Sensing Physical Fluid Properties in Microcavities Utilizing Diamagnetic Levitation

This contribution presents a concept for the measurement of density and viscosity of fluids in microfluidic systems. To do so, we utilize diamagnetically stabilized levitation of a small floater magnet, which is integrated and confined in a small cavity. When liquid is fed into the microreactor, buoyancy forces act on the floater magnet. Keeping the levitation height of the floater magnet constant in different liquid surroundings by accordingly adjusting the lifter magnet, the buoyancy force and, therefore, the density of the fluid can be determined. For viscosity measurements, we add an additional ac-driven coil to the setup, which yields a superposed alternating force causing periodic vibrations of the floater magnet. The vibrations are damped according to the viscosity of the surrounding fluid. By performing a frequency sweep, the frequency response of the damped spring mass resonator can be obtained.