Add sensors to model

Hi,

I am modelling wave propagation in plates LS-DYNA and need to use multiple sensor elements attached to the plate with different material properties to obtain normal displacements. I am using 2-D shell elements for both sensor element and plate. When I don't define any contact between the plate and sensor elements (merged nodes), the sensor element is somehow seen to extremely distort the waves (due to huge difference in density) and I am not getting expected results. Is there any way I can define any contacts/keywords such that the sensor element does not effect the model and is only used as extracting the displacement required? I have been stuck with this for a while and any help would be highly appreciated.

Thanks

Manoz