RESEARCH ON VIBRATION MODES OF THE CHINESE CHIME STONE

Nearfield acoustical holography is a powerful tool for imaging of acoustic sources. In this article, the basic theory treating steady-state acoustic radiation with generalized holography has been discussed. By holographic imaging, the vibration characteristics of irregular objects, the Chinese ancient musical instrument, the one-tone chime stone and the two-tone chime stone provided by the Institute of Archaeology, the Museum of Hubei Province, have been researched. The results show that the ancient chime stone has two main vibration modes, which make up the base of sound produced by the instrument. As for the two-tone chime stone, it is not so long and wide as the single-tone chime stone, but thicker and smoother than the single-tone chime stone. When it is excited at different positions, although it radiates sounds of different frequencies, its vibration modes are similar. This may be related to its dimensions and shape. The research is helpful for studying the sound producing system and the radiated field characteristics of the chime stone.     

光纤干涉成像阵列全息相位校正研究

针对光纤传输和干涉成像阵列中的相位误差, 提出了一种基于特殊光子晶体的全息相位校正方法。首先分析了光纤干涉阵列成像的基本原理和相位信息的传输过程, 以一维线性阵列建立成像系统相位误差模型, 通过对参考光束和探测器前的快门交替打开和闭合, 来分别实现在晶体上写入由光纤阵列的出射光束与参考光束干涉形成的含有相位误差的光栅函数, 和光纤中出射光束被该光栅衍射和相位偏移以消除相位误差, 从理论上分析了上述基于光子晶体的全息法相位校正原理。最后采用所建立的含有相位误差的干涉阵列进行成像仿真, 对未加校正、采用本文方法和采用冗余基线校正的结果进行了对比分析。     

RESEARCH ON VIBRATION MODES OF THE CHINESE CHIME STONE

Nearfield acoustical holography is a powerful tool for imaging of acoustic sources. In this article, the basic theory treating steady-state acoustic radiation with generalized holography has been discussed. By holographic imaging, the vibration characteristics of irregular objects, the Chinese ancient musical instrument, the one-tone chime stone and the two-tone chime stone provided by the Institute of Archaeology, the Museum of Hubei Province, have been researched. The results show that the ancient chime stone has two main vibration modes, which make up the base of sound produced by the instrument. As for the two-tone chime stone, it is not so long and wide as the single-tone chime stone, but thicker and smoother than the single-tone chime stone. When it is excited at different positions, although it radiates sounds of different frequencies, its vibration modes are similar. This may be related to its dimensions and shape. The research is helpful for studying the sound producing system and the radiated field characteristics of the chime stone.     

Digital phase shift holographic interferometry and its application in the experimental flow study

The application of digital phase shift holographic interferometry to flow-visualization and flow temperature measurement of a 2D thermal flow field was experimentally investigated. An improved recording system for two reference beam phase shift holographic interferometry is set up for this experiment, and details of this experimental technique are described. The phase distribution obtained by this technique presents an excellent picture of flow visualization. From this phase image, temperature distribution of the 2D thermal flow field is also calculated and compared with some measured values obtained using thermocouple probes.     

用于超声悬浮场可视化的光学全息相位倍增方法研究

基于二次曝光全息干涉测量原理,采用四倍相位倍增光路对声悬浮声压场分布进行了可视化研究.拍摄了给定模式的超声悬浮场在不同超声换能器激励电流时的光学全息图并进行光学再现,由再现光波的全息干涉条纹图样得到了反映声压场分布的光波波前相位变化,并进行了对比分析.结果表明,与无相位倍增光路相比,采用四倍相位倍增光路可使同一声压场的全息干涉条纹数目大大增加,测量灵敏度明显提高,为进一步研究声悬浮场声压分布提供了一种有效方法.     

