A theoretical and experimental study of the noise behavior ofsubharmonically injection locked local oscillators

A method for the phase-noise characterization of optically controlled subharmonically injection-locked oscillators that is based on a nonlinear model of synchronized oscillators is presented. It allows FM noise degradation at large-signal levels to be predicted easily and accurately. The theoretical analysis shows that (1) the nth-order subharmonic injection locking oscillator is primarily locked by the nth harmonic output of an injected signal, which is generated by the nonlinearity of the active device; (2) the minimum FM noise degradation factor of the nth-order subharmonically locked oscillator is n² when the injection power is sufficiently strong; and (3) a subharmonic injection locking LO with low injection power, good FM noise degradation, and large locking range can be designed by determining the optimum injection power level, by selecting the optimal nonlinear multiplication factor, and by decreasing the intrinsic noise level of the active device. The experimental results confirm the accuracy of the analysis     

Optical synchronization of millimeter-wave oscillators fordistributed architecture

A review of various methods of phase and frequency synchronization of active MMIC based transmit/receive modules is presented, and particular emphasis is placed on the synchronization of oscillators through the use of an indirect subharmonic optical injection locking technique. In this approach, the nonlinear behavior of large-signal modulated laser diodes and solid-state oscillators is exploited to extend the bandwidth of the synchronizing link to the millimeter-wave frequency range. Experimental results of the phase and frequency coherency of two 21.5 GHz FET oscillators are reported. Optimum performance is achieved at a subharmonic factor of 1/4, with a locking range of 84 MHz and a phase noise degradation of only 14 dB. The phase coherency measurement of two injection-locked oscillators points to a phase shift, which is introduced as a result of the frequency detuning between the slave and master oscillator signals. A scheme to correct for this phase error is presented     

An efficient self-oscillating mixer for communications

The optical control of the distributed electronics in phased array antennas requires specialized circuits which are compatible with the T/R level data mixing architecture. This paper presents a novel circuit, a push-pull self-oscillating mixer, that can provide the following important advantages: 1) very stable free running oscillation and low FM noise without using a frequency stabilizing dielectric resonator; 2) large subharmonic injection locking range; 3) high frequency conversion efficiency; and 4) low noise figure for the self-oscillating mixer. This proposed circuit efficiently oscillates and mixes with a low prime power consumption. A circuit topology based on this concept was analyzed and designed at 12 GHz using a MESFET pair. Efficient subharmonic injection locking was demonstrated by selecting the optimum operating point corresponding to efficient mixing. The measured down-conversion gain was as high as 13 dB with a double sideband noise figure of 8 dB. This topology can be directly applied for MMIC applications     

Radiation effects on elasticity of metals

For a metal containing a periodically arranged (three-dimensional) system of voids, explicit analytical expressions are developed for the bulk and the shear moduli (and, consequently, Young's modulus and the Poisson ratio), on the assumption that the metal is initially (nonirradiated) homogeneous and isotropic. These expressions include the effect of the interaction between adjecent voids and the void size, but do not take into account the effects of the void shape. The results are compared with previous estimates by other investigators who did not include the influence of the interaction between adjacent voids. The interaction effect becomes more pronounced with the increasing volume fraction of the voids. Hence, the present results provide more realistic estimates of the material elasticity. These and related results are illustrated by means of numerical examples. Then the mechanism of void and gas bubble formation in irradiated metals is briefly discussed and some relevant theoretical and experimental results are summarized. In particular, curves are developed which relate the reduction in elastic moduli to the neutron fluence, temperature, and other relevant parameters. Finally, on the basis of an approximate model we give a rough estimate for the reduction in the yield stress due to irradiation.     

A broadband out‐of‐phase gysel power divider based on a dual‐band circuit with a single fixed isolation resistor

Based on the double‐sided parallel‐strip lines with an inserted conductor as a virtual ground, a high power divider with dual‐band/broadband response and frequency‐independent 180° phase difference between the output ports is implemented in this paper. The circuit topology employs a single commercially available external isolation resistor as well as moderate line impedances (15–100 ohm), making it suitable for high‐power applications. Precise closed‐form design equations on the basis of even‐ and odd‐mode analysis are derived. In addition to the wide range of frequency band ratios from 1 to 2.65, broadband response is also obtained by selecting the proper value of frequency band ratios. To substantiate the design equations and theory, a circuit with 2:1 frequency ratio and 84.5% bandwidth referring to 16 dB isolation and 12 dB return loss values is developed. To the authors' knowledge, this is the widest bandwidth reported for out‐of‐phase high power dividers. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2016.     

