System and method of diagnosing tube sensor integrity by analysis of excited stress waves

1. A structural health monitoring apparatus, comprising:

a plurality of transducers coupled to a structure, the structure comprising an outer structure having a hollow cavity and an inner structure extending into the cavity, the outer structure surrounding and coupled to the inner structure by a plurality of couplings that are separate from and discontinuous with each other, the transducers further coupled to only the outer structure and near one or more of the couplings so as to transmit stress waves through the outer structure, through at least one of the couplings and into the inner structure, and back into the outer structure through at least one of the couplings, so as to receive the transmitted stress waves from the outer structure after they have passed through the inner structure; and

an analyzer configured to detect a presence of damage within the inner structure according to the received transmitted stress waves from the outer structure.

2. The apparatus of claim 1 , wherein the analyzer is further configured to detect the damage without reference to a baseline signal.

3. The apparatus of claim 1 , wherein each of the transducers is configured for coupling to the outer structure through a waveguide.

4. The apparatus of claim 1 , wherein the analyzer is further configured to generate an acoustic energy profile on the basis of the received transmitted stress waves from the outer structure.

5. The apparatus of claim 4 , wherein the generated acoustic energy profile represents acoustic energy levels corresponding to a plurality of regions along a length of the structure.

6. The apparatus of claim 5 , wherein the analyzer is further configured to:

compare the acoustic energy levels of differing regions, and

determine the presence of damage in one or more of the regions on the basis of the comparison and an energy loss threshold.

7. A method of conducting structural health monitoring, the method comprising:

providing a structure comprising an outer structure having a hollow cavity and an inner structure extending into the cavity so that the outer structure surrounds and is coupled to the inner structure, wherein the inner and outer structures are coupled by a plurality of couplings that are separate from and discontinuous with each other;

sending excitation signals to a plurality of transducers coupled to the outer structure and near one or more of the couplings to cause the transducers to generate stress waves within the outer structure, so that the stress waves propagate through the outer structure, into the inner structure through at least one of the couplings, and back into the outer structure through at least one of the couplings;

receiving from the transducers response signals corresponding to the stress waves that have returned to the outer structure from the inner structure; and

determining a presence of damage in the inner structure on the basis of the received response signals.

8. The method of claim 7 , wherein the determining further comprises determining the presence of damage according to an energy loss of the stress waves, without reference to a baseline signal.

9. The method of claim 7 , wherein determining the presence of damage in the inner structure includes generating an acoustic energy profile on the basis of the received response signals.

10. The method of claim 9 , wherein the generated acoustic energy profile represents acoustic energy levels corresponding to a plurality of regions along a length of the structure.

11. The method of claim 10 , wherein determining the presence of damage in the inner structure includes:

comparing the acoustic energy levels of differing regions, and determining the presence of damage in one or more of the regions on the basis of the comparison and an energy loss threshold.