摘要
用于声／电转换的超声相控阵驱动器是超声相控阵检测系统的关键组成部分之一,通过延时控制,超声相控阵驱动器具有自动聚焦和偏转的能力,可以对被测结构进行多方位快速扫描。由于相控阵驱动器直接产生超声波,因此它的结构形式及性能直接影响超声相控阵检测的性能和成像质量。针对复杂工程结构损伤特性及现有超声相控阵检测技术中驱动器存在的不足,在压电正交异性机理研究基础上,通过理论分析、数值仿真与实验验证研究了伸缩型压电正交异性纤维复合材料(Orthotropic piezoelectric fibe composite, OPFC)元件及相应的用于金属结构和混凝土结构损伤检测的OPFC超声相控线阵换能器,拓展了复杂工程结构无损检测新技术,为超声相控检测技术提供了理论和实验指导。
基于力-电耦合理论,构造了伸缩型振动的压电正交异性纤维复合材料(OPFC)元件,系统地分析了各相材料特性、结构尺寸对OPFC驱动元件性能的影响规律,并对其驱动性能进行了测试分析。针对现有的超声相控阵换能器应用中单一PZT阵元力/电参数可设计性不足等原因,设计相应的用于金属结构和混凝土结构损伤检测的OPFC超声相控线阵换能器,突显出其驱动电压低,有效地抵制了栅瓣对有效信号的干扰；结合声场指向性分析,采用有限元法对金属中聚焦声场分布分析,研究不同参数变化时聚焦点处总位移的变化,得出最佳相控阵阵元间距、阵元宽度、阵元数等参数。
研究了用于金属结构和混凝土结构损伤检测的OPFC驱动器的制备方法,对自行研制的叉指式OPFC元件进行了性能测试,并与常规PZT元件性能进行了对比分析,得出用于金属结构检测的叉指型OPFC具有低声阻抗和高机电耦合系数,而用于混凝土结构检测的OPFC超声驱动器的得灵敏度和带宽比传统换能器分别提高了3.9dB和27.21%。
为有效克服材料阻尼对超声波传播过程的衰减,基于现场可编程门阵列(FPGA)的高集成度、高运行速度和可编程的特性,研制了16通道的相控延时和可控强度聚焦偏转发射/接收装置,实现了任意波形信号的直接数字合成,对OPFC超声相控驱动技术进行了结构损伤检测实验验证,取得了预期的效果。
实验结果表明与现有超声相控阵驱动技术相比,其驱动聚焦能量、检测灵敏度都能得到提高,检测范围进一步扩大,验证了将OPFC超声相控线阵驱动/传感器用于结构损伤检测的可行性。
Ultrasonic phased array actuator for acoustic-to-electronic transformation is the key part of ultrasonic phased array system. Ultrasonic phased array actuator has the capacity of auto-focus and deflection by time delay controlling and can be used for multi directional scanning of objects. As the phased array actuator is used for excitation of ultrasonic, the design and preparation of the phased array actuator determine the performance of array detection and imaging quality. Based on the piezoelectric orthotropic mechanism research, thickness expansion type orthotropic piezoelectric fiber composite (OPFC) element and related OPFC ultrasonic phased array transducer which applied in damage detection of metal and concrete structures are researched by theoretical analysis, numerical simulation and experimental verification methods. The newly develop NDT technology in complex engineering structure provides the theory and experiment guidance for ultrasonic phased array detection technology.
Based on theory of electric-mechanical coupling relationship, the influence of the material characteristics and geometry parameter on actuating performance is studied while thickness expansion type orthotropic piezoelectric fiber composite (OPFC) elements are constructed. In view of insufficiencyin the mechanic-electronic parameter design of existing single PZT element for modern ultrasonic phased array transducer, the related OPFC ultrasonic phased array transducer which used in metal and concrete structural damage detection is designed, which havethe advantages such as low voltage and restrain the effects on grating lobe. The focusing acoustic field distribution is analyzed by finite element method combined with directivity analysis in metal material. The optimal array parameters such as phased array element interval, array element width and element numbers are obtained by studying the total displacement changes as different parameters changes at focus point.
The preparation of OPFC actuator used in metal and concrete structural damage detection is studied. The performance of interdigital OPFC element is also obtained by testing and comparing with the traditional PZT element. The results show that OPFC has some lower acoustic impedance and higher mechanical coupling factor. The sensitivity and bandwidth of OPFC ultrasonic actuator used in concrete structure detection are improved by3.9dB and27.21%respectively.
To overcome the attenuation of ultrasonic due to material damp, a16-channel time delay phased array actuating/receiving device along with a strength controlling focus and deflection actuating/receiving device are developed based on the features of Field-programmable gate array (FPGA) such as high integration, high speed and programmable features. The directly digital synthesis of arbitrary waveforms is also achieved.. The structural damage detection methods are validated by experiment with OPFC ultrasonic phased array transducer and the promising results are gotten.
Comparing with traditional technology, the performances of the new type ultrasonic phased array actuator, such as actuating focus energy, sensitivity and testing scope are improved. The feasibility of OPFC ultrasonic phased array transducer for damage detection is validated.
引文
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