科研成果 by Type: Conference Proceedings

This paper proposes an energy recovery rectifier suitable for the use in outphasing and/or linear amplification with nonlinear components (LINC) transmitters. The proposed application oriented rectifier consists of a high-efficiency resistive rectifier and a stepped-impedance resonator (SIR) which stores the energy in order to reduce load sensitivity of the circuit. The rectifier is designed including harmonic frequency control to improve conversion efficiency and to provide a resistive input impedance at the fundamental frequency. The proposed rectifier has been implemented in hybrid technology. The fabricated circuit provides peak RF-to-DC efficiency of 73.5 % at 2.3 GHz and more than 60 % over a dynamic range of 8 dB. Furthermore, measurements show good agreement with simulation results.

This paper presents a dual-band rectifying circuit for wireless power transmission working at 2.45 GHz and 5.8 GHz. A modified dual-band matching network is adopted to realize the highly efficient dual-band rectifier. Source-pull simulations are performed, to determine the proper impedances at the two different frequencies. The proposed dual-band rectifier has been implemented and the measurements show good agreement with simulation. With a dual-band input matching network, the measurement results for an input power level of 10 mW show peak RF-to-DC efficiencies of 66.8 % and 51.5 % at 2.45 GHz and 5.8 GHz respectively.

This paper proposes a highly selective bandpass filter suitable for lowpass delta-sigma RF transmitters. The proposed filter is characterized by a low insertion loss, high selectivity and a transfer function tailored for filtering the close-up out-of-band noise of lowpass delta-sigma transmitters. The circuit design is based on a modified stub-loaded ring resonator structure. The proposed filter has been implemented and the measurements show good agreement with simulation. The proposed filter provides a fractional 3-dB bandwidth of 14.6 %, an insertion loss of less than 1.3 dB, a suppression of more than 15 dB on both sides of desired band, and a sharp cut-off frequency response.

北京大学教育学院教育技术系承办的2013年"新媒体与学习"暑期学校,从2013年7月15日到26日在北大举行。本暑期学校经过精心筹备和严密组织,在研究生院和计算中心的大力支持下,第一次采用面授加网络在线的混合式学习方式,较大幅度地增加了招生数量、扩大了受益面;借助课程管理系统较为严格地对全体学员的考勤、作业、测试和论文情况进行监控,有效地保障了教学质量;通过小组合作汇报等方式促进所有学员的参与和协作学习;采用同步课程视频直播和在线讨论等方式,确保在线学员取得与面授学生差别不大的学习体验;授课专家中一半来自海外,三分之一的授课采用全英文进行,国际化程度较高。根据考核结果,在录取的485名学员中,共有297名学员取得结业证书和学分,结业率为61.2%。51名学员获得优秀论文奖,65名学员获得优秀学员奖,39名学员获得优秀小组成员奖。对学生测验成绩的分析表明,面授学生和在线学生的以测验成绩为标志的学习效果无统计意义上的显著性差异。作为一次中规模混合式学习的研究生课程实践,本项教学研究结果对于全世界范围内正在广泛开展的大规模开放在线课程(MOOC)具有一定的借鉴和参考价值。

本文研究了含非均匀界面相球形粒子填充复合材料的有效体积模量和有效热膨胀系数。本文采用的细观力学模型是包含界面相的复合球模型,界面相位于夹杂和基体之间(如图1)。在复合球的外边界施加静水压的边界条件,并假设复合球内有一个均匀的温度变化。首先求解复合球内的位移,对于均匀相(夹杂相和基体相),位移、应变和应力有通解,而对于不均匀的界面相,直接求解位移比较困难,本文将界面相剖分为n层等厚薄层(如图2),假设每层薄层性质是均匀的,将这些薄层由内而外编号为区域1到n,并定义夹杂相和基体相为区域0和区域n+1。薄层的性能参数取为界面相内模量和热膨胀系数分布函数在每层薄层中心处的值。

阿富汗巴基斯坦乱局已久。2012年,旧乱难息,新乱渐起。美国撤军不仅耗资巨大,还面临至少两大政治考验,即如何确保安全顺利撤离,如何最大限度保存过去十年在阿富汗的战争和建设成果。美国和北约战斗部队撤离阿富汗,作为阿巴政局的重大变量,导致地区国际关系出现变化,一方面,阿富汗战争在阿巴以本土化方式继续进行,美一印一阿关系继续强化;另一方面,随着巴自主独立外交的进展,俄罗斯和伊朗因素在巴阿舞台逐渐凸显,地区局势变得更加复杂。

This paper presents a high-efficiency rectifying circuit for wireless power transmission at 2.45 GHz. A filtering and matching network designed by quarter wavelength stubs was developed for suppressing the second and the third order harmonics of 2.45 GHz, 4.9 GHz and 7.35 GHz, respectively. The measured RF-to-DC conversion efficiency is 66.5 % for an input power level of 10 mW.