Understanding vibrating systems in nature and technology requires sophisticated, flexible and ideally non-invasive vibration measurement tools. Laser Doppler vibrometry has proven to be the most accurate and reliable method of vibration measurement. In industrial research and development, Polytec vibration measurement systems are used to study objects of many different sizes, ranging from entire car bodies, aircraft components, engines and buildings to tiny micro-machines and hard disk drive components. There are countless other research applications in mechanical engineering, acoustics and many other engineering-related disciplines. Measure remotely on red-hot surfaces, on rotating components, analyze high-frequency ultrasonic tools and fully understand the dynamic behaviour of the most complex and delicate structures in 3D. See how Polytec's vibration measurement technology helps to reveal the true vibration, acoustics and dynamics of vibrating structures.
Applications of optical vibration measurement
A pumping heart, wings vibrating, sounds are emitted and detected – life without vibrations is hard to imagine. Understanding vibrating systems in nature and technology requires sophisticated, flexible, and ideally non-invasive measurement tools. Recent innovations like the QTec® multi-path interferometry further push the limits.
Measuring vibrations with light
Laser vibration measurement systems aka laser Doppler vibrometers (Figure 1) rely on the principle of laser interferometry, using an eye-safe laser (e.g. HeNe with λ = 633 nm, P < 1 mW) as light source. Inside the vibration measurement head, an optical beam splitter separates the laser beam into two components: a reference beam and a measuring beam. The measuring beam hits a spot on the vibrating surface and the backscattered light is frequency-shifted because of the Doppler effect. This light then mixes with the reference beam and a beat frequency is produced.
How to measure vibrational velocity?
The frequency modulation of the light intensity is proportional to the vibration velocity. Whenever the measured vibrating object moves by half a wavelength of the HeNe laser (λ = 316 nm), the intensity will run through a full light-dark cycle. A light-sensitive sensor converts the changes in light intensity into an electronic signal. The frequency fD of these light-dark cycles is proportional to the speed v of the measured object as follows:
fD= 2 × v/ λ
Download the full whitepaper about the advantages of optical vibration measurement.
Currently, shot-noise-limited vibration measurement achieves an amplitude resolution far below a picometer during displacement demodulation. Today, laser vibration measurement has almost unlimited potential and is used in a wide range of applications. Vibration measurement data can therefore now be obtained with greater precision and efficiency, even for applications where conventional vibration sensor technology cannot be used.