水下蛙人被动探测测向实验研究

为了对携带开式呼吸器的水下蛙人进行被动探测,本文采用四个水听器组成的十字阵在浅海水域对水下开式蛙人进行了被动探测、测向实验。结果表明:蛙人辐射噪声具有周期性特征,其周期与蛙人的呼吸频率有关;另外,蛙人呼吸辐射噪声具有显著频带,并且其频带与蛙人携带的呼吸器有关。根据蛙人辐射噪声的显著频带和周期性特征,设计信号处理算法实现了对蛙人的被动声学探测识别。使用互相关方法处理一对水听器的接收信号,可以确定蛙人的方位,但是根据理论分析会出现一个假方位。对比十字阵中两对水听器的测向结果可确定蛙人的准确方位。     

基于Hilbert变换的水下多源声信号频率的相干探测

为实现水下中低频声信号的探测识别,通过研究水下多声源相干探测信号的特征,理论上给出了相干探测信号频谱混叠情况下的特征表达式,并提出了一种基于Hilbert变换的信号解调处理方法,实现了水下多声源相干探测信号频谱混叠情况下各声源发声频率的解调.该方法将探测信号经过滤波平滑处理之后进行Hilbert变换,得到信号的解析形式,然后对解析信号模值的平方进行二次滤波平滑等处理,分离混叠在一起的频带,将得到的信号进行频谱分析,根据频移值计算得到水下各个声源的发声频率.在光学暗室下搭建激光相干探测系统,对2~6kHz的水下声信号进行实验,实验结果表明,该方法可以有效分离探测信号中混叠在一起的信号频带,并准确提取各水下声信号的发声频率,频率提取重复性不大于2.5Hz.     

基于激光水下爆炸声源的声探测技术

基于激光水下爆炸的声探测技术,设计了激光声水下目标探测器。对激光水下爆炸声源的产生机理进行研究,并开展水下探测器发射声信号检测的实验。实验结果表明:强脉冲激光聚焦于水介质产生爆炸性球面声源,探测器内部的声反射面将球面声信号转变为高指向性的平面波信号。通过对探测器的发射信号和接收的目标回波信号进行数值计算,得到探测器发射信号具有波束指向性窄、距离分辨力高和探测距离远等特点,满足水下目标探测的应用需求。     

应用于微电容超声换能器的信号处理电路设计*

针对微电容超声换能器的输出信号特征及检测要求,文中设计了换能器的微弱信号处理电路,包括基于跨阻的微弱电流信号检测和多重反馈带通滤波电路。通过搭建水下测试平台,对电路性能及功能进行实际测试,并进行水下测距实验。实验结果表明,该电路可对微电容超声换能器输出的400 k Hz信号进行检测放大与滤波;电路的线性度为0.18%,滤波电路中心频率为396 k Hz,带宽为55 k Hz。该电路可用于CMUT的接收信号处理并应用于超声测距及成像的前端信号处理。     

任意复包络信号的匀速运动目标回波脉间补偿及相干积累

现代声呐、水下制导等水声探测系统常常使用窄带脉冲、调制、编码、伪随机等种类繁多的发射信号波形来满足低信噪比检测、高分辨估计、抗干扰、主动隐蔽探测的应用需求.针对这一情况,本文研究了任意信号的长时间积累问题,给出了一种任意复包络信号的匀速运动目标回波脉间补偿及相干积累检测方法.通过构建任意发射信号波形的广义模糊函数,将匹配滤波器输出表示为所构造的广义模糊函数,使得任意复包络信号的脉压波形不仅能够用统一的数学模型来表述和计算,而且能够提供多脉冲回波的距离走动信息和多普勒频移信息,为多脉冲距离位置对齐和Fourier变换(FFT)积累提供了依据.对于用广义模糊函数表示的匹配滤波器输出,采用Keystone变换将复包络对齐,消除了距离走动,采用FFT补偿多普勒频移项,实现了任意复包络信号的长时间相干积累.对于水下探测中使用的连续波信号、线性调频信号以及复杂的m序列编码信号、Costas跳频编码信号波形进行了信号积累及检测的计算机仿真,验证了任意复包络信号的匀速运动目标回波脉间补偿及相干积累的正确性.消声水池实验验证了该方法的有效性.     

