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置于一个整体的角度，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在结构健康监测方面的理论和应用经验产生了两个总体结论。首先，从理论角度来看，换能器设计必须关注关键部件和附着点的分布式、局部测量，这一点已经被接受。这是因为全球测量的低灵敏度，如模态振型和固有频率，对任何种类的退化。其次，应用研究和示范项目的丰富经验表明，一个成功的换能器必须满足以下所有要求：单位成本低，安装方便，适用性广；高灵敏度和高信噪比；功耗低；具备无线操作或远程讯问能力；基于导波探测原理的结构状态监测传感器，如瑞利-兰姆波传感器，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不能满足所有必要的要求。针对这一需求，提出了一种基于聚偏氟乙烯（PVDF）压电聚合物薄膜的交叉式瑞利-兰姆波换能器。这种换能器的成功演示将结合有吸引力的超声导波测试方法和为射频SAW器件或高场、高力压电陶瓷致动器开发的高度进化的交叉电极（IDEs）能力，以及用于结构监测的PVDF薄膜的高度理想性能。这将大大增加可用于维持国家基础设施组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.