To place the problem of condition monitoring in structures into an overall perspective and to highlight the growing need for guided wave condition monitoring strategies, it is important to note that the past decade of theoretical and applied experience in structural health monitoring has yielded two overarching conclusions. First, from a theoretical perspective, it has become accepted that transducer design must focus on distributed, localized measurements at critical members and attachment points. This is because of the low sensitivity of global measurements, such as mode shapes and natural frequencies, to degradation of any kind. Secondly, extensive experience from applied research and demonstration projects has indicated that a successful transducer must incorporate all following requirements: low unit cost, easy installation and wide applicability; high sensitivity and high S/N ratios; low power consumption; capability for wireless operation or remote interrogation; and long-term durability
Transducers for condition monitoring of structures based on guided wave interrogation principles, such as Rayleigh-Lamb wave transducers, address in principle both sets of concerns. However, transducers based on conventional piezoceramics do not meet all the necessary requirements. To address this need, it is proposed to develop an interdigitated Rayleigh-Lamb wave transducer based on polyvinyldine fluoride (PVDF) piezoelectric polymer films. The successful demonstration of such a transducer will combine the attractive approaches of ultrasonic guided wave testing and the highly evolved capabilities of interdigitated electrodes (IDEs) developed for RF SAW devices or high field, high force pizeoceramic actuators, with the highly desirable properties of PVDF films for structural monitoring. This will significantly enlarge the choice of piezoelectric materials available for maintaining the performance of the nation's infrastructure components.
