Research On Estimation Method Of Acoustic Parameters Of Liquid Materials Based On System Identification

The nondestructive testing of liquid materials has the vital significance in the field of petroleum chemical industry, food industry and the pharmaceutical and health care. As an important method of detection of liquid material, ultrasonic nondestructive testing technology has been widely used in industry. Liquid ultrasonic testing is mainly using the ultrasonic pulse test to estimate the acoustic characteristic parameters of liquid (the speed of sound, sound attenuation, acoustic impedance, etc.), and then to analyze the physical properties of the liquid. In order to get accurate and reliable parameter values in the liquid, we need to study the estimate method. At present, commonly used methods mainly include passing zero method, nonparametric model method and parameter model method, etc.In this paper, we first establish parameterized model of liquid medium, and then use the method of system identification for containing liquid ultrasonic propagation characteristics to identify the parameters model, finally use the transfer function of the parameters model to achieve estimating the liquid acoustic parameters. The specific research work is as follows:1. Apply the systematic theory in the study of liquid acoustic characteristics by abstracting the propagation of acoustic wave in the liquid as a nonlinear system. The first and second echo of the sound waves in liquid are put as the input and output signals of the nonlinear system. And then use least squares method for parameterized modeling system.2. Ultrasonic pulse echo experiments have been carried out to test the ultrasonic echo of the saline solution. On the basis of the ultrasonic pulse echo experiments, we use the system identification to get the system transfer function of the saline solution acoustic characteristics, and then analyze the effectiveness of the system function.3. We derived the liquid velocity analytical expression from the system transfer function. By using system identification to get the system function, we achieve to estimating the velocity of the physiological saline solution. By comparing the results with the method of nonparametric model, we find the results that the parameter model method's estimate results have the higher estimation precision. Except for, this method can also avoid the parameter model method in the process of Fourier transform error caused by phase unwrapping.4. Ultrasonic pulse experiment container wall brings a certain impact in the ultrasonic transmission. In the acoustic attenuation and acoustic impedance estimation process, using the system check method in this paper. With distilled water as the standard liquid, we respectively identify the transfer functions of the liquid system and the standard liquid system to overcome the container wall on the result of estimation. We use test echoes to estimate the acoustic attenuation coefficient and acoustic impedance of the physiological saline solution, the results showed within the test frequency, acoustic attenuation on frequency of quadratic was positively than growth, in accordance with engineering experiment measurements.5. Experiments respectively have been carried out to test the ultrasonic echoes for sucrose solution, milk, fruit vinegar drink three kinds of liquid food. We use the method of parametric model to estimate the acoustic parameters, and obtain the acoustic parameters of the liquid food and the quantitative relation between physical properties. The results for acoustic parameter estimation method provide the basis for the analysis of the quality of liquid food.In this paper, the research of ultrasonic nondestructive testing technology has certain significance in the application of the quality analysis of liquid food.