Experimental study on the effect of molecular weight and chemical composition distribution on the mechanical response of high-density polyethylene

This article aims to appraise the effect of microstructure comprising molecular weight distribution and chemical composition distribution on the mechanical properties of high-density polyethylene (HDPE). HDPE resins were synthesized using several titanium–magnesium-supported Ziegler–Natta catalysts in the industrial gas phase reactor under the same polymerization condition. Gel permeation chromatography and crystallization elution fractionation (CEF) were conducted on the resins to characterize the molecular weight and comonomer distribution. Crystallization, thermal and rheological behavior were evaluated following differential scanning calorimetry, polarization light microscopy, and rheometric mechanical spectrometry. The resins with higher soluble fraction in trichlorobenzene below 80°C (highly branched low molecular weight chains) exhibited longer crystallization time based on the crystallization kinetic obtained from the Avrami model. Rheological determination of the molecular weight between entanglements (M_e) and the average lamella thickness based on the Gibbs–Thomson equation revealed that the entanglement density and impact strength decreased, and the average lamella thickness increased with an increase in the ratio of CEF eluted fraction below 80°C to the crystallizable fraction in the range of 80–90°C.     

Monitoring the fluidized bed reactor for polyethylene polymerization based on fibre optic acoustic emission sensor

This paper presents applications of a new class of fibre optic acoustic emission (FOAE) sensor to monitor the operation of fluidized bed reactors used in polyethylene production. Specifically, the sensor was implemented to detect undesired, abnormal phenomena related to particle agglomeration, wall sheeting, fine overflow, and variations in the superficial gas velocity. The experiments were executed using a fluidized bed cold model setup for polyethylene powders with average particle sizes of 250, 1000, and 2000 μm. The results demonstrated that the presence of agglomerated particles in the fluidized bed reactor increases the kurtosis of the acoustic emission (AE) signal. Furthermore, the overflow of small particles can be detected by mounting the FOAE sensor below the gas distributor plate and monitoring an increase in the root mean square (RMS) of the AE signal. The AE signal RMS increased with the rising superficial gas velocity. Besides, forming a sheet layer on the reactor wall decreased the AE signal RMS. The proposed sensor's main benefits are its simple design, rapid response to abnormal conditions in the fluidized bed reactor, immunity against electromagnetic noise, high-temperature resistance, and safety in hazardous areas.     

Machine vision-based automated earthquake-induced drift ratio quantification for reinforced concrete columns

This paper presents a novel method for estimating the seismic peak interstory drift ratio (IDR) in reinforced concrete (RC) columns after an earthquake using surface crack image analysis. The quantitative representation of the complexity and irregularity of crack images in damaged RC columns is obtained through the consideration of the generalized fractal dimensions. The authors have compiled a comprehensive database consisting of 445 crack maps obtained from cyclic experiments conducted on 110 rectangular RC column specimens exhibiting double-curvature deformation mode. This database is utilized by the authors to develop and validate the proposed procedure. The research database contains a wide range of structural and geometric features. Five closed-form equations are developed with the objective of estimating the peak IDR experienced by the RC columns during a seismic event. The predictive equations are derived through the utilization of symbolic regression technique, with the input parameters varying according to the availability of columns characteristic parameters. Results reveal that generalized fractal dimensions, especially D₋₁, are strong vision-based indicator of damage in RC columns having correlation coefficients with IDR ranging from 0.82 to 0.92 across the considered plans. The seismic peak IDR obtained through the empirical equations can serve as the input engineering demand parameter (EDP) in the seismic loss estimation frameworks. This allows for the determination of the probability of exceeding damage states for structural and nonstructural components of concrete buildings. Finally, the practical implementation of the methodology is examined by its application to an actual case of a damaged column during the Kermanshah earthquake of magnitude 7.3 that occurred in 2017.