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Measuring MEMS in Motion by Laser Doppler Vibrometry
Published in Wolfgang Osten, Optical Inspection of Microsystems, 2019
Christian Rembe, Georg Siegmund, Heinrich Steger, Michael Wörtge
A laser Doppler vibrometer provides a real-time velocity or displacement signal of a single spot on the specimen surface. Therefore, a vibrometer can measure non-repeatable transient or chaotic processes. However, there are restrictions if a scanning measurement is performed because the surface measurement points of the operational deflection shapes need to have a defined phase relation. To do so, the specimen can be excited with a periodic signal. This signal can contain a large number of harmonic frequency components. The data acquisition needs to be synchronized with the excitation or some reference signal that corresponds to the specimen oscillation. The vibrometer signals obtained on every measured spot are fast Fourier transformed and the spectrum is saved. The scan method is especially effective and accurate if the frequencies contained in the excitation signal accord with the FFT lines of the spectrum. The combination of the spatially distributed oscillations at an FFT line results in phase-dependent ODSs. The resolution for the measurement of an oscillation amplitude at a single frequency in the spectrum depends on the width of the FFT line. Very high resolution can be achieved for narrow width of the FFT lines. The noise limit is typical far below 1 pm/Hzwithout averaging at frequencies higher than 50 kHz for a well-designed vibrometer with a digital decoder.
Structural dynamic assessment of a footbridge under human-induced loadings
Published in Alphose Zingoni, Insights and Innovations in Structural Engineering, Mechanics and Computation, 2016
J.G.S. da Silva, G.L. Debona, C.M.R. Gaspar
Secondly, a Single-Input Single-Output (SISO) test was performed combining the Polytec vibrometer PDV-100 and a Dytran impact hammer, as illustrated in Figure 8. The basic functioning of the Laser Doppler Vibrometry methodology is related to a laser beam focused on the tested structure so that the relative movement between the laser and the structure causes the presence of the Doppler Effect i.e. the relative change in wavelength and frequency of a wave when the observer and the source are moving (Prislan 2008).
Optical laser microphone for human-robot interaction: speech recognition in extremely noisy service environments
Published in Advanced Robotics, 2022
Takahiro Fukumori, Chengkai Cai, Yutao Zhang, Lotfi El Hafi, Yoshinobu Hagiwara, Takanobu Nishiura, Tadahiro Taniguchi
The sound recording quality of the conventional microphones would also be affected when an object emitting the noise exists behind the speaker. The sound wave is attenuated if a microphone is distant from a speech source, which makes the energy of speech low and decreases the signal-to-noise ratio (SNR). Thus, we should develop a microphone robust to these possible conditions in service environments. In the research field of measurement, the laser Doppler vibrometer (LDV) [2] has been developed to directly record the vibration around a target object. The use of the LDV for the purpose of sound recording is called an optical laser microphone, which has recently attracted much attention [3,4]. Using a laser to measure the vibration of objects near a speaker, we can obtain the clean speech uttered by the speaker avoiding the noise around the microphone.