A numerical study on planar gradient acoustic impedance matching for guided ultrasonic wave detection

Abstract

Increasing the service-life of engineering structures such as e. g. airplanes is a major issue in order to enhance their cost-effectiveness and to reduce the carbon footprint. One possibility to achieve this goal is to determine the current (structural) health state and to derive respective measures e. g. in order to increase the structure’s technical reliability.For doing so, a structural health monitoring system consisting of both an actuator and a sensor network may be applied. Whereas the actuator induces a wave-field of guided ultrasonic waves, the measuring data of the sensors allow to determine the health state of the respective structure. However, both actuators and sensors in most cases distort thesewave fields. This distortion may lead to false-detection of damages: both the number and severity of damages may be over- or underestimated. The former leads to an unnecessary high effort for retrofitting the structure whereas the latter reduces the structure’s technical reliability. Several measures exist in order to avoid such false-detections. In thepresent contribution, focus is set on reducing the distortion of the wave field which is caused by a sensor. The reduced distortion of the wave field is achieved by an acoustic impedance matching with a functionally graded material which is based on a mechanical model. The approach additionally results in amplified measuring signals of the sensor. Bymeans of a numerical study the applicability of the proposed approach is shown.