Highly resonant controller for multimode piezoelectric shuntdamping

A new controller structure for piezoelectric shunt damping is proposed. The controller has a highly resonant structure and is implemented digitally on a piezoelectric laminate structure. Experimental results are presented demonstrating the effectiveness of the controller in suppressing structural vibrations     

Antispecular reflections in the backward-wave multimode systems

A specific backward-wave antispecular reflection from the interface of structures or media is analyzed. The reflection coefficients are calculated, and the dominant contribution of the alternative reflection is demonstrated. The supercritical (with respect to angle of incidence and frequency) total reflection and improper surface wave or edge wave in the plate are considered. It is demonstrated that the effect is similar to the Andreev quantum reflection of electrons (which is also alternative) and the elastic reflection of a mechanical top.     

一种改进的多模数字下变频结构及其FPGA实现

针对目前多种通信模式的共存和发展趋势,对传统DDC结构进行改进,以适用于多模系统。提出了多模数字下变频改进结构与参数设计,完成了各模块Verilog代码编写和Modelsim仿真,并对Modelsim仿真结果进行分析和验证,验证了改进数字下变频的可行性;最后将代码移植到FPGA,并结合ETTUS射频板、自主设计的中频板以及友晶TR4 FPGA开发板多模硬件平台进行了板级调试,验证了多模功能的可行性,充分证明该结构能兼容WCDMA和TD-LTE两种模式,具有较高的实用性和通用性。     

Evaluation of modal noise in multimode fiber-optic systems

Modal noise at fiber connecting points is studied theoretically and experimentally. Simple formulas for calculating modal-noise power, noise bandwidth, and nonlinear distortions are obtained by introducing a visibility concept. Modal noise for multimode operating LD is also analyzed. These theoretical results are applied to high-bit-rate digital systems and analog systems using direct IM. Then, it is shown that a 3-dB connection loss limits effective signal-to-noise ratio (SNR) to 22 dB in high-bit-rate digital systems, and that in analog systems, the SNR is improved more than 20 dB by using a superimposed pulse modulation with a frequency that is 100 times the baseband signal bandwidth.     

Correlation and channel capacity of MIMO systems employing multimode antennas

A novel way of exploiting higher modes of antennas as diversity branches in multiple-input-multiple-output (MIMO) systems is introduced. Essentially, antennas employing multiple modes offer characteristics similar to an antenna array, through multiple modes and using only a single element. The physical mechanism that yields different received signals is the fact that each mode has a different radiation pattern. Analytical expressions for the correlation between signals received by different modes are presented for a biconical and a circular microstrip antenna that employs higher order modes. It is found that the correlation is low enough to yield a significant diversity gain. Furthermore, the channel capacity of a MIMO system using a multimode antenna, i.e., an antenna employing multiple modes, is found to be comparable to the capacity of an array. Since only one element is needed, the multimode antenna offers several advantages over traditional arrays, and is an interesting antenna solution for future high capacity MIMO systems.     

Modeling and analysis of systems with multimode components anddependent failures

A model for the reliability and performance analysis of systems where components can degrade in a statistically dependent manner is presented. This cause-based multimode model is based on the idea that deviations of components from the up state have underlying physical causes which can be explicitly identified and are statistically independent. The effects of several causes can be combined in a flexible manner. System reliability and performance measures can be computed approximately by considering the most probable states. Such states can be efficiently generated by algorithms developed for the earlier multimode, statistically independent failure model     

BDD-based reliability analysis of phased-mission systems with multimode failures

This paper proposes a new algorithm (DEP-BDD) based on binary decision diagram (BDD) for reliability analysis of phased-mission systems (PMS) with multimode failures. DEP-BDD is a BDD-based combinatorial model which can be used to deal with more than one kind of dependences by applying dependence algebra, which is a generalization of phase algebra that handles more complex dependences. The nature of the BDD contributes the efficiency and low computational complexity of this algorithm. Two examples are analysed to illustrate the applications and advantages of our approach.     

Orthogonal frequency-division multiplexing in wirelesscommunication systems with multimode fiber feeds

The feasibility of using multimode fiber as an inexpensive cell feed in broad-band indoor picocellular systems is investigated in this paper. The performance of coded orthogonal frequency-division multiplexing (OFDM) for a variety of multimode fiber profiles, including stepped index and α-profile graded index fibers, is assessed. In addition to its ability to perform well in a frequency-selective multipath environment, OFDM is shown to offer good protection against the frequency selectivity of a dispersive multimode fiber. Data rates in excess of 100 Mb/s (without equalization) over a multimode fiber channel are possible, whereas they may be limited to some 20-30 Mb/s using conventional ASK modulation     

Secure implementation of identification systems

In this paper we demonstrate that widely known identification systems, such as the public-file-based Feige-Fiat-Shamir scheme, can be insecure if proper care is not taken with their implementation. We suggest possible solutions. On the other hand, identity-based versions of the Feige-Fiat-Shamir scheme are conceptually more complicated than necessary.Gilles Brassard's research is supported in part by Canada's NSERC. A part of this research was done while Yvo Desmedt was sponsored by NFWO (the Belgian NSF). A later part was done while he was visiting professor at the Département IRO, Université de Montréal. A part of his research is now supported by NSF Grants NCR-9004879 and NCR-9106327. This research was done while Jean-Jacques Quisquater was at the late Philips Research Laboratory, Belgium. Parts of this research were presented at Crypto '86, Crypto '87, and Securicom '88.     

