Design Of Electromagnetic Ultrasonic Transducer Used For Detecting Buried Depth Of Guardrail Column Of Expressway

Highway guardrail can prevent vehicles from rushing out of the road or driving into the opposite lane in the event of an accident,thus minimizing the accident loss,which is called the last safety belt to protect the driver’s life.However,in the construction process,the phenomenon of jerry-building and material reduction of guardrail columns often occurs,and the buried depth often fails to meet the construction requirements,resulting in great potential safety hazards.Therefore,it is very necessary to detect the buried depth of the guardrail column.The traditional method is pulling the pipe directly to detect,which is time-consuming and laborious and can cause damage to roadbed.Elastic wave method can detect the buried depth of guardrail column,but it also has some shortcomings,such as high noise,serious attenuation,multimode in the receive signal and so on.In view of the shortcomings of the above methods,this paper presents a method of detecting the buried depth of the column by using EMAT(electromagnetic acoustic transducer)to excite ultrasonic guided waves in the guardrail column.Firstly,the basic concept of ultrasonic guided wave is introduced.The characteristic equation of ultrasonic guided wave propagation in a free hollow cylinder is deduced,and the dispersion curve is drawn.The multimode,dispersion and displacement distribution of L mode guided wave,T mode guided wave and F mode guided wave are analyzed.Secondly,the working principle of EMAT is analyzed,and the working mechanism of Lorentz force and magnetostrictive force is mainly studied.After comparative study,it is decided to design an EMAT based on Lorentz force mechanism.Thirdly,the structure of EMAT is proposed to excite torsional guided waves.The runway coil is selected as the excitation coil,and the cosine signal modulated by Hanning window is used as the excitation signal.The simulation software COMSOL is used to simulate the transducer’s energy transfer process and the propagation process of ultrasonic guided wave in the column.Finally,the basic principle and steps of using EMAT to detect the buried depth of columns are pointed out,and the test results are in line with the requirements of national standard for the detection of the buried depth of columns in different buried depth.