Development of an accelerometer-based underwater acoustic intensity sensor

An underwater acoustic intensity sensor is described. This sensor derives acoustic intensity from simultaneous, co-located measurement of the acoustic pressure and one component of the acoustic particle acceleration vector. The sensor consists of a pressure transducer in the form of a hollow piezoceramic cylinder and a pair of miniature accelerometers mounted inside the cylinder. Since this sensor derives acoustic intensity from measurement of acoustic pressure and acoustic particle acceleration, it is called a p-a intensity probe. The sensor is ballasted to be nearly neutrally buoyant. It is desirable for the accelerometers to measure only the rigid body motion of the assembled probe and for the effective centers of the pressure sensor and accelerometer to be coincident. This is achieved by symmetric disposition of a pair of accelerometers inside the ceramic cylinder. The response of the intensity probe is determined by comparison with a reference hydrophone in a predominantly reactive acoustic field.     

基于声矢量传感器的水声通信技术研究

基于声矢量传感器声压和振速联合加权处理可以提高空间处理增益的原理,将声矢量传感器应用于相位调制的高速水声通信中,并结合自适应均衡算法,研究了相干解调和解码的方法。基于声矢量传感器声强处理可以抵消各向同性干扰、提高信噪比的原理,研究了在频率调制的水声通信系统中,利用声强解码代替声压解码的方法。理论分析、仿真研究和湖上试验结果表明:利用声矢量传感器相对于声压传感器来说,可以提高解码处理增益,进而提高了水声通信系统的作用距离、降低误码率。     

The study of underwater acoustic communication technology based-on the acoustic vector sensor

Underwater acoustic (UWA) communication based on an acoustic vector sensor is studied. The method of joint weighted sound pressure and velocity processing is used in phase modulation high-speed UWA communication system combined with coherent demodulation and adaptive equalization algorithm to demodulate and decode. Whereas the sound intensity could be used instead of pressure for frequency decoding in frequency modulation UWA communication system. The results of theory analysis, simulation calculations and lake trials have shown that either in phase modulation or in frequency modulation UWA communication system, the processing gain can be evidently increased, so that the BER (bit error rate) can be effectively reduced and the telemetry distance can be enlarged by using the acoustic vector sensor.     

基于多重信号分类法的一种声矢量阵方位估计算法

为了提高声矢量阵高分辨方位估计的性能,文中提出了一种矢量阵MUSIC方位估计算法。该算法先构造声矢量阵声压和振速组合输出的互协方差矩阵,然后进行MUSIC方位估计。理论分析和计算机仿真表明,文中算法比传统声矢量阵MUSIC方位估计算法有更好的双目标分辨能力和弱目标方位估计能力,湖试结果也表明文中算法有更好的目标方位估计性能。该算法基于矢量传感器声压和振速的相干性原理,充分利用声压振速组合指向性抗干扰能力,可以更好地抑制各向同性干扰,提高阵列的处理增益,从而有更好的方位估计性能。     

吸声材料对水下小平台上矢量传感器声学特性的影响研究

本文围绕粘贴黏弹性吸声材料方法对水下小平台上安装矢量传感器的指向性和测向的影响展开理论分析和实验研究.首先建立了吸声材料和平台结构组成的复合层结构的数学模型,对声波经过复合层结构的声学特性进行了分析,在此基础上利用有限元耦合边界元法对粘贴吸声材料前后的水下小平台上的矢量传感器的声学特性进行研究.通过理论计算和数值分析研究了吸声材料对矢量传感器的各通道的指向性的影响,并计算了覆盖吸声材料前后矢量传感器的测向精度.水池实验验证了分析结果的正确性.     

Robust adaptive acoustic vector sensor beamforming using automated diagonal loading

In this paper, a novel robust adaptive acoustic vector sensor beamformer based on shrinkage is derived. Unlike many existing methods, the proposed method is completely automatic (or so-called user parameter-free), which means, it do not need the choice of user parameters. The proposed diagonal loading algorithms use shrinkage-based covariance matrix estimates, instead of the conventional sample covariance matrix, in the standard Capon acoustic vector sensor beamforming formulation. The numerical results show that our method is robust against errors on the steering vector and small sample sizes, and meanwhile gives high output signal to interference plus noise ratio (SINR).     

