Planar omnidirectional magnetoimpedance-based sensors with micro-spiral patterns

The present work introduces a novel magneto-impedance (MI) planar micro-sensor. Various spiral-style (N-sided regular concentric polygons with N = 4, 5, 6 and 7), and line-style (single line, meander type) sensors were fabricated from 20 μm-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 the 150 observed in conventional meander-type sensors. In addition, the resonant frequencies of spiral sensors dramatically decrease below 1 GHz in comparison to that of 4 GHz in the meander one and are fully explained through the LCR resonance circuits. 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. © 2001-2012 IEEE.