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For more than 20 years Laser Doppler Vibrometry (LDV) is an established tool in vibration engineering for non-contact vibration measurements. The LDV method is not only limited to measurements on single test points. Utilizing a pair of galvanoelectrical mirrors for steering the laser beam in x and y directions across the surface the vibration pattern of full areas can be mapped. Such scanning LDVs (SLDV) have found many applications in the automotive industry as well as in institutional research. However the use of the SLDV technology is limited to stationary objects and rotating objects with smooth uninterrupted structures such as brake discs or tires. Up until now measurements on objects with complex noncontinuous structures such as bladed discs, fans, propellers have not been possible yet. Furthermore, interpretation of travelling non-stationary modes which can be found on rotating tires, saw blades, etc. has been difficult with conventional SLDV technology.

Laser Doppler Vibrometry (LDV) is an established tool in automotive engineering for non-contact vibration measurements. The LDV method is not limited to measurements on single test points. Complete structures can be tested by utilizing a pair of galvano-electrical mirrors for steering the laser beam in x and y directions across the surface. Such scanning LDVs (SLDV) have found many applications in the automotive industry. However for full body modal analysis use of scanning LDVs has so far been restricted due to the fact that only the out-of-plane (OOP) component of the velocity vector can be measured whereas tri-axial accelerometers provide OOP and in-plane data simultaneously. This limitation has been overcome with three-dimensional scanning LDVs which were first introduced towards the end of 2002. A 3D SLDV consists of three independent SLDV measurement heads, each measuring the vibration of a scan point from a different direction.