# Analysis and Comparison of Electromagnetic Microrobotic Platforms for Biomedical Applications
## 1 Introduction  
Magnetically actuated microrobots are of great interest for the development of innovative biomedical operations. The need to improve interventional operations has led to a wide range of minimally invasive procedures. Since most current operations are limited by the manual action of the surgeon, various robotic systems have been proposed to enhance minimally invasive surgery (MIS) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]. Unlike the need of using rigid instruments with dexterous distal wrists, it is commonly more appropriate to use robotic tools that access internal tissues through small skin incisions [15, 16, 17, 18, 19]. Thanks to these medical robotic solutions the acceptance of their uses in clinical practice has been improved. For instance, researchers from the robotics field have developed solutions like robotized tele-echography to provide skilled medical care to isolated patients [20]. Meanwhile, various microrobotic systems have arisen to further reduce trauma, create new diagnosis tools and therapeutic procedures. For example, wireless microrobots with size of less than a millimeter are investigated to navigate within the body for targeted therapies [21, 22, 23].  
Indeed, the design of miniaturized and versatile microrobotic systems potentially allows access to the entire human body, thus offering localized diagnoses and treatments with more precision and efficiency, but also to consider new procedures. For example,wireless microrobots, smaller than a millimeter, can navigate the body to perform targeted therapies [21; 22; 23]. A key issue lies in the actuation of such untethered microrobots within the human body. Among the various techniques developed so far, electromagnetic actuation (EMA) is considered to be the most promising one [13; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50]. To this aim, many EMA platforms have been proposed to control untethered magnetic microrobots for biomedical applications [29; 42; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78]. Using EMA system circumvents the need of embedding power power sources into the microrobot [13; 21; 22; 25; 46; 82]. Magnetic microrobots can be operated remotely and precisely by controlling external electromagnetic fields. This allows the microrobots to assist the surgeon by increasing the dexterity of the MIS procedure [13; 14; 22; 25; 46; 57; 78; 81].  
To properly manipulate magnetic microrobots for the realization of reliable given biomedical applications, the EMA platform is one of the key elements. Consequently, the choice, the number and the placement of its magnetic sources are of prime importance [81]. Basically, magnetic sources can 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]. Nevertheless, most of the numerous EMA designs proposed by researchers do not follow any specific rule. It is not easy to choose the appropriate solution for a given application. This review aims to summarize and compare the existing EMA systems regarding MIS procedures, focusing on those using electromagnets. At first, the electromagnetic sources of EMA systems could be organized either in a two-dimensional (2D) or in a three-dimensional (3D) arrangements, and apply properly to the different parts of the human body, as presented in Figure 1. As illustrated in Figure 1A, the 2D placement of magnets could be useful for surface operations such as angioma or cosmetic treatments. In the meanwhile, most MIS interventions require a 3D workspace, hence, the EMA system should be arranged in 3D above Figure 1B or around Figure 1C the workspace as well.