Improving ultrasonic imaging of aluminum plates using phase modulation

Conventional techniques for ultrasonic image beamforming use amplitude information to produce the im-ages. Although amplitude images can be obtained with high quality, they can also present limitations regarding dead zone, artifacts and detection of far reflectors. Coherence techniques based on signal phase result in images that can be used to in-dicate the presence of a defect or reflector, with improve-ments over those limitations. This work proposes the use of phase modulation in the excitation signal and the application of the Pearson correlation to the instantaneous phase image. Simulations and experimental tests in an aluminum plate with artificial defects using Lamb waves and a linear piezo-electric array were conducted. The frequency response of the transducers-plate system was considered, leading to images with reduced artifacts and dead zone, and improvement in lateral resolution when compared to amplitude and instantaneous phase images without modulation.