应用匹配滤波法估测水下介质声阻抗的初步研究

对一种新的反演方法──匹配滤波法应用于水下地声探测中的声阻抗定量估测问题作了研究，论述了这种方法的原理和算法，并且给出了对其进行改进的方法。模拟声呐记录的试算结果表明，匹配滤波法是一种原理简单，计算量小，容噪性好的水下介质声阻抗反演方法．     

基于组合线阵的近程运动小目标被动定位跟踪

针对水下运动小目标被动探测与定位问题,提出了分段组合子阵联合处理探测方法,各探测子阵采用相互垂直结构布局,克服了单阵方位模糊及无法定位等问题。研究了分段组合子阵的宽带最小方差无畸变失真响应近场聚焦目标定位方法,实现了近程蛙人等水下小目标被动高精度定位。在此基础上,采用卡尔曼滤波算法对目标运动轨迹进行预测估计,将目标定位信息与跟踪轨迹信息进行匹配,实现高背景噪音下的运动小目标的跟踪处理。理论分析及仿真结果表明,分段子阵联合处理能有效对水下运动小目标进行定位和跟踪,海试试验进一步验证了该方法的有效性。     

基于小波变换的激光水下测距

提出一种基于小波变换思想的水下测距方法.根据信号的能量一致性以及小波的带通滤波特性,并以二元样条插值为架构,实现信号的时频结合.该方法先将时域信号进行小波时域分解滤波,获得较为完整的时域有效信息,然后对初步处理的时域信号进行小波频域分解,通过找寻信号时频域对应的能量最值位置锁定目标,实现精确测距目的.进行不同衰减长度水体的连续光水下测距实验,分析该方法对连续光水下探测的影响.经实验验证,该测距方法在输出功率2.3 W内,成功实现对8个衰减长度内目标的准确测量,其测距精度小于1 cm.     

基于远程脉冲激光外差探测的匹配滤波过程研究

以远程脉冲激光外差探测系统为模型,推导了系统的信号与噪声的表达式,给出了脉冲激光外差探测系统匹配滤波算法流程,对匹配滤波技术在中程导弹与国际空间站目标探测中的详细应用过程进行了仿真,分析了目标距离、散射截面面积、数字采样率对探测能力的影响。仿真结果表明:在100 MHz采样率的数字处理能力下,分别用蒙特卡罗法仿真了500次匹配滤波过程,对于散射截面面积为5m2、距离为100km的中程导弹,回波信号载噪比为3.29dB,匹配滤波后信号载噪比为25.13dB,信号强度增强了152倍,距离精度为27 m,速度精度为0.17m/s;对于散射截面面积为100m2、距离为500km的国际空间站,回波信号载噪比为-6.12dB,匹配滤波后信号载噪比为18.49dB,信号强度增强了289倍,距离精度为117m,速度精度为2.1m/s。目标距离越小,散射截面面积越大,数字采样率越高,匹配滤波提取增强信号的能力越强。     

浅海中利用单水听器的声源被动测距

针对浅海声波导中远距离脉冲声源被动测距问题,提出了一种利用单水听器接收信号自相关函数进行warping变换的声源被动测距方法。理想水下声波导中,接收信号warping变换输出的傅里叶变换频谱中具有不变性频率特征,即与声源距离无关的各简正波截止频率;信号自相关函数中不同简正波相干成分也存在不变性频率特征;推导了未知声源距离时特征频率提取值与不变性频率特征之间的近似关系式。这些规律可推广到实际浅海声波导,并用于声源被动测距。利用声场计算模型来提供具有不变性频率特征的频谱,对2011年12月北黄海海域水声实验中单水听器接收的脉冲声数据进行了处理,验证了方法的有效性,测距结果和实际距离符合良好,平均测距误差在10%以内。      

Breathing noise elimination in through-water speech communication between divers

Breathing noise and bubble noise are the main factors affecting the subjective quality of through-water speech signals in communications between divers wearing full-face masks or aural-nasal masks. Only breathing noise is considered here, which can be gated out by applying a combination of zero-crossing detection and energy measurements to noisy speech signals above predetermined threshold values. The signals are picked up by a microphone placed close to the diver's mouth in the air cavity of the mask. Results were obtained during diving trials with four different types of masks.     

Comodulation masking release: evidence for multiple cues

Signal detection was determined in conditions where the masker was a 10-Hz-wide noise band centered on the signal, and in conditions where either a comodulated or noncomodulated noise band (centered at 0.8 times the signal frequency) was also present. Signal frequencies of 500 or 2000 Hz were investigated. In one condition of the first experiment, the signal was exactly the same 10-Hz-wide noise band as the masker, added to the masker in phase. This condition was designed to limit the availability of cues based upon dip listening, suppression, beating, or across-frequency differences in noise envelope correlation, but to afford a cue based upon across-frequency envelope amplitude difference. The narrow-band noise signal resulted in approximately the same magnitude of comodulated masking release (CMR) as was found for a pure-tone signal. This result suggested that one important cue for CMR is an across-frequency difference in envelope amplitude. Stimulus conditions in the second experiment were intended to disrupt cues of across-frequency envelope amplitude difference, but to afford cues based upon across-frequency differences in noise envelope correlation. In this experiment, cues based upon envelope amplitude were impoverished by randomly varying the level of the flanking band from interval to interval, and by adjusting the level in the on-signal band to be the same in the nonsignal intervals as the level of noise plus signal in the signal interval. Again, substantial CMRs occurred, suggesting that another cue for CMR may be envelope pattern or correlation. The results of these experiments indicated that CMR is probably based upon more than one stimulus variable.     

