基于单片机计数计时仪的设计与制作

该设计以三线摆测量转动惯量实验为例.文章详细介绍了单片机作为控制核心的计数计时仪器制作方法,并采用光电传感器作为计数装置,解决了传统仪器中激光发射器和接收器的调整问题,简化了仪器的操作步骤.     

单摆振动周期随摆角变化实验之讨论

本文就如何选择恰当的计时仪器来测量单摆振动周期随摆角变化的问题进行了讨论。主要说明要根据具体的实验装置和具体的实验内容合理地选择仪器的灵敏度。     

使用光电传感器自制计数计时仪

本设计采用光电传感器作为计数装置,解决了传统仪器中激光发射器和接收器的调整问题,简化了仪器的操作步骤。同时选用51单片机作为控制核心,接收计数信号,处理按键信息,利用定时器计时,输出计数和计时结果到数码管进行显示。通过自制实验仪器,可提高教师业务能力,并减轻了实验仪器更新换代的压力。     

数字毫秒计的故障排除

数字毫秒计是气垫导轨的重要附属计时仪器,它和光电门所组成的光控计时电路,具有较高的灵敏度.因而,实验前应仔细检查电源电压是否正常和测试光电门所属的光控电路是否有断路故障.以保证实验中毫秒     

气垫导轨上运动物体加速度测量方法的改进

利用计数计时测速仪测量气垫导轨上滑块运动的加速度,其测量精度直接依赖于2个光电门之间距离的测量,而在实验中该距离的测量往往不易达到很高的精度,致使加速度的测量精度不高.对计数计时测速仪的电路和单片机程序稍加修改,使之能测出滑块从一个光电门运动到另一个光电门所需时间,就无需测量2个光电门之间的距离,因而提高了加速度的测量精度,节约单片机的资源并缩短运行时间.     

如何选择数字计时器的时基

数字计时器是物理实验中经常使用的一种精度较高的数字式计时仪器,每种的型号仪器都有几个时基选择档,不同的时基选择档对应不同的计时精度和最大计时范围。学生在实验中由于不会选择时基档,经常导致实验出错。 比如滑块通过两个光电门的实验时间是3.689s,选择0.1ms时基档,显示窗显示的结     

用磁化率测量普朗克常量的新方法

基于普通物理实验仪器———磁天平,开发出用于近代物理实验测量普朗克常量的简易新方法.     

非接触千分尺的设计及实验验证

利用大学物理实验室中使用的分光计并结合线阵CCD等常用实验仪器,设计了一个可以同时实现非接触测量玻璃厚度和折射率的实验方案.通过不确定度的分析,给出了方案满足千分尺测量精度的仪器要求.在此基础上,通过实验具体地测量了一平板玻璃的厚度和折射率,实验结果证明了设计方案的可行性.     

用恒流法自制仪器精确测定液体的黏度

介绍了用恒流法自制仪器精确测定液体的黏度.该自制仪器,能有效地保证底部的密封性、液体水位恒定和可操作性.另外,还增设一个玻璃管连通器,并附加一根标尺和游标,可使液体水位的测量精确度提高.在接毛细管输出液体的量筒处加上光电计时,可使测量液体的流速的精确度提高.再将相关数据送入已编好程序的电子仪器进行计算并显示出黏度.另外该仪器可调换不同管径的毛细管,因此应用本方法能快速准确地测量多种液体的黏度.     

单摆实验仪的改进

针对传统单摆实验,小球在摆动时容易产生圆锥摆现象,导致周期测量不准,影响实验结果的准确性.对此,本文采用双线摆取代单线摆,避免小球产生圆锥摆现象;同时采用光电门对摆动进行计时和计数,减少人为误差的引入,进而提高实验精度.     

Artificial sieves for quasimassless particles

Brownian motion on a symmetric vibrated periodic substrate is shown to be extremely sensitive to the particle mass even in the regime of large damping. This phenomenon is the most apparent for high vibration frequencies, a condition of technological interest, which is investigated here both analytically and numerically. When plotted versus the damping constant, both the particle mobility and the diffusion coefficient develop sharp (correlated) peaks, thus suggesting efficient schemes for separating submicron particles according to their mass or geometry.     

Regularities in penetration of electromagnetic waves through metallic magnetic films

Penetration of millimeter electromagnetic waves through permalloy films under magnetic resonance conditions is studied experimentally and theoretically. Measurements are taken on film samples from 40 to 200 nm in thickness in a frequency range from 26 to 38 GHz. Magnetic resonance, antiresonance, and spin-wave resonance are observed. The resonance spectrum is reconstructed. The Gilbert damping constant is determined for a series of films. It is shown that the damping constant decreases upon an increase in the film thickness. The resonance line profile is calculated, and the dependences of resonance line amplitude and width on experimental conditions and material parameters of the film are determined.     

Interband damping of long-wavelength bulk plasmons

The contribution of interband transitions of electrons to the damping of plasma oscillations in a metal is investigated in the long-wavelength limit using two different approximation schemes: (i) a method using sum rules and (ii) a perturbative approach. We show that the first method leads to unphysical results, but the perturbation theory is justified for those metals in which the lattice periodicity can be represented by a weak pseudopotential. The numerical value of damping is computed for aluminium. The calculated frequency dependence of the imaginary part of the dielectric constant of Al is shown to be in good agreement with the same curve obtained from optical data.     

