3D high-resolution acoustic imaging of the sub-seabed

Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable frequency-modulated source signature to produce vertical seismic reflection cross-sections of the sub-seabed. Here a 3D Chirp system is described that operates in the frequency range of 1.5-13 kHz, to produce a three-dimensional image of the sub-seabed, with typical penetration of 10-30 m and decimetric horizontal and vertical resolution. The system design incorporates a rigid frame that contains the Chirp source array together with 60 receiver elements, with positioning provided by an integrated real-time-kinematic (RTK) global positioning system (GPS). The system can be surface towed from a small survey vessel and can be applied to targets of marine geological, engineering, archaeological and defence interest. Data acquisition and processing are described for a case study which images a buried engineering structure in the Port of Southampton.     

脉冲声测量技术在光纤水听器测量中的应用

本文介绍了脉冲声测量技术在非消声水池中光纤水听器测量中的应用。理论上分析了脉冲宽度的选择标准，并搭建了实验系统，对某一光纤水听器的声压灵敏度进行了测量，实验结果验证了该技术用于光纤水听器测量的可行性。     

Automatic 3D scanning surface generation for microphone array acoustic imaging

This work presents a new technique for automatically generating the 3D scanning surface for acoustic imaging using microphone arrays. Acoustic images, or maps, of sound coming from spatially distributed sources, may be generated from microphone array data using algorithms such as beamforming. Traditional 2D acoustic maps can contain errors in the near-field if the object being imaged has a 3D shape. It has been shown that using the 3D surface geometry of an object as a scanning surface for beamforming can provide more accurate results. The methods used previously to generate this 3D scanning surface have either required existing CAD (Computer-Aided Design) models of the object being acoustically imaged or have required separate equipment which is generally bulky and expensive. The new method uses one or more cameras in the array, a data projector, and structured light code to automatically generate the 3D scanning surface. This has the advantage that it is inexpensive, can be incorporated as an add-onto existing microphone arrays, has short scan time, and is capable of being extended to imaging dynamic scenes. This technique is tested using beamforming and CLEAN-SC (CLEAN based on spatial Source Coherence) algorithms for a spherical array and an Underbrink multi-arm spiral array. For sound sources located about 1.2 m from the array, the mean position errors obtained are 6 mm. This is a quarter of the diameter of the mini-speakers being used as a sound sources.     

Elastic properties of composites: periodical homogenisation technique and experimental comparison using acoustic microscopy and resonant ultrasonic spectroscopy

The macroscopic elastic properties of two composites (Duralumin/air and Duralumin/tungsten carbide (WC)) have been calculated using periodical homogenisation methods and the elastic properties of each phase (measured by high frequency acoustic microscopy). In order to check the validity of such an approach, acoustical resonant spectroscopy has also been applied. Thanks to the comparison between the resonant frequencies predicted and measured, two major conclusions have been obtained: the homogenisation method is very accurate for the composite Duralumin/air, but not for the Duralumin/WC sample: the experimental results are not in very good agreement with the simulation. This result can be then explained by the major role of interfacial state between Duralumin and tungsten carbide.     

镀镍碳纤维复合材料的电磁脉冲屏蔽效能

研究了连续碳纤维表面化学镀镍工艺,并利用扫描电子显微镜（SEM）,X射线衍射仪(XRD)分析了纤维的微观形貌、镍层成分和镍层结构。测试了镀镍碳纤维和镀镍碳纤维复合材料的导电性能。制备了镀镍纤维为增强材料的抗电磁脉冲复合材料。在场强大于20 kV/m的环境下测试了复合材料在频率为1.3,2.8,4.3,9.4 GHz处的高功率微波电磁脉冲屏蔽效能。结果表明复合材料的高功率微波电磁脉冲屏蔽效能均大于60 dB,其中2.8 GHz下出现最大值91 dB。     

High-resolution non-invasive 3D imaging of paint microstructure by synchrotron-based X-ray laminography