Selecting passive and active materials for 1.3 composite power transducers

1.3 PZT-polymer composites were fabricated using the dice and fill method with various PZT types and volume fractions. These composites were evaluated for power underwater transducer applications with an air backed and no matching layer configuration. Electrical input and acoustical output powers were monitored as a function of the drive level. Total acoustic power densities of 30 W/cm2 were obtained with a P189/epoxy piezocomposite vibrating at 350 kHz with a low duty cycle (1-5%) and with a 90% efficiency. Power densities up to 20 W/cm2 were measured with a 50% duty cycle. Evolution and destruction of the transducers were monitored versus increasing averaged power. It was observed that better efficiencies were obtained with low volume fraction configurations allowing natural acoustic impedance matching to water. It was found that hard PZT type (Navy III) are optimal compositions even for piezocomposite transducers. It is shown that, unlike a common belief, the polymer mechanical losses are comparable to those of the active ceramic justifying that 1.3 piezocomposites are suited for low-cost power applications. In fact, the main limitation induced by the polymer phase is a strong thermal breakdown when the temperature of the transducer approaches the glass transition region of the polymer. Measurements of the polymer losses as a function of the temperature were obtained confirming this point and offering interesting new alternatives for future composite power transducers.     

声纳导流罩吸声障板声学特性的研究

本文研究内容属于舰艇声兼容性技术研究的一部分。应用声学软件SYSNOISE计算了,声纳定向发射时某试验用声纳导流罩及尾部吸声障板的声场特性,同时进行相同工况的水下模型试验。计算结果与试验结果吻合良好,说明应用声学软件对声纳声场进行计算是一种可行的方法,有可能推广至其他的水下模型的声场计算。结果数据反映了吸声障板对声纳定向发射时声场的影响,为舰艇总体声纳导流罩内吸声障板的结构设计、声兼容设计提供依据。     

A spiral wave front beacon for underwater navigation: transducer prototypes and testing

Transducers for acoustic beacons which can produce outgoing signals with wave fronts whose horizontal cross sections are circular or spiral are studied experimentally. A remote hydrophone is used to determine its aspect relative to the transducers by comparing the phase of the circular signal to the phase of the spiral signal. The transducers for a "physical-spiral" beacon are made by forming a strip of 1-3 piezocomposite transducer material around either a circular or spiral backing. A "phased-spiral" beacon is made from an array of transducer elements which can be driven either in phase or staggered out of phase so as to produce signals with either a circular or spiral wave front. Measurements are made to study outgoing signals and their usefulness in determining aspect angle. Vertical beam width is also examined and phase corrections applied when the hydrophone is out of the horizontal plane of the beacon. While numerical simulations indicate that the discontinuity in the physical-spiral beacon introduces errors into the measured phase, damping observed at the ends of the piezocomposite material is a more significant source of error. This damping is also reflected in laser Doppler vibrometer measurements of the transducer's surface velocity.     

Angular spectrum approach for the computation of group and phase velocity surfaces of acoustic waves in anisotropic materials

The decomposition of an acoustic wave into its angular spectrum representation creates an effective base for the calculation of wave propagation effects in anisotropic media. In this method, the distribution of acoustic fields is calculated in arbitrary planes from the superposition of the planar components with proper phase shifts. These phase shifts depend on the ratio of the distance between the planes to the normal component of the phase slowness vector. In anisotropic media, the phase shifts depend additionally on the changes of the slowness with respect to the direction of the propagation vector and the polarization. Those relations are obtained from the Christoffel equation. The method employing the fast Fourier transformation algorithm is especially suited for volume imaging in anisotropic media, based on holographic detection in transmission of acoustic waves generated by a point source. This technique is compared with measurements on crystals performed by phase-sensitive scanning acoustic microscopy.     

