分布反馈式光纤激光水听器拖曳线列阵实验研究

为了进一步增大光纤拖曳阵的探测距离,研制了缆径为16mm的32元分布反馈式光纤激光水听器拖曳线列阵.阵元在10~2 000Hz频率范围内的平均声压灵敏度为-142.7dB(re 1rad/μPa),波动幅度小于±2dB.基于声光调制器的时分、波分联合复用技术实现了32元光纤激光水听器的多路复用,各个阵元之间以及各个通道之间的串扰均小于-40dB,并完成了静态和动态拖曳湖上实验.实验结果表明,研制的32元分布反馈式光纤激光水听器拖曳线列阵无论是在静态,还是在6~16节的动态拖曳状态,都能对目标形成稳定的波束指向,与GPS轨迹记录完全一致,展现了分布反馈式光纤激光水听器拖曳线列阵在工程上的应用前景.     

新型阵列式片状放大器全口径增益实验研究

 利用行波法对一台闪光灯泵浦、通光口径为29cm×29cm的新型高功率固体激光阵列式片状放大器的全口径平均增益进行了实验测试，在充电电压为23kV、泵浦能密度为10J/cm³的条件下，新型4×2×3阵列式片状放大器端部模块全口径平均增益为4.925%cm^-1，内部模块全口径平均增益为5.519%cm^-1。     

新型阵列式片状放大器全口径增益实验研究

利用行波法对一台闪光灯泵浦、通光口径为29cm×29cm的新型高功率固体激光阵列式片状放大器的全口径平均增益进行了实验测试,在充电电压为23kV、泵浦能密度为10J/cm3的条件下,新型4×2×3阵列式片状放大器端部模块全口径平均增益为4.925%cm-1,内部模块全口径平均增益为5.519%cm-1。     

新型阵列式片状放大器全口径增益分布均匀性实验研究

利用CCD增益测试系统对一台闪光灯抽运、通光口径为 2 9cm× 2 9cm的新型高功率固体激光阵列式片状放大器的增益分布进行了实验测试 ,在充电电压为 2 3kV、抽运能密度为 11J/cm3 的条件下 ,新型 4× 2× 3阵列式片状放大器全口径范围内的小信号增益系数的峰值与平均值之比为 1.10∶1。     

阵列式等离子体射流处理芽孢的实验研究北大核心CSCD

研制了一套单极性微秒脉冲阵列式等离子体射流系统,该系统可在大气压下激发产生等离子体射流,实现大面积的灭菌处理。该系统可产生峰值电压20 kV、频率15 kHz的高压脉冲,激发产生的射流均匀稳定,覆盖面积达37.7 cm2,射流长度达6 cm,射流功率为40.05 W,处理5 min可使射流覆盖范围内的枯草芽孢杆菌的芽孢基本全部失去活性。考察了不同参数对灭菌效率的影响,结果表明,灭菌率与工作电压、脉冲频率、处理时间呈正相关,在氦气氛围下有较好的灭菌效果。SEM显示等离子体射流能够对枯草芽孢杆菌的芽孢外壳结构造成损坏,导致芽孢无法正常代谢,最终死亡。     

