Resonant magnetic sensor using concentration of magnetic field gradient by asymmetric permalloy plates
This paper demonstrates a novel resonant magnetic sensor that utilizes a concentrator to obtain a large magnetic-field gradient. A silicon-cantilevered resonator, with a 10-µm-diameter magnetic particle on the tip, is placed between two asymmetric permalloy plates, which function as the concentrator; one of the plates has a narrow tip, whereas the other has a wide one. This asymmetric-plate pair generates a large magnetic gradient, which generates considerable force on the magnetic particle. The resonant-frequency varies, depending on the force applied on the particle. The extremal magnetic field can be determined by monitoring the changes in the resonant frequency. The magnetic gradient generated by the concentrator is theoretically calculated using the finite element method, obtaining a gradient of 5.4 × 104 T/m for a magnetic field of 1 T. A resonant magnetic sensor is fabricated using conventional microfabrication techniques, and the magnetic force-dependent resonant-frequency change is observed. The experimental magnetic sensitivity is estimated to be 5.1 × 10−7 T, considering the minimum noise level (3.29 ppm).
Part of this research was performed at the Micro/Nanomachining Research Education Center and the Nishizawa Center of Tohoku University.
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