For all slab cases (Case 0, 1, 2, and 3), eigenvalue analysis was conducted to obtain their modal frequencies and mode shapes. Table 3 shows the first two bending modal frequencies (Modes 1 and 3) and the first torsion mode (Mode 2). As expected, the three modal frequencies in Case 1, 2, and 3 were all smaller than those in Case 0; when damage occurred somewhere in the slab (Case 1, 2, and 3), the modal frequency dropped.However, it is difficult to localize the damage in the slab merely from the frequency change. Comparing the three modal frequencies from Case 1, 2, and 3, no clues are found to localize the damage. This is because modal frequencies do not provide any spatial information. To localize damage while focusing on mode shapes (e.g., see Figure 8 for Case 0), it is proposed to install the MEH devices on multiple panels to catch the relative change in energies harvested from different locations. The proposal is further discussed in Section 3.