The masking level difference for signals placed in masker envelope minima and maxima

Previous data on the masking level difference (MLD) have suggested that NoSpi detection for a long-duration signal is dominated by signal energy occurring in masker envelope minima. This finding was expanded upon using a brief 500-Hz tonal signal that coincided with either the envelope maximum or minimum of a narrow-band Gaussian noise masker centered at 500 Hz, and data were collected at a range of masker levels. Experiment 1 employed a typical MLD stimulus, consisting of a 30-ms signal and a 50-Hz-wide masker with abrupt spectral edges, and experiment 2 used stimuli generated to eliminate possible spectral cues. Results were quite similar for the two types of stimuli. At the highest masker level the MLD for signals coinciding with masker envelope minima was substantially larger than that for signals coinciding with envelope maxima, a result that was primarily due to decreased NoSpi thresholds in masker minima. For most observers this effect was greatly reduced or eliminated at the lowest masker level. These level effects are broadly consistent with the presence of physiological background noise and with a level-dependent binaural temporal window. Comparison of these results with predictions of a published model suggest that basilar-membrane compression alone does not account for this level effect.     

Envelope order tracking for fault detection in rolling element bearings

An envelope order tracking analysis scheme is proposed in the paper for the fault detection of rolling element bearing (REB) under varying-speed running condition. The developed method takes the advantages of order tracking, envelope analysis and spectral kurtosis. The fast kurtogram algorithm is utilized to obtain both optimal center frequency and bandwidth of the band-pass filter based on the maximum spectral kurtosis. The envelope containing vibration features of the incipient REB fault can be extracted adaptively. The envelope is re-sampled by the even-angle sampling scheme, and thus the non-stationary signal in the time domain is represented as a quasi-stationary signal in the angular domain. As a result, the frequency-smear problem can be eliminated in order spectrum and the fault diagnosis of REB in the varying-speed running condition of the rotating machinery is achieved. Experiments are conducted to verify the validity of the proposed method.     

基于光腔衰荡光谱的便携式呼气异戊二烯分析仪性能评估

呼气异戊二烯是一种内源性代谢产物,其含量与人体血液中的胆固醇水平存在关联。但人体呼气影响因素众多,寻找其与胆固醇水平诊断参数的定量相关性,需要对选取的特定人群进行有效的呼吸气体分析（实时、在线、高灵敏度、高选择性、高精度的大量呼气数据获取）。光腔衰荡光谱（CRDS）是一种具有极高灵敏度、稳定性和选择性的光谱技术。采用目前市场在售的单波长紧凑型半导体紫外激光器,搭建了一套基于CRDS的呼气异戊二烯分析仪,该分析仪主要由激光系统、真空腔体、光电探测模块以及数据采集模块构成。线性拟合的结果显示所获得的衰荡信号接近单指数衰减（R2=0.998 39）,符合朗伯-比尔定律。探究了不同信号平均次数对衰荡信号稳定性的影响,综合考虑衰荡信号的稳定性和分析仪的响应时间,采用128次作为实验过程中的信号平均次数。对呼气异戊二烯分析仪的性能进行了测试,为了表征分析仪的稳定性,持续测量了分析仪16 min的真空衰荡时间。使用氮气、空气和呼吸样本,测量了呼气异戊二烯分析仪的重复性和响应速度。为了测试分析仪的线性度,测量了不同粒子数密度的异戊二烯标准气体（10×10-9,30×10-9,50×10-9,100×10-9,200×10-9）的衰荡时间。最后分析了在224 nm测量异戊二烯存在的光谱干扰问题（NO,N₂O和丙酮）。实验表明：分析仪具有高的灵敏度（检测极限为0.49×10-9）、良好的重复性、稳定性（0.48%）、近实时的响应速度（1秒测量一个数据）和良好的线性度（R2=0.993 13）,将检测极限提高至现有水平的1/1 000。研究证明基于CRDS的便携式呼气异戊二烯分析仪可实现对人体呼气异戊二烯的有效分析。     

