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

为了将结构中的状态监测问题置于整体视角中，并突出导波状态监测策略的日益增长的需求，重要的是要注意，过去十年的理论和应用经验在结构健康监测中产生了两个总体结论。 首先，从理论的角度来看，它已成为公认的传感器设计必须集中在分布式，局部测量的关键成员和附着点。 这是因为全球测量的敏感性低，如模态和自然频率，任何种类的退化。第二，应用研究和示范工程的丰富经验表明，一个成功的传感器必须具备以下所有要求：单位成本低、安装方便和适用性广;高灵敏度和高信噪比;低功耗;和长期耐用性基于导波询问原理的结构状态监测传感器，如瑞利-兰姆波传感器，原则上解决这两类问题。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。为了解决这一问题，提出了一种基于聚偏氟乙烯（PVDF）压电聚合物薄膜的叉指型瑞利-兰姆波换能器。 这种传感器的成功演示将结合联合收割机的超声导波测试和高度发展的功能的叉指电极（IDE）的RF SAW器件或高场，高力压电陶瓷致动器的吸引力的方法，与PVDF膜的结构监测非常理想的属性。这将大大扩大可用于保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.