An Interdigitated PVDF Guided Wave Transducer for Large Array Condition Monitoring of Steel Structures

为了将结构状态监测问题放在一个整体的角度来看待，并强调对导波状态监测策略的日益增长的需求，重要的是要注意到，过去十年结构健康监测的理论和应用经验已经产生了两个重要的结论。首先，从理论的角度来看，人们已经接受这样的观点，即换能器的设计必须侧重于关键构件和连接点的分布式、局部化测量。这是因为振型和固有频率等全局测量对任何类型的退化的敏感性都很低。其次，应用研究和示范项目的丰富经验表明，成功的换能器必须包括以下所有要求：低单位成本、易于安装和广泛适用；高灵敏度和高S/N比；低功耗；无线操作或远程询问的能力；以及长期耐用性；用于基于导波询问原理的结构状态监测的换能器，如瑞利-兰姆波换能器，原则上解决了这两组问题。然而，基于传统压电陶瓷的换能器并不能满足所有必要的要求。为了满足这一需求，提出了一种基于聚偏氟乙烯(PVDF)压电聚合物薄膜的交指型Rayleigh-Lamb波换能器。这种换能器的成功展示将把吸引人的超声导波测试方法和为射频声表面波器件或高场、高力陶瓷致动器开发的交指电极(IDE)的高度进化能力与PVDF薄膜用于结构监测的高度期望的性能相结合。这将大大增加可用于维持国家基础设施部件性能的压电材料的选择。

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 durabilityTransducers 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.