The Mechanism Research On Ultrasonic Ice Density Detection Method

This topic study on the mechanism of ultrasonic ice density detection method,which is funded by “The comprehensive inspection and evaluation of Polar environment”(ID:CHINAER 2015-02-02) and the National Natural Science Foundation of China, “Research of sea ice thickness monitoring method based on sensor technology”(ID:41176080).The mechanical parameters of ice are closely related to the temperature,density and salinity in the growth process. At present, the methods of measuring ice density are mainly the liquid discharging method and the weight-volume method. As Drainage method,people measured ice density by Shulekin cylinder in history;water or kerosene used as reference liquid at present,therefore, the density of ice can not be monitored on line real time automatically. According to the principle of ultrasonic transmission, the COMSOL simulation of ultrasonic wave in fresh water ice is carried out,the author designs the experiment system of ultrasonic ice density detection. Ultrasonic ice density testing system includes two parts: the ultrasonic testing device and ice density measurement device. The ultrasonic detecting device comprises the ultrasonic transmitting unit and a receiving unit circuits,the density measurement part puts forward two kinds of measuring methods, and design of corresponding measuring device are presented, such as the anti freezing liquid method and were taken by weight-volume method of taking ice samples at different temperatures. Through a large number of experiments, the peak-peak value of ultrasonic wave in the ice was measured, the author analyzes the relationship between the attenuation andice temperature, the relationship among the ice density, temperature and peak-peak value of ultrasonic signal propagation in ice medium(freshwater ice and sea ice). Thus, the following two conclusions are drawn:(1)Ultrasonic propagation characteristics in freshwater ice: when the fresh water temperature dropped to 0 degrees Celsius, the water began to crystallize,and the peak-peak value decreased gradually,which explains that the ultrasonic wave attenuation is larger in the solid-liquid mixed state. When the temperature is changed from minus 0.1 to minus 0.2 degrees Celsius, the mixed state is changed into the solid state, and the peak-peak value is reduced to the minimum value. The temperature continues to decrease(below 0.2 degrees Celsius), the critical solid state is transferred to the solid state, the structure tends to be stable,the ice density increases gradually, and the peak-peak value of the ultrasonic signal is increased. Meanwhile, the results show that the frequency of 50 kHz is suitable for monitoring the ice density changes of temperature between 0 and minus 5 degrees Celsius, the frequency of 50 kHz for temperature of ice between minus 5 and minus 15 degrees Celsius,When the density of ice was detected by ultrasonic wave.(2)Ultrasonic propagation characteristics in sea ice: temperature of Sea water is maintained at the freezing point minus 0.3 degrees Celsius when the sea water is in the ice water mixture state ultrasonic signal peak value attenuation is larger, the sea water is in a state of ice water mixture, the peak-peak value of ultrasonic signal attenuation is larger. When the temperature of sea ice is from minus 0.3 to minus 10 degrees Celsius, the peak-peak value of the ultrasonic signal received by the penetrating layer of ice is decreased. When the temperature is lower than minus 10 degrees Celsius, the peak-peak value of ultrasonic signal begins to increase gradually. Meanwhile, the results show that the frequency of 50 kHz is suitable to detect the change of sea ice density at the temperature between minus 0.3 and minus 15 degrees Celsius, the frequency of50 k Hz for the temperature between minus 0.3 and minus 25 degrees Celsius,when salinity of sea ice is 11 per thousand(the freezing point is about minus 0.3degrees Celsius) in the experimental conditions.Above research shows that it is feasible to to detect the ice density by ultrasonic wave, which provides a theoretical basis for the further design of ultrasonic ice density detection sensor and a new method to realize the automatic detection of ice density.