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A non-dispersive infrared (NDIR) sensor system has been designed to monitor the state of contamination and degradation of aviation hydraulic fluids. Core part of this system is a MOEMS subsystem consisting of a micro cuvette, a MEMS thermal IR emitter and a four-channel thermopile array. For ruggedness, this MOEMS subsystem is integrated into a high-pressure resistant metal package. The MOEMS subsystem measures the transparency of the fluid under test at four specifically chosen spectral channels. Three of these channels allow the water content, the total acidity number and the remaining acid scavenger reserve to be monitored. The forth channel serves for calibration and self-test purposes. Fluid monitoring systems of this kind will form key components in an innovative AIRBUS aircraft maintenance system.

On-going pressure to reduce operating costs and increasing concerns about the environment are forcing industrial equipment operators to condition monitoring procedures and improve maintenance practices to achieve optimal fluid and component service life. Realization of these goals without compromising system performance or component life often requires that new and more sophisticated condition monitoring devices need to be used. Increasingly, these can be installed directly in-line, which eliminates delays associated with off-line analysis, decreases response time, and facilitates the decisionmaking process should remedial action prove necessary. This paper describes operational principles of a rugged microelectromechanical system (MEMS) sensor that comprises four sensing elements suitable for in-line condition monitoring of hydraulic and lubricating oils. Preliminary laboratory data suggest that the sensor exhibits an excellent correlation with conventional laboratory viscosity and acid number (AN) data.

For the fabrication of a micro fluidic high pressure oil sensor (400 bar) based on an infrared transmission measuring principle the bonding of 2 mm silicon wafers is necessary. Conventional bonding techniques such as silicon fusion bonding or anodic bonding are not suitable for bonding thick and inflexible silicon wafers, because these techniques can not compensate for the wafer bow. We present a new bonding procedure for silicon substrates thicker than 1 mm using a silicon adapted LTCC tape as an intermediate leveling layer. The wafers are preprocessed by etching a nano structured silicon surface on the internal side. The silicon wafers are aligned and stacked with pre-structured green LTCC tapes by an optical stacking unit. During the hot isostatic lamination at 55 bar the structured LTCC tape is adjusted to the silicon. A subsequent pressure assisted sintering leads to a wafer bonding strength up to 5000 N/cm2. With the bonding technique it is possible to create cavities and channels between the thick wafers by the use of punched and laser cut LTCC. The fabrication steps of the sandwich build-up especially the sequential lamination and the optical adjusting procedure of the flexible (LTCC) and inflexible (2 mm Wafer) substrates will be explained in detail. A method to reduce the shrinkage and distortion of the green LTCC during handling is demonstrated. The distribution of the bonding and bursting strength of the single fluidic systems on a complete sandwich substrate is analyzed.

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