Dynamic stability of parametrically-excited linear resonant beams under periodic axial force

The parametric dynamic stability of resonant beams with various parameters under periodic axial force is studied. It is assumed that the theoretical formulations are based on Euler-Bernoulli beam theory. The governing equations of motion are derived by using the Rayleigh-Ritz method and transformed into Mathieu equations, which are formed to determine the stability criterion and stability regions for parametricallyexcited linear resonant beams. An improved stability criterion is obtained using periodic Lyapunov functions. The boundary points on the stable regions are determined by using a small parameter perturbation method. Numerical results and discussion are presented to highlight the effects of beam length, axial force and damped coefficient on the stability criterion and stability regions. While some stability rules are easy to anticipate, we draw some conclusions： with the increase of damped coefficient, stable regions arise; with the decrease of beam length, the conditions of the damped coefficient arise instead. These conclusions can provide a reference for the robust design of parametricallyexcited linear resonant sensors.

Resonant Beam Communications:A New Design Paradigm and Challenges

Resonant beam communications (RBCom), which adopts oscillating photons between two separate retroreflectors for information transmission, exhibits potential advantages over other types of wireless optical communications (WOC). However, echo interference generated by the modulated beam reflected from the receiver affects the transmission of the desired information. To tackle this challenge, a synchronization-based point-to-point RBCom system is proposed to eliminate the echo interference, and the design for the transmitter and receiver is discussed. Subsequently,the performance of the proposed RBCom is evaluated and compared with that of visible light communications(VLC)and free space optical communications (FOC). Finally, future research directions are outlined and several implementation challenges of RBCom systems are highlighted.

Electromagnetic Resonance of Astigmatic Gaussian Beam to the High Frequency Gravitational Waves

The high frequency gravitational waves （around lOS-lO12 Hz） could interact with a specially designed electro- magnetic resonance system. It is found that the power of transverse perturbative photon flux （PPF） of an electromagnetic resonance system can be improved significantly by virtue of an astigmatic Caussian beam. Cor- respondingly the signal-to-noise ratio （SNR） would also be improved. When the eccentric ratio of waist satisfying w0x ： w0y 〉 1, the peak value of signal photon flux could be raised by 2-4 times with typical systematic parameters, while the background photon flux would be depressed. Therefore, the ratio of transverse PPF to background photon flux （i.e., SNR） can be further improved 3-8 times with dimensionless amplitude of relic gravitational wave ht = 10-36.

A bistable, self-latching inverter by the monolithic integration of resonant tunnelling diode and high electron mobility transistor

This paper reports that the structures of AlGaAs/InGaAs high electron mobility transistor （HEMT） and AlAs/GaAs resonant tunnelling diode （RTD） are epitaxially grown by molecular beam epitaxy （MBE） in turn on a GaAs substrate. An Alo.24Gao.76As chair barrier layer, which is grown adjacent to the top AlAs barrier, helps to reduce the valley current of RTD. The peak-to-valley current ratio of fabricated RTD is 4.8 and the transconductance for the 1-μm gate HEMT is 125mS/mm. A static inverter which consists of two RTDs and a HEMT is designed and fabricated. Unlike a conventional CMOS inverter, the novel inverter exhibits self-latching property.

Effects of Adhesive Characteristic on the Test Results of Damping Material's DMP

In the measurement of damping material's dynamic mechanical performance(DMP) using flexural resonating cantilever beam method,the specimen's adhesive characteristic influences the test precision and accuracy. Taking its effect into account,the improved measurement equations based on the resonance method are presented. The simulated results show that,for the sake of weakening the adhesive's influence on the measured results,the adhesive should be spreaded as thin as possible when specimen is prepared,the adhesive's density and loss factor should be selected as small as possible also,and its Young's modulus should be selected according to the damping material being measured;the same adhesion condition effects differently on the test results of different damping materials,i.e. the error due to the adhesive is more inconspicuous if the damping layer has bigger thickness,modulus,loss factor and a certain density according to the damping material being measured. These conclusions provide theoretical basis for selecting adhesive,improving adhesion technology,and designing specimen.

几何非线性条件下微纳米梁型谐振器的非线性支撑损失

作为微纳米机械谐振器主要的能量耗散源之一,支撑损失主要采用未考虑中面拉伸效应的线性理论进行研究.然而该理论却无法适用于大挠度非线性振动状态谐振器的支撑损失.为此,我们研究了考虑几何非线性和轴向预拉力的两端固支微梁谐振器处于面内弯曲振动模式时的支撑损失,旨在准确模拟大挠度振动下高性能谐振器的支撑损失.本文不仅考虑了支撑结构与谐振器连接区域受中面拉伸产生的正应力作用而引起的支撑损失,也考虑了受剪应力作用而引起的支撑损失,并且理论结果与有限元模拟以及文献中实验结果一致.另外,本文还研究了轴向预拉力对谐振器非线性振动特性的影响,并讨论了谐振器的振幅、长高比以及轴向预拉力对支撑损失的影响.理论结果表明,相比于线性振动状态下谐振器的支撑损失,由谐振器大变形振动产生的中面拉伸效应会引起更大的支撑损失,并且会随非线性振幅的增大而增大.本文提出的非线性支撑损失模型有望对评估非线性振动谐振器的支撑损失以及阐明支撑损失随非线性振幅增大的现象提供理论指导.

Laser beam characteristic for laser resonators with diffraction optical elements

The matrix eigenvalue method is used to analyze a laser resonator composed of diffraction optical elements. The results show that this type of resonator can separate fundamental mode and high order modes effectively. The output beams can be designed for different requests.

A preliminary study of the feasibility of using superconducting quarter-wave resonators for accelerating high intensity proton beams

The superconducting （SC） cavities currently used for the acceleration of protons at a low velocity range are based on half-wave resonators. Due to the rising demand on high current, the issue of beam loading and space-charge problems has arisen. Qualities of low cost and high accelerating efficiency are required for SC cavities, which are properly fitted by using SC quarter-wave resonators （QWR）. We propose a concept of using QWRs with frequency 162.5 MHz to accelerate high current proton beams. The main factor limiting SC QWRs being applied to high current proton beams is vertical beam steering, which is dominantly caused by the magnetic field on axis. In this paper, we intend to analyze steering and eliminate it to verify the qualification of using QWRs to accelerate high intensity proton beams.