Study On Signal Processing Technology And Their Applications In Ultrasonic Detection Of Sediments Thickness

Too thick sediment in the bottom of borehole is a main factor which much affects the quality of the bored pile. So far the advanced and exact instruments to measure the sediments thickness are deficient. Based on this status, a new method to measure the sediments thickness by ultrasonic technology has been proposed and a series of research work about the ultrasonic signal processing as filtering, signal enhancing and sound travel time obtaining has been developed. The major work of this dissertation includes six parts as the following:1. The four work modes of ultrasonic detection systems and the relations between the parameters of ultrasonic transducer and detection indexes have been analyzed. According to them, the characteristics of ultrasonic transducer needed in ultrasonic detection system to measure the sediments thickness in borehole has been determined. Using the specially made ultrasonic transducer and necessary instruments such as waveform generator, power amplifier, digital oscillograph and so on, experiments in simulation environments have been carried out and clear echoes of the sediments interfaces have been obtained.2. Gabor filtering in time domain and transform domain has been studied. According to the analysis of the features of Gabor expansion coefficients, a new method to select Gabor transform filter's threshold based on the first larger probability in histogram of class separation distance, and its detail process steps have been given. Using the presented threshold, the Gabor transform filter can achieve good effect in processing both the simulation signal and the real ultrasonic detection signal.3. The iterative passive time reverse mirror (PTRM) has been used to enhance ultrasonic detection signal. As for iterative PTRM, its principle of time-varying enhancement and the enhancement multiple have been analyzed and deducted. The experiments results have shown that iterative PTRM can enhance signal with a time-varying gain even the characteristics of the ultrasonic transmitting in the media is unknown. In addition, iterative PTRM can de-noise to some extent.4. The concepts of band and spectral subtraction have been introduced into singular value spectrum entropy and the way how to plot out the bands has been given. On this base, spectral subtraction band singular value spectrum entropy (SS-B-SVSE) has been proposed and applied to detect and locate the wave head of ultrasonic signal. The experiments have shown SS-B-SVSE is a high precise, strongly anti-interference and robust method for locating wave head in ultrasonic signal.5. Virtual matrix MUSIC (VM-MUSIC) has been presented to estimate the time delays of the echoes. Furthermore, the way how to construct the signal of virtual matrix elements and the least matrix elements in virtual matrix have been discussed and determined. In the experiments of the ultrasonic detection signal, VM-MUSIC has gotten high precise and high resolution time delay estimation.6. The proposed signal processing algorithms above have been used to process the ultrasonic echoes which are obtained by experimenting in the simulation environments. The satisfied results have verified the feasibility of the method of measuring the sediments thickness in borehole by ultrasonic and the validity of the processing algorithms.