| Summary: | 碩士 === 國立清華大學 === 微機電工程研究所 === 94 === Since the invention of MRI in the beginning of 1980s, it has been extensively applied to fields of life science and clinic diagnosis. When it comes to MRI, its general impression for people is that patients who are about to be examined will lie on the sickbeds and be put through a large coil so as to proceed a series of examinations and detections. If we use a traditional MRI system to take single cell detection such as the embryo growth scan, the devices are overly large and its resolution is not enough. Furthermore, its manufacturing cost is so expansive that it might be valued at hundred millions of dollars(NTD). Therefore, it can be applied to neither general education nor laboratories of academic organizations extensively.
According to above reasons, we are developing a new desktop nano-MRI system with the following characteristics: lower manufacturing cost, smaller volume, better resolution and signal-to-noise ratio. First, super-conducting magnet can be replaced by permanent magnet as the source of the magnetic field since the volume of the device would be reduced. Second, the newly developed MEMS manufacture fabrication is applied to make micro coils.
The main purpose of this thesis is to design and manufacture a permanent magnet with a high magnetic field intensity for MRI application. The material is NdFeB of level N42. In the design of the magnet, a cylinder type of Halbach configuration is constituted by 24 slices of magnets. Each slice is composed by 6 little magnet. The total number of magnets is 144. The rotations of the space position and the polarization of the magnetization direction were used. Without using electricity, the magnet has a magnetic field intensity of 4 Tesla to serve as the source of the major magnetic field of a nano-MRI system. The cylinder type arrangement is used for the ease of the sample loading. In the core area of the magnet, special-designed clamping-apparatus were used to fix the iron core which was made of soft ferrite. The purpose was to create a uniform magnetic field with enhanced magnetic flux density. Due to the extremely strong repulsion, a series of manufacturing tools were designed for the assembly of the magnets. This work only finished the assembly of the odd number pieces of magnets, and we used a Hall probe to measure the magnetic field intensity and the measured field strength is 1.98 Tesla, which is useful for a MRI system.
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