Peripheral arterial diseases like thrombosis are dangerous for global health. Having blood clots in your blood vessels can lead to conditions like acute limb ischemia (ALI), where blood flow to a limb is suddenly decreased, which threatens its viability. There are already ways to treat these blood clots, all with their advantages and disadvantages. A new way to treat these blood clots is with untethered magnetic robots (UMRs). UMRs are already used for blood clot removal in ex vivo tissue environments. These UMRs are controlled by a robotic arm with a rotating permanent magnet (RPM) on it, which moves the UMR within the blood vessel using a magnetic field. At low actuation frequencies, the UMR synchronously rotates with the rotating magnetic field. However, when the RPM rotates above a certain frequency, the applied magnetic torque is not strong enough to counteract the drag torque, causing the UMR's angle to not be synchronised with the magnetic field anymore. This frequency is called the step-out frequency. When actuating above the step-out frequency, the velocity of the UMR quickly declines.
Recent research suggests that adding a second RPM could lead to higher UMR step-out frequency, which results in a higher propulsive thrust. This could improve UMR performance when swimming against a flow, which could help get closer to using UMRs in the human body.
In this assignment, a second RPM was implemented in the system. First, a controller was designed to synchronise the angles of the two RPMs when the RPMs are rotating. After this, the step-out frequency of the UMR with varying UMR-RPM distances was modelled. The step-out frequency of a UMR was measured for the single RPM setup and the two RPM setups for multiple UMR-RPM distances to validate this model.
In the end, both the model and the experiments proved that a two RPM setup improves the step-out frequency of a UMR. The average increase in step-out frequency was 84.5% in the experiment and 74.5% for the model calculations.