三维超声驻波场的数字全息测量与重建研究

利用数字全息干涉术研究了超声驻波场的三维分布特征,由所记录的不同角度的超声驻波场的数字全息图,经数值再现,得到了超声驻波场的强度和相位差分布图,进而由迭代重建算法重建出超声驻波场的三维分布曲线。结果表明,数字全息干涉术与迭代重建算法相结合是测量与重建三维超声驻波场的一种方便有效方法。     

A quality of parametric wave phase conjugation of ultrasound

The criterion, known from optics, of wave phase conjugation quality is accommodated for acoustical experiment. An incident focused sound beam at 5 MHz is propagated towards a supercritical magnetoelastic conjugator through an introduced random phase layer, and the conjugate beam propagates backwards through the layer to the source. 1D and 2D distributions of wave field are measured for the conjugate beam of finite amplitude using a membrane hydrophone. The maximum sound intensity of 640 W/cm2 and acoustic power of 4 W are registered in the focal maximum of the conjugate wave. The quality of WPC is calculated from the ratio between the power in the central maximum and the total power of the conjugate beam. The method is applied to compare two operation modes of a supercritical parametric conjugator. It is shown that in the linear mode the conjugator provides higher quality than in the nonlinear (0.54 compared to 0.24).     

High-resolution quantitative phase microscopic imaging in deep UV with phase retrieval

High-resolution three-dimensional (3D) microscopic imaging requires the use of short wavelengths. Quantitative 3D imaging techniques, such as digital holographic microscopy, require interference between the object beam and a known reference background for the extraction of phase information. At shorter wavelengths, due to short coherence lengths, it may be difficult to implement a two-beam off-axis setup. Thus, a single-beam technique, which provides complete phase information, may be better suited for short wavelengths. This Letter describes the development of a quantitative microscopy technique at 193 nm using multiple intensity samplings and phase retrieval.     

Digital holographic microscopy for automated 3D cell identification: an overview (Invited Paper)

Digital holographic （DH） microscopy is a promising technique for quantitative phase contrast imaging. It provides complex amplitude of the object wavefront, which in turn yields the thickness distribution of the object. An added advantage of the technique is its ability for numerical focusing, which provides the thickness distribution of the object at different axial planes. In this invited paper, we present an overview of our reported work on two beam DH microscopyto acquire different cell parameters for cell imaging and automated cell identification. Applications to automated cells and automated identification of malaria infected red monitoring of stem cells without destroying the blood ceils are discussed.     

统计最优平面近场声全息原理与声场分离技术

测量孔径尺寸的有限性，在基于空间傅里叶变换的平面近场声全息中会带来窗效应和卷绕误差. 为了克服窗效应和卷绕误差，引入了统计最优平面近场声全息技术. 运用声场叠加原理，证明了统计最优平面近场声全息的理论公式.通过在空间波数域限定kx,ky的取值范围，并离散其确定的空间波数面的途径，提出了一种确定波数矢量的方法.为了克服常规统计最优平面近场声全息技术的应用局限性——全息面一侧的声场必须为自由声场，提出了适用于统计最优平面近场声全息的、基于双全息面测量的空间声场分离技术. 通过实验和数值仿真对理论推导的正确性进行了验证. 关键词： 统计最优 平面近场声全息 波数矢量 声场分离     

Reconstruction and prediction of coherent acoustic field with the combined wave superposition approach

The routine wave superposition approach cannot be used in reconstruction and prediction of a coherent acoustic field, because it is impossible to separate the pressures generated by individual sources. According to the superposition theory of the coherent acoustic field , a novel method based on the combined wave superposition approach is developed to reconstruct and predict the coherent acoustic field by building the combined pressure matching matrixes between the hologram surfaces and the sources. The method can reconstruct the acoustic information on surfaces of the individual sources, and it is possible to predict the acoustic field radiated from every source and the total coherent acoustic field can also be calculated spontaneously. The experimental and numerical simulation results show that this method can effectively solve the holographic reconstruction and prediction of the coherent acoustic field and it can also be used as a coherent acoustic field separation technique. The study on this novel method extends the application scope of the acoustic holography technique.     