Low-frequency piezoelectric energy harvesting prototype suitable for the MEMS implementation

A low-frequency piezoelectric energy harvester based on impact vibration assembled with a compliant driving beam and two rigid generating beams is presented. The ambient low frequency is up-converted to high resonant frequency by the periodic impact between the driving beam and the generating beams. The advantages of the harvester are: restricting the large displacement of the compliant driving beam, improving power density and being especially suitable for a compact MEMS approach. The 1.53 mW average power of the macroscale impact vibration harvester is achieved at 20.1 Hz under 0.4g acceleration. The power density is 93.2 μW/cm³, which is 6.8 times that of conventional counterpart (13.6 μW/cm³). The measured results demonstrate the potential of the device applied to portable and implantable electronics benefited from the MEMS batch-fabrication technology.     

Dispersion and noise of 1.3 μm multimode lasers in microwavedigital systems

The intensity noise and the performance in a 1.7 Gb/s digital system of 1.3 μm InGaAsP multilongitudinal mode lasers is discussed. The total intensity noise, mode partitioning, and the impact of dispersion on optical noise are measured. It is found that under CW conditions the total simulated emission from unpackaged lasers is inherently quiet, with an integrated optical signal-to-noise ratio (SNR) of 26.8±1.5 dB over a bandwidth of 1.5 GHz and 5 mW/facet. The optical SNR decreased as a function of increasing reflection. Intense mode partitioning decreased the SNR of the main mode by ~20 dB and reduced the effective coherence length to ~2 cm in glass fiber. At 1.7 Gb/s, the power penalities associated with laser bias and fiber dispersion are reported. The best receiver sensitivity is obtained when the laser is biased 1.3 mA below threshold. In general, it is found that as the bit rate increases, the optimum transmitter design becomes progressively more restrictive     

Performance comparison of DA-TDE and CMA for MIMO equalization in multimode multiplexing systems

In this paper, we compare performances of the constant modulus algorithm (CMA) and data-aided time domain equalization (DA-TDE) algorithm for mode demultiplexing in few mode transmission systems. Simulation results of \(4\times 56\ \hbox {Gbit/s}\) QPSK mode-division multiplexed system show that the maximum required OSNRs with CMA are less than that of DA-TDE by 0.8 and 4.6 dB for high maximum coupling coefficient of 0.15 and 0.20.     

Design consideration for digital systems using multimode fibre with lossy cladding

Digital systems using multimode fibres with a step-index profile, a lossy cladding and a low-loss core are treated in the letter. The influence of fibre numerical aperture (n.a.) on repeater spacing is examined when the total core-cladding interface loss results from Fresnel reflection. It is shown, by way of example, that in this case there is no advantage in using low n.a. values, even at moderate modulation rates, owing to a diminishing receiver incident optical power with decreasing n.a.     

Design and implementation of flexible and stretchable systems

This paper presents a summary of the modeling and technology developments for flexible and stretchable electronics. These technologies can achieve mechanically bendable and stretchable subsystems by incorporating the electronic circuit into a matrix made of a soft polymer. The base substrate used for the fabrication of flexible circuits is a uniform polyimide layer, while silicones or polyurethanes materials are preferred for the stretchable circuits. The method developed for chip embedding and interconnections is named Ultra Thin Chip Package (UTCP). Extensions of this technology can be achieved by stacking and embedding thin dies in polyimide, providing large benefits in electrical performance and still allowing some mechanical flexibility. These flexible circuits can be converted into stretchable circuits by replacing the polyimide by a soft and elastic silicone material.The integration of ultra thin dies at package level, with thickness in the range of 10-30 μm, into flexible and/or stretchable materials are demonstrated. Furthermore, the design and reliability test of stretchable metal interconnections at board level are analyzed by both experiments and finite element modeling. We have shown through finite element modeling and experimental validation that an appropriate thermo-mechanical design is necessary to achieve mechanically reliable circuits and thermally optimized packages.     

