多元相控聚焦探测器的方向特性

研究了多元线性阵列探测器的主频、阵元个数和阵元间距对探测器方向性的影响.实验结果表明,采用主频为2～5 MHz,阵元数为5～15,阵元间距为0.3～0.9 mm的多元线性阵列探测器,其方向性好,将有利于光声信号的探测与成像.     

基于超声波干涉的峰谷法计算声速值及实验误差探讨

介绍了基于Cassy Lab软件下的超声波干涉实验,提出了利用超声波干涉现象测量声速的方法.根据干涉理论推导了峰谷法测量声速的计算公式.分析和探讨了峰谷法计算声速的误差来源和改进方法.     

Experimental assessment of a multicarrier underwater acoustic communication system

This paper presents a multicarrier communication system which transmits information on independent subcarriers to achieve an increased data rate. For this system, a passive-phase conjugation (PPC) based receiver structure is assessed by processing data collected in sea trials. Based on temporal diversity (pulse compression) exploited by PPC processing, an adaptive multichannel decision feedback equalizer is used to remove intersymbol interference, where spatial diversity is exploited by adaptive multichannel combination. The digital phase-locked loop (DPLL) technique is implemented for carrier-phase tracking. In the scenario of low input signal-to-noise ratios (SNRs), the receiver structure achieved superior performance using a common DPLL. In a depth-fluctuated environment, two sea experiments were conducted over ranges of 2 km and 4 km, respectively, and this communication system was assessed with a data rate of 4 kbps. In terms of mean square error, output SNR and bit error rate, this receiver structure has demonstrated its performance for the multicarrier communication system.     

Coherent underwater communication using passive time reversal over multipath channels

Passive time reversal exploits underwater acoustic channels’ spatial and temporal diversity. It can refocus multipath propagated signal at the receiver and can be realized simply by the passive phase conjugation (PPC) method. By the temporal focusing, time delay spread caused by multipath propagation is mitigated for spectral efficient coherent communications. However, the PPC method is unable to eliminate multipath and is limited by channel variations. An adaptive equalizer is therefore needed to compensate residual multipath after refocusing and to track channel temporal variations. Spatial diversity is obtained by using a vertical receiving array. In this paper we used 4-hydrophone array and demonstrated that the adaptive decision feedback equalization in conjunction with PPC significantly decreased the bit error rate.     

Potential solutions to improved sound performance of volume based lightweight multi-storey timber buildings

Lightweight building systems in general suffer from poor sound insulation, especially in the low frequency region. Since no reliable mathematical models that can predict the impact sound pressure level exists, the lightweight building design is to a high extent based upon previous experience and upon measurements. A special difficulty is related to experimental measurements since the variation among identical units must not be neglected. A modern volume based lightweight wooden building concept has here been tested by numerous well controlled measurements, in laboratory as well as in more field like conditions. The volume construction technique offers new possibilities and challenges to improve sound insulation in light weight timber construction. The main purpose was to investigate how different constructional solutions in the floor, like plaster board, mineral wool, elastic glue, dividing board, floating floor etc., affect the sound insulation. Many of the tested modifications resulted in only marginally changed impact sound pressure level but parameters that substantially can improve the sound insulation were found in using elastic glue to mount the floor boards, to install extra board layers and to use floating floors.     

反射式Sagnac干涉光纤电流互感器的传感头误差研究

阐述了反射式Sagnac干涉型电流传感器的原理,对Sagnac型光纤电流传感器进行了深入的理论研究,建立了完整的系统理论模型。采用偏振系统的Jones矩阵对反射式Sagnac干涉型电流传感器的偏振误差进行了研究,并对光纤传感头中的线性双折射、圆双折射对测量准确度的影响进行了模拟分析,从理论上得到了反映影响规律的曲线。仿...     

Effects of the piezoelectric field on the modulation of exciton–polaritons by surface acoustic waves

Surface acoustic waves (SAWs) provide a powerful tool for the modulation of polaritons in GaAs-based microcavities. In this contribution, we compare the modulation introduced by SAWs propagating along piezoelectric and non-piezoelectric crystal directions of the sample surface. Strain calculations reveal that the type-I band-gap modulation induced by the strain field is comparable for both SAW types. Piezoelectric SAWs have, however, an intrinsic longitudinal electric field, which can dissociate quantum well (QW) excitons and, thus, degrade the modulation. Images of the polariton far-field photoluminescence reveal this behavior for different excitation conditions.     

舰船辐射噪声模拟发射系统的设计研究

本文依据典型舰船噪声的频谱特性规律,设计研制了一套舰船辐射噪声发射系统实验样机,包括信号结构设计、换能器选择配置、系统构成设计等,本噪声模拟发射系统具有100Hz～16kHz频带噪声的模拟发射功能,包括线谱、连续谱成分,频谱分配和谱线形式可调可控,信号总声源级动态范围达60dB。     

船用超声液位传感器的分析与设计

介绍了一种船用某型超声液位传感器的基本结构和工作原理。在对脉冲式超声探头的轴向声压分布特点及其声透射强度分析研究的基础上,给出了该传感器的超声信号发射端与接收端之间距离d和压电晶片保护膜的壁厚δ值的确定方法。最后设计了一套超声液位传感器性能测试实验平台,对上述理论研究结论进行了实验验证。     

全息声压场的加权范数外推方法

全息声压外推是Patch近场声全息技术的关键步骤.本文提出了全息声压的加权范数外推方法,该方法首先通过实测声压数据的功率谱信息构造频域加权范数,然后通过极小化频域加权范数实现全息声压外推.由于外推过程中同时利用了声压信号的波数域带宽和波数谱形状信息,因此其外推结果优于传统带限外推方法.数值仿真结果表明,该方法无论在外推精度还是计算效率上都明显优于经典的全息声压波数域外推方法.刚性箱体上的声激励固支板声压外推实验进一步验证了该方法的有效性和实用性. 关键词： 近场声全息 全息声压外推 加权范数