Dynamic susceptibility of thin films with perpendicular magnetic anisotropy

We investigate the spin dynamics related to the Gilbert damping constant in infinite continuous thin films with perpendicular magnetic anisotropy (PMA), based on numerical and analytic approaches. We obtain the dynamic susceptibility of the infinite continuous thin films with various PMA energies by using micromagnetic simulations with periodic boundary conditions. These results are compared with the analytic solution that we derived from the Landau–Lifshitz–Gilbert equation. Based on our numerical and analytic studies, we support the physical analysis for results in the experimental determination of the Gilbert damping constant for PMA materials.     

Micromagnetic simulation of ferromagnetic resonance of perpendicular granular media: Influence of the intergranular exchange on the Landau-Lifshitz-Gilbert damping constant

A micromagnetic approach was used to simulate ferromagnetic resonance frequency (FMR) profiles of perpendicular granular CoCrPt-oxide thin films. From the obtained FMR line-width we computed the effective damping constant. The influence of the intergranular exchange on the effective damping was investigated, showing an increase in the damping constant with increase in intergranular exchange coupling. Moreover, the effective damping constant increases with decrease in mesh size of the model, and eventually saturates for mesh sizes of about 1 nm. These dependencies are explained in terms of different modes that can be excited in the granular medium due to interactions between the individual spins.     

Point mobility of a cylindrical plate incorporating a tapered hole of power-law profile

The paper describes the results of experimental measurements of point mobility carried out on circular plates containing tapered holes of quadratic power-law profile with attached damping layers. The obtained results are compared to the developed numerical model, as a means of validation. The profiles of the tapered hole in the plates are designed to replicate near zero reflection of quasi-plane waves from a tapered hole in geometrical acoustics approximation, also known as acoustic black hole effect. The driving point mobility measurements are provided, showing a comparison of the results for a constant thickness circular plate, a constant thickness plate with a layer of damping film applied and a plate with a quadratic power-law profile machined into the center, which is tested with a thin layer of elastic damping material attached. The results indicate a substantial suppression of resonant peaks, agreeing with a numerical model, which is based on the analytical solution available for the vibration of a plate with a central quadratic power-law profile. The paper contains results for the case of free boundary conditions on all edges of the plates, with emphasis placed on the predictions of resonant frequencies and the amplitudes of vibration and loss factor.     

Investigation of multi-layer sandwich beams through single degree-of-freedom transformation

The dynamic behaviors of multi-layer sandwich beams are investigated through single degree-of-freedom (SDOF) transformation. The frequency response of the multi-layer sandwich beam is obtained using finite element code COMSOL and is transformed to a SDOF system with the same frequency response. Hence, the mass, spring constant and damping coefficient of the sandwich beams with different lengths and number of visco-elastic layers can be investigated. Further, viscous damping and structural damping models are individually employed to simulate the damping effect of the sandwich beam. The frequency responses from both models are compared with that from COMSOL and experiment. The resonant peak and resonant frequency of the SDOF system using structural damping model is more consistent with that from COMSOL. The experimental result demonstrates that the response of the sandwich beam can be predicted through COMSOL and SDOF transformation.     

Theoretical limit of the minimal magnetization switching field and the optimal field pulse for Stoner particles

The theoretical limit of the minimal magnetization switching field and the optimal field pulse design for uniaxial Stoner particles are investigated. Two results are obtained. One is the existence of a theoretical limit of the smallest magnetic field out of all possible designs. It is shown that the limit is proportional to the damping constant in the weak damping regime and approaches the Stoner-Wohlfarth (SW) limit at large damping. For a realistic damping constant, this limit is more than 10 times smaller than that of so-called precessional magnetization reversal under a noncollinear static field. The other is on the optimal field pulse design: if the magnitude of a magnetic field does not change, but its direction can vary during a reversal process, there is an optimal design that gives the shortest switching time. The switching time depends on the field magnitude, damping constant, and magnetic anisotropy.     

Acoustic excitation of nuclear spin waves in the easy-plane antiferromagnetic material KMnF3

Ultrasound damping at T=4.2 K in single crystal easy-plane antiferromagnetic KMnF₃ is studied experimentally as a function of the magnitude and direction of a constant magnetic field H at frequencies of 640–670 MHz, corresponding to the frequencies of nuclear spin waves. Two experimental situations are examined: in the first, the vector H lies in the easy magnetization plane (001), and in the second, H forms an angle with (001). For longitudinal ultrasound waves propagating along the hard magnetization axis [001], it is found that the damping depends resonantly on the magnitude of the field H. In the first case a single damping maximum is observed, and in the second, two damping peaks that are well resolved with respect to the field. The angular dependence of the resonance damping signals on the direction of the constant magnetic field is found to have a 90° periodicity in all cases. The observed effects are explained by resonant ultrasonic excitation of nuclear spin waves. On the basis of an analysis of the magnetoacoustic interaction energy, it is shown that in the first case, nonzero oscillations of the antiferromagnetism vector L occur only in the basal plane, while in the second, oscillations of L occur both in the basal and a vertical plane, which are associated, respectively, with two branches of the nuclear spin waves. It is also shown that the 90° periodicity in the angular dependence of the damping signals is associated with a fourth order [001] axis. Zh. éksp. Teor. Fiz. 112, 1830–1840 (November 1997)