Active feedback control of sound radiation in elastic wave metamaterials immersed in water with fluid-solid coupling

Due to their potential properties unlike traditional materials and structures,elastic wave metamaterials have received significant interests in recent years.With the coupling between the acoustic and vibration,their mechanical characteristics can be tuned by the active feedback control system at low frequency ranges in which the traditional passive control is limited.This work illustrates that the superior performances of the effective mass density and sound pressure level(SPL)of an elastic wave metamaterial can be significantly changed by the active control,in which the periodic array of local resonators and orthogonal stiffeners are included.Significantly,based on the locally resonant mechanism,the negative density occurs over a frequency range.Due to the effects of lattice constant,structural damping and other parameters,the SPL with the function of fluid-solid coupling are illustrated and discussed.

Electromagnetic-thermal-mechanical characteristics with active feedback control in a high-temperature superconducting noinsulation magnet

High-temperature superconducting(HTS) magnets consisting of no-insulation(NI) double-pancake coils(DPCs) with high thermal stability have been proposed for use in the preparation of high-field magnets. However, increased ramp time is a known disadvantage of the NI approach. To solve this problem, a proportional and integral(PI) active feedback control has been proposed in the charging experiments of the NI magnet. In this study, the electromagnetic-thermal-mechanical characteristics of an NI magnet with and without PI are analyzed to ensure the safety and reliability of PI control. Due to the increase in the radial current of the magnet, the turn-to-turn loss energy of the magnet with PI is more than twice that without PI. However, the magnetization loss energy of the magnet has a small difference with and without PI. It can be also found that the NI magnet with PI has a large temperature rise, and thus it has a low thermal stability margin. Moreover, in the high field, the hoop stress and hoop strain peaks of a magnet with PI are larger than those without PI. Thus, PI control can induce a relatively high risk of mechanical damage in the applications of NI magnets.

Feedback of Active Galactic Nuclei in Seyfert 2 Galaxies

It is well accepted that feedback from active galactic nuclei （AGNs） plays an important role in the coevolution of the supermassive black hole （SMBH） and its host galaxy, but the concrete mechanism of feedback remains unclear. A considerable body of evidence suggests that AGN feedback suppresses star formation in the host galaxy. We assemble a sample of Seyfert 2 galaxies with recent observational data of compact nuclear starbursts and estimate the gas surface density as a function of column density to illuminate the relation between feedback and AGN properties. Although there are some uncertainties, our data still imply the deviation from the star formation law （Kennicutt-Schmidt law）. Further, they indicate that： （1） Feedback correlates with the Eddington ratio, rather than with the mass of SMBH, as a result of decreasing star formation efficiency. （2） The SMBH and the torus are probably undergoing coevolution. Conclusions presented here can be refined through future high resolution CO or HCN observations.

Duffing Oscillator’s Vibration Control under Resonance with a Negative Velocity Feedback Control and Time Delay

An externally excited Duffing oscillator under feedback control is discussed and analyzed under the worst resonance case.Multiple time scales method is applied for this system to find analytic solution with the existence and nonexistence of the time delay on control loop.An appropriate stability analysis is also performed and appropriate choices for the feedback gains and the time delay are found in order to reduce the amplitude peak.Different response curves are involved to show and compare controller effects.In addition,analytic solutions are compared with numerical approximation solutions using Rung-Kutta method of fourth order.

Design of Controller for New EAST Fast Control Power Supply

The effectiveness of the magnetic confinement of plasma can be improved by elongat- ing the plasma cross-section in tokamak devices. But elongated plasma has vertical displacement instability, so a feedback control system is needed to restrain the plasma＇s vertical displacement. A fast control power supply is needed to excite the active feedback coils, which produces a magnetic field to control the plasma＇s displacement. With the development of EAST, the fast control power supply needs to keep on enhancing the fast response and output current. The structure of a new power supply is introduced in this paper. The method of multiple inverters paralleled with the current sharing reactor is presented to meet the need for large current and fast control. According to the design demands of the EAST fast control power supply, the adjuster of the current close loop is applied to the inverter, which can advance its ability to restrain the loop current in low frequency and DC output. The result of the experiment confirms the validity of the proposed scheme and control strategy.

