A2.4 - Precise Characterization of Structure-Borne Sound Transmis-Sion Applied on Crash Sensing Technologies

SENSOR+TEST Conferences 2009
2009-05-26 - 2009-05-28
Congress Center Nürnberg
Proceedings SENSOR 2009, Volume I
A2 - Ultrasonic Sensors
M. Luegmair - University of Applied Sciences Ingolstadt, Ingolstadt, Germany, University of Magdeburg, Magdeburg, Germany, S. Wöckel - Ifak Institut für Automation und Kommunikation e.V., Magdeburg, Germany
65 - 70


The non-destructive prospection by ultrasonic or structure-borne waves within solids is a common indirect measurement technique beside the conventional body acoustic. It is used for quality control during the production cycle or online surveillance of tools, bearings, engines and machine structures by detection of defects or location of faults like unbalanced masses.
In the frame of a car safety system the structure-borne sound method is used to distinguish crash situations in civil cars. The device uses the information on the crash that is decoded in the high frequency range of the structure-borne sound caused by the deformation in the first few milliseconds of the impact. Usually the corresponding acceleration-sensor is placed in a central processing unit in the middle of the car. Hence the sensor position is not in the deformation zone, the impact-deformation sound signal is affected on its propagation through the car structure. In order to detect the signal beside multiple disturbing signals and to distinguish different crash situation, the characteristics of the propagation path within the car body need to be known.
On one hand these techniques require a sophisticated signal analysis (signal and pattern recognition) and on the other hand the wave behaviour and especially the influence of dispersion within the complex technical structure (system) need to be known with a high precision.
In order to design such prospection and surveillance sensor systems a tool is needed to estimate the behaviour of structure-borne sound propagation within a large scale structure. Further an appropriate simulation technique is indispensable in an early stage of the design process considering the development of structure-born sound based inspection sensors and their integration as a new technology into car. The description of the high frequency wave effects is either solved by simple linear models or enhanced FEA-simulation (Finite-Element-Analysis). Even if FEA-simulations are necessary in case of very complex structures they can perform calculation on a small scale only (due to the rising number of elements) and are not applicable to real time tasks up to now. That’s why alternative approaches like linear modelling are used to describe the elastic sound propagation - with a precision needed for signal analysis.
The current paper discusses such a linear approach building on the transmission line method and a linear model (e.g. Mason-theory). Here the crucial step in developing a fast and effective simulation method for the prediction of the sensor signal during a crash - in the last case - is the reduction of the complexity of the physical system. Using the Mason-theory and mason graph it is possible to get a semi-analytical solution of an acceleration wave transmitted from the excitation to an arbitrary point in the structure. With the including of the dispersion, one of the main dominant physical effects will be taken into account. The validation of these assumptions is shown by comparing the linear solution with FEA-simulations and simulation of corresponding structures with the new technique. In the following the assumptions and the characteristic behaviour are related to measurement results of a real car structure. At the End a conclusion and an outlook for further optimization of the simulation technique will be given.