High‐Performance Piezoelectric,Pyroelectric, and Triboelectric Nanogenerators Based on P(VDF‐TrFE) with Controlled Crystallinity and Dipole Alignment

Poly(vinylidenefluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)), as a ferroelectric polymer, offers great promise for energy harvesting for flexible and wearable applications. Here, this paper shows that the choice of solvent used to dissolve the polymer significantly influences its properties in terms of energy harvesting. Indeed, the P(VDF‐TrFE) prepared using a high dipole moment solvent has higher piezoelectric and pyroelectric coefficients and triboelectric property. Such improvements are the result of higher crystallinity and better dipole alignment of the polymer prepared using a higher dipole moment solvent. Finite element method simulations confirm that the higher dipole moment results in higher piezoelectric, pyroelectric, and triboelectric potential distributions. Furthermore, P(VDF‐TrFE)‐based piezoelectric, pyroelectric, and triboelectric nanogenerators (NGs) experimentally validate that the higher dipole moment solvent significantly enhances the power output performance of the NGs; the improvement is about 24% and 82% in output voltage and current, respectively, for piezoelectric NG; about 40% and 35% in output voltage and current, respectively, for pyroelectric NG; and about 65% and 75% in output voltage and current for triboelectric NG. In brief, the approach of using a high dipole moment solvent is very promising for high output P(VDF‐TrFE)‐based wearable NGs.     

A continuously tunable microwave photonic notch filter with complex coefficient based on phase modulation

A continuously tunable microwave photonic notch filter with complex coefficient based on phase modulation is proposed and demonstrated. The complex coefficient is generated using a Fourier-domain optical processor (FD-OP) to control the amplitude and phase of the optical carrier and radio-frequency (RF) phase modulation sidebands. By controlling the FD-OP, the frequency response of the filter can be tuned in the full free spectral range (FSR) without changing the shape and the FSR of the frequency response. The results show that the center frequency of the notch filter can be continuously tuned from 17.582 GHz to 29.311 GHz with FSR of 11.729 GHz. The shape of the frequency response keeps unchanged when the phase is tuned.     

星空背景下红外弱小目标的快速检测

为了实时检测天基平台上超远距离成像的星空背景下红外弱小运动目标,提出了一种基于时空域方向滤波和最小二乘预测的算法。首先,介绍了传统的方向滤波及时序上的双向滤波两者的频域理论推导,并经过对比说明了双向滤波的优点。接着,在双向滤波基础上,提出了一种新型方向滤波算法,并分析了新型算法在时耗方面的优势。然后,在分析新型方向滤波算法性能的基础上,说明了基于过门限率的图像分割方法。最后,介绍了最小二乘预测的理论,并给出了相应的跟踪算法。实验结果表明:目标的位置跟踪偏差平均约为1个像素,在图像大小为256×256像素的情况下,20帧图像的检测跟踪时间平均约为1.137 s。检测跟踪效果满足精度要求,检测时间也基本能满足超远距离成像红外系统的实时性要求。     

非线性光学新晶体——二溴三丙烯基硫脲合镉(ATCB)

本文首次报道了一种非线性光学新材料——二溴三丙烯基硫脲合镉(化学式:Cd(C_4H_8N_2S)_3Br_2,简称ATCB)晶体。介绍了采用降温法自水溶液中生长的过程。已生长出的单晶尺寸为20×20×20mm。研究了ATCB单晶的性质。     

光放大与全光中继器

本文在综述和比较了各种正在研制中的光放大器的基础上,重点分析和阐述了掺铒光纤光放大器的工作原理和基本特征。用这种光放大器作光中继器替代现行的光-电-光转换式中继器是现代光纤通信技术的一大突破。它将在海底通信、超长距离通信、光孤子通信以及CATV、LAN、光交换等系统中得到重要应用。     

免疫扫描电镜样品的简单制备方法

本文介绍一种用免疫扫描电镜技术研究病毒感染的细胞表面的简易制样方法。适当控制镀金膜的厚度(约5nm厚),即可观察到直径仅20nm胶体金标记物的二次电子图象。与近年来发展起来的背散射成象法比较,细胞表面甚至病毒粒子的形貌更为清晰。     

射频溅射CoMnNiO非晶薄膜中空穴的迁移率

测量薄膜的热电动势,很容易确定薄膜中载流子的迁移率。本研究根据CoMnNiO非晶薄膜在200—350K温区的热电动势测量和直流电导,计算了薄膜中空穴的迁移率。结果表明,330K时,薄膜中空穴的迁移率为1.25cm~2v~(-1)(?)~(-1),且具有热激活性质。由此可以推断,射频溅射CoMnNiO非晶薄膜在常温下发生跳跃导电。     

Thin ferroelectric poly(vinylidene fluoride-chlorotrifluoro ethylene) films for thermal history independent non-volatile polymer memory

In this study, we investigated the molecular and microstructures of thin poly(vinylidene fluoride-chlorotrifluoro ethylene) (PVDF-CTFE) copolymer films with three different CTFE compositions of 10, 15, 20 wt% with respect to PVDF in relation with their ferroelectric properties. All PVDF-CTFE annealed at 130 °C showed consecutive TTTT trans conformation with β type crystals while films molten and re-crystallized from a temperature above their melting points exhibited α type crystals with characteristic TGTG conformation. Microstructures of the films treated with the two different thermal histories also supported the formation of β and α type crystals with hundreds of nanometer scale sphere caps and micron level spherulites, respectively. Interestingly, PVDF-CTFE films with both α and β type crystals gave rise to relatively high remnant polarization of approximately 4 μC/cm² in metal/ferroelectric/metal capacitors regardless of the composition of CTFE. The ferroelectric polarization of a PVDF-CTFE film independent of thermal processing history allowed a wide processing window and easy fabrication protocol, resulting in a non-volatile ferroelectric field effect transistor memory which exhibited saturated hysteresis loops with the current ON/OFF ratio of approximately 10³ at ±60 V sweep and reliable data retention.     

色散管理对高速准线性传输系统性能的影响

非线性效应对高速光纤通信系统的影响已成为限制系统性能的主要因素之一.作为高速光通信的一种优选方案,准线性光纤传输技术通过精细的色散管理设计,可将非线性效应降低到可忽略的程度.对160Gb/s高速准线性光传输系统设计了预补偿、后补偿和对称补偿三种色散管理方案,并对这三种方案进行了对比、分析和优化,最后根据各方案的Q值为依据得出优选方案,为实际系统的设计提供参考意义.