Identification of dynamic material properties, non‐destructive testing and study of vibroacoustic behaviour of different structures require the use of complex, pointwise and full‐field measurements, which are capable of providing data for experimental modal analysis or model updating. Nowadays, among other techniques, optical non‐contact techniques represent the favourite choice as they do not add mass, stiffness or damping to the structure under test. When the range of vibration amplitudes allows it, most of these techniques are based on interferometric principles. Development of laser sources and detectors leads to a continuous improvement of vibration measurement techniques. However, a hard choice still has to be made between spatial resolution and temporal resolution. Another difficult choice is between space bandwidth product and energetic sensitivity of the detector. While the number of pixels of a camera is continuously increasing, the pixel size seems limited at its lower end. The paper presents a comparative study of the vibration amplitude fields as measured by two full‐field non‐contact techniques, speckle interferometry and laser Doppler vibrometry, and predicted by finite‐element model. The measurements concern the free and the forced vibrations of a thick, composite plate with free boundaries.
In order to prepare for the construction phase of the two Deformable Mirrors (DMs), which will be used in the Thirty Meter Telescope (TMT) first light Adaptive Optics (AO) system, Cilas has advanced the design of these two large size piezo DMs and has manufactured and tested a scaled demonstration prototype. The work done allowed significant reduction of the risks related to the demanding specifications of the TMT DMs; the main issues were: (i) Large pupil (up to 370 mm) and high order (up to 76x76); (ii) Relatively low operational temperature (DMs working at -30°C); (iii) New piezo material. It is important to develop such a prototype to take into account these three specifications all together (dimension, low temperature and new piezo material). The new prototype is a 6x60 actuators and has the same characteristics as the future TMT DMs. In this paper, we give the conclusions of the work through the presentation of the following items: (i) Design and finite element analysis of the two DMs and prototype; (ii) Test results obtained with the prototype with validation of the finite element analysis and compliance with the TMT AO specifications; (iii) Special focus on thermal behavior, actuator reliability and shape at rest stability.
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