Measuring the smallest vibrations to the second: Young talent award for Ilmenau mechanical engineering graduate

Whether it's the sound of strings, a pumping heart, a car on a bumpy road or vibrating wings: highly complex measuring instruments are required to understand and investigate vibrating systems in the environment and technology. In his diploma thesis at the Optical Engineering Group at TU Ilmenau, mechanical engineering student Johannes May investigated how mechanical vibrations of even the smallest and most sensitive structures can be precisely measured using light, without contact and with as little feedback as possible. The use of such measuring instruments opens up numerous application possibilities, particularly in industrial research and development, but also in biomedicine - from the investigation of tiny sensors or micromachines to the analysis of aircraft parts, engines or high-frequency vibrating ultrasonic tools.

Point-by-point laser Doppler vibrometry has established itself as the standard for such measurements in industry. This technology uses laser sensors to measure surface vibrations, is versatile and extremely accurate: by directing the measuring beam at individual points on the object, it records the vibrations directly at the point of impact - up to 160 million times per second. This results in a wide range of applications and extremely high measurement accuracy, but also entails a comparatively long measurement period of several hours to several days.

In his work, Johannes May therefore investigated an alternative with a significantly shorter measurement time, so-called time-averaging digital holography, which, in contrast to laser Doppler vibrometry, does not measure objects point by point, but over a wide area. The technology makes use of the fact that light changes its frequency when it is diffusely reflected by a vibrating measurement object. In this way, the measurement technology enables high-precision measurement of vibration amplitudes in the picometer range within just a few seconds.

Johannes May put this measurement concept into practice in a so-called holographic sideband interferometer in his work under the supervision of doctoral student Florian Dötzer and head of group Prof. Stefan Sinzinger. To this end, he developed automated control and evaluation software and carried out various series of measurements. This enabled him to detect oscillation amplitudes from 0.4 to over 1000 nanometers. He also discovered that holographic image recording is particularly robust against interfering light and less susceptible to vibrations and other frequency shifts thanks to the use of a reference oscillation:

I am very happy about this award for my scientifically oriented diploma thesis with simultaneously great application potential, with which I was able to complete my education at the TU Ilmenau.

Johannes May is currently continuing his research in the field of applied technical optics as part of a doctoral position at the Laserzentrum Hannover e.V..

The DGaO Young Talent Award is presented each year for the best dissertation and master's or diploma thesis in applied optics at a German university. The winners receive prize money of 1000 euros for a doctoral thesis or 500 euros for a master's or diploma thesis and are invited to the annual conference, where they can present their work in a lecture.