Optical sound, vibration and strain measurement

// Measuring and Control Technology // Optics, Photonics and Laser Technology // Physical Technology // Sensors and Measuring Instruments
Ref-Nr: 16636


The invention provides for the optical detection of physical measurands. A modified Mach-Zehnder interferometer is used for this purpose. Compared to conventional Mach-Zehnder interferometers, the measuring range is not limited to the wavelength of the light used.

Fig. 1: Structure of the modified Mach-Zehnder interferometer for optical sound, vibration and strain measurement


Fiber optic sensors are used in a project of the HTW Berlin for the monitoring of switchgears. The aim is to record acoustic signals generated by partial discharges or mechanical vibrations during switching operations.


The simultaneous, high-precision acquisition of both high-frequency signals with small amplitudes and low-frequency signals with large amplitudes is possible.

Innovation / Solution

The inventive measuring principle provides that the phase angle between at least two light signals is measured. The light signals are guided through a reference or sensor fiber. If the fibers are of identical length, both light signals are superimposed. If there is a difference in the fiber length due to elongation or compression, the light waves shift against each other. Since the light waves repeat periodically, only one difference can be detected within one period. This corresponds to a wavelength of the light used. If you count the light-dark transitions in the interference pattern, you know how often you have to add 360° to the difference phase angle to know the total shift. The difference between compression or stretching can be determined by evaluating phase-shifted interference patterns.


Measurement of any aspect ratio with micrometer accuracy Recording of analog measurement data with a minimum of analog circuit technology Cost-effective detection of sound, vibration and strain in a wide frequency range

fields of application

The field of application for this invention is metrological tasks, e.g. the monitoring of switchgear. Since the invention represents a cross-sectional innovation, the range of applications is very broad: Acoustic sensors, pressure sensors, humidity sensors, temperature sensors.

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