Design of a Wireless Passive Micro-magnetic Stimulator Based on Closed-loop Neuromodulation of Magnetic Field Dose

The wireless passive micro-magnetic stimulation (WP-μMS) is a novel implantable research approach for neuro-magnetic modulation. Due to the small size of the WP-μMS micro-coil and the low coupling coefficient, the control of magnetic stimulation dose on micro-coil has traditionally relied on open-loop method, resulting in an inability to guarantee the accuracy of magnetic stimulation dose. This paper proposes a 3-tier construction of transmitter coil - detector coil - micro-coil based on magnetic coupling theory model. The detection coil for obtaining magnetic stimulation dose is designed external to the body, effectively resolving the challenges associated with detecting mutual inductance and current within the micro-coil in vivo. Additionally, this model achieves closed-loop control of magnetic field stimulation dose on the micro-coil while reducing the complexity of the micro-coil design structure. On this basis, a WP-μMS based on a closed-loop control strategy is designed and implemented. This device effectively detects the magnetic field dose on the micro-coil under a closed-loop control mechanism and automatically adjusts the output power of the transmitter based on detection information, thereby enhancing the accuracy of magnetic field intensity coupled to the micro-coil. Finally, experimental validation is conducted using ex vivo hippocampal brain slices. The results demonstrate that at the resonance frequency of 11 MHz, closed-loop magnetic stimulation, compared to open-loop magnetic stimulation, improves the stability of long-term potentiation (LTP) in the hippocampal CA1 region by 30.8%. This approach holds significant implications for the modulation of magnetic dose in WP-μMS.