Jean-Paul Collette

Quantitative Accelerated Life Testing of MEMS Accelerometers

Quantitative Accelerated Life Testing (QALT) is a solution for assessing the reliability of Micro Electro Mechanical Systems (MEMS). A procedure for QALT is shown in this paper and an attempt to assess the reliability level for a batch of MEMS accelerometers is reported. The testing plan is application-driven and contains combined tests: thermal (high temperature) and mechanical stress. Two variants of mechanical stress are used: vibration (at a fixed frequency) and tilting. Original equipment for testing at tilting and high temperature is used. Tilting is appropriate as application-driven stress, because the tilt movement is a natural environment for devices used for automotive and aerospace applications. Also, tilting is used by MEMS accelerometers for anti-theft systems. The test results demonstrated the excellent reliability of the studied devices, the failure rate in the “worst case” being smaller than 10-7h-1.

Space solar arrays and concentrators

Abstract This paper presents some research activities conducted at the Centre Spatial de Liege (CSL) in the field of space solar arrays and concentration. With the new generation of high efficiency solar cells, solar concentration brings new insights for future high power spacecrafts. A trade-off study is presented in this paper. Two different trough concentrators, and a linear Fresnel lens concentrator are compared to rigid arrays. Thermal and optical behaviors are included in the analysis. Several technical aspects are discussed: • Off-pointing with concentrators induces collection loss and illumination non uniformity, reducing the PV efficiency. • Concentrator deployment increases the mission risk. • Reflective trough concentrators are attractive and already proven. Coating is made of VDA (Aluminum). A comprehensive analysis of PV conversion increase with protected silver is presented. • Solar concentration increases the heat load on solar cells, while the conversion efficiency is significantly decreasing at warm temperatures. To conclude, this paper will point out the new trends and the key factors to be addressed for the next generation of solar generators.

Ion beam figuring of small BK7 and Zerodur optics : thermal effects

Ion beam figuring is a deterministic optical fabrication technique which efficiency has been mainly demonstrated on large optics these last years. One of the disadvantages of ion figuring is the high surface temperature of the workpiece. Temperature aspects have already ben mentioned by some authors but are weakly detailed. Therefore thermal effects on BK7 and Zerodur, mainly surface figure distortions and surface temperature measurements, have been investigated here in more detail.

Portable x-ray fluorescence spectrometer for coating thickness measurement

A handheld x-ray spectrometer has been realized and tested. The purpose of the device is to measure the thickness of coated samples in the range of 1-1500 nm in an industrial environment. Accuracy of approximately 3% has been achieved in this range with a measurement time of 1 min. Automated software has been implemented to allow utilization by a nonspecialist operator. An automated calibration procedure, based on measurements of reference samples, is used.

Figuring sequences on a supersmooth sample using ion beam technique

An ion beam figuring facility is operational at the Centre Spatial de Liege since 1997. Its present capabilities are described. An extensive characterization program is running in order to determine the optimized parameters for various materials and operating conditions. In this frame, tests have been performed on a spherical gold-coated aluminum mirror plated in between the with nickel. The nickel plating was used to be super-polished to a BRDF of 1 10-4 at 1 deg at 10 micrometers wavelength. Micro-roughness and etching rate measurements were realized and influence of ion bombardment on the coating has been established after removal of the gold coating. The gold coating removal of the gold coating. The gold coating removing was performed by using the ion beam flux. Finally, the mirror has been figure from the original sphere to a parabola. Surface characteristics evolution is also described in terms of micro-roughness and surface error. An overview of the research and development programs related to this facility is given. Results of this technique and potential impact on optics fabrication are then briefly exposed.

Diffractive microprism architecture for color fan-out beam splitter

This paper presents an innovative architecture where a micro-prism structure performs an in-line and wavelength-dependent extraction of the light injected at the edge of the device. This partial extraction of light is carried out by holographic mirrors coated onto each micro-prism oblique side. Thanks to the fabrication process, customization is possible and the number and the performances of each extractive faces can easily be tailored at will. These devices can be advantageous for any kind of applications where a high spectral selectivity is required or when a discrete extraction of spectral components has to be performed.