Research On The Sound Field Characteristics Of The Outer Ear Of The Chrysanthemum Bat

In the biosonar system of bats,the ear of bats is used to receive sound signals,and the structure of t he external ear(such as pinna,tragus,etc.)also has certain influence on the reception of sound.In this thesis,we reconstruct the structure of the external ear of Rhinolophus pearsoni and Rhinolophus affinis,and remove the pinna structure on the external ear,and then compare them to analyze the influence of the pinna structure on the acoustic field characteristics,as well as the influence of the of the external ear's different structures on the acoustic field characteristics of the two species of horseshoe bat.The research work and achievements in this thesis are as follows:The history of bat research,the bat sonar system,the characteristics of bat sonar signal and the current research status of bat were described.By analyzing the appearance,living habits and feeding requirements of horseshoe bats and combining with the current research status,two species of horseshoe bats were identified as research objects,namely,Rhinolophus pearsoni and Rhinolophus affinis.For numerical calculation,the acquisition of model,calculation method and representation of calculation result are introduced.In order to obtain the acoustic field characteristics of the external ear of horseshoe bat,the 3D digital models of the external ear structure of two species of horseshoe bat were reconstructed by using the technique of tomography and digital image processing.And on the basis of the complete external ear,the pinna structure was removed,and the 3D digital model without pinna s tructure was obtained.According to the principle of reciprocity,the characteristic of receiving beam is obtained by placing the transmitting signal in the ear canal.In this thesis,a Gaussian point sound source is used to obtain the near-field sound pressure amplitude by using the finite-difference time-domain method.In addition,the external ear's sound field directivity pattern of the far field is obtained according to the kirchhoff integral.And then from the radiation pattern to obtain the directivity index,far field radiation direction can be more intuitive expression.When FDTD is used for calculation,the absorption effect of the perfectly matched layer is calculated,and the number of layers with well absorption effect and not too much computation is selected to be used in the calculation in this thesis.By comparing the results of Rhinolophus pearsoni and Rhinolophus affinis,it is found that the pinna structures of the two species of horseshoe bat have convergent effect on the acoustic field.In the near field,the sound pressure amplitude of the complete external ear structure is obviously higher than that of the sound pressure amplitude without the pinna structure,and the beam propagates to the upper right along the pinna structure,while without the pinna structure,the beam propagates to the up.In the far-field directivity pattern,the main lobe of complete externl ear structure is thinner than th at of the main lobe without pinna structure,and the more thinner main lobe has higher directivity.Directivity index is obtained by directivity pattern,we can see that the direction of the external ear structure without pinna structure is obviously worse.Under different frequencies,the complete structure of the external ear directivity index curve with the removal of auricle structure is broadly in line,but remove the direction of the pinna structure index significantly below the direction of the compl ete structure of auricle.On the whole,the pinna structure of the two species of horseshoe bat have similar effects on the acoustic field characteristics,but the effects of the two pinna structures on the acoustic field characteristics were different at different frequencies.And the effect of pinna structure on the two species of horseshoe bat is also different.