Colour Control Farbmesstechnik (Germany)

The spectroscopy market is enduring and growing one, in which the near infrared spectroscopy by means of the advances plays an important and indispensable role. Some nameable advances are the noninvasive character, the rapidity, which allows real-time measurements or the flexible sampling and sample presentation. To establish near infrared spectroscopic methods and tests at a wide variety of applications new technological innovations are necessary. One of these technological innovations is a modern scanning micro mirror spectrometers. We have developed a small sized, light weight MOEMS-spectrometers for different spectral regions which are due to the optical parameters less expensive, more flexible and offer better performance than traditional spectrometers even yet. The central component of the optical set-up is a large area scanning micro mirror, which oscillates in resonance with 250Hz. Thus, to record a single spectrum only 4 milliseconds are necessary. One of the important factors of NIR spectroscopy, which affects qualitative and quantitative determination, is the sample presentation. For optimal signal processing different sample presentation techniques such as transmission and flow cells, integrating spheres and attenuated total reflection (ATR) probes were realized. Consequently in combination with chemometric methods e.g. partial least square or principal component analysis several applications could be performed and investigated. This article describes the principles and the advances of the promising technology as well as some realized applications. Furthermore influences of the sample presentation and calibration procedures will be discussed closer.

In modern optical diagnostics there is an increasing interest in compact and cost-effective devices, i.e. for the analysis of surfaces, thin films, solids, powders, pastes, gels, liquids and alike. Therefore fast and non-invasive measurements are necessary. For the realization of such devices, micro system technology especially Micro-Opto-Electro-Mechanical System (MOEMS) technology is suitable. Hence two main miniaturized optical analyzer modules employing MOEMS have been developed. They are based on the principle of spectral sensing in the infrared range by means of a scanning micro mirror with an integrated diffraction grating or in combination with a separate grating. Using these configurations it is possible to project a specific wavelength onto an exit slit in front of an infrared detector. The first packaging approach is based on assembled laser-cut stainless steel sheets and optical standard components. During the further development different setups with improved reliability and accuracy have been realized. Due to the requirement of compact dimensions and short optical paths modern methods e.g. rapid prototyping were utilized to optimize packaging and optical setup and therefore the performance of the complete system. In this work the characteristics and the measurement results of different development levels will be reviewed. Furthermore we address issues, challenges and performance optimization of MOEMS packaging with respect to ultra compact micro mirror spectrometers. Finally, the applications and the feasibility of such miniaturized spectrometer systems are discussed.

High-speed sensors have been developed for industrial color and position analysis. These sensors consist of Si-PIN- diodes covered by miniaturized RGB-interference filters, a micro-lens array, an imaging micro-lens, and a glass cover plate. The basic color-receiver comprises three rhombic Si- PIN diodes arranged in a basic hexagonal pattern with a diameter of 700 micrometers . To allow a simultaneous color and position control of still samples as well as for moving samples, e.g. samples lying on assembly lines or conveyor belts, the basic pattern has been arranged in two different receiver arrays. Both diode patterns each consisting of 64 diodes are arranged in user-defined arrays making efficient use of the available sensor area. The diodes are individually contacted to provide a rapid access to certain pixels or pixel clusters. Using interference filters the desired spectral band is transmitted to the detector almost without losses and the undersized band is blocked by reflection. The imaging microlens determines object distance, total visual field, and resolution. By using a coated glass cover plate the effective range is restricted to the desired spectral region. The object distance is adjustable between 10 mm and 50 mm and the diameter of the visual field is between 5 mm and 50 mm. The maximum variance in object height is 0.5 mm and the maximum lateral resolution is 0.5 mm by 0.5 mm. The operating frequency of the total sensor system depends on the data processing unit and is between 2 kHz and 10 kHz. These sensors make high- speed color analysis possible for a frequency range in which CCD-systems are too slow.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.