A new model is developed to predict the attenuation characteristics of torsional ultrasonic in the waveguide.Because the uniformity of waveguide is affected by machining process.The influence of internal variation of material on the detection signal is greater than that of the attenuation of ultrasonic propagation in the short distance.There is a new detection scheme.Compared with the existing models,the effect of material inhomogeneity can be filtered.The permanent magnet is fixed in the middle of waveguide.Removing damping at both ends.Both ends of the ultrasonic can be reflected.The ultrasonic attenuation coefficients can be measured by detecting the amplitude of the two echoes.The attenuation coefficients of Fe-Ga and Fe-Ni waveguides of 0.5 mm wire diameter are 1.34 dB/m and 1.57 dB/m under 65 kHz torsional ultrasound.Furthermore,the effects of the waveguide wire diameter,torsional ultrasonic frequency and stress on the attenuation coefficient have been analyzed.The attenuation coefficient increases with increasing the diameter wire of waveguide.It has obviously positive correlation with torsional ultrasonic frequency.Moreover,it decreases firstly and then tended to be stable with increment of stress.Research results provide a theoretical guidance for the optimal design of large range magnetostrictive displacement sensor (MDS).%为研制大位移磁致伸缩位移传感器,对扭转超声波在波导丝中的衰减特性进行研究.由于波导丝材料的均一性受拉伸等加工环节的影响,材料的内部变化对检测信号的影响大于超声波在短距离传播的衰减变化.提出的检测方案将永磁体固定在波导丝正中间,去掉两端的阻尼,使得向两端传播的超声波受到同样的反射,通过检测两个回波的幅值来测量超声波衰减系数,可以滤除材料不均匀性产生的影响.搭建了磁致伸缩位移传感器实验平台,基于所提实验方法,测得频率为65 kHz的扭转超声波在线径为0.5 mm且不受拉力作用下的Fe-Ga和Fe-Ni波导丝的衰减系数分别为1.34 dB/m和1.57 dB/m.实验还对比了不同线径Fe-Ga波导丝、不同扭转超声波频率和波导丝在不同拉力作用下的衰减系数变化,结果表明:衰减系数随波导丝线径的增大而增大;衰减系数与扭转超声波的频率呈正相关;衰减系数随波导丝两端拉力的增大先减小后趋于稳定.
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