【作者】 郭敏；

【导师】 尚志远；

【作者基本信息】 陕西师范大学 ， 声学， 2003， 博士

【摘要】 储粮害虫声测报技术是近年来生物声学学科中一个新的研究领域。与传统的储粮害虫检测方法相比，害虫的声测报技术作为一种快速、实用的新方法，正日益受到重视。在国外，通过监测储粮害虫声信号能够实现对储粮害虫侵害程度的量化，但在害虫声信号识别害虫种类方面的工作却鲜有报道。在国内，这一领域的研究基本处于空白。为了深入研究和有效监测粮堆内部深层害虫发出声信号的传播特性，本文首次采用驻波管法，对声信号在不同种类、不同厚度粮食中传播特性进行了检测和分析，并且进一步推广、发展了多孔介质中声传播理论，建立了粮食中声波传播模型。在声信号识别害虫种类方面进行了探索性的研究，对五种主要储粮害虫弱声信号(爬行声信号)进行了特征分析及识别，这一研究内容为有针对性地采取灭虫措施提供了依据，有利于及早确定防治对策，降低储粮损失。 为了有效地研究储粮害虫所产生声信号在各种粮食中的传播特性，本文采用驻波管法，对十一种不同种类粮食在不同堆积厚度情况下的吸声性能进行了实验研究，粮食吸声特性与其颗粒的大小、形状、排列方式及粮食堆积厚度等有关，存在一定的规律，得出如下结论：同一厚度下，颗粒大的粮食较颗粒小的吸声性能差，颗粒由大到小，吸声系数峰值频率向低频方向移动；球形颗粒粮食较长形颗粒吸声性能差。粮食厚度也是影响其吸声性能的一个重要因素，粮食厚度增加，吸收频带加宽，低频吸声系数增大，最大吸收峰个数增加，并向低频方向移动。大颗粒粮食的平均吸声系数普遍较小颗粒的平均吸声系数小，颗粒大的随厚度继续增厚，平均吸声系数增加的趋势却很弱，而颗粒小的随厚度增厚，其平均吸声系数一直呈增大的趋势。粮食吸声性能与其颗粒形状、大小有关，而受粮食品种影响甚微。 本文提出了粮食的吸声机理模型：当声波入射到粮堆表面时，认为主要由两种机理引起声波的衰减：一种是多孔性吸声机理。首次建立了准多孔介质的概念，可将堆积的粮食看作准多孔介质(颗粒介质)，透入粮食内部的声波在孔隙中传播时，由于粘滞性和导热性的效应，把声能逐渐变成热能耗散。另一种吸声机理来自亥姆霍兹共振腔。一定厚度的粮食可看作是一种组合式共振吸声结构，每层认为由许多个单独亥姆霍兹共振腔并联而成，而层与层的共振腔为串联关系，表现为共振性吸收，出现了共振吸收峰。因而，粮食吸声性能介于多孔介质和共振吸声结构之间，是在上述两种机理的共同作用下，实现对声波的吸收。 本文以广义出叭理论为基础，对Bi叶理论中忽略双相介质间热效应的问题进行了修改，将Johnson的多孔介质中声传播模型进行了推广改进，将其用于准多孔介质中，建立了粮食颗粒中声波传播理论模型，利用这一模型对粮食吸声系数的理论计算值与驻波管法测得实验值吻合较好。 考虑准多孔介质声传播中存在空气与颗粒间的粘滞力和惯性力，推导出准多孔介质中孔隙动态曲折度函数表达式。进一步考虑准多孔介质声传播中同时还存在空气与颗粒间的热效应，推导出准多孔介质中空气动态压缩率函数表达式。给出了准多孔介质中吸声系数的理论计算公式，它是动态曲折度和动态压缩率的函数。 利用准多孔介质中声传播模型，计算了堆积一定厚度的黄豆的吸声系数理论值。将粮食中孔隙看作既有圆柱形又有狭缝状是本文建立的一个新模型，这一模型与实际符合较好。 本文研究分析了五种主要储粮害虫弱声信号。害虫声信号采集系统由日本产TEAC＊；四通道录音机（数字记录仪）记录害虫爬行声信号，数字示波器将声信号转变为数字信号送计算机存储，由MATLAB软件对数据文件进行信号处理，包括信号的再现、放大、滤波、小波去噪、功率谱分析等工作。 由五种害虫时域信号可见，信号间差异比较明显，杂拟谷盗爬行声脉冲最密集，赤拟谷盗次之，谷羹最次，这可能与害虫爬行时速度快慢有关，锯谷盗和长头谷盗是两种体积较小、爬行较快的害虫，其爬行声信号较难采集，但从去噪后的时域图中仍然可见到保留下来的信号成分，由于两者爬行较快，信号都表现得较为杂乱、无规律。五种害虫声信号功率谱幅值（能量）也明显不同，幅值由大到小依次为赤拟谷盗、杂拟谷盗、谷蠢、锯谷盗、长头谷盗。认为害虫爬行声能量与其体重成正比，体重大的害虫具有较大的振动能量。五种害虫声信号的峰值频率和主要频域范围也存在差异。五种害虫时域及频域信号的差异是害虫种类差异的表现。更多还原

