Research On The Theory And Technology Of Ultrasonic Linear Phased Array Actuator Applied In Structural Damage Detection

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.