Existing neuroregulatory techniques can achieve precise stimulation of the whole brain or cortex, but high-focus deep brain stimulation has been a technical bottleneck in this field. In this paper, based on the theory of negative permeability emerged in recent years, a simulation model of magnetic replicator is established to study the distribution of the induced electric field in the deep brain and explore the possibility of deep focusing, which is compared with the traditional magnetic stimulation method. Simulation results show that a single magnetic replicator realized remote magnetic source. Under the condition of the same position and compared with the traditional method of stimulating, the former generated smaller induced electric field which sharply reduced with distance. By superposition of the magnetic field replicator, the induced electric field intensity could be increased and the focus could be improved, reducing the number of peripheral wires while guaranteeing good focus. The magnetic replicator model established in this paper provides a new idea for precise deep brain stimulation, which can be combined with neuroregulatory techniques in the future to lay a foundation for clinical application.
Transcranial magnetic stimulation (TMS), a widely used neuroregulatory technique, has been proven to be effective in treating neurological and psychiatric disorders. The therapeutic effect is closely related to the intracranial electric field caused by TMS, thus accurate measurement of the intracranial electric field generated by TMS is of great significance. However, direct intracranial measurement in human brain faces various technical, safety, ethical and other limitations. Therefore, we have constructed a brain phantom that can simulate the electrical conductivity and anatomical structure of the real brain, in order to replace the clinical trial to achieve intracranial electric field measurement. We selected and prepared suitable conductive materials based on the electrical conductivity of various layers of the real brain tissue, and performed image segmentation, three-dimensional reconstruction and three-dimensional printing processes on each layer of tissue based on magnetic resonance images. The production of each layer of tissue in the brain phantom was completed, and each layer of tissue was combined to form a complete brain phantom. The induced electric field generated by the TMS coil applied to the brain phantom was measured to further verify the conductivity of the brain phantom. Our study provides an effective experimental tool for studying the distribution of intracranial electric fields caused by TMS.
Transcranial magnetic stimulation (TMS) is widely used in the treatment of neuropsychiatric disorders, and the stimulation coil constitutes a critical component of TMS devices. Existing inductance calculations for figure-8 coils suffer from three notable shortcomings: they are mostly limited to single-layer geometries, they still rely on elliptic integrals, and they systematically overlook spatial mutual coupling among windings. To address these issues, we propose a high-precision analytical method that accommodates both flat spiral and multi-layer stacked coil configurations. Instead of adopting a conventional lumped-equivalent model, the proposed approach decoupled the total inductance into four independent contributions: self-inductance, coaxial layer-to-layer mutual inductance, coplanar mutual inductance, and non-coplanar mutual inductance. The self-inductance term was computed through a modified magnetic circuit procedure. The coaxial mutual inductance was obtained from parametric curves that incorporated the wire cross-section, built upon the geometric mean distance theory. The coplanar and non-coplanar mutual inductances were derived by combining the Maxwell–Wien series expansion with geometric perturbation theory. The overall coil inductance was then determined by analyzing the circuit connection. Finite element simulations and experimental measurements verified the accuracy and robustness of the method at both the individual-component level and the system level, laying a theoretical foundation for the optimal design of high-performance TMS coils.