Inter-Digitized Transducers (IDTs) for Structural Health Monitoring (SHM) Applications

Abstract

Single element piezoelectric plates having inter-digitized electrode patterns, specifically tuned to operate at several hundred kHz to several MHz of frequencies, have been designed and fabricated by a laser micro-machining process. These narrow band low profile sensors are extremely effective to induce Rayleigh surface waves directly on the surfaces of various materials including metals, plastics and composites. Ultrasonic signatures of flaws, defects and damages on the surfaces of materials are easy to interpret due to the non-dispersive wave property of Rayleigh waves. Laboratory tests prove that detection of a deterministic fatigue crack on a metallic structure is straightforward in terms of changes in amplitudes. As a first step toward SHM application of IDT sensors to composite materials, the ultrasonic properties of the test panels made from polyester and glass fiber have been measured with respect to the fiber directions. Unlike isotropic metallic structures, anisotropy caused by glass fiber directions affects the ultrasonic properties as well as detection of defects and flaws in composite panels. Artificially induced surface cracks and impact damage on test panels are used to quantify the size, location and severity of damage in terms of changes in amplitudes. It is estimated to cover a distance close to one meter with a set of IDT sensors, one transmitter and two receivers for the composite panels, while the distance coverage can reach several meters for metallic structures at a several hundred kHz of frequency.