Magnetostrictive sensor for active health monitoring in structures

A flat magnetostrictive sensor for active health monitoring of a large area of a structure has been developed. The sensor consists of a thin nickel foil and a coil placed over the nickel and, much like a strain gauge, is permanently bonded to the surface of a structure under monitoring. When activated, the sensor generates guided waves in the structure for interrogation and detects signals that are reflected back from the structural geometries and defects in the structure. Since guided waves can travel a long distance in the structure, a large area of the structure can be interrogated and monitored by using the sensor. By periodically acquiring the data and comparing it with the baseline data established at the time of sensor installation, structural changes occurred over that time can be quickly determined for suitable structural management decision. In addition to the ability to actively inspect and monitor a large area of the structure, the sensor is also rugged and inexpensive and therefore has high potential for practical use. As an example of its applicability to aircraft structure, data showing the monitoring of defect growth in fastener holes in a wing structure are presented.