Search

Due to the high-accuracy requirement of dimensional measurements for thin-walled structures of additive manufacturing products, the grayscale distribution of the industrial CT image and the location of the structural boundaries in the image space were derived. In addition, the validity of the half-height-width method and the maximum gradient method was compared and analyzed, and the limit of the dimensional measurement based on CT imaging was calculated. The thin-walled structures with different thicknesses were calibrated, and measured by industrial CT scanning and imaging experiment. The results show that the half-height-width method generates a smaller error compared with the maximum gradient method, when the thickness of the thin-walled structures is larger than the measurement limit of the CT system. Finally, the measurement limit can be obtained by numerical simulations based on the edge spread function with experimental measurements.

The application and new development trend of metal additive manufacture technique were introduced, as well as the characteristic and NDT difficulty of metal additive manufacture products. The research progress of NDT was analyzed in emphasis, including the classification of metal additive manufacture technique, the characteristics of defect and microstructure, the influence of defects on mechanical properties, the latest development of NDT methods and standards. Based on that, the key issues that will be focused were summarized at last, that is the application of new NDT methods, on-line monitoring technology, numerical simulation, measurement and characterization of stress, as well as the establishment and development of NDT standards.

In this paper, we, respectively, discuss the finite-time passivity (FTP) and finite-time synchronisation (FTS) of multi-output coupled complex networks (MOCCNs) under directed topology and undirected topology. Firstly, through designing an appropriate state feedback controller and adaptive state feedback controller, using some inequality techniques, we investigate the FTP of MOCCNs. Furthermore, we study the relationship between the FTP and FTS of the MOCCNs, and establish the sufficient conditions to ensure that MOCCNs can realise FTS based on the result we get about FTP. Lastly, we verify the proposed FTP and FTS criteria using two numerical examples. [ABSTRACT FROM AUTHOR]

In this paper, passivity is used to investigate the formation control problem for second-order multi-agent systems (MASs) with linear or nonlinear coupling. Firstly, the passivity of a single agent is studied by selecting appropriate adaptive state feedback controllers. Moreover, in order to ensure that MASs with nonlinear intrinsic dynamics and linear/nonlinear coupling can converge to a predefined formation, some appropriate control schemes are designed based on the passivity of a single agent. In addition, the passivity-based formation problem for the MASs with double-integrator dynamics is also studied. Finally, the effectiveness of the proposed formation control strategies is demonstrated through two numerical examples. [ABSTRACT FROM AUTHOR]

Based on the Fourier transform infrared spectrometer, a system for measuring the loss spectrum of hollow fiber is established. Loss spectra can be measured for hollow fibers with length ranging from several centimeters to 3 m. Two kinds of light source coupler are designed and fabricated for achieving stable coupling and a repeatable spectrum. One is a short waveguide, and the other is a tapered tube. Both are inner-coated with a silver layer and they are of the same inner diameter at the output end as the measured hollow fiber. Characteristics of the measuring system are discussed theoretically and experimentally when using the two couplers. Several kinds of hollow fibers are measured, and the properties of the loss spectra are discussed. The measured loss value is shown to be dependent on the output divergence angle of the coupler. The tapered coupler has a larger output divergence and causes higher measured loss than that of the waveguide coupler. [c] 2010 Optical Society of America OCIS codes: 230.7370, 310.6860, 120.7000, 060.2270, 120.6200.

We report the transmission characteristics of infrared hollow fiber with multi- AgI and Si[O.sub.2] inner-coating layers in the mid-infrared region. A three-dielectric-layer hollow glass fiber with a Si[O.sub.2]--AgI--Si[O.sub.2]--Ag structure was fabricated and low-loss property was obtained in the mid-infrared region. The Si[O.sub.2] films were coated by use of the liquid-phase coating method and a semi-inorganic polymer was used as the coating material. For deposition of the AgI film between the two Si[O.sub.2] films, a silver film was first plated by use of the silver mirror reaction method. Then the iodination process was conducted to turn the silver layer into silver iodide. A calculation method was also developed to estimate the film thickness of dielectric layers in each fabrication step according to the position of loss peaks in the measured loss spectra. Good agreement between calculated and measured loss spectra was demonstrated by taking into consideration material dispersion and surface roughness of inner-coating films. OCIS codes: 060.2390, 230.4170, 040.6040, 160.5470, 260.2030.

Silver-clad stainless steel pipe is used as the supporting tube for the fabrication of infrared hollow fiber. The hollow fiber has high mechanical strength and is highly durable for use in the medical sterilization process. Film of a cyclic olefin polymer layer or silver iodide (AgI) was coated internally to reduce the transmission loss. A liquid-filling method is proposed for coating the AgI layer. Multiple coating processes proved to be effective to increase the AgI film thickness. A treatment of sodium thiosulfate water solution is also proposed to reduce the film thickness. The film thickness can be accurately controlled by combining the coating and decoating techniques. A loss of less than 0.2 dB was obtained for C[O.sub.2] laser light for a hollow pipe with a length of 280 mm and an inside diameter of 0.75 mm. OCIS codes: 060.0060, 120.7000, 230.7370, 310.6860, 060.2270.