The characterisation of the microstructure and micromechanical behaviour of paint is key to a range of problems related to the conservation or technical art history of paintings. Synchrotron-based X-ray laminography is demonstrated in this paper to image the local sub-surface microstructure in paintings in a non-invasive and non-destructive way. Based on absorption and phase contrast, the method can provide high-resolution 3D maps of the paint stratigraphy, including the substrate, and visualise small features, such as pigment particles, voids, cracks, wood cells, canvas fibres etc. Reconstructions may be indicative of local density or chemical composition due to increased attenuation of X-rays by elements of higher atomic number. The paint layers and their interfaces can be distinguished via variations in morphology or composition. Results of feasibility tests on a painting mockup (oak panel, chalk ground, vermilion and lead white paint) are shown, where lateral and depth resolution of up to a few micrometres is demonstrated. The method is well adapted to study the temporal evolution of the stratigraphy in test specimens and offers an alternative to destructive sampling of original works of art.     

镀镍碳纤维复合材料的电磁脉冲屏蔽效能

研究了连续碳纤维表面化学镀镍工艺,并利用扫描电子显微镜(SEM),X射线衍射仪(XRD)分析了纤维的微观形貌、镍层成分和镍层结构。测试了镀镍碳纤维和镀镍碳纤维复合材料的导电性能。制备了镀镍纤维为增强材料的抗电磁脉冲复合材料。在场强大于20kV/m的环境下测试了复合材料在频率为1.3,2.8,4.3,9.4GHz处的高功率微波电磁脉冲屏蔽效能。结果表明复合材料的高功率微波电磁脉冲屏蔽效能均大于60dB,其中2.8GHz下出现最大值91dB。     

Interfacial debonding and slipping of carbon fiber-reinforced ceramic-matrix composites under two-stage cyclic loading

In this paper, the interface debonding and frictional slipping of carbon fiber-reinforced ceramic-matrix composites (CMCs) under two-stage cyclic fatigue loading have been investigated using micromechanics approach. Under cyclic fatigue loading, the fiber/matrix interface shear stress degrades with increasing cycle number due to interface wear. The synergistic effect of interface wear and fatigue loading sequence on interface debonding and frictional slipping has been analyzed. Based on the fatigue damage mechanism of fiber slipping relative to matrix, in the interface debonded region, upon unloading and subsequent reloading, the interface debonded length and interface slip lengths, i.e. interface counter-slip length and interface new-slip length, are determined using the fracture mechanics approach. The relationships between interface debonding, interface slipping, interface wear, cycle number, and different loading sequences are determined. There are two types of fatigue loading sequences considered, i.e. (1) cyclic loading under low peak stress for N₁ cycles, and then high peak stress; and (2) cyclic loading under high peak stress for N₁ cycles, and then low peak stress. The effects of peak stress level, interface wear, cycle number, and loading sequence on interface debonding and frictional slipping of fiber-reinforced CMCs have been analyzed. The fatigue hysteresis loops of cross-ply carbon fiber-reinforced silicon carbide composite corresponding to different cycle number under two-stage cyclic fatigue loading have been predicted.     

3D depth-coded photoacoustic microscopy with a large field of view for human skin imaging

Photoacoustic(PA) microscopy comes with high potential for human skin imaging, since it allows noninvasively high-resolution imaging of the natural hemoglobin at depths of several millimeters. Here, we developed a PA microscopy to achieve high-resolution, high-contrast, and large field of view imaging of skin. A three-dimensional(3D) depth-coding technology was used to encode the depth information in PA images, which is very intuitive for identifying the depth of blood vessels in a two-dimensional image, and the vascular structure can be analyzed at different depths. Imaging results demonstrate that the 3D depth-coded PA microscopy should be translated from the bench to the bedside.     

Application of spatially and temporally apodized non-confocal acoustic transmission microscopy to imaging of directly bonded wafers

Application of a line-shaped point spread function (PSF) to imaging of void defects in directly bonded wafers is considered. Two non-confocally adjusted spherical transducers are employed to implement an acoustic microscope operating in transmission with a time dependent point spread function, whose shape is optimized by both temporal apodization of the received signal and spatial apodization of the transducer aperture. Strong imaging artifacts resulting from the generation and detection of edge waves are eliminated in this way. It is shown by several examples that only a broadband system can be utilized in order to obtain a line-shaped PSF suitable for imaging.     

