Development of a laser-powered wireless ultrasonic device for aircraft structural health monitoring

In recent years, wireless sensor networks have emerged as a reliable method for structural health monitoring. The powering methods for these wireless sensors have become an important factor. In several applications, wireless sensors must be operated in locations that are difficult or even impossible to access, and these systems often have a desired operational life span that exceeds conventional batteries lifetime. Replacing the batteries is labor intensive and time consuming. It is very difficult or even impossible to replace batteries of embedded sensors in concrete or composite structures. Therefore, novel powering methods such as energy harvesting or wireless power transmission are necessary to guarantee long life spans for wireless sensors. This article presents a laser-powered wireless ultrasonic device, which is a wireless active sensor with wireless laser power transmission that provides long-lasting structural health monitoring. The laser beam is captured by a GaInP photovoltaic cell. The cell has a high spectral responsivity for the 532-nm laser beam. A supercapacitor is used to store and supply power to the device. Furthermore, to solve the line-of-sight issue, a smart component called the fiber optic bolt is also developed using a large-core hard polymer-clad fiber. The wireless ultrasonic device includes the actuator and the sensor interface to evaluate the structural damages. To demonstrate the feasibility of the device, we carried out the basic Lamb wave pitch-catch test to detect the structural damage (such as cracks and artificial corrosion) in an aircraft lug (which is an example of an inaccessible aircraft structure). Our investigations show that the results of the proposed wireless sensing system are in accordance with those of the wired system. This indicates the feasibility for implementing the proposed system for wireless structural health monitoring.