Master Thesis - OUFTI-1

Thanks to these results, the following conclusions can be drawn:
• The increase of mass brought by the sensor has an important eect on the value of
the natural frequencies. Indeed, it can be seen that, even with a sensor of 0.2 g,
the shift in frequency reaches a value of 13.87 Hz, which is not negligible. And this
eect becomes more important when the mass of the sensor increases. This problem
is essentially due to the fact that the studied structure has very restricted dimensions
and mass. So, any increase of mass, so small it is, involves interferences with the
PCB dynamic response.
• This eect can also be highlighted with the mode shape. Indeed, it can be seen that
the amplitude of the PCB deformation at the sensor location decreases when the
mass of the sensor increases.
So, in this particular case, it will be better to use a sensor which does not need to
touch the structure to perform the measurements (e.g., laser transducers, ...). This allows
to avoid any interference with the dynamic response of this structure.
Modeling of the P C 104 connector
The second analysis concerns the modeling of the P C 104 connector. It was choose to
represent it using a detailed FE model, for reasons exposed previously. But, the question
is: what does this particular choice involve on the PCB dynamic response To answer to
this question, the fourth mode of the OBC 2 card for the two dierent type of modeling,
is shown in Figure 4.24.
Figure 4.24: Inuence of a change of modeling strategy for the P C 104 connector on the
OBC 2 card's fourth mode
Thanks to these results, it can be seen that the inuence of the P C 104 connector on
the PCB dynamic response is stronger using the detailed FE model (the deformation of the
card is less important at the connector location and more important on the opposite side).
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