagnetic fluid influences the magnitude of the force. To optimize sensor performance, both magnetic field strength and paramagnetic ion concentration must be considered. In this study, two magnets in an anti-Helmholtz configuration (62 × 3 × 12 mm) were used, with a variable gap distance (g). Experimental analysis was conducted to investigate the effect of magnetic field strength and fluid concentration on levitation behavior. Initially, g was set to 1.8 mm, and Gadolinium-based paramagnetic fluid (Gadovist) was prepared at 30 mM, 45 mM, and 60 mM concentrations. Microplastic particles with densities of 1.05 g/cc and 1.09 g/cc were added into the solutions. Levitation heights, measured relative to the bottom magnet, increased with concentration: 0.60–0.51 mm and 0.43–0.39 mm at 30 mM; 0.70–0.66 mm and 0.49–0.47 mm at 45 mM; and 0.76–0.71 mm and 0.63–0.61 mm at 60 mM for 1.05 g/cc and 1.09 g/cc particles, respectively. In the second stage, g was increased to 2.4 mm and 3 mm using 60 mM fluid. Levitation heights were 0.69–0.68 mm and 0.55–0.49 mm at 2.4 mm; and 0.65–0.64 mm and 0.48–0.47 mm at 3 mm, respectively. These results were compared with theoretical calculations, and sensor performance was evaluated for different application scenarios, contributing to the development of future levitation-based sensing systems.