Research Of The Blade Structure Ultrasonic Guided-Wave Excitation Transducer Based On Terfenol-D Material

With the rapid development of national economy,the pipeline plays the more and more important role of transportation in fire-fighting,metallurgy,oil,etc.However,there are many pipeline leakage accidents caused by damage and corrosion.Although the accuracy of existing detection methods is high,efficiency is low and cost is expensive.We urgently need a rapid and efficient nondestructive detection technology.Ultrasonic guided wave nondestructive detection technology have received universal attentions due to its far detection range,while only the cladding layer of installation location are stripped.Because performance of excitation transducer directly determines the effect of the guided wave detection,and excitation performance of the transducer depends on the performance of sensitive material.At present,we commonly used PZT as sensitive material of making incentive transducer,however,its electromechanical coupling coefficient is low,and the driving force is not big enough,so the practicality of the transducer is limited.Compared with PZT,the advantages of Terfenol-D with giant magnetostrictive coefficient is high energy conversion efficiency and response speed of microsecond and low load voltage for excitating through the coil.Therefore,this article uses the Terfenol-D material as sensitive material of making incentive transducer,coupling the vibration of the transducer into the pipe to produce guided wave.By designing the terfenol-d material into blade structure,one side is thicker and the other is thinner,to solve the transducer’s failure to generate the waveguide at any middle position of the outer surface of the pipeline.Winding excitation coil on the thinner end,providing the bias magnetic field for Terfenol-D material with three pieces of permanent magnets placed in the thinner end.In order to excite the required alternating magnetic field with the minimum excitation power,we need to optimize the parameters of the coil,determine the size of the sensitive material sequentially,and evaluate the performance of the transducer.We need to get the effect of changes of size of thicker end on the performance of excitation transducer by the experiment.The experimental results show that echo reflection coefficient and signal-to-noise ratio meet the requirements when the thicker end size for the thickness of 2.5 mm,length is 13 mm.Conducting the theoretical analysis of the alternating magnetic field strength of the excitation coil and experimentalizing the effect of chanages of wire diameter and turns on the performances of transducer.The results show that transducer meets the requirements when wire diameter is 0.21 mm,and number of turns is 180.Experimentalizing the effect of backing layer of different thickness and adhesive on the absorption of clutter signal in the received signal.The experiment shows that performance of the transducer meets the requirements when the backing layer thickness is 5 mm,adhesive on the surface of thicker end of knife Terfenol-D material with epoxy resin.Contrasting the performances of the developed transducer and the traditional PZT transducer on the pipeline length of 10.34 m with three welds pipe.Experiments show that the echo reflection coefficient of defects and echo amplitude of weld are higher than PZT transducer,and the attenuation is lower,suggesting that the performance of the self-developed transducer is better than the traditional PZT transducer.