Invited lectures - XXVIII AIVELA Meeting

XXVIII A.I.VE.LA. Annual Meeting
17-18 December 2020
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INVITED LECTURES

The Meeting will feature the following invited lectures:
by ACADEMICS

"DISCOVERING LASER DOPPLER VIBROMETRY: 30 YEARS OF TEACHING AND RESEARCH"
by Prof. Enrico Primo Tomasini & Prof. Paolo Castellini, Università Politecnica delle Marche

by INSTRUMENTATION MANUFACTURERS

"BRIEF INTRODUCTION TO DIGITAL IMAGE CORRELATION and VIRTUAL DEMO SESSION"
by Stefano Somaschi, Luchsinger srl


"INTRODUCTION to LASER VIBROMETRY"
by Wolfgang Ochs, Polytec GmbH


ABSTRACT
Learn about the technique that is continuing to revolutionize the measurement of structural vibration and shock. The lecture will cover its widespread application to aerospace, automotive, civil, biological, medical and micro- structures, fields where laser vibrometry has had a major impact on product quality, performance, safety and durability as well as human quality of life.


"ADVANCEMENTS in LASER DOPPLER VIBROMETRY in respect to SPECKLE NOISE"
by Jörg Sauer, Polytec GmbH

ABSTRACT
Laser Doppler Vibrometry (LDV) has proven to be the non-contact vibration sensor technology with the highest amplitude resolution. It’s ability to measure on arbitrary surface structures makes it applicable in basic research as well as in industry. The output signal of a LDV is, like any other sensor, contaminated by a range of noise features from different sources. While electronic noise is fairly suppressed after changing to digital decoding technologies other sources are limiting the nominal resolution still. Basically, the amount of returned light to the photo detector carrying the information about the Doppler shift determines the noise floor for a given interferometer setup and laser output power. The received signal level indicator strength RSSI gives the user a hint about this property. It is a fact that a reflectivity has a positive impact on the signal-to-noise ratio (SNR).
Dealing with optically rough surface, the collected light is a random pattern of intensity and phase. The detector sees a coherent integral. Phase jumps in summed-up light from changing speckles create velocity spikes and low sum-intensity periods lead to noise bursts. In the frequency domain the achievable noise level can be far below the nominal values at full RSSI. In practice this leads to longer averaging time or repositioning of the laser spot. It is obvious that this accounts especially for fast traversing or rotating samples or scanning lasers.
A remedy to these noise sources is a heterodyne multi-path interferometer utilizing diversity reception. The concept named QTec is realized for the first time in a commercial LDV suppressing successfully the above described effects with single detector interferometers. The concept and the benefits in various applications are explained in this talk.


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