Structural changes in isothermal crystallization process of polyoxymethylene investigated by time-resolved FTIR, SAXS and WAXS measurements

Structural evolution in the isothermal crystallization process of polyoxymethylene from the molten state has been investigated by carrying out the time-resolved measurements of infrared spectra and synchrotron small angle X-ray scattering (SAXS) and wide angle X-ray scattering. In case of isothermal crystallization at 130 °C, for example, the infrared bands intrinsic of folded chain crystal (FCC) morphology appeared at first, and then the bands of extended chain crystal (ECC) morphology were detected with time delay of ca. 150 s. In the SAXS experiment at 130 °C, the lamellar stacking structure of the long period of ca. 15 nm was observed at first, which changed rapidly to ca. 12 nm in a short time. The SAXS peak with the long period of ca. 6 nm started to appear with a time delay of ca. 150 s after the initial lamellae appeared and coexisted with the initially-observed 12 nm peak. Judging from the timing to detect these characteristic infrared and SAXS signals, a good correspondence was found to exist between the stacked lamellar structure of 12 nm long period and FCC morphology and between the structure of 6 nm long period and ECC morphology. The quantitative analysis was made for the SAXS data on the basis of the lamellar insertion model combined with the paracrystalline theory of the second-kind of disorder. The following structural evolution was deduced from all these results. Immediately after the temperature jump from the melt to 130 °C, the stacked lamellar structure of FCC morphology was generated at first. New lamellae were formed from the amorphous region in between the originally-existing lamellae about 150 s later, where the random chain segments bridging the adjacent lamellae were extended to form the taut tie chains, giving infrared bands of ECC morphology. This inserted lamellar structure of 6 nm long period coexisted at a population of ca. 6% with the initially-formed lamellar stacking structure of 12 nm long period. When the experiment was made at 150 °C, only the formation of stacked lamellar structure of FCC morphology was observed and the insertion of new lamella did not occur.     

Performance characteristics of a therapeutic ultrasound wire waveguide apparatus

Therapeutic ultrasound angioplasty has been investigated, clinically, by a number of researchers and represents a potentially promising therapy for the treatment of atherosclerotic lesions. To date, there has been no detailed analysis of the effect of mechanical design parameters, such as wire geometry or damping characteristics, on wire waveguide performance. An apparatus capable of delivering therapeutic ultrasound down small diameter nickel–titanium (NiTi) wire waveguides is described. The output peak-to-peak (p–p) displacements at the distal tip of a 1.0 mm diameter waveguide were measured experimentally, by means of an optical microscope and image analysis software. The output was measured for a range of waveguide lengths from 118 to 303 mm. Wire waveguide distal tip displacements as high as 98 μm (p–p) at 23.5 kHz were measured. For the range of lengths tested, the experimental measurements show the critical relationship between the length of the waveguide and the output distal tip displacements. A finite element model that can predict the resonant frequencies and distal tip displacements of various wire waveguide geometries and configurations, including the effect of damping, is presented. This numerical model has been validated against the experimental displacement data obtained. This will be a valuable design tool for ensuring the safety and effectiveness of therapeutic ultrasound angioplasty procedures.     

The properties of lattice-shifted microcavity in photonic crystal slab and its applications for electro-optical sensor

In this paper, a micro electro-optic sensor structure and its sensing technique based on lattice-shifted resonant microcavity (H0-nanocavity) in a triangular lattice photonic crystals (PhCs) slab are presented. The H0-nanocavity is formed by only laterally shifting two adjacent holes outwards slightly in the opposite direction, which can realize a nanocavity with high quality factor (Q) value to meet the requirements of practical application. The electro-optic sensor is realized in hole-array based photonic crystal slab with triangular lattice air holes infiltrated with a nonlinear optical (NLO) polymer (n_poly = 1.6) in Silicon-on-Insulator (SOI) operating in the wavelength range from 1400 nm to 1600 nm. The simulation results of PhC electro-sensitive structure show that the optical properties of PhCs can be used to design sensing devices characterized by a high degree of compactness and good resolution. The properties of the sensor are analyzed and calculated using the plane-wave expansion (PWE) method and simulated using the finite-difference time-domain (FDTD) method. The simulation results display that the resonant wavelength of the mode localized in the microcavity shifts its spectral drop position following a linear behavior when a driving voltage ranging between 0.0 V and 3.2 V is applied, and the sensitivity of 31.90 nm/V is observed.     

自主水下航行器折叠天线设计

通过对水下机器人的主体外形以及传统水下机器人的外附体进行建模,运用CFD流体软件对其进行仿真分析,发现自主水下航行器外附体中,天线产生阻力最大.天线是自主水下航行器必不可少的通信模块.针对天线带来的大阻力问题,设计出两种折叠天线机构.运用ADAMS软件对比了两种折叠天线机构运动性能参数;运用SolidWorks的应力仿...     