Fairly adjusted multimode dynamic guard bandwidth admission control over CDMA systems

Guard-based call admission control schemes support admission priorities based on resources sharing with differentiated resource capacity limits. To minimize deviation from call blocking/dropping targets due to nonstationary call arrival condition, dynamic guard-based schemes with predictive adaptation control adjust differentiated capacity limits according to predicted future arrival rates based on specified estimation algorithms. Existing dynamic guard admission schemes are developed under the assumption of perfect estimation, which may not be possible in a highly nonstationary environment and, thus resulting in failures to maintain targeted blocking/dropping probabilities. This paper presents the fairly adjusted multimode-dynamic guard bandwidth scheme, which is a dynamic-guard-based scheme over code-division multiple-access systems with predictive adaptation control to adapt interference-based guard loading-limits under nonstationary call arrival condition; and reactive adaptation control to counteract arrival rate estimation errors. When the predictive adaptation control policy mode is not able to maintain long-term call blocking or dropping targets due to estimation error, this will trigger reactive adaptation control policy modes that include temporary blocking (preemption) of one or more lower priority classes subject to fairness constraints to ensure lower priority classes are not preempted at all costs during estimation error recovery. Analytical and simulation results show that proposed scheme is able to provide performance guarantees in terms of dropping probabilities under nonstationary traffic arrival and imperfect arrival rate estimation.     

横向压电效应变形镜优化设计

变形镜作为自适应光学系统中的关键部件,起到校正波前误差的作用。其中横向压电效应变形镜应用较为广泛,其设计参数对系统的性能有重要影响,因此需要进行优化设计。仿真表明,减小Si镜和PZT的厚度可以提高系统最大变形量,但会降低一阶固有频率。通过正交匹配两者的厚度参数可满足系统的工作要求。夹具的材料和结构参数会影响系统的热变形特性。使用与镜片材料相同的夹具,系统的热变形最小,对高度和壁厚进行优化可以减小甚至消除系统的热变形。最后,通过电压特性仿真得到了优化后变形镜各分立电极的影响函数。     

一种500 Mbps至4 Gbps连续速率的多模式CDR电路

提出了一种连续速率的时钟数据恢复(CDR)电路,可覆盖500 Mbps到4 Gbps数据率。该CDR电路在130 nm互补金属氧化物半导体(CMOS)工艺下实现,基于相位插值(PI)原理,采用数字投票电路和相位控制逻辑替代电荷泵和模拟滤波器以方便工艺移植。为缩小片上锁相环(PLL)输出时钟频率范围,同时避免PI电路处于非线性区,该CDR电路采用多种速率模式切换的方式将采样时钟频率限定在500 MHz~1 GHz之间。PI电路为7 bit精确度,线性度良好,4 Gbps数据率时,恢复时钟的峰峰值抖动约为25.6 ps。该CDR误码率在10-10以下,可跟踪最大±976.6 ppm的数据频偏,功耗约为13.28 mW/Gbps,测试芯片大小为5 mm2,其中CDR芯核部分为0.359 mm2。     

A mode-filtering scheme for improvement of the bandwidth-distanceproduct in multimode fiber systems

A scheme in which the bandwidth-distance product of a multimode fiber is extended, so that it can nearly support the transmission rate of single-mode systems, is studied. It is based on selective launching of lower order modes into the fiber at the transmitting end and on filtering out at the receiver the fraction of the energy that was coupled into the higher order modes throughout the propagation in the multimode fiber. The power penalty and the dispersion performance of the scheme are investigated. In particular, it is shown that the scheme carries about 6.5 dB penalty, and doubling of the bandwidth×distance value is demonstrated. The effect of splices on the performance is also presented. It is envisioned that this approach may be used to upgrade existing multimode systems without the need for rewiring. For example, it can be used to replace the FDDI (fiber distributed data interface) installations in future high-speed networks, when transmission rates increase from megabits per second to gigabits per second     

一种自适应增强谱线算法的优化设计与实现

自适应谱线增强(ALE)算法能够提高高动态、低信噪比信号的载波频率估计精度.针对实际应用中该算法消耗硬件资源多、结构复杂、使用效率低等问题,提出了结合可编程逻辑门阵列(FPGA)优化的ALE算法结构方法,简化了ALE硬件电路.设计结果表明,改进ALE方法后,可实现信噪比为0～20 dBHz、最大多普勒动态为800 Hz/s的测控信号载波频率准确估计.     

Energy harvesting using piezoelectric transducers for suspension systems

Energy harvesting by using functional materials in suspension systems bear potential to win-back certain (even if low) amounts of vibrational energy, otherwise dissipated via the conventional (passive) dampers. Piezoelectric (PE) ceramics are functional materials that can be used for transforming mechanical energy into electrical and vice versa. In this paper, we study the capabilities and efficiency of energy harvesting (EH) with PE transducers under two different kinds of external excitation: i) Periodic and ii) stochastic. An appropriate nonlinear lumped parameter electromechanical model (LPEM) is brought into the two-port network notation. Laboratory experiments were conducted under periodic external force-controlled excitation performed on a universal test machine (UTM). The two-port model parameters were identified and the model was validated by comparing results of numerical simulations and experiments. Extended simulations have been conducted to investigate the EH capabilities of PE transducers in automotive applications, i.e. EH in suspension systems under the standardized road conditions. The analysis results of the power conversion and EH efficiency are presented and discussed.