A novel optical fiber hydrogen sensor based on the dielectric/metal coated hollow fiber structure is proposed. The palladium (Pd) and ethylene-vinyl acetate (EVA) layers are sequentially coated on the inner surface of the hollow core of the silica capillary to fabricate the EVA/Pd coated hollow fiber sensor. Theoretical ray transmission model is carried out to analyze the influence of the thicknesses of the Pd and EVA films. The experimental transmission spectra of the proposed sensor filled with hydrogen gas of different concentrations are measured. The experimental results show that the interference peak in the spectrum has a red shift with the increase of hydrogen concentration. Then the hydrogen concentration can be obtained by measuring the wavelength of the interference peak. In the range of 0–4% hydrogen concentration, the total shift is 10.64nm and the average sensitivity is 2.66 nm/%. Compared to other optical fiber hydrogen sensors, the proposed sensor has the advantages of simple structure, easy fabrication, low cost, high sensitivity and good safety performance. [ABSTRACT FROM AUTHOR]

A method is proposed to evaluate the material dispersion of dielectric film in dielectric-coated silver hollow fiber. Cauchy's formulas that characterize the dispersion property were obtained for several commonly used dielectric materials by using the measured data of loss spectra of the hollow fibers. The wavelengths of the loss peaks and valleys in the loss spectra can be predicted more accurately when taking into consideration of the material dispersion. The derived Cauchy's formulas play an important role in the design of infrared hollow fiber for multiwavelength delivery. OCIS codes: 060.2280, 230.7370, 310.6860, 260.2030.

The techniques for fabricating a hollow optical fiber with an inner silver layer and a cyclic olefin polymer (COP) layer have been improved to reduce the surface roughness of these two layers. The loss spectrum was thereby drastically reduced over a wide wavelength range, from visible to near infrared. Optimization of the COP layer thickness resulted in low loss simultaneously at several key laser wavelengths. Infrared hollow fiber with low loss was developed for Er:YAG and Nd:YAG lasers. It can also deliver green and red pilot beams with low loss. Use of this fiber in therapeutic and pilot lasers should prove useful for research and development in laser medicine. OCIS codes: 230.7370, 170.3890, 310.1860, 140.7300.

We have experimentally quantified calculus fragmentation by Er:YAG laser light. Er:YAG laser light was delivered to an underwater target through a sealed hollow optical fiber. Fragmentation efficiency was obtained for an alumina ball used as a calculus model when sealing caps with various focusing effects were used. Three types of human calculus were analyzed, and their absorption properties at the wavelength of Er:YAG laser light were obtained. The relationships among the absorption properties, calculus constituents, and fragmentation efficiency are discussed. OCIS codes: 170.0170, 170.3890, 230.7370, 140.3500.

The penetration depth in water was measured for Er:YAG laser light in a high density relevant to clinical applications. Various types of focusing elements were used to guide the light efficiently. We found that the transmission distance depended strongly on the beam shape in the water. When we used a plano-convex type of focusing cap, the penetration depth was larger than that when a dome- or ball-type cap were used. OCIS codes: 120.4820, 140.3500, 230.7370, 170.3890.

A major advantage of fiber-optic beam delivery in laser materials processing is the ability to guide the laser power to the location where it is needed, leaving the laser itself remote and protected from the process. This is of special importance if the processing is to be performed in a hazardous environment. Particular problems are faced by the nuclear industry where weld repair and surface treatment work are required inside radioactive installations. By use of fiber beam delivery, only part of the delivery system and effector optics become contaminated, but the expensive laser system does not. However, in many cases the region where repair is required is not only radioactive but has only limited physical access, e.g., inside tubes or into corners, which prevents use of standard effector optics. We present a new design to deal with such constraints of a 2-mm outer diameter employing a hollow waveguide and gas shielding. This design is optically characterized and its performance assessed in welding and surface treatment applications. The potential of this compact effector optics in limited physical access situations is clearly demonstrated. OCIS code: 140.3390.

An Er:YAG laser light delivery system composed of a polymer-coated silver hollow waveguide and a quartz sealing cap has been developed for calculus fragmentation. Sealing caps with various distal-end geometries were fabricated, and the focusing effects of these caps for Er:YAG laser light were measured both in air and in water. Owing to the high power capability of the quartz sealing caps, a beam of Er:YAG laser light with an output energy of 200 mJ and a repetition rate of 10 Hz was successfully transmitted in saline solution by use of the system. Calculus fragmentation experiments conducted in vitro showed that the delivery system is suitable for medical applications in lithotripsy. We also found that the cap with a focusing effect is more effective in cutting calculi. The deterioration of the sealing caps after calculus fragmentation is also discussed. OCIS codes: 140.3070, 160.5470, 230.7370, 170.7230, 170.1610.

We propose sealing techniques for medical hollow fibers to protect the inner surface of fibers from debris or water that scatters from targets. First, hollow fibers are sealed with a film of polymer that is easily formed by use of a dipping technique. The transmission loss of 20-[micro]m-thick sealing film was 0.2 dB for Er:YAG laser light, and the maximum energy that is available for the film was 180 mJ. Second, a sealed glass cap was applied to the output end of hollow fiber. The silica-glass cap with a wall thickness of 400 [micro]m shows a transmission loss of 0.5 dB and was not damaged by radiation of 400-mJ energy pulses.

Flexible hollow fibers for delivery of the second, third, and fourth harmonic pulses of Q-switched Nd:YAG lasers are introduced. For the doubled (532-nm) wavelength, we fabricated a hollow fiber with an internal metal and polymer film by using a silver-mirror plating and a liquid-phase-coating method. For tripled (355-nm) and quadrupled (266-nm) Nd:YAG in the ultraviolet region, we fabricated aluminum hollow fibers with or without an internal polymer layer by using the metal-organic chemical-vapor deposition method. Both types of fiber show high stability for the transmission of high-peak power laser pulses with low transmission losses. OCIS codes: 060.2280, 060.2310.