基于矢量传感器的频率估计算法在水声通信中的应用

本文给出了基于矢量传感器的ESPRIT频率估计算法，并将其应用于频率调制水声通信系统中。与声强频率估计算法相比，ESPRIT频率估计可在小样本的情况下，获得高精度的频率估计。仿真和湖试结果表明，基于矢量传感器的ESPRIT频率估计算法可以提高通信速率并降低对通信系统的带宽要求。本算法对信噪比的要求较高，目前看，较适用于近程高速水声通信。     

第六讲水下声学传感器网络的发展和应用

文章主要介绍了正在发展中的水下声学传感器网络的一些概念和发展现状.在回顾了水声通信和水下网络的发展历史之后,首先从网络拓扑结构出发,指出多跳对等网络是适合于水声应用的一种网络结构,接着根据网络协议栈的概念,说明水下声学传感器网络在各协议层上所涉及的问题,并从物理层面,分析了水声介质的特殊性,和水下声学传感器网络所面临的一些主要的技术挑战.介绍了组成水下传感器网络的关键部件,以美国海网（Seaweb）为例,给出了一个水声传感器网实现的实例,对它的年度实验进行了介绍,最后,给出了中国未来的发展应用前景.     

High-frequency attenuation measurements using an acoustic microscope

An acoustic microscope was used to measure excess attenuation of aqueous solutions of sugars and proteins at 1.0 GHz. Interference pattern spacing and peak amplitude reduction of V(z) curves, obtained with these solutions as the acoustic microscope coupling liquid, were related to the solution wavespeed and attenuation, respectively. Consistent with published results for lower frequencies, solutions with molecular weight greater than 10,000 had a higher specific absorption than those with a molecular weight less than 1000 and within these two molecular weight ranges specific absorption was independent of concentration.     

A tunable gas sensor using an acoustic waveguide

A tunable gas sensor using surface acoustic waves (SAW) is described. It is designed on the basis of a waveguide delay line fabricated on a piezoelectric substrate made of 128° Y-cut LiNbO₃. A voltage applied between the waveguide and two electrodes causes a local change in the properties of the substrate near the waveguide and differently affects the sensor’s response to the vapors of various analytes. Some results of the experimental study of the sensor, which show the change in the selectivity under the effect of voltage, are presented. The analytes used for testing include a number of alcohols and deionized water. The possibilities for employing such a sensor in the sensor arrays of gas analyzers of the electronic nose type are discussed.     

声矢量传感器研究进展

声矢量传感器由传统的无指向性声压传感器和偶极子指向性质点振速传感器复合而成,可以同步共点测量声场中一点处的声压和质点振速若干正交分量,由此得到的幅度和相位信息为解决一些水声问题提供了新的思路。因其实际的和潜在的工程应用价值,所以在最近十年间与此相关的声矢量传感器技术备受水声界关注。本文尝试综述声矢量传感器技术近五十年间在物理基础、传感器设计制作、相关工程应用等各方面的发展历史、现状和所取得的一些研究进展。     

Flow noise of an underwater vector sensor embedded in a flexible towed array

The objective of this work is to simulate the flow noise of a vector sensor embedded in a flexible towed array. The mathematical model developed, based on long-wavelength analysis of the inner space of a cylindrical multipole source, predicts the reduction of the flow noise of a vector sensor embedded in an underwater flexible towed array by means of intensimetric processing (cross-spectral density calculation of oscillatory velocity and sound-pressure-sensor responses). It is found experimentally that intensimetric processing results in flow noise reduction by 12-25 dB at mean levels and by 10-30 dB in fluctuations compared to a squared oscillatory velocity channel. The effect of flow noise suppression in the intensimetry channel relative to a squared sound pressure channel is observed, but only for frequencies above the threshold. These suppression values are 10-15 dB at mean noise levels and 3-6 dB in fluctuations. At towing velocities of 1.5-3 ms(-1) and an accumulation time of 98.3 s, the threshold frequency in fluctuations is between 30 and 45 Hz.     

An acoustic chamber for sound intensity measurements

The construction and performance of an acoustic chamber suitable for sound intensity measurements is described. The walls and the ceiling of the room are treated with glass wool sheets, air gap and pleated carpet in that order for sound absorption. The final testing of the room shows that good sound absorption is obtained down to low frequencies. The sound absorption coefficient for the room varies between 0.83 and 0.91 for different frequencies.     

基于单矢量有源平均声强器的码分多址水声通信

基于单矢量传感器对码分多址水声通信进行了研究. 利用单个矢量传感器自身指向性进行方位估计最为常用的方法是平均声强器和复声强器, 但这些方法对于同频带的多用户来说, 理论极限仅能测量两个用户. 提出了有源平均声强器, 利用扩频通信中伪随机码优良的自相关和互相关特性, 可同时测得多个用户的方位, 利用估计的用户方位构建矢量组合, 调整矢量传感器的指向性, 实现各用户定向通信, 抑制多址干扰, 增加处理增益, 降低误码率. 对频带相同的扩频多用户通信进行了仿真及试验研究, 验证了有源平均声强器的有效性和实用性.     

