Diamagnetically levitating resonant weighing scale

Xianfeng Chen,Nimit Kothari,Ata Keşkekler,Peter G Steeneken,Farbod Alijani

doi:10.1016/j.sna.2021.112842

Xianfeng Chen, Nimit Kothari + Show 3 more

Open Access

https://doi.org/10.1016/j.sna.2021.112842

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Abstract

Diamagnetic levitation offers stable confinement of an object from its environment at zero power, and thus is a promising technique for developing next generation unclamped resonant sensors. In this work, we realize a resonant weighing scale using a graphite plate that is diamagnetically levitating over a checkerboard arrangement of permanent magnets. We characterize the bending vibrations of the levitating object using laser Doppler vibrometry and use microgram glass beads to calibrate the responsivity of the sensor's resonance frequency to mass changes. The sensor is used for real-time measurement of the evaporation rate of nano-litre droplets with high-accuracy. By analyzing the resonator's frequency stability, we show that the millimeter graphite sensor can reach mass resolutions down to 4.0 ng, relevant to biological and chemical sensing concepts.

Highlights

Mechanical resonators are nowadays being adopted in billions of products, including quartz crystals, Micro-Electro-Mechanical Systems (MEMS), and acoustic wave resonators for time-keeping, frequency referencing and electronic filtering, and for addressing a wide range of sensor applications in modern technology
To characterize the resonant response of the levitating plate, we place the bare plate on the magnets and excite the plate with a periodic chirp signal over a large frequency range
Once we identify a resonance peak, we perform a narrow-band frequency sweep around the resonance frequency while positioning the laser on the anti-node of the excited mode

Summary

Introduction

Mechanical resonators are nowadays being adopted in billions of products, including quartz crystals, Micro-Electro-Mechanical Systems (MEMS), and acoustic wave resonators for time-keeping, frequency referencing and electronic filtering, and for addressing a wide range of sensor applications in modern technology. These resonant sensors can be used to measure parameters like mass [1,2,3], stiffness [4], density [5], viscosity [6], and pressure [7], for a diverse range of applications, ranging from environmental monitoring to life sciences [8,9,10]. Q can be substantially degraded through clamping, friction, adhesion and aerodynamic losses [11]

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