Prediction of Excess Air Factor in Automatic Feed Coal Burners by Processing of Flame Images

In this study, the relationship between the visual information gathered from the flame images and the excess air factor k in coal burners is investigated. In conventional coal burners the excess air factor k. can be obtained using very expensive air measurement instruments. The proposed method to predict k for a specific time in the coal burners consists of three distinct and consecutive stages; a) online flame images acquisition using a CCD camera, b) extraction meaningful information(flame intensity and brightness)from flame images, and c) learning these information(image features) with ANNs and estimate k. Six different feature extraction methods have been used: CDF of Blue Channel, Co-Occurrence Matrix, L_∞-Frobenius Norms,Radiant Energy Signal(RES), PCA and Wavelet. When compared prediction results, it has seen that the use of cooccurrence matrix with ANNs has the best performance(RMSE = 0.07) in terms of accuracy. The results show that the proposed predicting system using flame images can be preferred instead of using expensive devices to measure excess air factor in during combustion.     

Integrated acoustic echo and noise suppression in modulation domain

The quality of speech transmission in mobile communication systems deteriorates due to the presence of background noise and acoustic echo. The background noises are the disturbances from the surroundings and acoustic echo is induced due to the reverberation of loudspeaker signal in the near end environment. In conventional acoustic echo suppression setup, the echo path effect is modelled either in time or in frequency domain, and to cancel the echo, a replica of the echo is created by estimating the echo path response adaptively in the corresponding domain. Recently, the modulation domain analysis, which captures the human perceptual properties, is widely being used in speech processing. Modulation domain conveys the temporal variation of the acoustic magnitude spectra which acts as an information bearing signal. In this work, a novel integrated system for acoustic echo and noise suppression in the modulation domain is developed. So far, no work in this context in modulation domain has been found as reported. An efficient method for modelling the echo path and estimating the echo in the modulation domain is introduced and implemented. The effects of echo and noise are suppressed using the modulation spectral manipulation and the performance of the proposed system is found to be better than other conventional integrated systems.     

Forced Commutated Cycloconverters for High-Frequency Link Applications

Forced commutated cycloconverters (FCC's) have been used successfully as static frequency changers for low-to-medium frequency applications. The use of FCC's for high-frequency applications and, in particular, in the role of high-frequency links (HFL's) is investigated. Such links are widely used as intermediate stage circuits to provide simultaneous power conditioning and ohmic isolation. The investigation shows that suitable HFL circuit topologies do exist for any combination of input-to-output number of phases. It also shows that, through the use of appropriate switching techniques, it is possible to obtain HFL output voltage and input current waveforms with low harmonic content and insignificant amplitude derating.     

Time-interleaved SAR ADC design with background calibration

In this article, a low power time-interleaved SAR (TI-SAR) ADC is presented. Background calibration is used to improve the linearity of the ADC. Offset, gain, and capacitor mismatches between interleaved channels are calibrated by postprocessing the ADC output. Besides, a novel trimming-based calibration algorithm is used to calibrate the timing mismatches between channels. The proposed calibration algorithm is more power-efficient compared with most of its counterparts. The ADC consists of 18 parallel channels, a reference channel with two dummy channels, and a channel for timing calibration. The timing calibration channel is clocked only when the reference channel samples. The dummy channels are utilized to equalize the input load over time as they sample one after another to fill the gap where the reference channel does not sample. There is no need for any other dummy channels for timing calibration channel since it has low kickback noise over input driver. Each parallel channel operates at 111 ms/s while the reference channel runs at 105 ms/s. The aggregate sampling speed of the converter is 2 GS/s, and 52-dB SNDR is accomplished near Nyquist frequencies.     

Synthesis of hexagonal graphene on polycrystalline Cu foil from solid camphor by atmospheric pressure chemical vapor deposition

Understanding of graphene nucleation and growth on a metal substrate in chemical vapor deposition (CVD) process is critical to obtain high-quality single crystal graphene. Here, we report synthesis of individual hexagonal graphene and their large cluster on Cu foil using solid camphor as a carbon precursor in the atmospheric pressure CVD (AP-CVD) process. Optical and scanning electron microscopy studies show formation of hexagonal graphene crystals across the grain, grain boundaries and twin boundaries of polycrystalline Cu foil. Electron backscattered diffraction analysis is carried out before and after the growth to identify Cu grain orientation correlating with the graphene formation. The influence of growth conditions and Cu grain structure is explored on individual hexagonal graphene formation in the camphor-based AP-CVD process.     

Spark plasma sintering and thermoelectric evaluation of nanocrystalline magnesium silicide (Mg2Si)

Recently magnesium silicide (Mg₂Si) has received great interest from thermoelectric (TE) society because of its non-toxicity, environmental friendliness, comparatively high abundance, and low production material cost as compared to other TE systems. It also exhibited promising transport properties, including high electrical conductivity and low thermal conductivity, which improved the overall TE performance (ZT). In this work, Mg₂Si powder was obtained through high energy ball milling under inert atmosphere, starting from commercial magnesium silicide pieces (99.99 %, Alfa Aesar). To maintain fine microstructure of the powder, spark plasma sintering (SPS) process has been used for consolidation. The Mg₂Si powder was filled in a graphite die to perform SPS and the influence of process parameters as temperature, heating rate, holding time and applied pressure on the microstructure, and densification of compacts were studied in detail. The aim of this study is to optimize SPS consolidation parameters for Mg₂Si powder to achieve high density of compacts while maintaining the nanostructure. X-Ray diffraction (XRD) was utilized to investigate the crystalline phase of compacted samples and scanning and transmission electron microscopy (SEM & TEM) coupled with Energy-Dispersive X-ray Analysis (EDX) was used to evaluate the detailed microstructural and chemical composition, respectively. All sintered samples showed compaction density up to 98 %. Temperature dependent TE characteristics of SPS compacted Mg₂Si as thermal conductivity, electrical resistivity, and Seebeck coefficient were measured over the temperature range of RT 600 °C for samples processed at 750 °C, reaching a final ZT of 0.14 at 600 °C.