音响里的误区

音响系统中把声频电信号转换为机械振动（声波）的电一声换能装置是扬声器系统——音箱。现代扬声器——动圈式扬声器的发明．使声音的高质量重放成为可能为了使放声效果和效率提高,扬声器需要装在一个适当的箱子里,这就是音箱。在当今世界上,音箱的品种繁多,外观各异,一般爱好者由于对相关知识了解不够．在选择音箱时很容易被某些媒体的广告宣传以及流传的说法所误导,进入误区。     

The dynamic characteristics of harvesting energy from mechanical vibration via piezoelectric conversion

As an alternative power solution for low-power devices, harvesting energy from the ambient mechanical vibration has received increasing research interest in recent years. In this paper we study the transient dynamic characteristics of a piezoelectric energy harvesting system including a piezoelectric energy harvester, a bridge rectifier, and a storage capacitor. To accomplish this, this energy harvesting system is modeled, and the charging process of the storage capacitor is investigated by employing the in-phase assumption The results indicate that the charging voltage across the storage capacitor and the gathered power increase gradually as the charging process proceeds, whereas the charging rate slows down over time as the charging voltage approaches to the peak value of the piezoelectric voltage across the piezoelectric materials. In addition, due to the added electrical damping and the change of the system natural frequency when the charging process is initiated, a sudden drop in the vibration amplitude is observed, which in turn affects the charging rate. However, the vibration amplitude begins to increase as the charging process continues, which is caused by the decrease in the electrical damping （i.e., the decrease in the energy removed from the mechanical vibration）. This electromechanical coupling characteristic is also revealed by the variation of the vibration amplitude with the charging voltage.     

机械振动分析的Matlab/Simulink仿真研究

振动在工程实际中普遍存在。为了研究和掌握振动规律,利用功能强大的仿真软件Matlab/Simulink对一个三自由度系统进行仿真,介绍Matlab/Simulink在机械振动分析中的3种建模方法,并针对第3种建模方法编写了相应的S函数和程序,可快速而有效地进行不同物理常数时的模态分析。该方法简单易行、准确可靠。     

用输液器制作"打点计时器"

用废弃的输液器制作了简易的“打点计时器”,可以在课堂上分析、判断直线运动以及研究机械振动.     

一类机械振动方程解的有界性与收敛性

的研究可参看文献[1]—[5],但这些文献未给出方程(2)解最终一致有界的估计.我们知道,方程解最终一致有界蕴含了方程周期解的存在性.此外,该界的具体估计对于方程解收敛的讨论也是必要的(参看[7]).本文给出了方程(2)解最终一致有界的估计,就其特     

车载电子设备的抗振设计与分析

分析了机械振动对车载电子设备的危害，结合振动理论，从四个方面对抗振设计的途径与方法进行了分析。     

物理学家对低语的研究得到新的结果

<正>生物物理学家们长期以来一直对于耳朵能听到极轻柔声音的能力感到惊奇。虽然已经知道内耳中数以千计的毛细胞可将入射声波产生的机械振动转换成电信号,再由大脑进行处理。但是,耳朵究竟如何实现这种极高的探测灵敏度,目前仍然是一个谜。如今,美国的物理学家们所进行的实验表明,那些毛细胞产生的自发振动可以与微弱的入射声音信号发生同步,从而使声音信号能够被探测。研究人员还提出,这种     

Quantum Transport through a Rigidly Connected Double Quantum-Dot Shuttle

We design a double quantum-dot （QD） shuttle （DQDS） model including two rigidly connected QDs that are softly linked to two leads via deformable organic materiaJs. Based on the full quantum mechanical approaches we explore the influences on the electron transport induced by the electrical and mechanical degrees of freedom. First of a/l the modified rate equations of the DQDS are derived theoretically and then a numerical investigation on the quantum transport through the DQDS is performed. For the classical DQDS, the time-dependent evolutions of the electron- occupation probabilities and the currents flowing through the DQDS show the periodic oscillations with their periods determined by the oscillation period of the DQDS. Both the mechanical oscillation amplitude and the interdot coupling can play crucial roles in adjusting the peak shapes of the currents and the probabilities. For the quantum DQDS, the current and electron-occupation probabilities of the DQDS evolve into a stationary state as time goes on, with no periodical oscillations observed. As a consequence, the sharp differences of the time-dependent properties between the c/assica/ and quantum DQDS systems are clearly demonstrated, which should be greatly helpful in designing new nanoelectromechanical devices. Also, this work is of great significance to understanding the kind of rigidly connected QD shuttle systems that have more than two QDs.