Planar Omnidirectional Magnetoimpedance-Based Sensors With Microspiral Patterns

The present work introduces a novel magnetoimpedance (MI) planar microsensor. Various spiral-style (N-sided regular concentric polygons with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N} =4$ </tex-math></inline-formula>, 5, 6, and 7) and line-style (single line (SL) and meander (MD) type) sensors were fabricated from 20-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>m-thick amorphous FeSiC ribbons by using laser ablation and wet etching techniques. These designs were later systematically investigated to evaluate their performance characteristics. The spiral-style sensors show an omnidirectional MI response with significant reduction or even elimination of the magnetic anisotropy typically observed in conventional line-style ones. Significantly, the overall relative MI value of the spiral sensors is approximately 120%, which is comparable to 150% observed in conventional MD-type sensors. In addition, the resonant frequencies of spiral sensors dramatically decrease below 1 GHz in comparison to that of 4 GHz in the MD one and are fully explained through the LCR resonance circuits. The magnetic domain structure as well as the transverse component contribution of magnetic moments obtained from simulations provide a comprehensive understanding of isotropic response mechanism. This study paves a new path in designing omnidirectional planar sensor devices for biomedical applications.