Design and evolution of a piezoelectrically actuated miniature swimming vehicle

This work details the design of a miniature swimming vehicle that propels itself through oscillations of a flexible fin mounted in the stern. The fin is driven through a mechanism that is actuated by two curved-beam bending piezoelectric actuators. An optimization routine is used to design the mechanism for rigid body guidance. The actuators are modeled statically using the Bernoulli-Euler method. Hamilton's principle is applied to the actuators and, by employing the modal analysis, a dynamic actuator model is developed and compared to experimental data. The physical evolution of the swimming vehicle is discussed, and a prototype for an on-board digital control circuit is evaluated. The latest vehicle design, which incorporates on-board digital control, is presented in terms of its design and experimentally determined the performance characteristics. The current swimming vehicle prototype achieves fish-like maneuvering and an approximate velocity of 0.25 m/s.     

压电致动微喷的压力波特征分析

提出了一种压电致动的阵列微喷 ,以面向吸入式药物治疗应用。该阵列微喷工作在器件的谐振点上 ,其工作性能决定于液体腔中的压力波的分布和大小。本文针对该类微喷建立了考虑压电 固 液耦合和压力波传播效应的等效模型 ,并利用有限元方法对整个器件的结构振动模态和压力驻波模态进行了分析。文章对不同振动模态下 ,液体腔中的声压力波分布以及对微喷设计的影响进行了讨论     

压电致动微喷的压力波特征分析

提出了一种压电致动的阵列微喷,以面向吸入式药物治疗应用。该阵列微喷工作在器件的谐振点上,其工作性能决定于液体腔中的压力波的分布和大小。本文针对该类微喷建立了考虑压电-固-液耦合和压力波传播效应的等效模型,并利用有限元方法对整个器件的结构振动模态和压力驻波模态进行了分析。文章对不同振动模态下,液体腔中的声压力波分布以及对微喷设计的影响进行了讨论。     

Arc root commutation from moving contacts in low voltage devices

This paper focus on the arc commutation from a moving contact and in particular on the anode motion of a high current arc in low voltage current limiting circuit breakers. Recent investigations have observed that the anode arc root motion is affected by arc chamber geometry. It was previously assumed that cathode root motion was the dominant process. The study uses a flexible test apparatus with a solid state high speed imaging system. The experimental results presented show the influence of arc chamber venting, current level, current polarity and contact velocity on arc motion, Particular emphasis is made on the anode motion. The physical processes occurring in the anode root are discussed and related to the observed motion. The results show that the anode root is retarded at the tip of the moving contact and that this is primarily related to the venting process in the arc chamber     

Arc motion and gas flow in current limiting circuit breakers operating with a low contact switching velocity

Arc motion in low voltage (240 VAC) high current (10/sup 3/-10/sup 4/A.) current limiting-circuit breakers is dominated by arc root mobility. The mobility is influenced by the gas flow and gas composition in the contact region, but there is little experimental data on these effects. New pressure and spectral data measurement during arc movement are presented using a flexible test apparatus and an arc imaging system. These measurements are used to investigate gas flow characteristics in the arc chamber. The chemical and physical phenomena occurring during the arc motion are discussed. The combination of optical and spectral data provides new insight into the arc motion. The influences of arc chamber material, contact material, and contact opening speed, are investigated to improve arc control for a low contact opening velocity.     

Study of the effects of gas flow on the performance of gas-blast circuit breakers

Experiments were carried out at a Siemens laboratory with specially designed circuit breakers to investigate the relationship between gas flow and arc behavior for various shapes and arrangements of gas nozzles, as well as for different types of gas and pressure conditions. The current, post-arc current, and voltage measurements were supplemented by the employment of optical methods. By using a high-speed schlieren camera, it was possible to obtain valuable information on the flow characteristics and density of the gas surrounding the arc and to estimate the influence of these quantities on the arc-quenching capacity of a breaker. The interaction of the electric power system and the arc could also be taken into account by using a dynamic arc model.     