Binaural detection at high frequencies with time-delayed waveforms

Recent research has demonstrated that the binaural system can utilize ongoing interaural time differences for lateralization at high frequencies as well as at low frequencies. The requirement is that the signal be complex so that the time difference appears as a delay in the envelope of the waveform at one ear. Reported here are several masking experiments that examine detection performance with time-delayed signals or maskers. In the first experiment, the signal was a 50-Hz band of noise centered at 4000 Hz that was time delayed by different amounts on different blocks of trials; the masker was similar band of noise, presented diotically. Large masking-level differences (MLDs) were obtained for some values of time delay, but the MLDs did not increase monotonically within time delay as they should were envelope time delay the basis for detection performance. Subsequent experiments in which the masker was time delayed and the signal was a diotic, high-frequency tone, revealed that detectability follows the autocorrelation function, and that MLDs as large as 24 dB can be obtained at 4000 Hz at time delays corresponding to negative values in the autocorrelation function. Examination of the signal-plus masker waveforms in these conditions reveals that ongoing interaural differences in level and cycle-by-cycle time exist in those conditions that yield MLDs. Since the time differences are small by usual standards, the basis for detection performance in these conditions appears to be the ongoing interaural level differences. In a final experiment, lateralization performance was measured for a time-delayed, complex waveform in the presence of maskers of various intensities. The results show that subjects are able to extract information about the time delay in the envelope even when the signal is added to a masker of equal intensity or greater. Thus, at the small signal-to-noise ratios used in our detection experiments, extraction of envelope time information was impossible, but also unnecessary, for detection was accomplished on the basis of another cue--most likely the ongoing interaural level differences.     

单腔双光梳拍频信号包络提取方法

对单腔双光梳拍频信号的包络提取方法进行了实验研究。在单个光纤激光器中引入具有强双折射的保偏光纤,使脉冲沿偏振正交的两个方向进行复用传输和锁模。精细调节腔内偏振态,实现了重频差在337 Hz～2.33 kHz范围内连续可调的双光梳生成。通过激光器腔外偏振态调节和偏振分束,获得了消光比分别为28.5 dB和38.2 dB的两路光频梳。两路光频梳经过异步采样后,采用所设计的包络检波电路对拍频信号的包络进行提取,与采用基于样条插值和希尔伯特变换的包络提取算法计算结果相比,所提取的包络峰值位置基本保持一致,验证了该方法的可行性。双光梳拍频信号包络提取实验研究可以快速实时提取包络形状和包络峰值位置,可进一步应用于包络信号触发和精密测距等领域。     

A new synthetic detection technique for trackside acoustic identification of railroad roller bearing defects

The detection of railroad roller bearing defects is of great importance for railway traffic. The acoustic defective bearing detector (ADBD) via a trackside acoustic detection system (TADS) is a popular and reliable tool for trackside identification of railroad bearing incipient defects. However, the defective trackside acoustic signal of bearing is confronted with three challenges: demodulation of acoustic signal, removal of Doppler effect and enhancement of defect frequency. This paper proposes a synthetic detection technique to overcome these difficulties successively. In the technique, the signal envelope is first extracted by a new variable-resolution ridge demodulation (VRRD) method. Then the Doppler effect is removed in the envelope via a dynamic signal resampling method. Finally, the rectified defect frequency is enhanced through the means of logarithmic transformation and piecewise linear detrending. The VRRD technique extracts the envelope from the signal time–frequency distribution (TFD) along the Doppler shift curve of resonance frequency traced by an improved ridge extraction algorithm. The resampling method is carried out on the envelope according to the Doppler shift curve of defect frequency obtained by the same ridge extraction algorithm. The sidebands around defect frequency can be suppressed by the logarithmic transformation and the low-frequency non-linear trend can be removed by the detrending method. The signal amplitude is unified at the same time. Two practical bearing signals with inner-race and outer-race defects separately verify the effectiveness of proposed technique.     

一种用于谐波检测过程中消除谐波背景方法的研究

针对可调谐半导体激光吸收光谱（TDLAS）连续检测技术中,二次谐波背景信号存在漂移的现象,提出改变激光器中心电流实时提取背景信号,以消除连续检测过程中背景信号的漂移对浓度反演的影响。依据波长调制理论推导了二次谐波背景信号的理论表达式,并分析了实际情况下影响二次谐波背景信号的因素。给出激光器在不同工作温度时电流和输出光强度之间的关系曲线,并分析了改变激光器中心电流实时提取背景信号的可行性。结合背景信号搜索方法设计了基于LabVIEW的背景信号提取流程图。设计以氨气为检测对象的TDLAS实验系统,选取了氨气的吸收谱线以及对应的吸收中心电流。在激光器电流全工作区间内只存在唯一吸收峰的情况下,确定实验中各参数的数值及搜索背景的电流范围。实验结果表明：该方法可实时提取谐波背景信号。结合线性最小二乘法拟合反演可有效地减小检测误差及背景信号对浓度反演精度的影响,提高浓度的检测精度及准确性。在连续检测实验中,反演浓度的标准差由2.688 3降到1.856 1,减小背景信号漂移对检测浓度准确性的影响,提高了连续检测的准确性。