Stress-induced optical path length changesin analogy to the previous equation ( 13). Note that the factor (n f.s. − 1 − L f.s. ) now involves a '−1'. However, a comparison with an all-FEM-based approach performed at NIST by Egan et al

We have developed a fabrication technology for thin-film sensors on metallic substrates with flat and curved surfaces. Physical vapour deposition by means of a magnetron sputtering system is used to deposit an insulating layer and a following functional layer. This layer is structured by distinct photolithographic steps utilizing a self-developed spray coating technique, four-axis robotics with micrometer precision and a UV laser with a spot size below 10 μm. This highly flexible technique allows a rapid change of design to produce various sensor layouts in a short time. Besides the fabrication technology, we present two realized applications for thin-film sensor technology in this paper. First, a tool wear sensor for rotating cutting tools, directly detecting the flank-wear land width, and second, sputtered resistance strain gauges for force measurement. Measurement results showing the potential of thin-film sensors are given briefly.

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Deformation monitoring requires the detection of smallest changes, always at the limits of technical feasibility. Trying to push these limits further, we have realised two terrestrial ranging instruments: a long-range 1D electro-optic distance meter and a 3D multilateration-capable sensor system of 50 m range. The former one is intended as primary standard for the calibration of geodetic instrumentation with low uncertainty to the SI definition of the metre. The latter one is intended for monitoring larger monuments like VLBI antennas. In this contribution, we describe the technical challenges and our solutions for such instrumentation. We use the two-colour method for inline refractive index compensation. As common optical source, we developed a versatile multi-wavelength generator based on two Nd:YAG lasers stabilised by a phase-locked loop realised by Field Programmable Gate Arrays (FPGA). The 1D interferometer uses custom-designed achromatic optics and a mechanical frame optimised for form stability under field conditions. The phase demodulation system allows for maximum range flexibility from several meters up to several kilometres. The base ranging unit of the 3D multilateration system adheres to a different demodulation technique, which allows a relatively simple interferometer head design. This approach requires a sophisticated source modulation scheme limiting the applicability to distances over 15 m up to approximately 50 m in our case.