Impact of EBG Structures' Positions on the Performance of an EBG Antenna

Six circularly polarized patch antennas with electromagnetic band gap (EBG) arranged at different locations were studied. These EBG antennas were compared in terms of impedance bandwidth, axial ratio (AR) bandwidth and radiation patterns. When the EBG cells were placed closer to the edge of the substrate, the EBG antenna had a larger front radiation and a narrower bandwidth. Integrating the EBG cells closer to the center of the patch resulted in a wider impedance bandwidth, a wider axial ratio bandwidth and a decreased front gain.     

Investigations on Structured Polyamide for Laser Sintered Body Armor

Stab resistance body armor (SRBA) is essential in protecting people from knife injuries. The protective parts of traditional SRBA are made of multi-layered ultra-high molecular weight polyethylene (UHMWPE), which causes heavy heat stress for people wearing it. The protective parts of SRBA manufactured using laser sintering (LS) 3D printing technology provide high manufacturing flexibility and low weight. Two different structures, plain plate and pyramid-structured plate, were investigated. The pyramid structure showed much higher stab resistance property then the plain plate, because of the angle and thickness effects. This is the first effort applying the LS technology and polyamide (PA) material (PA 3200) on SRBA. By applying the pyramid structure on the protective layer of the SRBA, the total weight could reduce 30%-40%.     

Synthesis and Characterization of Novel Biodegradable Poly (butylene succinate-co-triethylene glycol succinate)Copolymers

Novel biodegradable aliphatic polyesters,poly(butylene succinate-co-triethylene glycol succinate)(P(BS-co-TEGS))and poly(butylene succinate)(PBS),were synthesized through a two-step procedure of esterification and polycondensation with succinic acid and1,4-butanediol/triethylene glycol as raw materials as well as tetrabutyl titanate and diphenylphosphinic acid as the co-catalysts.The chemical structure and molecular weight of the copolymers were characterized by 1~H nuclear magnetic resonance(~1H NMR)and gel permeation chromatography(GPC),respectively.In addition,thermal properties,crystal structure and mechanical properties were also analyzed with various techniques.P(BS-co-TEGS)exhibited more excellent mechanical properties than PBS,especially in elongation at break.Meanwhile,the crystal structure and thermal stability of the P(BS-co-TEGS)have hardly changed.The crystallinity of P(BS-co-TEGS)was lower than that of PBS and decreased with the increase of mole ratio of triethylene glycol.With the increase of TEGS unit molar composition,the melting point(T_m),crystallization temperatures(T_c)and heat of fusion(ΔH_m)of P(BS-co-TEGS)decreased,while glass transition temperature(T_g)increased.     

Optimization of Waste Gate Drive Circuit of Two-Stage Turbocharging System

A two stage turbocharging control system was proposed, in which the pressure regulator valve with a close-loop pressure adjusting function instead of a high speed on-off solenoid valve, is used as a driving mechanism of waste gate. A digital-analog (DA)conversion circuit based on pulse width modulation (PWM) generates one analog voltage signal required by the pressure regulating valve control. The principle of the DA conversion circuit was analyzed, meanwhile, the performance of the conversion circuit was improved by adopting a speed-up capacitor, which helps to increase the stability and responsiveness of the control voltage generated by the conversion circuit; the structure parameters of the circuit was optimized by simulation. After the optimization, the ripple wave of circuit output voltage was kept within 16.mV under the 12.bit conversion accuracy, the conversion time of the circuit could be reduced to 4.ms. The engine bench test show that the turbocharging boost pressure control system which adopted the circuit had a rather good stable control accuracy(the steady state within 0.8%) and dynamic response(the regulation time is less than 4.s).     

Anticipating Degradation in State Estimation Accuracy via Online Nonlinear Observability Analysis

A methodology is proposed to enable real-time evaluation of the observability of local motions, and generate a local observability cost map to enable informed local motion planning in order to avoid potential degradation or degeneracy in state estimator performance. The proposed approach leverages efficient numerical techniques in nonlinear observability analysis and motion primitive-based planning technique to realize the local observability prediction with real-time performance. The degradation of the state estimation performance can be readily predicted with the local observability evaluation result. The proposed approach is specialized to a representative optimization-based monocular visual-inertial state estimation formulation and evaluated through simulation and experiments. The experimental results demonstrated the ability of the proposed methodology to correctly anticipate the potential state estimation degradation.     

