Study On The Characteristics Of Mass Ultrasonic Wave Propagation In The Mountainous Red Soil Base Of Yunnan Province

The planting amount of panax notoginseng in Yunnan accounts for more than 95%of the country.After planting and harvesting in the same piece of land,due to the prominent problem of continuous cropping,it is necessary to sow the seeds again after an interval of 10 to 15 years.The land resources used for panax notoginseng planting are very precious.The sowing process of panax notoginseng consists of ditching,seeding,soil covering and suppression,in which the sowing and soil covering process are carried out at the same time.The soil covering process has a disturbance effect on the seeds,resulting in changes in the seeding position.In order to test whether the seeding position meets the agronomic requirements,the statutory seed of soil section is used at present,and the detection accuracy of this method is low.Therefore,a method was proposed to detect the seeding position of panax notoginseng seeds in soil by ultrasonic testing.A single factor test was carried out by setting up an ultrasonic testing test platform,and the change law of ultrasonic propagation velocity,amplitude and attenuation coefficient in the soil particles,coal cinder particles,seeds of panax notoginseng and the red soil matrix of panax notoginseng in Yunnan province was selected as the research object.The main research contents are as follows:(1)Establishment of a test bed for substrate propagation characteristics of mountainous red soil.There are very few transducers for inhomogeneous media,and there are no transducers applied in mountainous red soil matrix.Therefore,this paper uses COMSOL software to build a simulation model for finite element sound field simulation,and calculate the parameters required by the transducer for soil detection.The parameters are submitted to a precision instrument research and development institution.The transducer was developed.The sensitivity of the amplifier was less than 1μV /1 digit,and the trigger sensitivity was ±0.2V.At the same time,the waveform detection stability reached more than 98%,meeting the detection requirements.At the same time,according to the requirements of pantoginseng mechanical planting,combined with the size of the transducer,the ultrasonic test bench with adjustable speed and height was made.The speed adjustment range of the test bench was 0.1m/s ～ 0.14m/s,and the height adjustment range was 0cm ～ 10 cm,and the detection test was carried out on the moving speed and detection height of the transducer.(2)Single factor test of ultrasonic propagation characteristics of red soil matrix.Soil particles,coal cinder and seeds of Panax notoginseng were used as test factors,and the propagation speed,amplitude and attenuation coefficient of ultrasonic wave in the matrix were used as indicators for transmission test,to explore the influence of test factors on test indicators.With humidity and compactness as test factors and ultrasonic propagation velocity,amplitude and attenuation coefficient in the matrix as indexes,plane detection tests were carried out to explore the influence of test factor changes on test indexes.Finally,the detection height and moving speed were selected as test factors,and whether there was echo signal was taken as test index to explore the influence of different detection height and different transducer moving speed on acoustic signal acquisition.(3)Based on the analysis of the test results,the conclusions of this study are as follows:1)In the acoustic transmission test,the increase of soil particle diameter leads to the decrease of acoustic signal propagation speed and attenuation coefficient,and the acoustic signal propagation presents a certain decreasing trend.The velocity and amplitude of seed acoustic wave propagation are between soil particles and coal cinder,and the difference is small,which has no reference significance for in situ detection of acoustic signal differentiation.The attenuation coefficient reached its maximum value in the detection of panax notoginseng seeds.In the in-situ detection of panax notoginseng seeds,the frequency of the transducer could be changed to avoid that the acoustic signal of panax notoginseng seeds would decay too fast,leading to the signal could not be detected.The transducer was manufactured according to the attenuation coefficient of panax notoginseng seeds in the transmitted data.2)In the ultrasonic plane reflection test,when the compactness is fixed,the humidity range of the optimal signal acquisition area is 20%-25%,and the velocity,amplitude and attenuation coefficient all decrease with the increase of humidity.When the compactness was a variable,the attenuation coefficient gradually increased with the increase of compactness.When the compactness was between 200 k Pa and 350 k Pa,the signal amplitude increased with the increase of compactness.When the compactness was between 350 k Pa and 400 k Pa,the signal amplitude decreased by about 39%.The velocity gradually increased with the increase of compacting degree,and the maximum value was 3163.7m/s at 400 k Pa,and the velocity difference was the most significant.3)When the distance between the transducer and the detection surface is at a level of every 5mm,from 0mm to 15 mm,the transducer fails to receive the echo signal at 20 mm,combined with practical application,the best detection height is10mm;The quantization amplitude of acoustic signal in frequency domain decreases during the process of the transducer moving speed from 0.10m/s to 0.14m/s at a level of 0.01m/s.The signal has better aggregation when the moving speed is 0.10m/s.The LF-CNN-LSTM acoustic signal propagation velocity prediction model is built according to the plane detection conclusions.By comparison,the model can predict the velocity changes more accurately.