Structural health and condition monitoring via electrical impedance tomography in self-sensing materials: a review

Much recent work has been devoted to utilizing changes in either the inherent or imparted electrical conductivity of self-sensing materials as an indicator of damage, deformation or strain, pressure, or general condition (e.g. moisture content, UV exposure, pH, etc). The scope of self-sensing materials is quite large and includes polymeric composites, cementitious and ceramic materials, specialized fabrics, and sensing skins or paints applied to materials which otherwise cannot be made to be self-sensing. Beyond just utilizing conductivity changes for mere detection, spatial localization and artifact shaping is highly desirable. For this, electrical impedance tomography (EIT) has received much attention (also referred to as electrical resistance tomography, ERT). Because of the diversity of materials which exhibit conductivity-based self-sensing, EIT has broad, far-reaching potential in areas such as structural health monitoring (SHM) and nondestructive evaluation (NDE), human-to-robot interactions and interfacing, and even biomedical implants, prosthetic devices, and human health monitoring via wearable sensor technology. Historically, EIT was developed for biomedical imaging and geophysical prospection—vast literature exists in these areas. However, new applications of EIT in conjunction with stimulus-responsive conductivity in engineered materials poses new challenges and new opportunities not seen in biomedical and geophysical applications. Therefore, a comprehensive review of EIT as it has been applied for damage, deformation or strain, pressure, and condition monitoring is herein presented in order to provide the reader with a perspective of results to date, best practices, and a road map for future development of this exciting technology.