Abstract
Incorporating linear-scanning micro-electro-mechanical systems (MEMS) micromirrors into Fourier transform spectral acquisition systems can greatly reduce the size of the spectrometer equipment, making portable Fourier transform spectrometers (FTS) possible. How to minimize the tilting of the MEMS mirror plate during its large linear scan is a major problem in this application. In this work, an FTS system has been constructed based on a biaxial MEMS micromirror with a large-piston displacement of 180 μm, and a biaxial H∞ robust controller is designed. Compared with open-loop control and proportional-integral-derivative (PID) closed-loop control, H∞ robust control has good stability and robustness. The experimental results show that the stable scanning displacement reaches 110.9 μm under the H∞ robust control, and the tilting angle of the MEMS mirror plate in that full scanning range falls within ±0.0014°. Without control, the FTS system cannot generate meaningful spectra. In contrast, the FTS yields a clean spectrum with a full width at half maximum (FWHM) spectral linewidth of 96 cm−1 under the H∞ robust control. Moreover, the FTS system can maintain good stability and robustness under various driving conditions.
Highlights
Fourier transform infrared spectroscopy (FTIR) [1] is a technique that is used to obtain absorption or emission infrared (IR) spectra of various matters and determine materials’ compositions and concentrations in both laboratory and field environments
ΔVstability, x or ΔVy, u by the H∞ controller output, Vcx or Vcy, block diagram of the Fourier transform spectrometer (FTS) system control structure is shown in Figure 7b, in which r is replaced by the position sensitive detector (PSD) reference input Vref, e by the PSD error ∆Vx or ∆Vy, u by the H∞ controller output, Vcx or Vcy, yo=[y
This setup is a Michelson interferometer-based Fourier transform spectrometer schemes. This setup is a Michelson interferometer-based Fourier transform spectrometer (FTS), which is composed of an micro-electro-mechanical system (MEMS) mirror to be controlled, a red He-Ne laser (632.8 nm) source (FTS), which is composed of an MEMS mirror to be controlled, a red He-Ne laser (632.8 nm) source (LS-R), a green laser (532 nm) source (LS-G), three beam splitters (BS), two dichroic mirrors, a position (LS-R), a green laser (532 nm) source (LS-G), three beam splitters (BS), two dichroic mirrors, a sensitive detector (PSD), two photodiodes (PD1 and PD2), a high speed data collector, an MEMS driver position sensitive detector (PSD), two photodiodes (PD1 and PD2), a high speed data collector, an to drive the four bimorph actuators in both x and y directions, and a digital controller realized with
Summary
Fourier transform infrared spectroscopy (FTIR) [1] is a technique that is used to obtain absorption or emission infrared (IR) spectra of various matters and determine materials’ compositions and concentrations in both laboratory and field environments. Conventional FTS systems are only for lab use, as they are expensive and bulky largely due to the complex scanning mirror system [1]. FTS systems based on micro-electro-mechanical system (MEMS) micromirrors begin to emerge, and such miniature FTS systems can enable real-time, in-field analysis in many environments such as national border checkpoints and in natural or manmade hazardous conditions [2,3]. For miniature FTS systems, the scanning characteristics of the moving MEMS micromirror are critical.
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