Nondestructive On-Site Detection of Soybean Contents Based on An Electrothermal MEMS Fourier Transform Spectrometer

Abstract

A portable spectrophotometer has been developed to provide on-site detection of soybeans' moisture, protein, and fat contents in a nondestructive manner. The core module of this soybean analyzer is a micro Fourier transform infrared spectrometer (μFTIR) based on an electrothermal microelectromechanical systems (MEMSs) mirror. The electrothermal MEMS mirror is capable of generating a large piston motion of 320 μm at only 8.5 Vdc. The tilting of the MEMS mirror plate during its piston scanning affects the spectral repeatability of the μFTIR. In this paper, the effect of the MEMS mirror tilting on the spectral repeatability is analyzed and an automatic tilt realignment algorithm is developed to maintain high spectral repeatability, which is better than 0.01 in long term use. The μFTIR module has a footprint of 125 mm × 90 mm with a height of 50 mm. The whole instrument is designed for portability and on-site operation as well as the convenience of loading soybeans. More than 300 samples of soybeans are collected, 80% of which are used to establish a prediction model using chemometrics methods. The standard error is no more than 3% when using the prediction model to test the remaining 20% samples.

A Review of Actuation and Sensing Mechanisms in MEMS-Based Sensor Devices

“…The actuation technique is a term given to the mechanism that transforms the input energy into a microstructure motion. There are different principles and approaches to actuate MEMS devices [7,[50][51][52][53][54][55], the most important of which include: electrostatic actuation [56][57][58][59][60][61][62][63][64], electrothermal actuation [4,44,[65][66][67][68], electromagnetic actuation [7,69], and piezoelectric actuation [48,70] (Fig. 2).…”

Wafer-Level Vacuum-Packaged Translatory MEMS Actuator with Large Stroke for NIR-FT Spectrometers

“…Various MEMS concepts for optical path-length scanning have been reported, typically targeting an out-of-plane translation with large stroke required for the classical dual-beam Michelson interferometer FTS set-up, consisting of fixed and moving mirrors (here realized by an MOEMS) and an optical beam splitter. For large-stroke out-of-plane translation of the MEMS mirror, different actuation principles have been investigated so far: electrostatic [ 5 , 6 , 7 , 8 ], piezoelectric [ 9 , 10 , 11 ], magnetic [ 12 , 13 , 14 , 15 ], and electrothermal [ 16 , 17 , 18 , 19 , 20 , 21 , 22 ], typically using resonant operation for larger strokes, e.g., [ 7 , 8 , 11 ], but also using quasi-static actuation, e.g., [ 10 , 17 ]. Most of these different MOEMS actuation mechanisms suffer from limitations in spectral resolution due to parasitic effects of MEMS-based path-length modulation: first of all, mirror tilt [ 11 , 17 , 19 ], deformation of the mirror due to dynamically (owing to inertia) or statically (due to mirror suspension or optical coating) induced mechanical stress.…”