基片集成波导正弦渐变槽单脉冲天线

为拓展工作带宽,以传统正反渐变槽天线为基础,利用基片集成波导馈电,该文提出了两种高增益、宽频带的正弦渐变槽天线。利用矩形波导3 dB定向耦合器和90移相器工作原理设计了半模基片集成波导单脉冲馈电网络,进而得到了对称型和非对称型正弦渐变槽单脉冲天线,带宽均超过了3.0 GHz,带内和波束最大增益在9.0 dBi左右,差波束零深在10.0 GHz处均低于-20 dB。其中,非对称型正弦渐变槽单脉冲天线具有更宽的工作频带和更平稳的天线增益,可以广泛应用于微波定向探测系统中。     

非对称十字孔双脊波导定向耦合器的设计

借鉴波导定向耦合器的设计原理,采用双脊波导的形式（本文采用标准双脊波导WRD650型号）设计大功率宽频带定向耦合器。由于双脊波导相比于矩形波导,最低模式的截止频率更低,单模工作的频带更宽,特性阻抗更低,所以采用双脊波导的形式比矩形波导在带宽方面更有优势。波导耦合器耦合方式有很多种,最常用的有小孔耦合和缝隙耦合,本文采用非对称十字孔耦合的方式,并与等孔径分布和切比雪夫分布的圆孔耦合比较来确定非对称十字孔耦合方式,在耦合平坦度、方向性方面有更好的改进。利用电磁仿真软件进行仿真对比其结果,通过一些具体措施改善双脊波导定向耦合器的性能,使定向耦合器的各种设计指标达到要求。     

Fabrication and characterization of large-core Yb/Al-codoped fused silica waveguides using dry etching

A deep inductively coupled plasma etching process was developed as a part of a continuous effort to develop an all-silica on-chip platform for high-power optical devices. Combined F and Cl based etching chemistry was found most suitable since silica matrix and Al doping are generally etched using different chemistries. First large-core (∼20 × 20 μm) Yb/Al-codoped fused silica waveguides on pure silica substrate were successfully fabricated, featuring ∼1 dB/cm optical propagation loss.     

Alkaline aluminum phosphate glasses for thermal ion-exchanged optical waveguide

Alkaline aluminum phosphate glasses (NMAP) with excellent chemical durability for thermal ion-exchanged optical waveguide have been designed and investigated. The transition temperature Tg (470 °C) is higher than the ion-exchange temperature (390 °C), which is favorable to sustain the stability of the glass structure for planar waveguide fabrication. The effective diffusion coefficient D_e of K⁺–Na⁺ ion exchange in NMAP glasses is 0.110 μm²/min, indicating that ion exchange can be achieved efficiently in the optical glasses. Single-mode channel waveguide has been fabricated on Er³⁺/Yb³⁺ doped NMAP glass substrate by standard micro-fabrication and K⁺–Na⁺ ion exchange. The mode field diameter is 9.6 μm in the horizontal direction and 6.0 μm in the vertical direction, respectively, indicating an excellent overlap with a standard single-mode fiber. Judd–Ofelt intensity parameter Ω₂ is 5.47 × 10⁻²⁰ cm², implying a strong asymmetrical and covalent environment around Er³⁺ in the optical glasses. The full width at half maximum and maximum stimulated emission cross section of the ⁴I_13/2 → ⁴I_15/2 are 30 nm and 6.80 × 10⁻²¹ cm², respectively, demonstrating that the phosphate glasses are potential glass candidates in developing compact optoelectronic devices. Pr³⁺, Tm³⁺ and Ho³⁺ doped NMAP glasses are promising candidates to fabricate waveguide amplifiers and lasers operating at special telecommunication windows.     

2.5Gb/s光外调制器及驱动器

文章对光外调制作了原理及实验上的分析,着重研究作为驱动器的大功率宽带放大器。对２．５Ｇｂ／ｓＮＲＺ伪随机码对放大器的低端截止频率和高端截止频率的要求进行了理论分析。提出并实验了几种放大器高频补偿技术,取得了好的效果。为满足输入输出阻抗为５０Ω的要求采用了共面波导计算方法,以确定印刷电路板导线尺寸。最后对光外调制器输出波形进行了测试。     

Numerical Simulation of Waveguides of Arbitrary Cross-Section

Finite difference equations are derived for the simulation of dielectric waveguides using an H_z-E_z formulation defined on a nonuniform triangular grid. The resulting equations may be solved as a banded eigenproblem for waveguide structures of arbitrary shape composed of regions of piecewise constant isotropic dielectric, and all transverse fields then computed from the solutions. Benchmark comparisons are presented for problems with analytic solutions, as well as a sample calculation of the propagation loss of a hollow Bragg fiber.