【Abstract】 The technique of detection acoustic signals of pests in stored grain represents the newly emerging field of Insect Acoustics in recent years. Compared with traditional inspection methods, the newly technique is a quick and practical method which is attracting increasing attention. It already can quantify the infestation in USA by detection the acoustic signals of pests that feed inside grain kernels. But there have been relatively few research efforts in identification the species of grain pests by the acoustic signals. To detect the sound produced by pest activity inside the grain it is necessary to understand the propagation properties of sound in various types of grain. This paper describes some experimental investigations of propagation properties of sound in various types and thickness of grain samples using the method of standing wave tube for the first time, extends the sound propagation theory in porous media and develops the sound propagation model in grain, analyzes and identifies the creeping sound signals of five species of pests. These researches provide us a basis for forecasting the pests in grain in earlier stage, accurately utilizing pesticides, improving the efficiency of prevention and reducing the loss of stored grain.The sound absorption properties of various types and thickness of grain are measured by means of the standing wave tube technique. The following conclusions can be drawn: For the same thickness the larger grains has a smaller sound absorption coefficient than the smaller grains. The kernel in spheroid has a smaller sound absorption coefficient than in non-spheroid. The thickness of grain sample is an important factor effecting on the sound absorption coefficient. The average sound absorption coefficients of larger grains are smaller than the small grains in general. The properties of sound absorption coefficient of grain are in close relationship with the shape and size of kernel, and have no relation with the texture of solid grain.We consider there are two kinds of mechanism causing the attenuation of sound in grain. One kind of mechanism regards the grain as quasi-porous media. It was the viscous resistance and heat conduction in the narrow passageways between the grain kernels that convert the sound energy into heat energy and lose it. The other kind ofmechanism regards the grain as a combined resonator. We regard every layer of grain as a lot of Helmholtz resonators in parallel, and regard different layer of grains as the paralleling resonators in series. The grain is a combined resonator in series and parallel.Based Biot’s theory of acoustic propagation in porous media this paper applies Johnson’s model to grain media. Considering the viscous interaction between the kernel and the air inside the grain the paper shows the dynamic tortuosity function in grain. Considering the thermal exchanges between the kernel and the air the paper shows the dynamic permeability function in grain. We consider the pores in grain both cylindrical pore and parallel slits. Further there has been the formula of the sound absorption coefficient of grain. The agreement between calculation and measurement is good.This paper analyzes and identifies the creeping sound signals of five species of pests. We collect the signals using a recording. The signals are transformed into digital signals and sent to a computer. Digital signal processing includes amplifying the sound signals, low-pass filtering, wavelet transform for de-noise and analyzing power spectra using MATLAB software. For different species of pests the acoustic characteristics are different in time domain and frequency domain. In time domain it is different in the number of sound pulse. In frequency domain it is different in the amplitude and main peak frequency range. These differences may be caused by the weight and creeping speed of different species of pests.更多还原