The role of ambipolar phenomena in the mechanism of the post-zero current in vacuum circuit breakers

This paper attempts to develop a theory of the role of ambipolar phenomena in the mechanism of the post-zero current in high-current vacuum circuit breakers on a more general and more accurate basis that can be found in the literature. Several cases of interest are compared and discussed and their probable range of validity established. Whereas the theory presented in this paper is probably adequate when the density of the neutral gas is low (mean free path comparable to electrode separation), it should probably be combined with other recognized mechanisms, notably gross gas motions and turbulence, when the pressure is higher during the afterglow. No numerical check is presented here, most of the basic data still being much too uncertain.     

Implantation angle periphery effects on non-alloyed Si-implanted ohmic contacts for AlGaN/GaN high electron mobility transistors

We report on the effect of implantation angle on contact resistance of non-alloyed ohmic contacts to selectively implanted source/drain regions in AlGaN/GaN high electron mobility transistor (HEMT) heterostructures. Three different components of contact resistance are observed for such contacts: (i) contact resistance between the metal and the semiconductor, (ii) resistance of the implanted region and (iii) an additional resistance attributed to a transition region between implanted and non-implanted region. This third component varies strongly with implantation angle. The variation with implantation angle shows that the ratio of lateral implantation damage to penetration depth is critical for implantation of AlGaN/GaN HEMT source/drain contact regions. Our results also show that increasing the implantation angle in combination with reducing the implantation width can reduce contact resistance.     

NBTI related time-dependent variability of mobility and threshold voltage in pMOSFETs and their impact on circuit performance

Threshold voltage (V_T) and mobility (μ) shifts due to process related variability and Negative Bias Temperature Instability are experimentally characterized in pMOSFETs. A simulation technique to include the time-dependent variabilities of V_T and μ in circuit simulators is presented and used to evaluate their effects on CMOS inverters performance. The results show that mobility degradation under NBTI stresses could have to be considered for the evaluation of the circuit performance after device aging.     

Nanocrack formation in AlGaN/GaN high electron mobility transistors utilizing Ti/Al/Ni/Au ohmic contacts

AlGaN/GaN HEMTs are poised to become the technology of choice in RF and power electronics applications where high operating frequencies and high breakdown voltages are required. The alloyed contacting scheme utilized in the formation of the source and drain contacts of these devices affects the conduction of electrons through the 2DEG from the moment of ohmic contact formation onward to operation in the field. Analysis of the ohmic contacts of as-fabricated and electrically stressed AlGaN/GaN HEMTs, via chemical deprocessing and Scanning Electron Microscopy, indicates the presence of cracks oriented along the [11-20] directions, which nucleate at metal inclusions present under the alloyed ohmic source/drain contact metal. Cracks which form at the edges of these contact regions can extend into the channel region. It appears that electrical biasing induces additional growth in the longest cracks present within the channel regions of these devices.     

Power performance and scalability study of AlGaAs/GaAs double-recessed pseudomorphic high electron mobility transistors on unthinned substrate for coplanar waveguide circuit applications

We have investigated the power performance and scalability of AlGaAs/GaAs Double-Recessed Pseudomorphic High Electron Mobility Transistors (DR-PHEMTs) at 10 GHz on an unthinned GaAs substrate for CoPlanar Waveguide (CPW) circuit applications. It was found that the output power varied linearly with the logarithm of the device’s gate width ranging from 200 to 1000 μm. It increased at a rate of 0.01 dB/μm. That worked out to a doubling of output power (or 3 dB) for every 300 μm increase in the gate width. Gain decreased at a rate of about 0.005 dB/μm while PAE generally improved when the gate width was increased. As for DC measurement, the maximum transconductance of the device was about 375 mS/mm at V_G = −0.5 V and V_DS = 3 V. The gate-drain breakdown voltage (BV_GD) measured was −20 V, defined at I_G = −1 mA/mm. The microwave performance of the devices was measured on-wafer using a load-pull system at a bias of V_G = −0.5 V and V_DS = 8 V. For a device with a gate width of 1 mm, its saturated CW output power, gain and PAE value at 10 GHz was 27.5 dBm (0.55 W), 8 dB and 48%, respectively. At this same set of bias conditions, the value of f_t and f_max was 40 and 80 GHz, respectively.     

