# Analysis and Comparison of Electromagnetic Microrobotic Platforms for Biomedical Applications
## 3 The Electromagnetic Microrobotic Systems  
The magnetic microrobot can be efficiently actuated by the utilization of magnetic field and/or its gradient. This magnetic field could be generated from an EMA platform, that must obviously comprises some electromagnetic sources. The magnetic sources could be produced by either permanent magnets [29; 51; 52; 53; 54; 55; 56] or electromagnets [42; 48; 49; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78], that  
Figure 3: The diagram of the specifications of EMA system design for (**a**) 2D and (**b**) 3D workspace. should be selected according to the specified biomedical application. The main advantage of permanent magnet sources is that they do not require an external power supply, and they exhibit an advantageous volume to field-strength ratio [52]. However, in such case the magnetic fields can not be accurately adjusted or switched off [54]. In contrast, electromagnets can generate appropriate and flexible magnetic fields to effectively control the movement of microrobots. This study focuses on applications where magnetic fields and/or their gradients need to be continuously changed, and EMA setups using electromagnets are primarily considered in the following. The simplest electromagnet is wrapped around an air-filled core. In such case, the magnetic fields or their gradients can be uniformly defined in the workspace, and linear relationship can be expressed with their input currents. However, in such case, the strength of the magnetic field is weaker than using a permanent magnet on an equivalent volume. To increase the strength, a magnetic core with a high magnetic permeability can be added inside the coil to confine and guide the magnetic fields. The magnetic field is related to the electric current as well as to the properties of the magnetic core. Nevertheless, EMA system with several core-filled electromagnets may exhibit nonlinear and coupled behavior. Furthermore, the EMA systems can also be distinguished into stationary and mobile. Stationary magnetic sources commonly use Helmholtz, Maxwell and saddle coils [61, 62, 63, 64, 65, 67, 69, 71, 74, 84], as in MRI system [85, 86, 87, 88], to induce magnetic fields and gradients that only are controlled by the current flowing into the electromagnetic coils. With such stationary configurations, the magnetic manipulation of the microrobot together with the workspace geometry remains limited by the stationary arrangement of coils. Conversely, moving magnets (e.g., actuated by a robotic system) can move around the target to enhance the manipulability of microrobots [88, 89]. As the magnetic sources usually remain close to the microrobot, the moving coils also reduce the energy demand. In addition, they can change the local field distribution by adjusting the positions and/or orientations of the magnets [60, 73]. As shown in Figure 4a, [PERSON] et al. [51] propose the use of nonuniform magnetic fields emanated from from a single rotating-permanent magnet manipulator for the control of magnetic helical microrobots, where the robotic arm brings the magnet closer to the patient, and the axial and radial controls cause the local magnetic field to change. Stereotaxis Inc. (Stereotaxis Inc., St. Louis, MO, USA, [[http://www.stereotaxis.com](http://www.stereotaxis.com)]([http://www.stereotaxis.com](http://www.stereotaxis.com)) accessed on: 23 November 2021 has developed and commercialized the Niobe(r) robotic magnetic navigation system presented in Figure 4b. Niobe(r) uses two permanent magnets mounted on pivoting arms and positioned on opposing sides of the operating table to control proprietary catheters and guide-wires that have very small magnets at their distal tips. To circumvent the uncontrollability of the magnetic field generated by permanent magnets, [PERSON] et al.