Test And Study On Time And Characteristics Of Sound Wave Propagation In Grain

Acoustic temperature field detection is a method of computerized tomography.It is a reconstruction technique that uses external projection data to detect internal feature images.It belongs to a non-contact detection method.The safe storage of food is essential.But every year in the world,the loss caused by mildew and pests in the storage process is astonishing.In the process of grain storage,the occurrence of mildew and insect pests is accompanied by the increase of local temperature.Therefore,grain temperature monitoring is an important means of grain monitoring,At present,contact temperature measurement is widely used at home and abroad.If mildew and insect pests do not happen near the monitoring point,they can be detected only when hot spots spread to large areas.Therefore,it is of great significance to study non-contact acoustic temperature measurement of stored grain.In this paper,the time and characteristics of sound wave propagation in grain are studied based on acoustic temperature measurement of stored grain.Firstly,the function relationship between the speed of sound wave propagation and temperature is expounded,and the form of sound wave propagation in grain is introduced.A sound wave propagation time measurement system based on LabVIEW is established,and the method of measuring sound wave propagation time between two microphones based on cross-correlation method is introduced in detail.When the system is used,it will inevitably be disturbed by various noises.When the correlation of noise collected by two microphones is very weak,the sound propagation time obtained by cross-correlation method still has good accuracy and stability.But when the same noise source is received by two microphones,that is,when the correlation of the noise collected by two microphones is very strong,the results obtained by direct cross-correlation method have great errors,even can not be used.In order to solve this problem,this paper presents a method for measuring the propagation time of sound wave by combining FastICA with cross-correlation.Firstly,the FastICA algorithm is used to separate the sound source signal from the noise signal,and then the required sound wave propagation time is obtained by cross-correlation and window screening.The feasibility of the proposed method in improving the anti-jamming ability of the system is preliminarily verified by the actual sound source signal and noise signal collected by the microphone.Acoustic signal received by microphone has enough energy,which is an important factor to ensure the accuracy of acoustic propagation time measurement.The attenuation of sound wave in grain is much greater than that in air.It is of practical significance to study the propagation characteristics of sound wave in grain for the design of sound source signals.In this paper,the impedance tube transfer function method is used to measure and study the sound absorption and insulation coefficients of several kinds of grain.The acoustic characteristic curves of different thickness and different kinds of grain in the range were drawn.The effects of grain thickness,particle shape and size on sound absorption and sound insulation performance are compared and analyzed.It is concluded that grain has high sound absorption and low sound insulation.