Transducers and sensor-near signal processing for structural health monitoring of composite structures

This thesis delves into innovative transducer designs focused on directional sensing and acoustic wave generation, particularly through electrode patterning, for applications in Structural Health Monitoring (SHM). Ultrasonic Guided Waves (GWs), especially Lamb waves, have become widely used in SHM systems for plate-like structures due to their ability to travel long distances with minimal attenuation, while interacting with various types of defects, and convey information that can be detected by remote receiver. This unique property of GWs opens up possibilities for exploring their potential for transmitting information for inspection purposes. The research aims to overcome limitations of current SHM systems, such as weight, complex circuitry, and maintenance concerns, by introducing novel piezoelectric transducers known as shaped transducers. These transducers, including Frequency Steerable Acoustic Transducers (FSATs), leverage electrode patterning to enhance directional capabilities without requiring extensive phase control or managing numerous channels. The thesis prototypes FSATs to operate in actuation mode for Piezoceramic substrates and introduces unidirectional FSATs to address wave propagation ambiguities observed in previous designs. The design is further improved by introducing a third generation of FSATs, significantly reducing side lobes in beam patterns and enhancing imaging resolution. Expanding on the FSAT design, the thesis applies it to various SHM applications including acoustic data and power transmission, pipeline monitoring, and acoustic source localization. Discrete FSATs are developed for targeted transmission at multiple frequencies, while specialized designs facilitate helical wave generation for pipeline defect detection and wide-band acoustic emission monitoring for impact or defect growth detection. Additionally, an FSAT design tool is developed to streamline the design process for various transducer geometries.