Specific contact resistance and noise in contacts on thin layers

A method is presented for the calculation of the specific contact resistance and noise of contacts on thin layers. The contribution to the contact resistance and noise of the interface between the contact and the layer is determined from experimental results. Using the developed method on thin Cu_xS layers with a sheet resistance of 42.5 Ω values for the specific contact resistance of 4 × 10^?2 Omega; cm² and 2.5 Ω cm² were observed for two different contact technologies.     

Characteristics of films developed in fretting experiments on tinplated contacts

A series of experiments were conducted to characterize oxide films that develop during fretting degradation. It was found that while the rate of change in resistance depends on contact force, the oxide film characteristics depend strongly on the number of fretting cycles. Moreover, after about 1000 fretting cycles, the oxygen content reaches a saturation level which corresponds to tin volume fractions below the percolation limit for metallic conduction (<0.4). Consequently, it is concluded that conduction is primarily due to the semi-conductor properties of tin oxide (SnO). In addition, sub-micron size particles, composed of tin and tin oxide, were found dispersed over the surface. These particles had tin fractions near the percolation limit and may play a role in the mechanism that causes short-term discontinuities in contact resistance     

基于LabVIEW的音圈电机驱动小角度转台系统辨识方法

通过分析逆重复伪随机序列(L序列)的生成原理,设计了一种基于LabVIEW的L序列生成方法,将其作为音圈电机驱动的小角度转台的辨识输入信号,同时以转台上测角装置的测量值作为反馈输出信号,用最小二乘法对输入输出信号进行参数辨识,从而确定了转台的传递函数。最后,将输入信号代入传递函数与实际输出信号进行了对比,并对一系列的频率点进行了验证。结果表明,这种方法具有较高的辨识精度,对研究转台的高精度控制算法具有重要的参考价值。     

视频电路中若干技术问题的讨论

对视频电路中的视频放大、视频复用、视频分配等问题进行了分析讨论,给出了有关芯片在电视技术中的典型应用。     

Effect of photovoltage on current flow in metal-semiconductor schottky-barrier contacts

It is shown that changes in device characteristics and an increase in the light-to-electrical energy conversion efficiency in metal-semiconductor Schottky barrier contacts are associated with a peripheral electric field built into the contact. For contacts with longer perimeters, variations in device characteristics and the light-to-electrical energy conversion efficiency are significantly larger. Since the photovoltage and peripheral electric fields in the contact region are codirected with the intrinsic electric field of the space-charge region, contact illumination results in a larger increase in the “dead” zone in forward portions of current-voltage characteristics, a larger decrease in the effective Schottky barrier height, and an increase in the field electron emission. An increase in the reverse field emission under photovoltage leads to an increase in the recombination current in the space-charge region, which provides dc photocurrent flow in the circuit.     

Further study on interaction enhancement of Raman processes in miniature OPFIRL

The interaction of Raman processes leads to the change of the properties of a miniature NH3-OPFIRL much, such as lasing efficiency, spectral characteristics and optimum operating gas pressure. The influences on FIR spectrum and optimum operating gas pressure of such system were studied experimentally and theoretically.     

Residual stress effect on electron mobility in ZMR-SOI

N-channel enhancement-mode MOSFETs have been fabricated in silicon-on-insulator (SOI) films prepared by both infra-red and laser zone-melting recrystallisation (ZMR). The SOI films are subjected to a lateral tensile stress due to the thermal expansion coefficient difference between silicon and silicon dioxide. The devices in the stressed films exhibit higher surface electron mobilities than those in bulk single crystal silicon. This phenomenon has been attributed to the influence of the stress through the change of the band structure as well as redistribution of carriers in k space.<>