P12 -Out-of-plane Translatory MEMS Actuator with Extraordinary Large Stroke for Optical Path Length Modulation in Miniaturized FTIR Spectrometers
- Event
- SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Nürnberg - Band
- Proceedings IRS² 2011
- Chapter
- IP - Poster Session
- Author(s)
- T. Sandner, T. Grasshoff, H. Schenk, A. Kenda - Fraunhofer Institut (IPMS), Dresden (Germany)
- Pages
- 151 - 156
- DOI
- 10.5162/irs11/ip12
- ISBN
- 978-3-9810993-9-3
- Price
- free
Abstract
Fourier Transform Infrared (FT-IR) spectroscopy is a widely used method to analyze different materials - organic and inorganic. Current FT-IR spectrometers are large, usually static, and are operated by qualified personnel. By using translational MOEMS devices for optical path length modulation instead of conventional highly shock sensitive mirror drives a new class of miniaturized, robust, high speed and cost efficient FTIR-systems can be addressed. An early approach of a miniaturized MEMS based FTIR spectrometer has been developed in the past by IPMS and the CTR. It was a combination of classical infrared optics with a translatory 5 kHz MEMS mirror using a folded bending spring mechanism. Due to the limited amplitude of ± 100μm a spectral resolution of 30 cm-1 was realized allowing dynamic FTIR measurements in the ms-range. To enhance the stroke IPMS introduced a first translational MEMS device with two pantograph mirror suspensions – originally designed for larger stroke of 500 μm. But due to superimposed parasitic torsional modes only ±140μm amplitude could be measured.
In this paper, we now present an optimized MEMS device which overcomes the previous limitations enabling an extraordinary large stroke of 1 mm. The novel translatory MOEMS actuator was specially designed to enable a miniaturized MEMS based FTIR spectrometer with improved system performance of 5 cm-1 spectral resolution (λ=2.5…16μm), SNR > 1000 and fast operation of 7 500 scans / sec. Hence, a large mirror aperture of 5 mm, enhanced amplitude of ± 500 μm and a small dynamic deformation of < λ/4 is required. Due to the significant viscous gas damping in normal ambient the translatory MEMS devices have to operate in vacuum – requiring a long term stable optical vacuum package with broadband IR window. The paper discusses the design, fabrication and experimental characteristics of the novel translatory MEMS actuator including first results of the optical vacuum packaging.
To realize a large stroke of the mirror plate a pantograph like suspension was chosen. The new translatory MEMS actuator consists of four symmetric pantograph suspensions in contrast to two pantographs used for a previous MEMS design, where only ± 140μm amplitude could be achieved due to parasitic tilt modes. One single pantograph consists of six torsional springs – two springs arranged on the same axis – and connected by stiff levers. The torsional springs are used us deflectable elements instead of bending springs which reduces significantly parasitic mirror deformation due to mechanical stress. Due to the optimized mechanical design using 4 pantograph suspensions the new translatory MEMS actuator can provide a precise out-of-plane trans¬lation with ± 500 μm amplitude in vacuum of 50 Pa at 90V. This enables a completely new family of low cost handheld FTIR analyzers with a spectral resolution of up to 5cm-1, 500 scans/s and SNR > 1000 e.g. applied by individuals for ad-hock inspection of food or environmental parameters.