空气声被动定位的误差分析

本文讨论了了空气中声被动定位系统的误差来源,给出了相应的误差公式,并分析了各种误差对测向及测距精度的影响,为确定和提高被动声定位系统的精度提供了有价值的参考数据。     

超声速反舰导弹被动声定位算法研究

针对雷达体制反舰导弹矢量脱靶量测量系统在复杂电子干扰环境中存在的不足,在建立被动声定位模型后,基于极大似然估计思想,采用搜索方式解算反舰导弹攻靶段飞行轨迹的最优解。仿真计算结果表明,当反舰导弹在靶船上方飞过时,绝大部分区域解算精度优于2m,满足试验评定要求。     

二级Kalman滤波的被动声定位后置处理方法

阵列定位的计算结果中往往存在大量的野值,需要用后置处理方法从结果中选取真实目标信息。本文提出了一种基于Kalman滤波的二级后置处理方法,建立了相应的滤波模型,并对主要参数进行讨论选取,同时给出了外场实验结果。结果表明此方法后置处理效果明显,并可以满足系统实时性的要求。     

一种超声速运动目标的被动声定位算法

超声速运动目标在空气中飞行时产生激波,本文利用激波到达时间,提出了一种基于波前方向矢量的算法,确定目标的速率和位置。最后,通过对三站均匀圆阵的估计精度的分析计算,讨论了该算法的有效性。     

一种超声速运动目标的被动声定位算法

超声速运动目标在空气中飞行时产生激波,本文利用激波到达时间,提出了一种基于波前方向矢量的算法,确定目标的速度和位置。最后,通过对三站均匀圆阵的估计精度的分析计算,讨论了该算法的有效性．     

高频空气声换能器研究现状与展望

本首先阐述高频空气声换能器的设计要点,然后介绍空气声换能器在测距、成象、材料特性无损评价等方面的初步应用,最后讨论空气声换能器进一步研究的发展方向及应用前景。     

炉内管道泄漏声检测与定位系统的研究现状

电站锅炉管道泄漏的声检测与定位系统,已经越来越广泛地应用于电站锅炉。该系统主要利用声学技术检测炉内管道的泄漏状态,并利用多传声器定位机理对泄漏点进行定位,有效地减少了由管道泄漏引起的非计划停炉,这对电站锅炉来说意义尤为重要。本文分析了炉内管道泄漏声检测与定位系统的关键技术,介绍了该系统的发展概况及应用现状,并提出了改进方向。     

浅海空气声入水传播特性分析

结合射线和波数谱积分方法,对空气声入水传播途径进行了分析,利用海上试验数据进行了比较检验。结果表明,在浅海环境中,对水下声场有主要贡献的空气声入水传播途径,主要是透射穿过海面边界的折射直达声以及后续的海底反射声途径,其中折射直达声途径的贡献主要集中在声源正下方附近区域,当距离较远时,由于声线扩展损失效应以及直达声影区两方面的限制,折射直达声传播损失显著增加,对接收声场起主要贡献的是可以到达更远水平距离上的海底反射声,包括海底海面多次反射声。     

利用圆阵实现声目标的全空域被动定位

为实现声目标的被动定位,提出了一种平面圆阵的定位方案,并利用最小二乘原理导出了多阵元模型的定位算法。该算法不仅能对空中目标进行定位,而且也能对地面目标进行定位,同时该算法消除了目标方位变化对测距精度的影响,因而具有较好的测距能力。计算机数值计算和仿真结果表明,该系统具有较好的定位性能。     

水平变化浅海声波导中模态特征频率与声源距离被动估计

针对水平变化浅海声波导中声源宽容性被动测距问题,理论分析了海底地形水平缓变浅海波导中卷绕变换基础上的低频声场特征频率.推导了绝对硬海底时水平变化波导中声场模态时频到达结构以及模态瞬时相位的表达式,由该表达式给出了特征频率与收发距离的变化关系,进而提出了水平变化浅海波导中声源距离被动估计的修正方法,通过仿真和实验对理论与方法进行了验证.     

非同步的多普勒水声跟踪定位原理

提出了一种新的水声跟踪定位方法,它仅测量目标非同步声信标到达各测量基元的接收信号和频率,来对目标声学跟踪定位,称之为非同步多普勒定位方法,本文介绍其原理,处和仿真结果。     

闪光灯泵浦的Cr:LiSAF激光器

A new construction and comparison method for accurate non-reflective event locating in optical time-domain measurement is described. We defined the backscatter impulse response, and established the convolution equations, in which the two elements: q(t) and y(t) are measurable. With this method, we can improve the accuracy of locating of non-reflective event to one sampling span, with the same the probe pulse width.     

Accuracy analysis of parallel plate interferometer for angular displacement measurement

The measurement accuracy of a parallel-plate interferometer for angular displacement measurement is analyzed. The measurement accuracy of angular displacement is not only related to the accuracy of phase extraction, but also related to initial incident angle, refraction index and thickness of plane-parallel plate as well as wavelength's stability of laser diode, etc. Theoretical analysis and computer simulation show that the measurement error of the angular displacement bears a minimum value when choosing an optimal initial incident angle in a large range. These analytical results serve as a guide in practical measurement. In this interferometer, reducing the refraction index or increasing the thickness of the parallel plate can improve the measurement accuracy; and the relative error of the phase measurement is 3.0×10⁻⁴ corresponding to 1 °C temperature variation. Based on these theoretical and experimental results, the measurement accuracy of the parallel-plate interferometer is up to an order of 10⁻⁸ rad.     