Design of hydraulic shift mechanism for AMT vehicles based on the collaborative optimization method

Based on multidisciplinary design optimization (MDO), a new design method is put forward for hydraulic shift mechanism of heavy-duty vehicle automated manual transmission (AMT). Taking a shift cylinder for example, the collaborative optimization (CO) method for the design problem of a cylinder is devided into one system level design optimization problem and three subsystem level design optimization problems. The system level is an economic model and the subsystem level is mechanics, kinetics, and a reliability model. Application of the multidisciplinary design optimization software iSIGHT modeling and solving, optimal solution of the shifting cylinder CO model is obtained. According to the optimal solution, oil cylinders are machined out and installed on the gearbox of an AMT system for the bench cycle shift test. The results show that the output force and action speed of the optimized mechanism can meet requirements very well. In addition, the optimized mechanism has a better performance compared to the structure of the traditional design method, which indicates that the CO method can optimize the design of hydraulic transmission.     

Analysis on the gear-shifting schedule of hydraulic automatic transmission

With an advanced foreign hydraulic automatic transmission as the objective, an analytical method for the gear-shifting schedule is proposed. First the demanded maximum gradient of test is estimated. Then a test scheme and analytical procedure is formulated by initial test and hypothetical shift parameters. Finally through gear-shifting tests under different road conditions, load, accelerator pedal position limitation, throttle opening and output shaft speed are found to be the gear-shifting parameters. Under a common road condition, the gear-shifting schedule is a double-parameter schedule. Based on the driver''s demands on braking and dynamic performance, different shift schedules are made under downhill, uphill and quick releasing acceleration pedal conditions. The operation criteria of down-shift schedule on abrupt grade are proposed.     

Photonic crystal fiber Mach-Zehnder interferometer with microholes ablated by a femtosecond laser for refractive index sensing

A new structure of the photonic crystal fiber (PCF) based Mach-Zednder interferometer (MZI) is fabricated and presented. The structure has microholes ablated by a femtosecond laser. The fringe visibility can be enhanced more than 10.dB compared with the interferometer without a microhole. The interferometer is characterized by sodium chloride solutions for refractive index (RI) sensing. The RI sensitivities are greatly increased by the hole fabrication since it directly changes the cladding modes of the PCF. For the interferometer sensor with two holes, the RI sensitivity is 157.74 nm/RIU, which is 5.times than that of the sensor without a microhole. Microholes ablation with a femtosecond laser on PCF can increase the sensor''s sensitivity dramatically. Femtosecond laser has a wide application prospect in the field of performance improvement of the sensors.     

Polarimetric super-resolution algorithm for radar range imaging via spatial smoothing processing

A full-polarimetric super-resolution algorithm with spatial smoothing processing is presented for one-dimensional (1-D) radar imaging. The coherence between scattering centers is minimized by using spatial smoothing processing (SSP). Then the range and polarimetric scattering matrix of the scattering centers are estimated. The impact of different lengths of the smoothing window on the imaging quality is mainly analyzed with different signal-to-noise ratios (SNR). Simulation and experimental results show that an improved radar super-resolution range profile and more precise estimation can be obtained by adjusting the length of the smoothing window under different SNR conditions.     

QoE-driven voice quality evaluation model of VoIP based on network simulation

The quality of experience (QoE) evaluation model for voice over IP (VoIP) service is studied to analyze the impact of network parameters on voice quality and monitor voice quality in real-time for operators. Firstly, the influence of some network parameters on the voice quality of VoIP is investigated. Then, a simulation platform for VoIP transmission is built to collect voice data under different network enviornments. According to the simulation results, a new mapping model between these arguments and VoIP voice quality is deduced. Finally, the accuracy of this voice quality evaluation model is examined and the results demanstrate that it has high reliability and feasibility.