A new technique in ramp response for acoustic imaging of underwater objects

The ramp response of an underwater object yields information about the object's size, orientation and geometrical shape. Based on the physical optics approximate, a simple relation between ramp response and the profile function has been obtained in the illuminated region of the object. The same relation in the shadow region has also been presented. With the profile data from three arbitrary looking angles, the 3-D image of the object can be generated through the technique known as “approximate limiting surface”. Instead of the FFT method, a new technique has been developed to obtain a fairly good ramp response. Several different non-dimensional frequency range cases have been discussed for sphere and ellipsoid. And 3-D images have been shown. The study indicates that a fairly good ramp response can be obtained with less frequency domain data.     

Experimental investigation of the pulse inversion technique for imaging ultrasound contrast agents

The application of ultrasound contrast agents aims to detect low velocity blood flow in the microcirculation. To enhance discrimination between tissue and blood containing the contrast agent, harmonic imaging is used. Harmonic imaging requires the application of narrow-band signals and is obscured by high levels of native harmonics generated in an intervening medium. To improve discrimination between contrast agent and native harmonics, a pulse inversion technique has been proposed. Pulse inversion allows wide-band signals, thus preserving the axial resolution. The present study examines the interference of native harmonics and discusses the practical difficulties of wide-band pulse inversion measurements of harmonics by a single transducer. Native harmonics are not eliminated by pulse inversion. Furthermore, only even harmonics remain and are amplified by 6 dB, alleviating the requirement for selective filtering. Finally, it is shown that the contaminating third harmonic contained in the square wave activation signal leaks through in the emitted signal. The spectral location of the contaminating third harmonic is governed by the transducer spectral characteristics while the location of the native and contrast agent second harmonics is not. Thus the contaminating third harmonic and the native and contrast agent second harmonics may overlap and interfere. Optimal discrimination requires a balance between maximal sensitivity for the second harmonic at reception and minimal interference from the contaminating third harmonic.     

High-resolution cardiac imaging using an interleaved 3D double slab technique

A three-dimensional (3D) gradient-echo sequence with interleaved double-slab excitation was developed and optimized for the requirements in pediatric cardiac imaging. For this purpose high contrast between blood and myocardium signal should be obtained without the use of contrast agents. An acceptable measuring time for a large region examined with high spatial resolution should be achieved as well, especially with regard to the small structures of the heart and vessels of infants. The presented approach works with gradient moment nulling and a short echo time of 5.5 ms resulting in generally high signal intensity and only minor signal losses due to turbulent flow. The sequence allows simultaneous ECG-gated recording of two separately excited slabs with small thickness (10 mm) and with a distance of several centimeters between them. Thus, common effects of presaturation in 3D imaging can be avoided, although a relatively short measuring time is achievable. In order to get a 3D data set with good signal homogeneity of blood and of the other structures across a large volume of interest several double-slab measurements with suitable positions must be performed. The latter aspect is especially important for postprocessing techniques as multiple planar reconstruction and maximum intensity projection. Examples of applications of the new technique and appropriately postprocessed images are presented allowing demonstration even of subtle cardiac malformations.     

井下前视声波偏移聚焦成像方法

介绍了一种可用于检测油井套管形态的前视声波成像方法。本方法采用由多个独立阵元组成的面阵式换能器,每个阵元均能独立发射,将所有阵元接收的波形数字化后,采用偏移聚焦成像方法,实现井下油井套管形态的前视声波三维成像。本文对数字偏移聚焦成像的基本原理进行了介绍,并用数值模拟和成像实验进行验证。表明本方法能够在阵元个数有限的情况下得到具有较高分辨率的图像,并可以简化井下仪器的电路结构。     

An acoustic imaging system of migration technique used in borehole

In order to detect the damage of casing boreholes, an acoustic imaging method with a two-dimensional ultrasonic array was presented. Each element of the array independently emits down ultrasonic waves, the echoes received by all elements are sampled and transmitted to a computer on ground surface, where the dynamic migration method is used to form a 2 or 3-dimensional image of the situation in the borehole. The numerical simulation and experiment are conducted that demonstrate a high imaging accuracy with a small number of elements used in array. Since the delay circuits used in the traditional phased array imaging system is not needed in this system, and all data process could be completed in a ground system. the complexity and the volume of system in borehole may be significantly simplified, which is critical to the borehole instrument.     