Subjective and Objective Evaluation of Voice Quality in Patients With Asthma

OBJECTIVES: To evaluate the voice quality in patients with mild-to-moderate asthma by subjective and objective methods. STUDY DESIGN: Comparative, controlled, cross-sectional study. METHODS: Patients with mild-to-moderate asthma (n=40) and age- and sex-matched healthy controls (n=40) were included. Acoustic analyses were performed by the Multi-Dimensional Voice Program (MDVP; Kay Elemetrics Corporation, Lincoln Park, NJ) and the movements of the vocal cords were examined by videolaryngostroboscopy (VLS). In addition, the duration of illness, maximum phonation time, "s/z" values, and vital capacity were evaluated. Voice Handicap Index (VHI) and GRB scales were used for subjective evaluations. RESULTS: Maximum phonation time values were significantly shorter both in male and female asthma patients compared with controls (P<0.0001). Also, average shimmer values in MDVP were higher for both sexes in the patient group compared with controls (P=0.002 and P=0.04, respectively). There was a significant difference between female patients and sex-matched controls with regard to mean noise-to-harmonic ratio values (P=0.006). Female patients with asthma had higher average jitter values compared with sex-matched controls (P<0.0001). A significant difference was noted between asthma and control groups with regard to GRB scale (P<0.0001, P<0.001, and P<0.0001, respectively). The VHI score was above the normal limit in 16 (40%), and VLS findings were abnormal in 39 (97.5%) asthmatics. CONCLUSION: In asthmatic patients, maximum phonation time, frequency, and amplitude perturbation parameters were impaired, but the vital capacity and the duration of illness did not correlate with these findings.     

Acoustic voice analysis in patients with essential tremor

To quantify several acoustic features of the voice in patients with essentialtremor (ET), 28 patients and 28 age- and sex-matched controls were studied. ET severity was assessed with the rating scale for tremor of Fahn, Tolosa, and Marín. The Computerized Speech Lab 4300 program (Kay Elemetrics) was used. Two-second samples of a sustained /a/ and a sentence were captured with a microphone and laryngograph equipment. Measures included fundamental frequency (F₀), frequency perturbation (fitter, Koike algorithm), intensity perturbation (shimmer, Horii algorithm), and harmonic-to-noise ratio (H/N, Yumoto algorithm) of the vowel /a/, and the frequency and intensity variability of the sentence, phonational range, and dynamic range at the natural frequency, maximum phonational time, and s/z ratio. All subjects underwent indirect laryngoscopy and/or laryngeal fibroscopy. When compared with controls, ET patients showed higher jitter, lower H/N ratio (the last one only with laryngographic signal), of the vowel /a/, lower frequency variability in the microphonc signal, lower intensity variability in the laryngographic signal of the sentence, and significantly lower dynamic range at natural frequency of phonation. ET patients reported higher frequency of the presence of high voice intensity, tremor, and struggle. Several acoustic parameters were influenced by the severity of the disease, including shimmer, jitter, H/N ratio, frequency variability of the sentence, and s/z ratio, although neither of the acoustic analysis values or the phonetometric measurements were affected by the presence of voice tremor or by a successful pharmacological treatment of ET.     

Non reflective Event Locating Based on Impulse Response in Optical Time domain Measurement

１ＩｎｔｒｏｄｕｃｔｉｏｎＯｐｔｉｃａｌｔｉｍｅｄｏｍａｉｎｒｅｆｌｅｃｔｏｍｅｔｒｙ（ＯＴＤＲ）ｉｓａｃｏｍｍｏｎｌｙｕｓｅｄｔｅｃｈｎｉｑｕｅｆｏｒｃｈａｒａｃｔｅｒｉｚａｔｉｏｎａｎｄｆａｕｌｔｌｏｃａｔｉｎｇｏｆｏｐｔｉｃａｌｆｉｂｅｒｔｒａ...     

Development of sound measurement systems for auditory functional magnetic resonance imaging

Auditory functional magnetic resonance imaging (fMRI) requires quantification of sound stimuli in the magnetic environment and adequate isolation of background noise. We report the development of two novel sound measurement systems that accurately measure the sound intensity inside the ear, which can simultaneously provide the similar or greater amount of scanner- noise protection than ear-muffs. First, we placed a 2.6 x 2.6-mm microphone in an insert phone that was connected to a headphone [microphone-integrated, foam-tipped insert-phone with a headphone (MIHP)]. This attenuated scanner noise by 37.8+/-4.6 dB, a level better than the reference amount obtained using earmuffs. The nonmetallic optical microphone was integrated with a headphone [optical microphone in a headphone (OMHP)] and it effectively detected the change of sound intensity caused by variable compression on the cushions of the headphone. Wearing the OMHP reduced the noise by 28.5+/-5.9 dB and did not affect echoplanar magnetic resonance images. We also performed an auditory fMRI study using the MIHP system and presented increase in the auditory cortical activation following 10-dB increment in the intensity of sound stimulation. These two newly developed sound measurement systems successfully achieved the accurate quantification of sound stimuli with maintaining the similar level of noise protection of wearing earmuffs in the auditory fMRI experiment.