超声波速度测定中影响因素的实验研究

Study on the Laboratory for the influence factors in ultrasonic velocity measurement

超声波测波速时,会受到样品长度、换能器频率、信号放大倍数以及耦合剂和耦合力等因素影响.为了定量地了解这些因素对测量结果的影响,本文用550 KHz、50 KHz二种频率换能器测量了近百块不同长度、空气干燥样品的波速.发现波速随长度的增加由一维"杆"中的波速逐渐增大并稳定在三维"无限大"中的波速,在此过程中长度对550 KHz波速变化的影响要小于50 KHz;一定长度后,频散趋于稳定且与样品Q值有关;波速随信号放大倍数、耦合剂的使用及耦合强度增大而增大.实验数据与波动理论、波速频散公式相符合.利用结果对Q<30的样品用频散法进行了Q测量,与频谱振幅比法结果有1%～11%相差;对地震仪和声波仪频率下测得的岩体完整性系数频散修正后二者平均相差由8%降到1.4%.

During ultrasonic velocity measurements, the result would be affected by the length of the samples, the transducer＇s frequency, signal amplification, coupling agents, coupling strength and other factors. In order to quantitatively understand these factors on the results, two different frequencies （550 KHz, 50 KHz） transducers are used to measure the velocities of nearly a hundred samples with different lengths. It was found that, with the increase of the length, the velocity changes from the velocity of one-dimensional ＂bar＂ to the velocity of three-dimensional ＂infinity＂. In this process, the impact of the length on 550 KHz＇s velocity was less than that on 50 KHz＇s~ after a certain length, dispersion became a stable value which related to the sample＇s Q; velocity increased with the signal amplification, coupling agents and coupling strength. The results are consistent with the wave theory and dispersion formula. By the dispersion formula, the results of Q from dispersion method has a difference of 11% according to the spectral amplitude ratio method for the samples （ Q〈 30 ）. After the dispersion correction, the average difference between the coefficient of rock mass integrity tested by seismograph and the one by acoustic instrument decreases to 1.4% from 8%.