Study On Ultrasonic Propagation Characteristics And Noise Reduction Methods In Rod

Extruder is one of the most important equipments in the field of polymer processing. The mixed state of polymer in different positions of extruder and the quality of the final products are closely related. However, all the methods of detecting for polymer mixed state are off-line and the feedback information can not be real-time.Ultrasonic technology can be used in on-line detecting for polymer mixed state in extruder. However, in the process of polymer blending, the temperature of molten polymer is quite high and ultrasonic probe can only work at a normal temperature. Therefore, a temperature buffer rod coupling between ultrasonic probe and the high temperature polymer is needed. There are lots of trailing pulses appear in the propagation of ultrasonic in rod and seriously affect the extraction of characteristic signals. In this background, the paper studied on the ultrasonic propagation characteristics in rod, the causes of the trailing pulses and the noise reduction methods. It could provide the optimized designs for development of ultrasonic sensor in detecting for polymer mixed state.The main contents and the results of this paper are given by the following:Firstly, by adopting the input-output method in the frequency-domain, this paper abstracted the ultrasonic propagation process to a transduction process of the signals in system and established an analytic model for ultrasonic propagation in uniform diameter cylinder, which was based on the Pochhammer-Chree theory. It completed the analytical simulation for sampling signals and got the similar results with the actual sampling signals. Through the calculation of each individual propagation modes in rod with uniform diameter, it indicated the main distribution of the time-domain signals energy concentrated in six modes. After the summations of all the individual propagation modes, the paper concluded that: the trailing pulses were the contributions of all individual propagation modes in rod.Secondly, the paper established the finite element model for ultrasonic propagation in uniform diameter cylinder and realized the visualization of ultrasonic propagation process by converting the displacements of entire nodes to gray images in all time steps. Aiming at the calculated results of SNR in rod and the observation of instantaneous fluctuations, such as the uniform diameter, tapered and double-tapered structure of temperature buffer rods, it could be observed that: variable diameter buffer rod had good inhibition effects, especially on the tapered structure and ultrasonic excitations loaded on the smaller diameter of rod had the maximum SNR.Finally, it concluded that this paper provided the optimized designs for development of ultrasonic sensor in detecting for polymer mixed state using the analysis of ultrasonic echoes in actual temperature buffer rods.