H_∞ drift control of time-delayed seismic structures

In this paper, an optimal H∞ control algorithm was applied to the design of an active tendon system installed at the first story of a multi-story building to reduce its interstory drift due to earthquake excitations. To achieve optimal control performance and to guarantee the stability of the control system, an optimum strategy to select control parameters γ and α was developed. Analytical expressions of the upper and the lower bounds of γ and α were obtained for a single degree-of-freedom system with state feedback control. The selection ranges for both γ and α are graphically defined so that the controlled system is always stable and the control performance is better than by the conventional LQR control algorithm. Numerical results from a controlled three-story building under real earthquake excitations demonstrate that the peak first interstory drift can be significantly reduced with maximum control force around 10% of the building weight. An optimum design flow chart was provided. In addition, for a time-delayed structure, this study gave explicit formulae to calculate the critical values of γ and a. The system stability and control performance can thus be guaranteed even with time delay.

Sound Transmission Comparisons of Active Elastic Wave Metamaterial Immersed in External Mean Flow

Using the active feedback control system on the elastic wave metamaterial,this research concentrates on the sound transmission with the dynamic effective model.The metamaterial is subjected to an incident pressure and immersed in the external mean flow.The elastic wave metamaterial consists of double plates and the upper and lower four-link mechanisms are attached inside.The vertical resonator is attached by the active feedback control system and connected with two four-link mechanisms.Based on the dynamic equivalent method,the metamaterial is equivalent as a single-layer plate by the dynamic effective parameter.With the coupling between the fluid and structure,the expression of the sound transmission loss(STL)is derived.This research shows the influence of effective mass density on sound transmission properties,and the STL in both modes can be tuned by the acceleration and displacement feedback constants.In addition,the dynamic response and the STL are also changed obviously by different values of structural damping,incident angle(i.e.,the elevation and azimuth angles)and Mach number of the external fluid with the mean flow property.The results for sound transmission by two methods are compared,i.e.,the virtual work principle for double plates and the dynamic equivalent method corresponding to a single one.This paper is expected to be helpful for understanding the sound transmission properties of both pure single-and double-plate models.

A 40 Gbit/s fully integrated optical receiver analog front-end in 90 nm CMOS

A fully integrated 40 Gbit/s optical receiver analog front-end （AFE） including a transimpedance amplifier （TIA） and a limiting amplifier （LA） for short distance communication is described in this paper. The proposed TIA employs a modified regulated cascode （RGC） configuration as input stage, and adopts a third order interleaving active feedback gain stage. The LA utilizes nested active feedback, negative capacitance, and inductor peaking technology to achieve high voltage gain and wide bandwidth. The tiny photo current received by the receiver AFE is amplified to a single-ended voltage swing of 200 mV（p-p）. Simulation results show that the receiver AFE provides conversion gain of up to 83 dBΩ and bandwidth of 34.7 GHz, and the equivalent input noise current integrated from 1 MHz to 30 GHz is about 6.6 μA（rms）.

Low power 13 Gbit/s VCSEL current driver in 0.18 μm CMOS for optical interconnection

A design of 13 Gbit/s vertical cavity surface emitting laser （VCSEL） driver using 0.18 μm complementary metal oxide semiconductor （CMOS） technology is presented in this paper. The core unit of the driver consists of pre-amplify stage and output stage circuit. Techniques of three stages differential amplifier with low impedance load and active feedback are employed in pre-amplify stage, and technique of C3A is adopted in output stage to acquire low power consumption and high speed. The experimental results show that the circuit can work at the data rate of 10 Gbit/s and maximum of 13.2 Gbit/s. The output modulation current is up to 12.5 mA and the power dissipation is only 68 mW with a 1.8 V power supply.