University of Twente Student Theses


Development and comparison of open- and closed-loop control of untethered microrobots in a tuneable magnetic trap

Weerd, G.J. van de (2023) Development and comparison of open- and closed-loop control of untethered microrobots in a tuneable magnetic trap.

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Embargo date:25 September 2025
Abstract:Magnetic actuation of microparticles has several potential application in bio medicine. For example, the control of microrobots in the human body allows for local and selective engagement of human cells and tissue. [1] This gives possibilities for minimally invasive surgeries, in many regions of the body including abdomen, heart, brain, eye, ear and vascular system. [2] Microrobots can be used for delivering of therapeutic substances via the bloodstream, micromanipulation of cells and development of new drugs. [3] [4] Through the research of driving and controlling microrobots, it is found that energy supply is the most challenging part. Energy supply of microrobots can be divided in chemical drive and physical drive. Physical drive mainly uses electric field, magnetic field light field and sound field. [5] In this research physical drive by magnetic field will be investigated. This concept of generating force on a microrobot by magnetism has been considered as a promising technique. In the current-state-of-art, different methods are investigated to actuate the microrobot. One of the methods is the trapping and actuation of the microrobot by gradient pulling using the OctoMag system. [2] [6] A set of 8 external electromagnets, that can surround a human head, provide a magnetic field in a 3D workspace with a diameter of 25 mm. One of the disadvantages of this system is the large distance between the coils and the electromagnets, which makes it difficult to create high magnetic field gradients, so creating high magnetic forces is a challenge. A second method is a device called Microrobotic Infrastructure Loaded into Magnetically-Actuated Catheter (MILiMAC). This device uses three miniaturized electromagnets, which can be delivered to a microsurgery site and be deployed, creating a two-dimensional workspace. [3] However, this miniaturized coils can create only small amount of magnetic force without getting heated, what limits the opportunities of this method. A third method is the insertion of three needle-shaped electromagnets around the target site. [7] With that, a compact 2D workspace can be created where the particle is trapped and can be actuated. The biggest disadvantage of this system is the creation of heat inside the human body, what limits the magnitude of the magnetic field that can be used. In this work a system is investigated that uses external coils for creating a magnetic field, and 3 local ferrite rods for creating the field gradient. With this system, large magnetic fields are created without heating of the human tissue, and large gradients and forces are created using local actuation of the microrobot by magnetized ferrite rods. For this system image-based control of the microrobot is investigated. To enable this, image analysis is used for tracking of the microrobot. An open loop and closed loop control system are created, tested and compared.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Biomedical Technology BSc (56226)
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