Research of an Active Tunable Vibration Absorber for Helicopter Vibration Control

Significant structural vibration is an undesirable characteristic in helicopter flight that leads to structural fatigue, poor ride quality for passengers and high acoustic signature. Previous Individual Blade Control (IBC) techniques to reduce these effects have been hindered by electromechanical limitations of piezoelectric actuators. The Smart Spring is an active tunable vibration absorber using IBC approach to adaptively alter the 'structural impedance' at the blade root. In this paper, a mathematical model was developed to predict the response under harmonic excitations. An adaptive notch algorithm was designed and implemented on a TMS320c40 DSP platform. Reference signal synthesis techniques were used to automatically track the shifts in the fundamental vibratory frequency due to variations in flight conditions. Closed-loop tests performed on the proof-of-concept hardware achieved significant vibration suppression at harmonic peaks as well as the broadband reduction in vibration. The investigation verified the capability of the Smart Spring to suppress multiple harmonic components in blade vibration through active impedance control.

Active tunable terahertz bandwidth absorber based on single layer graphene

In this paper,an active tunable terahertz bandwidth absorber based on single-layer graphene is proposed,which consists of a graphene layer,a photo crystal plate,and a gold substrate.When the Fermi energy(Ef)of graphene is 1.5 eV,the absorber shows high absorption in the range of 3.7 THz–8 THz,and the total absorption rate is 96.8%.By exploring the absorption mechanism of the absorber,the absorber shows excellent physical regulation.The absorber also shows good adjustability by changing the Efof graphene.This means that the absorber exhibits excellent tunability by adjusting the physical parameters and Efof the absorber.Meanwhile,the absorber is polarization independent and insensitive to the incident angle.The fine characteristics of the absorber mean that the absorber has superior application value in many fields such as biotechnology and space exploration.

A compact and reconfigurable low noise amplifier employing combinational active inductors and composite resistors feedback techniques

A compact and reconfigurable low noise amplifier(LNA)is proposed by combining an input transistor,composite transistors with Darlington configuration as the amplification and output transistor,T-type structure composite resistors instead of a simplex structure resistor,a shunt inductor feedback realized by a tunable active inductor(AI),a shunt inductor peaking technique realized by another tunable AI.The division and collaboration among different resistances in the T-type structure composite resistor realize simultaneously input impedance matching,output impedance matching and good noise performance;the shunt feedback and peaking technique using two tunable AIs not only extend frequency bandwidth and improve gain flatness,but also make the gain and frequency band can be tuned simultaneously by the external bias of tunable AIs;the Darlington configuration of composite transistors provides high gain;furthermore,the adoption of the small size AIs instead of large size passive spiral inductor,and the use of composite resistors make the LNA have a small size.The LNA is fabricated and verified by GaAs/InGaP hetero-junction bipolar transistor(HBT)process.The results show that at the frequency of 7 GHz,the gain S_(21)is maximum and up to 19 dB;the S_(21)can be tuned from 17 dB to 19 dB by tuning external bias of tunable AIs,that is,the tunable amount of S_(21)is 2 dB,and similarly at 8 GHz;the tunable range of 3 dB bandwidth is 1 GHz.In addition,the gain S_(21)flatness is better than 0.4 dB under frequency from 3.1 GHz to 10.6 GHz;the size of the LNA only has 760μm×1260μm(including PADs).Therefore,the proposed strategies in the paper provide a new solution to the design of small size and reconfigurable ultra-wideband(UWB)LNA and can be used further to adjust the variations of gain and bandwidth of radio frequency integrated circuits(RFICs)due to package,parasitic and the variation of fabrication process and temperature.