Micro-magnetic stimulation for neuromodulation: technological evolution from discrete inductors to MEMS and wireless passive systems

Micro-magnetic stimulation (µMS) has emerged as a pivotal paradigm, providing high spatial precision and temporal resolution while eliminating direct electrode-tissue interactions. This review systematically traces the technological evolution of µMS systems, from discrete-inductor prototypes to high-precision MEMS-based micro-coils, array architectures, and wireless passive stimulators. Fabrication strategies, including standard MEMS and heterogeneous integration, are compared, and the impact of coil geometry on field focalization and selectivity is examined. The strategic transition from wired active driving to wireless passive operation, facilitated by resonant WPT and multi-frequency resonant compensation (MFRC) networks, is highlighted. Recent breakthroughs in FDMA and autonomous power allocation for multi-site targeting are discussed. Persistent challenges include the scaling limits of passive units, inter-channel crosstalk, and the mechanistic complexity of broadband neuromodulation. Future advances will focus on sub-millimeter-scale integration, power-signal co-optimization, and intelligent closed-loop neural interfaces for next-generation, large-scale neuromodulation systems.