Research On The Ultrasonic Measurement Technique Of Liquid Acoustic Characteristics

The ultrasonic measurement of liquid acoustic characteristics has very importantmeaning in petrochemical industry, liquid food industry and medical diagnosis field. Manyphysical and chemical constants such as density, concentration and viscosity of liquid can beobtained by measuring the sound velocity, acoustic impedance and acoustic attenuationparameters which has been more and more widely applied in various fields. Under this topicbackground, aiming at the shortcomings of traditional measurement methods, this paperstudies the ultrasonic liquid acoustic characteristics measurement system based on the linearfrequency modulation continuous wave. The main research contents and results are asfollows:(1) Based on ultrasonic propagation at the interface between different media, itestablishes a three bounded medium transmission model to measure the acoustic characteristicof liquids. Through the detail analysis of ultrasonic propagation changes in the measurementmodel, it designs effective method and steps for liquid velocity, acoustic impedance andacoustic attenuation parameter measurement.(2) Combined with the high speed data transceiver system and DSP digital integratedcircuit of National Engineering Technology Research Center for Mobile Ultrasonic Detection,it builds up a complete ultrasonic liquid acoustic characteristics measuring system. And it useslinear frequency modulation continuous wave which has pulse compression characteristics,superior noise and anti-jamming performance and big wide bandwidth as the signal source.Then set the parameters according to the probe model.(3) It designs a predistortion processing scheme based on amplitude compensation toimprove the traditional constant envelope LFM signal. The simulation and experimentalresults show that, predistortion processing can effectively solve the amplitude attenuation andsevere jitter problem of received signal.(4) In the experiment system, it chooses to test three kinds of liquids: ethanol solution,olive oil and milk. Then it uses time domain autocorrelation algorithm and FOCUSSalgorithm to estimate the transmission time delay and magnitude of received signal, andcalculates the ultrasonic velocity, acoustic impedance and acoustic attenuation of threedifferent liquids. Through Matlab simulation and experimental results contrast, it can be seenthat these two kinds of algorithm can accurately estimate the LFM signal propagation delayand amplitude attenuation, and the result error is within a reasonable range.