Study On Time Delay Magnification System And Sound Source Localization Based On The Auditory Coupling Mechanism Of Ormia Ochracea

Sound source localization technology has been a research focus for both national and foreign researchers in recent years.It related to many technology fields,such as acoustic,signal detection,digital signal processing,and so on,and it is always of great application value in military,industry,and civil fields.In order to realize the localization of sound sources,microphone arrays with certain geometric shapes are usually involved.Directional cues are interelement time difference(ITD)and interelement intensity difference(IID).Therefore,for the purpose of obtaining sufficient acoustic field information and ensure localization accuracy,not only enough elements but also large element spacings of microphone arrays are required.As a result,scales of localization devices are always large.However,in some special applications,such as miniature transportation vehicles and portable electronic devices,spaces are always limited.Localization devices are required to accomplish the high-accuracy localization by a relatively compact structure.Facing the special requirements of these applications,new technologies are demanded.A small parasitic fly called Ormia ochracea offers the possibility to make it.The fly's hearing organ is so small that the distance separating its ears is only about 0.5mm,but surprisingly,the fly can accurately detect the direction of its host's calling with a resolution of 2°.Studies show that this remarkable ability attributes a lot to the special coupling mechanism between its ears.It magnifies the extremely small interaural time and intensity differences of received signals,which equivalently enlarges the distances between two ears by tens of times.The coupling mechanism may provide preferable solutions for above applications.This present dissertation is completed under this background.Main works are given in detail as follows:(1)Mechanical model of Ormia ochrace's coupled ears is studied,and the time delay magnification property is analyzed.By extending the dimension of the coupling model,and a high-dimensional coupling model is built.The advantage of the coupling model is that it can realize the ITD magnification between multiple input signals.By solving output responses of the coupling model and analyzing its vibrational characteristics,relationships between model parameters and the magnification factor of the ITD are deduced.On this basis,restriction conditions of the ITD magnification are discussed and design principles of model parameters are provided.In addition,we analyze the influence of sound frequencies on the ITD magnification and reveals the limitation of the coupling model.Studies show that the coupling model can only be applied to single-frequency sound sources.(2)On the basis of theoretical research on the coupling model,a coupling module is derived.It maintains a stable delay gain in a wide frequency range.By changing the gain element,the magnification factor of the ITD can be flexibly adjusted.Studies show that the coupling module can be applied to single-frequency,multi-frequency and broadband sound sources.Compared with the coupling model,the scope of application is widened.Based on the coupling module,a time delay magnification system(TDMS)is then presented.The TDMS is implemented as follows: Firstly,input signals are pre-processed by filters;secondly,ITDs between filtered signals are magnified by several time delay magnification units which consist of the coupling module,delay estimation module,and delay unit;finally,the output signals that occupy desired time delays are restored by the final delay unit.By transforming a large magnification factor into several small magnification factor,the TDMS effectively enlarges the selection range of the magnification factor.Simulations are conducted to verify the time delay magnification property of the TDMS and investigate the time delay estimation ability of the TDMS under different signal-to-noise ratios.The influence of noise on the TDMS is analyzed.(3)Microphone arrays are designed for planar and spatial sound sources respectively.Factors that affect the accuracy of localization,such as the spatial layout,element spacing and so on,are discussed.Based on the microphone array,the single-source localization problem is comparatively studied with and without the TDMS.Results show that the TDMS has an advantage on improving the sound source localization accuracy.In order to apply the TDMS to multi-source localization,a new time delay estimation method which combines the traditional cross-correlogram technique with the TDMS is proposed.Results show that the localization accuracy of this new method is significantly improved compared with the traditional one due to the effect of the TDMS.(4)The experimental platform for sound source localization is built,and experiments are conducted.Time delay magnification properties of the coupling model and the TDMS are verified,and influences of the TDMS on the accuracies of time delay estimation and sound source localization are validated.All the experimental results validate the correctness of the theoretical analysis and the effectiveness of the simulation in this paper.