Quick Simple and Sensitive Tomography by Nonlinear Ultrasonic Mixing Spectroscopy

摘要

Principles of nonlinear ultrasonic mixing impulse spectroscopy (NUMIS) show great potential advantages in comparison with other nonlinear ultrasonic methods. It is first of all from the point of view of sensitivity and possibility of quick, simple and precise localization of a defect. This paper elaborates on the principles and algorithms of calculation of the defect place for this method. The point idealization of ultrasonic transducers and receivers are supposed for this aim. A successive increase in delay of the second excitation pulse can to obtain the image distribution of defects on the tested body in a 2D plane in few seconds. The main idea of this method consists in sending of two impulses (bursts) with the harmonic signals with different frequencies f_1 and f_2. These bursts are mutually time shifted in successive steps. When two waves come across in the place of defect with nonlinear properties, the new frequency component with different frequency f_d will be created. Optimum choice of exciting frequencies lets using of enough analog pre-filtration and on the other hand the wave length of f_d component enables enough precise localization. The ultralinear analog prefiltration enables rejection of exciting signals. It allows to this system with subsequent analog and digital signal processing to use a signal processing with considerably greater dynamic range. Therefore, it processes very small signals compared with the excitation signal and he has so much higher sensitivity than conventional methods of nonlinear ultrasonic spectroscopy. Further this principle is generalized to 3D tomographic testing of various bodies and structures.