: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

The present paper is a wide review on AC surface dielectric barrier discharge (DBD) actuators applied to airflow control. Both electrical and mechanical characteristics of surface DBD are presented and discussed. The first half of the present paper gives the last results concerning typical single plate-to-plate surface DBDs supplied by a sine high voltage. The discharge current, the plasma extension and its morphology are firstly analyzed. Then, time-averaged and time-resolved measurements of the produced electrohydrodynamic force and of the resulting electric wind are commented. The second half of the paper concerns a partial list of approaches having demonstrated a significant modification in the discharge behavior and an increasing of its mechanical performances. Typically, single DBDs can produce mean force and electric wind velocity up to 1 mN/W and 7 m/s, respectively. With multi-DBD designs, velocity up to 11 m/s has been measured and force up to 350 mN/m.

/pdf/electrical-and-mechanical-characteristics-of-surface-ac-1mbx9840kz.pdf

Electrical and mechanical characteristics of surface AC dielectric barrier discharge plasma actuators applied to airflow control

The triboelectric nanogenerator (TENG) is a new type of energy generator first demonstrated in 2012. TENGs have shown potential as power sources for electronic devices and as sensors for detecting mechanical and chemical stimuli. To date, studies on TENGs have focused primarily on optimizing the systems and circuit designs or exploring possible applications. Even though triboelectricity is highly related to the material properties, studies on materials and material designs have been relatively less investigated. This review article introduces recent progress in TENGs, by focusing on materials and material designs to improve the electrical output and sensing performance. This article discusses the current technological issues and the future challenges in materials for TENG. The development of materials for a technology that uses the movement of the human body to provide power has been reviewed by scientists in South Korea. A triboelectric nanogenerator converts mechanical energy into electricity by harnessing the fact that two surfaces rubbing against one another can become electrically charged. This is known as the triboelectric effect. One exciting use for these nanogenerators is in wearable electronics, where the motion of the body provides the power. Unyong Jeong and colleagues from Pohang University of Science and Technology have reviewed recent progress in material advances in the four main elements of a triboelectric nanogenerator: the charge-generating layer, the charge-trapping layer, the charge-collecting layer, and the charge-storage layer. These improvements all aim to increase the electrical output of such devices. Over the last decade, triboelectric nanogenerator (TENG) has been verified to be an effective way of converting daily mechanical energy into electric power or detecting various stimuli in the external environment. To promote the material researches in TENG, we introduce recent progresses in materials and material designs to improve the power generation and sensing performance. Also, we discuss on the future challenges and suggest possible approaches to solve the challenges.

/pdf/material-aspects-of-triboelectric-energy-generation-and-2j8tumglpy.pdf

Material aspects of triboelectric energy generation and sensors

https://iopscience.iop.org/article/10.1088/0963-0252/25/6/063001/pdf

Dynamics of near-surface electric discharges and mechanisms of their interaction with the airflow

Space charge formation in polymeric materials can cause some serious concern in real operation, because it has significant influence on the performance of polymers. For example, space charge in some insulating materials can severely distort the electric field, even lead to materials degradation. On the contrary, in the case of its applications, space charge stored in electrets can greatly improve their properties. It is therefore important to understand trapped charge distribution in materials as it is considered to be a novel indicator for effective evaluation of aging status and electric withstanding strength of insulating materials. In this paper, a model based on isothermal surface potential decay (ISPD) is proposed to study the distribution of trapped charges by considering the physical mechanism of the detrapping process. By measuring the ISPD characteristics of polymeric materials and fitting the data according to the assumption of shallow and deep traps, the distribution of trapped charges is obtained, which may be related to the change of aggregation structure of polymers. In order to verify the model, it is used to analyze different ISPD decay curves of polypropylene (PP) and low density polyethylene (LDPE), as well as the ISPD data of PP electrets with/without pressure expanding treatment. The results show that the proposed ISPD model is effective and convenient. Two peaks are observed on the curve of the trapped charge density versus the trap level. The obtained distribution of the trapped charges in polymers can reveal the different nature of electron/hole traps and the different transportation behavior of hole/electron carriers, i.e., the electron-type traps show an inter-chain character while the character of hole-type traps is intra-chain. In addition, the distribution of trapped charge is further related to aggregation structure of PP and LDPE, as well as PP electrets with/without pressure expanding treatment.

