Magnetic flux concentration at micrometer scale

This paper presents the study of magnetic flux concentration phenomenon of magnetic flux concentrators (MFCs) at the micrometer scale. The main physical principles of magnetic flux concentration were studied by using analytical calculations and finite element method (FEM) simulations. The dependences of achievable maximum magnetic gain on the three critical parameters were analyzed. It shows that material, aspect ratio, and shape are three critical parameters for designing MFCs. Three typical MFCs were designed for magnetoresistive (MR) sensors in applications. The magnetic gain and linear working range of the MFCs were studied and compared. By using the same high-permeability magnetic material (nickel–iron alloy, μr ≈ 104−105), the MFCs of different geometries perform differently in magnetic amplification. The T-shaped concentrator shows higher magnetic amplification with magnetic gain G = 56 but comparatively narrower linear working range of 1.6 mTesla. The bar-shaped concentrator occupies smaller space and provides 62.5% wider linear working range (2.6 mTesla) than the T-shaped concentrator but at the expense of 32.1% smaller magnetic gain (G = 38). In the respect of magnetic gain, the triangle-shaped concentrator (G = 51) is comparable with the T-shaped concentrator. It provides a 42.3% wider linear working range (3.7 mTesla) than the bar-shaped concentrator.

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► We study MFCs for MR sensors to be applied in ultralow field detection.
► We focus on the magnetic flux concentration in the micrometer dimension.
► We study the MFC principles regarding material, aspect ratio, and shapes.
► We provide guiding principles applied in MFC design at micrometer scale.