Mini/micro coil design and optimization for wearable and implantable magnetic stimulation

The first-generation magnetic stimulation technology, transcranial magnetic stimulation, has been successfully applied in various neurological disorders’ treatment. However, this technology’s limitation is enlarged with higher requirements of stimulation precision in nowadays and the next-generation invasive and nano-invasive magnetic stimulation technologies featuring precision and wearable/implantability are in urgent need of development. As new specialized coils are considered to be key factors for the future development of the next-generation magnetic stimulation methods. Novel coil design and efficient manufacturing will significantly accelerate the development of this field. For invasive magnetic stimulation, this project proposes a hypothesis to explain the questions remain in the selective stimulation mechanism and brings up three optimization routes which enhance the resolution and selectivity. Besides, innovative laser-assisted cleanroom manufacturing process is innovated, which reduced the fabrication period from weeks to days, and meanwhile enables biocompatible integration of traditional non-biocompatible metals (such as aluminum), thereby broadening material choices and reducing costs. For nano-invasive stimulation, this project first minimizes coil designs to cm scale with generating mT level magnetic field. There are two experimental designs explored here, planar coils, and slinky coils. Three planar coil fabrication methods, laser processing, ultra-thick lithography, and physical cutting are tested, optimized, and evaluated. Here, an alignment method of laser process is brought up, an optimized recipe of ultra-thick (over ninety micrometer) photoresist method is proposed, and a cheap fast cutting fabrication method is invented reducing the cost three to four orders of magnitude. On the other hand, the first successful miniaturization of slinky coils to the centimeter scale can achieve high-intensity magnetic fields and improved high-frequency performance with resonant circuit assistance. Overall, this thesis provides cutting-edge techniques for the development of non-invasive, invasive, and nano invasive magnetic stimulation technologies and explores the coils’ design and microfabrication methods for next-generation applications. Especially, the innovation in fabrication method brings much faster fabrication speed and much lower manufacturing cost, which builds a bridge between lab research and industry/clinical wide demand. The contributions will accelerate the development and application of next-generation magnetic stimulation technologies in daily life.