## 3 Description of the Experimental Setups  
### Experimental Setup for the SHM Plate  
Figure 6 depicts the experimental setup. The _SHM plate_ is placed in a climate chamber (left figure) at a constant target temperature of 23 \({}^{\circ}\)C and a relative humidity of 50% (DIN EN ISO 291). On the top and bottom of the structure, two Pt-100 temperature sensors were attached to the surface of the _SHM plate_ to detect potential thermal gradients within the climate chamber. The temperature sensors were coupled to a PT-104A device (Omega Engineering, Deckenpfronn, Germany) which enables temperature measurements with a resolution of 0.001 \({}^{\circ}\)C and an accuracy of 0.01 \({}^{\circ}\)C.  
For GW actuation, piezoceramic transducers are used to excite the signal. A Handyscope HS5 (TiePie Engineering) is employed to generate arbitrary waveforms and to record signals by analog-to-digital conversion (14 bit resolution). A broadband amplifier PD200 (PiezoDrive Ltd, Shortland, NSW 2307, Australia) enhances the excited waveforms and feeds the signals to a dedicated multiplexing device that is described in greater detail in [32]. This custom device is also used to measure all actuator-receiver pairs by time-division multiplexing. A sine with five cycles was Hann-windowed which is represented by \(w(t)\) in the subsequent formula  
\[U(t)=\hat{U}w(t)\sin(2\pi f_{c}t). \tag{1}\]  
The voltage amplitude was defined as \(\Omega=\)100 V. The central frequency \(f_{c}\) is in a range from 40 kHz to 260 kHz in steps of 20 kHz. Moreover, a broadband excitation was used (see Figure 7), namely a linear up-chirp with 0.125 ms duration, start frequency of 20 kHz and stop frequency of 500 kHz. The structured process of data acquisition regarding the _SHM plate_ consists of seven phases. For measurements with reference damage, only a single defect \(D_{1}\), \(D_{2}\) or \(D_{3}\) was used at the same time. Figure 6: Front view of the _SHM plate_ in the climate chamber (**left**). Two temperature sensors were installed on the top right and bottom right for surface temperature measurements. Side view (**right**) before the fixation of a reference damage using a metal block and the electromagnet. Phase 1  
Five baseline measurements of the pristine structure were recorded. Phase 2  
Reference defects were attached to the plate at position \(D_{1}\), see Table 4. For maximum reliability an electromagnet supported by a metal block was used to press the reference damage to the structure. In a next step, the electromagnet was removed so that only the reference damage was in contact with the structure. For every of the 13 damage sizes and each damage position, the measurement was repeated independently five times. Each time the procedure includes the following steps: fixation of the model defect with tacky tape, measurement, detaching, removal of tacky tape, renewed fixation. Phase 3  
Another 5 baseline measurements were recorded without any applied reference damage. Phase 4  
the damage positions \(D_{2}\), see Table 4, was considered and the procedure of phase 2 was followed. Phase 5  
Another 5 baseline measurements were recorded without any applied reference damage. Phase 6  
The damage positions \(D_{3}\), see Table 4, was considered and the procedure of phase 2 was followed. Phase 7  
Finally, in the last phase, five baseline measurements were acquired. The temperature in the climate chamber showed a standard deviation of 0.12 \({}^{\circ}\)C (sensor on top), 0.08 \({}^{\circ}\)C (sensor at the bottom) and an average temperature gradient between both temperature sensors \begin{table}
\begin{tabular}{c c c} \hline \hline
**Damage ID** & **x-Coordinate (mm)** & **y-Coordinate (mm)** \\ \hline \(D_{1}\) & 210 & 350 \\ \(D_{2}\) & 130 & 100 \\ \(D_{3}\) & 290 & 150 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Coordinates of damage position (center position of the elliptical disc). Figure 7: Depiction of the employed actuation waveforms: Exemplary time-domain signals (**left**) and the spectrum of all waveforms (**right**).