Micro helical robots actuated by an external magnetic field have been investigated for a possible application to treat occlusive vascular disease. It requires a high-speed rotating magnetic field (RMF) which generates fast drilling motion of the micro helical robot to tunnel the clogged lesions in blood vessels.1-3 The RMF is generated by the magnetic navigation systems (MNSs) composed of multiple coils or electromagnets. However, as the frequency increases, the impedance from the inductance of the coils decreases the current and the magnetic field. To overcome this problem, prior researchers utilized a resonance by including additional capacitance to their MNS.2,3 The electromagnets with magnetic cores generate a large magnetic field.4 Unlike the MNS with coils only, the MNS with electromagnets has significant mutual-inductance due to the magnetic flux linkages between electromagnets, but any resonance method suppressing the self and mutual inductances of the electromagnets of the MNS has not been reported. We propose a method to suppress both the self and mutual-inductance effect of the 3-phase MNS with multiple electromagnets. First, we set the imaginary part and the real parts except the resistance in the voltage equation to be zero to express the resonance. After solving the real part of the voltage equation and the actuation matrix equation which relates applied current with flux density together, we can determine 3-phase currents and corresponding phases at resonance. The capacitance at resonance can be determined by solving the imaginary part in the voltage equation. Fig. 1 shows the 3-phase MNS developed for the experiments and Fig. 2 shows the calculated and measured 3-phase currents and RMF with the application of the proposed method to generate a magnetic flux density of 10 mT. It shows that the calculated current matches well with the measured one within 5 % discrepancy. The proposed method in this research can contribute to improving the tunneling performance of micro helical robots by generating a high-speed RMF even in the MNS with the electromagnets.

References:

1Q. Wang, X. Du, and L. Zhang, “Real-time ultrasound Doppler tracking and autonomous navigation of a miniature helical robot for accelerating thrombolysis in dynamic blood flow,” ACS Nano, vol. 16, no. 1 (2022).
2K. T. Nguyen, B. Kang and J. Park, “High-frequency and High-powered electromagnetic actuation system utilizing Two-stage resonant effects,” IEEE/ASME Transactions on Mechatronics, vol. 25, no. 5 (2020).
3J. Nam, W. Lee, and G. Jang, “Magnetic navigation system utilizing resonant effect to enhance magnetic field applied to magnetic robots,” IEEE Transactions on Industrial Electronics, vol. 64, no. 6 (2017).
4J. Nam, W. Lee, E. Jung, and G. Jang, “Magnetic navigation system utilizing a closed magnetic circuit to maximize magnetic field and a mapping method to precisely control magnetic field in real time,” IEEE Transactions on Industrial Electronics, vol. 65, no. 7 (2018).