基于单矢量有源平均声强器的码分多址水声通信

基于单矢量传感器对码分多址水声通信进行了研究. 利用单个矢量传感器自身指向性进行方位估计最为常用的方法是平均声强器和复声强器, 但这些方法对于同频带的多用户来说, 理论极限仅能测量两个用户. 提出了有源平均声强器, 利用扩频通信中伪随机码优良的自相关和互相关特性, 可同时测得多个用户的方位, 利用估计的用户方位构建矢量组合, 调整矢量传感器的指向性, 实现各用户定向通信, 抑制多址干扰, 增加处理增益, 降低误码率. 对频带相同的扩频多用户通信进行了仿真及试验研究, 验证了有源平均声强器的有效性和实用性.     

Nonperturbing measurements of spatially distributed underwater acoustic fields using a scanning laser Doppler vibrometer

Localized changes in the density of water induced by the presence of an acoustic field cause perturbations in the localized refractive index. This relationship has given rise to a number of nonperturbing optical metrology techniques for recording measurement parameters from underwater acoustic fields. A method that has been recently developed involves the use of a Laser Doppler Vibrometer (LDV) targeted at a fixed, nonvibrating, plate through an underwater acoustic field. Measurements of the rate of change of optical pathlength along a line section enable the identification of the temporal and frequency characteristics of the acoustic wave front. This approach has been extended through the use of a scanning LDV, which facilitates the measurement of a range of spatially distributed parameters. A mathematical model is presented that relates the distribution of pressure amplitude and phase in a planar wave front with the rate of change of optical pathlength measured by the LDV along a specifically orientated laser line section. Measurements of a 1 MHz acoustic tone burst generated by a focused transducer are described and the results presented. Graphical depictions of the acoustic power and phase distribution recorded by the LDV are shown, together with images representing time history during the acoustic wave propagation.     

基于矢量传感器的水下双址接入研究

针对水声信道的特殊性,提出一种适用于水声通信的双址接入方法。旋转矢量传感器的组合指向性,使其零点对准某一信源,则该信源被屏蔽,此时信宿可以与另一信源进行通信,反之亦然。矢量传感器的空间指向性不随频率变化,该方法可以实现宽带双址异步通信。此外,当两信源之间的开角大于34.8°时,通过对矢量传感器声压和振速输出的联合处理,可以使分离出的不同信源所发射的信号获得一定的信噪比增益。理论分析、数值仿真和湖上实验结果表明:基于矢量传感器的双址通信算法实现简单,信道资源利用率高,可以与其它多址接入技术结合使用,并且矢量传感器的空间增益可以有效降低系统的误码率。由于水声信道的特殊性,水下信息网须采用多种多址接入技术,本文所提出的双址通信方案将是其它多址接入技术的有益补充。     

Numerical prediction of envelope line-spectrum intensity in underwater acoustic waveguides

In order to predict the detectible range and region of passive sonar in underwater channel,the attenuation causes of envelope line-spectrum height during vessel noise propagation are analyzed and an approach of numerical prediction is proposed.In the paper a model for vessel radiated noise is established by a periodically locally stationary random process,two formulae of the envelope line-spectrum height with and without background-noise are deduced, therefore the attenuation rule of the envelope line-spectrum height is obtained.It is shown that the transmission loss of the sound level of the envelope line-spectrum is same as the sound level of the stationary spectrum,but the decrease of envelope line-spectrum height depends on a modified scale of amplitude modulation depth which is variable with the ratio of signal to noise. An approach of numerical prediction for envelope line-spectrum height is as follows:first,the transmission loss of the stationary radiated noise is derived using the numerical approaches of normal modes or wavenumber integration or PE etc.,then the ratio of signal to noise on sound field is calculated,finally the decrease of envelope line-spectrum height is obtained according to the modified scale,and the envelope line-spectrum height in sound field is predicted.The theory and the numerical prediction approach possess certain innovation,practicality,simplicity and suitability for engineering.     

声矢量圆阵宽带相干目标MVDR方位估计*

针对宽带相干目标的远程探测问题，本文提出一种基于声压振速联合处理和矢量重构的声矢量圆阵MVDR波束形成方法。该方法利用相位模态变换技术，将声矢量圆阵变换为与信号频率无关的虚拟线阵，并构建虚拟线阵声压与组合振速的互协方差矩阵，利用声压与振速各分量间的空间相关性有效地抑制各向同性环境噪声；并对宽带相干信号的互协方差矩阵进行矢量重构，即将最大特征值对应的特征向量划分为相互重叠的子向量，从而构建前/后向Hermitian矩阵；最后，基于MVDR波束形成器实现宽带相干目标的方位估计。仿真计算和实验数据处理结果表明，该方法具较强的解相干能力和噪声抑制能力以及较高的方位估计性能。