The energy distribution of trapped charges in polymers based on isothermal surface potential decay model

Oil-polypropylene (PP) composite insulation has been widely used in power capacitors, and also being extended to other equipment such as specific transformers, etc. As discharge can readily creep along PP surface, the interface between oil and PP is a weak point in the insulation structure. The oil-PP insulation degrades under the impact of thermal and electrical stress during normal operation. In this study, the influence of thermal degradation on surface discharge characteristics for oil-PP insulation is investigated. Degraded samples are obtained by thermally accelerated aging of virgin oil-PP samples. The microscopic morphology of PP samples are observed with SEM, and the physical and electrical properties of degraded oil are measured. In addition, the isothermal surface potential decay (ISPD) measurement is employed to investigate the charge keeping capability of PP samples. After that, surface discharge detection experiments under AC voltage are performed for the virgin and degraded samples. The ISPD results indicate that charge decay rate of degraded PP sample is faster than virgin sample, which imply that space charge memory effect of virgin PP samples is more remarkable. For this reason, the PD inception phase of virgin sample is smaller than those of degraded samples. It is found that thermal degradation of oil-PP insulation enhances the surface discharge activity. It is considered that rough surface profile and higher bubble conservation capability of degraded PP sample, and impurities in degraded oil are responsible for the enhancement effect of thermal degradation on surface discharge.

Influence of thermal degradation on surface discharge characteristics for oil-polypropylene insulation

Increasingly more incidents of insulation breakdown in underground cable network have been found in recent years. Considering the unique structure of single core cable compare with overhead line (OHL), this presentation focused on the characteristics of transient overvoltage in metallic sheath of cables. Electromagnetic transient model of typical 110kV cable network in Shaanxi province is established with the use of EMT-type program. Firstly, it is found that sheath voltage in system frequency 50Hz is much lower than the conduction voltage of sheath voltage limiter (SVL). After that, difference of closing timings of circuit breaker is considered to study the influence of residual charge on voltage. Calculation results indicate that sheath overvoltage of single-end bonding points becomes more severe than cross-bonding points, due to the fact that the close loop for residual charge exists while employing cross-bonding configuration. Moreover, profile of frequency characteristics is much rougher while considering the effect of residual charge indicating more severe oscillation of sheath voltage. Hence, more severe electric stresses are imposed on cable insulation.

Research on the Characteristics of Transient Sheath Overvoltage in Underground Cable Lines

Polymers, especially polyethylene (PE), are widely employed as insulating materials in electrical power transmission systems. However, the insulation still faces the problem of space charge, which distorts the electric field distribution and accelerates electrical aging. Experimental results show that after the fluorination process, less charge injection occurs compared with pure PE. To clarify the mechanism, classical molecular dynamics was employed to build a PE/fluorinated layer interfacial model and first principles calculation was utilized to get the band offset at the interface. The results calculated by both the bulk plus band lineup method and the layer-decomposed density of states method show that the energy band of the fluorinated PE layer is overall lower than that of the PE side, and the band offsets are around 2 eV. Charge transport results based on Marcus theory and kinetic Monte Carlo simulations also show that charge can easily accumulate at the interfacial area under an electric field and the band offset can suppress charge injection. The conduction band offset acts as an energy barrier for the excess electrons at the fluorinated layer side to cross the interface, while the valence band offset has the same effect on hole transport because of the energy barrier caused by the inverted region. Our findings provide a fundamental and theoretical basis for material modification and space charge inhibition.

First-principles investigation of band offset and charge transfer characteristics at the PE/fluorinated layer interface.

Dielectric response(DR) measurement has been deployed as a non-destructive and potential diagnostic method for moisture or aging condition of power system apparatuses. In order to promote the application of DR method, development of precise, easy-to-use and cost-effective testing devices is an urgent issue, in which accurate acquisition of the insulation current is critical. In this paper, a DR testing device which combine time-domain Polarization and Depolarization Current(PDC) and Frequency-Domain Spectroscopy(FDS), which are two major approaches for DR measurement, is developed. Firstly, the principle of PDC and FDS is introduced. Then the technical specification, hardware and software structure are demonstrated. In addition, using high input impedance PCI data acquisition card, phase lag error of the current measurement module is calibrated by measuring the voltage signal at both the input and the output ends of current measurement module. Finally, PDC and FDS test waveform of XLPE cable and bushing sample are demonstrated, and the effectiveness of this device is proved.

Development of time and Frequency Domain dielectric response testing device for power apparatus insulation

Partial discharge (PD) ultra-high frequency (UHF) sensors are widely used for condition monitoring and defect location in gas insulated substation (GIS). There are many designs of UHF sensors which can detect electromagnetic waves that radiate from PD sources. The general types of UHF sensors are disc, monopole, probe, spiral, and conical types with each type of sensor having different characteristics and applications. Sensitivity is an important index for evaluating the performance of UHF sensors. In order to test the electrical sensitivity, a simulation model to calculate the effective height is created by using FDTD Microwave software, and the size of UHF sensor are optimally designed. After that, an internal disk sensor is machined and tested with the GTEM cell. The results indicate that the effective height of UHF sensor is basically above 10 mm in the frequency region of 300MHz to 1500MHz.

Junbo Deng

Papers

Influence of thermal degradation on surface discharge characteristics for oil-polypropylene insulation

Research on the Characteristics of Transient Sheath Overvoltage in Underground Cable Lines

First-principles investigation of band offset and charge transfer characteristics at the PE/fluorinated layer interface.

Development of time and Frequency Domain dielectric response testing device for power apparatus insulation

Design and development of internal UHF sensor for partial discharge detection in GIS