分析了检测信号的特征，并采用截止频率法成功地提取了微弱的缺陷回波信号。
The characteristics of the test signals were analyzed and weak defect echo signals were successfully extracted by cut-off frequency technique.
采用摄动法研究了楔形杆轴的固有纵扭振动，并且推导出了其固有纵扭振动的振型函数及频率特征方程。
The natural longitudinal or torsional vibration of a wedge-shaped shaft is studied with perturbation method. The vibration mode function and the frequency characteristic equation are derived.
采用矢量场法，得到了在弱导条件下传导模式的特征方程和截止频率的近似计算公式。
The eigenvalue equation and approximate formula for cut-off frequencies of guided modes are obtained by vector-field-method.
应用推荐