Frequency- and Path-Dependent Guided-Wave Sensitivity Assessment of an Aerospace-Type Sandwich Composite Floor Panel Under Bonded Patch-Induced Perturbations Using Piezoelectric Sensor Networks

Sandwich composite floor panels are widely used in aircraft interior structures because of their lightweight and high stiffness-to-weight characteristics. However, the guided-wave response of such panels is strongly influenced by their multilayer configuration, honeycomb core, attenuation behavior, sensor-path geometry, and excitation frequency. In this study, an active guided-wave-based Structural Health Monitoring (SHM) configuration was experimentally evaluated on an aerospace-type sandwich composite floor panel using a piezoelectric (PZT) sensor network. The specimen consisted of glass fiber reinforced polyetherimide (GFR-PEI) face sheets and a phenolic-coated aramid honeycomb core. Controlled bonded patch-induced surface perturbations were sequentially applied over 25 predefined panel regions to introduce repeatable local mass-loading and damping changes. Guided-wave measurements were performed using an Acellent ScanGenie system over a frequency range of 75–600 kHz with 25 kHz increments and twelve directed actuator–receiver paths. The results showed that the measured Damage Index (DI) response depends strongly on excitation frequency, sensing path, and perturbation location. The 400–450 kHz range produced relatively higher DI values under the tested configuration, and 425 kHz yielded the highest mean DI among valid measurements. However, the valid sensing coverage at 425 kHz was only 50%; therefore, this frequency was not interpreted as the most robust overall monitoring frequency. Lower frequencies around 100–150 kHz provided full sensing coverage while maintaining relatively high DI values. Frequencies above 550 kHz showed reduced measurement reliability due to increased attenuation and poor usable signal response. Overall, the study provides a comparative sensitivity assessment of a guided-wave-based PZT network on a sandwich composite floor panel under controlled bonded patch-induced perturbations, rather than a direct validation of realistic internal sandwich-panel damage mechanisms.