Subsurface defect of amorphous carbon film imaged by near field acoustic microscopy

Amorphous carbon films were examined by low frequency scanning-probe acoustic microscopy (LF-SPAM). Local elastic properties as well as topography were imaged in the acoustic mode. Two kinds of subsurface defects were revealed by the LF-SPAM method. The influence of the subsurface defects on the elastic properties was also discussed. The ability to image subsurface defects was dependent on the scan area and the scan speed. Our results showed that the low frequency scanning-probe acoustic microscopy is a useful method for imaging subsurface defects with high resolution. PACS 68.37.Ps; 68.37.Uv; 61.43.Dq; 68.35.Gy     

单基阵三维纯方位水下信标声学定位方法

针对水下静止信标的纯方位定位问题,提出一种基于单基阵平台纯方位信息的定位方法。通过水下无人运动平台两次量测的空间角度信息建立非线性方程,利用拟牛顿迭代方法实现稳定数值求解。同时,对量测信息进行预处理和定位后置处理,以进一步提高算法的稳定性和精度。利用计算机模拟水下声传播环境进行定位仿真,结果表明,基于常规波束形成的方位估计结果,在方位量测误差标准差为1°时,所提方法的定位结果相对误差可达3.5%以内。同时,研究了不同方位量测误差条件下、不同海深测量误差条件、观测平台和目标不同态势下定位算法的定位性能。结果表明,此方法可用于对水下静止信标的声学定位,且鲁棒性好。     

Properties and microstructure of composites derived from polycaproamide and multiwall carbon nanotubes

Composites were synthesized by anionic in situ polymerisation of ?-caprolactam in the presence of 0.1–5.0% of multiwall carbon nanotubes. It is found that nanotube filling increases rigidity and improves the friction characteristics of polycaproamide. The friction coefficient decrease is especially significant at a nanotube concentration of 0.1%. It is shown that nanotubes affect the composite film microstructure.     

Occlusion removal technique for improved recognition of partially occluded 3D objects in computational integral imaging

In this paper, we propose an occlusion removal technique for improved recognition of 3D objects that are partially occluded in computational integral imaging (CII). In the reconstruction process of a 3D object which is partially occluded by other objects, occlusion degrades the resolution of reconstructed 3D images and thus this affects negatively the recognition of a 3D object in CII. To overcome this problem, we introduce a method to eliminate occluding objects in elemental image array (EIA) and the proposed method is applied to 3D object recognition by use of CII. To our best knowledge, this is the first time to remove occlusion in CII. In our method, we apply the elemental image to sub-image (ES) transform to EIA obtained by a pickup process and those sub-images are employed for occlusion removal. After the transformation, we correlate those sub-images with a reference sub-image to locate occluding objects and then we eliminate the objects. The inverse ES transform provides a modified EIA. Actually, the modified EIA is considered to be an EIA without the object that occludes the object to be reconstructed. This can provide a substantial gain in terms of the image quality of 3D objects and in terms of recognition performance. To verify the usefulness of the proposed technique, some experimental results are carried out and the results are presented.     

3D imaging of a rice pollen grain using transmission X‐ray microscopy

For the first time, the three‐dimensional (3D) ultrastructure of an intact rice pollen cell has been obtained using a full‐field transmission hard X‐ray microscope operated in Zernike phase contrast mode. After reconstruction and segmentation from a series of projection images, complete 3D structural information of a 35 µm rice pollen grain is presented at a resolution of ～100 nm. The reconstruction allows a clear differentiation of various subcellular structures within the rice pollen grain, including aperture, lipid body, mitochondrion, nucleus and vacuole. Furthermore, quantitative information was obtained about the distribution of cytoplasmic organelles and the volume percentage of each kind of organelle. These results demonstrate that transmission X‐ray microscopy can be quite powerful for non‐destructive investigation of 3D structures of whole eukaryotic cells.