KEYWORDS: Sensors, Microbolometers, Electronics, Satellites, Prototyping, Head, Infrared imaging, Digital signal processing, Analog electronics, Microelectromechanical systems
MEMS technology now makes possible to produce active microdevices combining detection, signal processing, and data storage with accuracy and compactness. In view of their characteristics, it can be expected that such microsensors will be used extensively in space applications dedicated to micro and nano satellites.
For this purpose, a specific investigation dealing with the complete development of a micro-earth sensor used for attitude control of Low Earth Orbit satellites is under realization and test. Based on an infrared uncooled 320x240 microbolometer the experimental characterization of the final active system consists of three microsensors linear arrays of 240 pixels of the same technology, radialy spaced at 120°, watching and receiving earth IR radiations. The transition between excited and non excited pixels will determine the IR image of the Earth/Space transition hidden in IR atmosphere response. Specific on-chip algorithms have been implemented to extract the transition and compute the attitude satellite position in roll and pitch.
The complete physical system modeling of one linear 240 pixels array including earth models, optic characteristics, microbolometer behavioral models, mixed analog/digital electronics and associated algorithms is consistent (at ±8% ) with the breadboard measurements.
A self-mixing laser interferometer has been combined with a compact and robust optical system including an adaptive
optical element in the form of a voltage controllable liquid lens. The use of the liquid lens enables the self-mixing
interferometer to adjust the optical focus position and the beam spot diameter on the target surface, and subsequently the
feedback level within the laser cavity. The optical system has been designed to focus the beam at distances from a few
centimetres from the front facet of the laser diode to infinity. With such a simple arrangement, it is possible to modify
and control the intensity of the back reflected light from the target surface into the laser cavity, by simply changing the
voltage applied to the lens to modify the focus condition on the target surface. The final effect obtained is full active
control of the feedback level of the self-mixing effect taking place. This has allowed keeping the feedback level of the
interferometer in the desired regime for measurements along very long distances and for different measurement
situations, so extending the capabilities of a classical self-mixing interferometer. The advantage of the proposed adaptive
optical head is thus its combination of precise metrology capabilities plus a great potential in automated feedback control
and operator-free industrial applications. Signal reconstruction of the target vibration amplitude presents a maximum
error of λ/16 as compared with a commercial capacitive sensor in the whole focusable range for displacement
measurements. An improved working range of 6.5 cm to 280 cm staying in the same feedback regime has been
experimentally demonstrated.
A displacement sensor enabling us to perform measurements under moderate feedback has been designed with a resolution up to 40 nm. Its performance can be optimized by using the wavelet transform when the signal is disturbed by electromagnetic fields, mechanical coupling, or speckle effect. By determining the repeatability and the reproducibility of this sensor, we have also demonstrated that this measuring device is suitable for statistical process control when an interval of tolerance of ±300 nm is required.
This presentation looks back over this last twenty years, the French activity in IR detectors. Photon and thermal detectors, cooled and uncooled focal plane arrays are considered. Two specific experiences are described on Automation Home IR Systems and Earth horizon IR sensing for Space Applications. The discussion is focussed on low cost devices and perspectives which are to be open in obstacle detection for Automotive Applications.
MEMS technology now makes possible to produce active microdevices combining detection, signal processing, and data storage with accuracy and compactness. In view of their characteristics, it can be expected that such microsensors will be used extensively in space applications dedicated to micro and nano satellites. The advanced architecture of a MicroInfraRedEarthSensor generic system based on a Vox microbolometer array associated with optics and electronics 'on the shelves' for signal processing and depointing computation, used to control the attitude of satellites in low earth orbits, has been completely developed, through the design of a virtual prototype combined with a breadboard implementation of an IR camera (called MST, and has been developed by EADS-SODERN, in the frame of IASI project). The correlation of the virtual prototyping approach, has allowed to build one complete optical head part of the instrument with efficient and optimized parameters where the performances are consistent with the main mission specifications (pointing accuracy <EQ 0.1 degree(s), measurement frequency > 10 Hz, aperture angle: > 36 degree(s), volume <EQ 250cm3, self contained measurement system able to operate self-calibration, should operate 24 hours a day). In addition, this standard and compactness electronics is very generic, which means that the system can be adapted to any kind of microbolometer, for LEO and also GEO (by the way of a new software) ADCS control and be used even in other fields of remote sensing.
MEMS technology now makes possible to produce active microdevices combining detection, signal processing, and data storage with accuracy and compactness. In view of their characteristics, it can be expected that such microsensors will be used extensively in space applications dedicated to micro and nano satellites. For this purpose, a specific investigation dealing with the complete development of a micro-earth sensor used for attitude control of Low Earth Orbit satellites is under realization and test.
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