The design and testing of an ultrasensitive device with embedded phononic crystals for the detection and localisation of nonlinear guided waves

This work proposes a novel approach for designing and testing a sensing device with a high capability of filtering frequency bands. The purpose of the device is the detection and localisation of nonlinear guided waves. Nonlinear guided waves are often associated with the presence of damage in structural components (considered here) but also can emanate from the cancerous tissue. Therefore the provided design framework applies to the broad class of problems. The proposed method is active and consists of a piezoelectric transducer attached to the inspected structure exciting a narrow frequency band wave packet and sensors placed at the proposed ultrasonic devices with embedded phononic crystals. Unit cells of phononic crystals are optimized to open a band gap at the excitation frequency so that the excited waves are attenuated, while the sensitivity to detection of higher harmonics is increased. The proposed approach is tested numerically and validated experimentally by considering various manufacturing methods, materials, and unit cell geometries. A parametric study of the angle of attachment of the ultrasonic devices with the embedded phononic crystals to the inspected structure is performed. Band gaps and filtering capabilities of several prototypes are tested. Numerical simulations of guided wave propagation that include the effect of delamination clapping proved that the proposed designs are sensitive enough to detect higher harmonics by simple signal thresholding. The most promising prototype is tested experimentally showing its capability of detection and localisation of a simulated damage.