DAC Technique Research Articles

On-site Insulation Tests for MV cable using Very Low Frequency and Damped AC Techniques

MV cables are vital components in urban power networks. Several insulation test techniques are proposed for guaranteeing the operation of MV cables. In this paper, two kinds of off-line testing techniques are introduced, namely Tanδ measurement using VLF and PD detection using DAC. Firstly, the operation principle of each technique is introduced. Then, a simulation model was built in Simulink platform to demonstrate the operation processes of detecting the defects in the cable. At last, an on-site case using both VLF and DAC techniques is introduced for presenting the functions of different techniques.

Sp2-to-sp3 transitions in graphite during cold-compression.

Pressure-induced sp2-to-sp3 transitions in graphite have been studied for decades by experiments and simulations. In general, pressures of 15-18 GPa are needed to initiate structural transitions in graphite at room temperature, and the high-pressure phases are usually unquenchable, as evidenced by in situ resistivity and optical transmittance measurements, X-ray diffraction (XRD), and inelastic X-ray scattering (IXS). However, our in situ Raman results show that the onset transition pressure can be as low as 9.7 GPa when using the methanol-ethanol-water (MEW) mixture as the pressure-transmitting medium (PTM), indicated by an additional GD Raman peak caused by the sp3 bonding between adjacent graphite layers. Moreover, using a combination of XRD, Raman, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM), we show that a small amount of sp3 bonds associated with a unique feature of cross stacking are present in the recovered samples. Our findings will be useful to understand the intricate structural transitions in graphite-like materials under compression.

Raman high-pressure study of butane isomers up to 40 GPa

Raman spectroscopy studies on n and i-butane were performed at pressures of up to 40 GPa at ambient temperatures using the DAC technique. Normal butane undergoes two phase transitions at 1.9(5) GPa and 2.9(5) GPa and isobutane at 2.7(5) GPa and 3.5(5) GPa. These phase transitions were identified based on observations of the splitting Raman modes and the appearance or disappearance of particular Raman peaks. Our results demonstrate the complex, high-pressure behavior of butane isomers.

An Interleaved Full Nyquist High-Speed DAC Technique

A 9 bit 11 GS/s DAC is presented that achieves an SFDR of more than 50 dB across Nyquist and IM3 below 50 dBc across Nyquist. The DAC uses a two-times interleaved architecture to suppress spurs that typically limit DAC performance. Despite requiring two current-steering DACs for the interleaved architecture, the relative low demands on performance of these sub-DACs imply that they can be implemented in an area and power efficient way. Together with a quad-switching architecture to decrease demands on the power supply and bias generation and employing the multiplexer switches in triode, the total core area is only 0.04 mm2 while consuming 110 mW from a single 1.0 V supply.

A continuous time delta-sigma modulator with reduced clock jitter sensitivity through DSCR feedback

The performance of continuous time delta-sigma modulators is limited by their large sensitivity to feedback pulse-width variations caused by clock jitter in their feedback DACs. To mitigate that effect, a dual switched-capacitor-resistor feedback DAC technique is proposed. The architecture has the additional benefit of reducing the typically high switched-capacitor-resistor DAC output peak currents, resulting in reduced slew-rate requirements for the loop-filter integrators. The feedback technique has been implemented with a third order, 3-bit delta-sigma modulator for a low power radio receiver, in a 65 nm CMOS process, where it occupies an area of 0.17 mm2. It achieves an SNDR of 70 dB over a 125 kHz bandwidth with an oversampling ratio of 16. The power consumption is 380 μW from a 900 mV supply.

Pressure dependence of color of natural uvarovite: the barochromic effect

The electronic absorption spectra of natural uvarovite containing 62 mole% of the Cr3+ end-member were studied at pressures between 10−4 and ca. 13 GPa using DAC techniques combined with microscope spectrometric device. With increasing pressure, a barochromic effect with change from green to red color of the garnet specimen was observed. This change could be interpreted on the basis of the spectra and the data points derived in an ICE color card. The evaluation of crystal field data from the spectra showed that 10Dq of chromium increases on pressure while the Racah parameter B, and thus the nature of the chemical bond of Cr–O does not change significantly.

The high-pressure phase transformation and breakdown of MgFe2O4

The high-pressure transformation of MgFe2O4 was studied by Mossbauer and Raman spectroscopy and synchrotron X-ray diffraction using the DAC technique and laser annealing at temperatures of 1500–2000 K. The high-pressure phase of MgFe2O4 was observed from in situ Mossbauer spectra at 17 ± 1 GPa after laser annealing by the appearance of two quadrupole doublets. This indicates a disordered distribution of Mg and Fe in an early stage. The displacive nature of the transformation of the spinel into its high-pressure polymorph was shown at increasing pressure by the redistribution of iron into only one site. After decompression Mossbauer spectroscopy revealed the presence of Fe2O3 in the sample. This was further confirmed by Raman spectroscopy at ambient conditions and by in situ high-pressure XRD, indicating a partial breakdown of the spinel into its constituent oxides MgO and Fe2O3. The XRD pattern of the high-pressure phase of MgFe2O4 can be indexed in agreement with the CaMn2O4-type structure, with cell parameters a = 2.775(2), b = 9.283(16), and c = 9.446(5) A at 23 ± 2 GPa. The multiphase spectra from all three analytical methods suggests that inhomogeneous conditions prevailed in the DAC experiments, resulting in two different reactions at high pressure and temperature, i.e., T 1800 K: MgFe2O4 → hp-MgFe2O4.

ＤＡＣ技術入門 ＩＩ ＤＡＣの超伝導探索への応用

ＤＡＣ技術入門 ＩＩ ＤＡＣの超伝導探索への応用

ＤＡＣ技術入門 高圧下の赤外吸収測定

ＤＡＣ技術入門 高圧下の赤外吸収測定

ＤＡＣ技術入門 低温技術

ＤＡＣ技術入門 低温技術