目标光源差异对阵列式光谱辐射计测量的影响及紫外杂散辐射修正研究

应对气候变化预测与灾害天气防范等科学难题,空间观测领域提出高精度的光谱辐射度定标需求。阵列式光谱辐射计存在内部结构缺陷和光学元器件不理想等问题,导致杂散辐射,严重影响光谱辐射度测量结果的准确性。测量多种典型阵列式光谱辐射计的杂散辐射特性,考虑外场目标光源与实验室定标光源不一致对杂散辐射修正的影响,分别基于带通滤光片和可调谐激光器研究紫外杂散辐射修正方法。首先,利用不同光谱透过率的带通滤光片,测量可见及红外光谱辐射引起的紫外杂散信号。针对杂散辐射分布特点,建立数学修正模型,实现高效快捷的杂散辐射修正。地基验证场的光谱辐射亮度测量结果修正后,紫外杂散辐射信号显著降低。对于连续分布的宽谱段光源,带通滤光片修正法具有实验简便易行、测试过程高效等优点。然而,实现非连续分布或窄带光源的高精度杂散辐射修正存在困难。为此,建立基于可调谐激光器的杂散辐射测量系统,解决了各个像素点杂散辐射线扩展函数的测量难题。改变可调谐激光器的输出波长,精细化测量各个像素点的杂散辐射线扩展函数,再推导出杂散辐射信号分布函数,通过MATLAB软件将矩阵反演运算,得到各像素点的杂散辐射修正结果,实现杂散辐射的高精度修正。利用不同类型的阵列式光谱辐射计验证了该修正方法,对于非连续分布的窄带光源,测量结果修正后杂散辐射信号降低了一个数量级,并且谱线两边的杂散宽峰显著消除,大幅降低了紫外波段的测量偏差。针对不同光谱分布的光源,建立了两种优势互补的杂散辐射修正方法,有效改善了阵列式光谱辐射计的紫外测量结果偏差,进一步确保我国地球观测数据的准确性和国际等效互认。     

Accelerated steered response power method for sound source localization using orthogonal linear array

In microphone arrays application, it is a difficult task to accurately and fast localize sound source in a noisy, reverberant environment. In order to solve this problem, many approaches have been presented. Among them, the steered response power-phase transform weighted (SRP–PHAT) source localization algorithm has been proved robust. However, SRP–PHAT requires high computation cost for searching a large location space. To overcome this shortcoming, an improved SRP–PHAT will be presented that reduces a two-dimension searching space into a couple of one-dimension ones by using an orthogonal linear array. In this method, the parameters of direction of arrival (DOA) are separated. The main computation can be carried out independently in two one-dimension spaces, thus the computational load will be greatly cut down. Simulations show that there is no loss in accuracy in the proposed method.     

Development of a hand-held sensor probe for detection of sound components radiated from a specific device using surface intensity measurements

In this paper, a hand-held sensor probe is developed for surface intensity measurements. The sensor probe is composed of a 1/2-in. condenser microphone and a lightweight accelerometer of 1 g (=10⁻³ kg) which are connected with a vibration damper made of silicon rubber. The reliable measurement range of the sensor probe is examined and shown to be 100 Hz to7 kHz for sound and vibration. The precision of intensity measurements is confirmed by experiments in noisy environment. The precision is shown to be less than 3 dB for a random noise environment when the S/N is greater than −10 dB and for pure tone environment when the S/N is greater than −5 dB. The sensor probe is applied to determine the sound power level of a hard disc drive unit of a personal computer in an office setting. Good agreement is obtained for A-weighted sound power levels determined by the ISO method.     

基于声压-质点速度声强探头的材料吸声系数的测量

通过由一个声压换能器和一个质点速度换能器所构成的传感器(p-u声强探头)同时测量材料表面附近的声压和质点振动速度,可直接得到其声学阻抗,进而得到材料的反射因子、吸声系数。本文利用一个p-u探头声强测量系统,在半消声室内测量了三聚氰胺泡沫的吸声系数,分析了声源高度和入射角度、材料样本尺寸和厚度对吸声系数测量的影响,并和阻抗管中测量得到的法向吸声系数进行了对比。最后分析了声阻抗率的幅值和相位误差对吸声系数的影响,推导了它们的误差传递公式。     

线阵声强缩放方法在水下声源辐射功率估算中的应用

为了解决水下声源辐射声功率难以计算的问题,利用线阵声强缩放方法在波束形成声源识别的基础上,根据波束输出结果与声源辐射声功率之间的换算关系来获得相应的声功率。为了提高线阵声强缩放方法的水下声功率估算精度,给出了一定动态范围限制的主瓣区域积分方法,并通过仿真验证了该方法的有效性。在消声水池中开展了水下声功率估算的实验研究。在不同的测试距离下,对双声源条件下的单频以及宽带声源在阵列侧的辐射声功率进行了估算,以混响法的测量结果为参考值,研究了估算误差随声源频率、测试距离等影响因素的变化规律。实验结果表明,无论是单频还是宽带声源,声功率的最大估算误差不超过2.6 dB,在高频时不超过1.6 dB。验证了线阵声强缩放方法应用于水下声源辐射声功率估算的正确性与可行性。     

