An Fourier Transform Spectrometer (FTS) based on an H-shaped electrothermally actuated microelectromechanical system (MEMS) scanning mirror has been developed. The MEMS scanning mirror can generate about 200 μm at 5 Hz with only 5 Vpp and maintain a very small tilting of about 0.029 • without using any complex compensation or closed-loop control. This high scanning performance is achieved by using a unique H-shaped frame supported by symmetrically distributed thirty-two pairs of innovative three-level-ladder bimorph actuators. This MEMS FTS can cover a wide spectral range of 1000-2500 nm. A spectral resolution of 64.1 cm −1 , or 11 nm at 1310 nm, is achieved.
This paper presents a micro Fourier transform infrared spectrometer (μFTIR), enabled by an H-shaped electrothermal microelectromechanical systems (MEMS) mirror. A special driving method was developed for obtaining a linear, uniform-speed motion of 186 μm, and the tilting angle of the MEMS mirror was as small as 0.06°, so there was no need of complex closed-loop control. A telecentric lens was employed in the interferometer of the μFTIR to reduce the influence of the MEMS mirror tilting effect. Also, a new phase interpolation algorithm, instead of the traditional fringe interval method, was applied in the process of the spectral reconstruction to improve the spectral stability. Finally, the new μFTIR was applied in the composition prediction of soybeans, and the experimental results show that it can accurately measure grain moisture, protein, and fat contents.
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.
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