Electromechanical Impedance - Based Structural Health Monitoring Instrumentation System Applied to Aircraft Structures and Employing a Multiplexed Sensor Array

ABSTRACT: The electromechanical impedance method has been seen as a promising tool for structural health monitoring regarding different types of structures and purposes. Most importantly, this method can be used in real-time applications. Frequently, massive, high-cost, single-channel impedance analyzers are used to process the time domain data, aiming at obtaining the complex, frequency-dependent electromechanical impedance functions and therefore infer about the presence, position and extent of an existing damage. However, for large structures, it is desirable to deploy an array of piezoelectric transducers over the area to be monitored and interrogate these transducers successively, in order to increase the probability of successful detection of damage at an early phase. The literature describes many miniaturized systems that can monitor large structures, however, presenting serious restrictions on data acquisition capabilities. This paper presents a hardware that is not limited to any data acquisition restriction, exhibiting an innovative way to measure the electromechanical impedance of multiplexed bonded transducers. Each logical block of the proposed architecture is presented in detail. The proposed system not only avoids costly fast Fourier transform analyzers/ algorithms, but also evades high-speed data acquisition hardware. A prototype using inexpensive integrated circuits and a digital signal processor was built and tested for two different types of structures: an aluminum beam and an aircraft aluminum panel. Simulated damages were introduced to each structure, and the detection performance of the prototype was tested. The actual prototype uses a universal serial bus connection to communicate with a personal computer.

摘要：机电阻抗法已被视为适用于各类结构与应用场景的结构健康监测（Structural Health Monitoring, SHM）极具前景的技术手段。尤为关键的是，该方法可适配实时监测场景。常规而言，研究人员多采用体积庞大、成本高昂的单通道阻抗分析仪处理时域数据，以获取与频率相关的复机电阻抗函数，进而推断结构中现存损伤的存在与否、位置与损伤程度。然而，针对大型结构，若要提升早期损伤的有效检出概率，需在待监测区域布设压电换能器（piezoelectric transducers）阵列，并依次对各换能器进行激励检测。现有文献中已提出多款可用于大型结构监测的小型化系统，但这类系统普遍存在数据采集能力受限的显著缺陷。本文提出一款不受数据采集能力限制的硬件系统，其采用创新方案实现多路粘贴式换能器的机电阻抗测量。本文对所提架构的各个逻辑模块进行了详细阐述。所提系统不仅无需使用成本高昂的快速傅里叶变换（Fast Fourier Transform, FFT）分析仪或算法，还规避了对高速数据采集硬件的依赖。研究人员采用低成本集成电路与数字信号处理器（digital signal processor, DSP）搭建了原型样机，并针对铝制梁与航空用铝合金面板两类结构开展测试。科研人员为两类测试结构分别引入模拟损伤，以此对原型样机的损伤检测性能进行验证。实际原型样机采用通用串行总线（universal serial bus, USB）与个人计算机进行通信。