声强测量技术在水下结构辐射噪声近场测量中的应用

本文介绍了强测量技术在水下结构辐射近场测量中的实际测量系统，特别是水下声系统的扫描平面的实现方法及定位误差控制方法，最后讨论和分析了实际测量结果，从而说明该系统用水下声强测量是可行的。     

Orthogonal contributor number for the measurement of sound power

Orthogonal contributors to a global error represent a very efficient design method in terms of both sensing and control of noise radiation. In practice the price of a sensing system will be determined by the number of errors it must resolve. Therefore predicting the most efficient way of measuring radiation power is an important problem. Recently work has compared sensing the number of vibration modes to the number of orthogonal contributors to radiated power. The required number of vibration modes was based on the proximity of the structural mode resonance frequency and the excitation frequency. While ultimately this technique will result in a valid estimate of radiated power, it is shown here that the number of structural modes can be minimized by first considering orthogonal radiators based on structural mode amplitudes. Two disturbance cases are considered: a point force and an even disturbance coupling to each structural mode. Also, under these conditions the practicality of estimating the number of orthogonal radiators when it is assumed that each contributor is equal in amplitude is examined. Finally in an attempt to optimism the number of signals to be sensed, a variable error margin for the estimate of power, based on the ratio of the sound power at each frequency to the maximum peak in the considered frequency range is proposed and analyzed.     

水听器线列阵近场声压测量误差实验研究

本文介绍了用于近场声压的测量水听器中阵元水听器测量声压的可靠性检验方法和实验结果,提出了元水听器测量球面波场中声传播衰减的曲线与现想球面波声场中场传播衰减的曲线对比的检验,要用球面声源声中心测量值对收发距离进行修正的方法,实验水池中对线列阵上十元水吸器在球形声源水池中进行了传播衰减曲线的测量分析,验证了基阵的弱散散射性能,表明线阵可用于距离小至1／7波长的极近场的扫描测量。     

High power nonuniform linear vertical-cavity surface-emitting laser array with a Gaussian far-field distribution

A 980 nm bottom-emitting vertical-cavity surface-emitting laser (VCSEL) array with a nonuniform linear arrangement is reported to realize high power with a Gaussian far-field distribution. This array is composed of five symmetrically-arranged elements of 200 μm, 150 μm, and 100 μm diameters, with the center spacing of 300 μm and 250 μm respectively. This structure makes it possible to discriminate against the higher order array supermodes. The theoretical simulation of the far-field distribution is in good agreement with the experimental result. An output power of 880 mW with a power density of 1 KW/cm² is obtained. The divergence angle is below 20° in the range of operating current from 0 A to 4 A. The comparison between this nonuniform linear array and the conventional two-dimensional array is carried out to demonstrate the good performance of the linear array. A peak power of over 20 W is achieved under a short pulsed operation with a repetition frequency of 1 kHz.     

Experimental study of sound propagation in a street

This paper presents an experimental study of the sound propagation in a street, performed during July 2002, in order to measure impulse responses at numerous locations in a street canyon, and, for several positions of the sound source. A specific attention has been paid on the processing of the experimental data, in order to obtain accurate values of the reverberation time and the steady-state sound pressure level, including also the compensation of the atmospheric attenuation. In total, 11 592 useful data have been collected during this experiment, and are available by contacting the corresponding author. Reverberation times and sound levels, in the narrow street, are then analyzed and compared, for the 4 source positions in the street. This experimental study gives interesting results on the behavior of the sound field in the street.     

水声声强测量分析系统及其在水下噪声鉴别中的应用

本文将空气中能形成测量分析系统的声强测量技术引入到水介质中，建立了一套水声声强测量分析系统，讨论了此套水声声强测量分析系统的硬，软件组成及特征，实验验证了本系统的可靠性，利用此声强分析系统对水下双噪声源的近场作了平面扫描测量，可以定位和鉴别这两个噪声源。