An approach for sensing marine plankton using digital holographic imaging

The goal of this paper is to use digital holographic imaging for sensing marine plankton in recording sampling volume. The process stage of this approach includes: wavefront recording using in-line holographic recording set up and numerical reconstruction using Fresnel approximation and convolution algorithm. So, by capturing hologram of marine plankton and reconstructing hologram, the recorded optical field of marine plankton is retrieved. Digital holographic imaging is an extremely powerful technique for the study of marine plankton fields as it allows instantaneous, noninvasive, high-resolution recording of substantial volumes. Finally, this paper presents that it is possible for digital holographic imaging system to sense marine plankton according to laboratory results.     

用于大景深单分子定位显微的多功能全息相位片的设计及数值模拟

发展具有大轴向定位范围的单分子定位技术对于实现厚样品的超分辨成像具有重要的价值.基于波前编码技术,将变形多值纯相位光栅与双螺旋点扩散函数相位片相结合,提出一种可以通过空间光调制器实现的具有高衍射效率的新型全息相位片的设计方法.这种全息相位片可以将样品内多个层面的分子信息以双螺旋的形式成像在同一个探测面的不同位置,在无需扫描的情况下提高双螺旋点扩散函数工程的轴向定位范围和分辨率,解决活细胞内单分子定位和示踪技术中的大景深探测难题.数值模拟表明,设计的5×5全息相位片可以将样品内25个层面上的分子信息以双螺旋的形式成像在同一探测面上的不同位置,相邻两个层面的间隔为0.5μm,实现了轴向12μm的探测范围,证明了设计的可行性.     

Acoustic beam interaction with a rigid sphere: The case of a first-order non-diffracting Bessel trigonometric beam

Mathematical expressions for the acoustic scattering, instantaneous (linear), and time-averaged (nonlinear) forces resulting from the interaction of a new type of Bessel beam, termed here a first-order non-diffracting Bessel trigonometric beam (FOBTB) with a sphere, are derived. The beam is termed “trigonometric” because of the dependence of its phase on the cosine function. The FOBTB is regarded as a superposition of two equi-amplitude first-order Bessel vortex (helicoidal) beams having a unit positive and negative order (known also as topological charge), respectively. The FOBTB is non-diffracting, possesses an axial null, a geometric phase, and has an azimuthal phase that depends on cos(?±?₀), where ?₀ is an initial arbitrary phase angle. Beam rotation around its wave propagation axis can be achieved by varying ?₀. The 3D directivity patterns are computed, and the resulting modifications of the scattering are illustrated for a rigid sphere centered on the beam's axis and immersed in water. Moreover, the backward and forward acoustic scattering by a sphere vanish for all frequencies. The present paper will shed light on the novel scattering properties of an acoustical FOBTB by a sphere that may be useful in particle manipulation and entrapment, non-destructive/medical imaging, and may be extended to other potentially useful applications in optics and electromagnetism.     

Underwater hybrid near-field acoustical holography based on the measurement of vector hydrophone array

Hybrid near-field acoustical holography(NAH) is developed for reconstructing acoustic radiation from a cylindrical source in a complex underwater environment. In hybrid NAH,we combine statistically optimized near-field acoustical holography(SONAH) and broadband acoustical holography from intensity measurements(BAHIM) to reconstruct the underwater cylindrical source field. First,the BAHIM is utilized to regenerate as much acoustic pressures on the hologram surface as necessary,and then the acoustic pressures are taken as input to the formulation implemented numerically by SONAH. The main advantages of this technology are that the complex pressure on the hologram surface can be reconstructed without reference signal,and the measurement array can be smaller than the source,thus the practicability and efficiency of this technology are greatly enhanced. Numerical examples of a cylindrical source are demonstrated. Test results show that hybrid NAH can yield a more accurate reconstruction than conventional NAH. Then,an experiment has been carried out with a vector hydrophone array. The experimental results show the advantage of hybrid NAH in the reconstruction of an acoustic field and the feasibility of using a vector hydrophone array in an underwater NAH measurement,as well as the identification and localization of noise sources.