  In this work, a novel approach for the detection and localisation of
nonlinear guided waves often associated with the presence of damage in
structural components is proposed. The method is active and consists of a
piezoelectric transducer bonded 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 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.
