Electric Field Levels Research Articles

Unusual magnetic order in CeT2Al10(T=Ru, Os) in comparison with localized NdFe2Al10

We have investigated the magnetic properties in the well localized compound NdFe${}_{2}$Al${}_{10}$ and the Kondo semiconductor Ce${T}_{2}$Al${}_{10}$ ($T=\text{Ru}$, Os) to clarify the origin of the unusual magnetic order in Ce${T}_{2}$Al${}_{10}$. In NdFe${}_{2}$Al${}_{10}$, the experimental results of the magnetic properties could be reproduced very well by the mean-field calculation for the two-sublattice model. In Ce${T}_{2}$Al${}_{10}$ we could reproduce the anisotropic magnetic susceptibility in the paramagnetic region above 60--100 K very well by the mean-field calculation for the two-sublattice model introducing an anisotropic exchange interaction and the recently determined crystalline electric field (CEF) level scheme from Strigari et al. [Phys. Rev. B 86, 081105 (2012)]. However, in the antiferromagnetic (AFM) ordered state, we could not reproduce the experimental results at all in the framework of the mean-field calculation for the two-sublattice model. We propose that although the magnetic properties in the paramagnetic region above 60--100 K could be understood well by a localized picture, the ordered state could not, and that the $c$-$f$ hybridization, especially along the $a$ axis, is associated with the unusual magnetic order in Ce${T}_{2}$Al${}_{10}$.

An improved procedure to accurately assess the variability of the exposure to electromagnetic radiation emitted by GSM base station antennas

Long-term human exposure around Global System for Mobile Communications (GSM) base station antennas has not yet been precisely established; this is of interest from human health and epidemiological perspectives. Actual exposure is difficult to assess accurately, mainly because there is a lack of technical information directly from the GSM operators. The in situ measurement standards available at present provide only a worst-case prediction method; the present work goes beyond this and proposes a methodology that, without the need for data from operators, allows a reliable way to express real exposure with a greater accuracy than all other methods proposed to date. The method is based on dual measurements of the signal strengths in the frequency domain and the time domain and takes into consideration the instantaneous traffic in GSM channels. In addition, it allows a channel-individualized exposure assessement, by making possible the separate analysis of the electric field level in the two types of channel of the GSM standard—the traffic channels and the control channels.

Crystalline Electric Field Effects and Hidden Order in URu2Si2

We show that an antiferro-octupole order of E u ( x ( y 2 - z 2 ), y ( z 2 - x 2 )) symmetry accounts for the rotational symmetry (RS) reduction of the basal plane magnetic susceptibility in the hidden order (HO) phase of URu 2 Si 2 . We determine the crystalline electric field level scheme with lower singlet-doublet levels, which can stabilize the E u octupole order, as well as the quadrupole order of E g ( y z , z x ) symmetry. Both orders can explain the RS reduction, but the octupole order breaks the time reversal symmetry, in agreement with the ligand NMR measurements, while the quadrupole order does not. Consequently, the E u octupole order is favorable for the HO of URu 2 Si 2 .

Pr magnetism and its interplay with the Fe spin-density wave in PrFeAsO1−xFx(x=0,0.15)

We have studied the magnetism of the Pr3+ ions in PrFeAsO_1-xF_x (x = 0; 0.15) and its interaction with the Fe magnetic order (for x = 0). Specific heat data confirm the presence of a first excited crystal electric field (CEF) level around 3.5 meV in the undoped compound PrFeAsO. This finding is in agreement with recent neutron scattering experiments. The doped compound is found to have a much lower first CEF splitting of about 2.0 meV. The Pr ordering in PrFeAsO gives rise to large anomalies in the specific heat and the thermal expansion coefficient. In addition, a field-induced transition is found at low temperatures that is most pronounced for the magnetostriction coefficient. This transition, which is absent in the doped compound, is attributed to a reversal of the Fe spin canting as the antiferromagnetic Pr order is destroyed by the external magnetic field.

Superposition of DC Voltage and Submicrosecond Impulses for Energization of Electrostatic Precipitators

This paper discusses the development of an impulsive microelectrostatic precipitation technology, which uses superposition of submicrosecond high-field pulses and dc electric field. Short impulses allow the application of higher voltages to the ionization electrodes of a precipitation system without the initiation of breakdown. These higher levels of electric field generate higher ionic concentrations, resulting in more efficient charging of the airborne particles, and can potentially improve precipitation efficiency. This work is focused on the analysis of the behavior of impulsive positive corona discharges in a coaxial reactor designed for precipitation studies. The efficiency of precipitation of coarse and fine particles has been investigated using different dc and impulse voltage levels in order to establish optimal energization modes.

Application of pulsed x-ray induced partial discharge measurements

The use of short x-ray pulses (duration 50 ns) has shown to eliminate the statistical time lag by providing start electrons for the partial discharge (PD) development in a void, making it possible to detect very small voids at low electric field levels. A single x-ray pulse of a given dose produces a certain number of electron-ion pairs in a given gas volume, depending on the gas parameters. A minimum x-ray dose is thus needed to provide at least one start electron in the void for successful pulsed x-ray induced partial discharge (PXIPD) inception. In the application of x-rays to a conventional PD measurement, it is necessary to consider that photons emitted by the x-ray source are attenuated by every barrier material which is located between the source and the void of the insulator. This paper presents guidelines on how to design a successful PXIPD measurement with any given pulsed x-ray source. To do so, the theoretical background of PDs and the attenuation phenomena of x-ray are shown. The minimum x-ray dose for PD inception in artificially produced spherical voids is determined experimentally and evaluated theoretically.

Strength properties of aged poled lead zirconate titanate subjected to electromechanical loadings

Electric field and aging time are two important factors that affect the mechanical strength and long-term reliability of lead zirconate titanate or PZT actuators. In the present work, a commercial PZT-5A aged four years was examined using ball-on-ring (BoR) mechanical testing under coupled electric fields. The electric field range of −3Ec to +3Ec (Ec, coercive electric field) was studied (i.e., −3Ec, −Ec, 0, +Ec, +2Ec, and +3Ec) with a controlled electric loading path. A Weibull distribution was used to interpret the mechanical strength data. With an electric field preloaded from 0 to −3Ec, it was found that subsequent increases in the electric field resulted in an asymmetrical V-shaped curve of mechanical strength against the electric field. The bottom of the V curve was located near the zero electric field level. Microscopy analysis showed that pores were the strength limiter for the tested PZT under electromechanical loadings.

Biaxial flexural strength of poled lead zirconate titanate under high electric field with extended field range

In the present work, as-received poled lead zirconate titanate, or PZT, was examined using ball-on-ring (BoR) mechanical testing coupled with an electric field. Electric fields in the range of ±4EC (EC, coercive field) with controlled loading paths were applied, and mechanical tests at a substantial number of characteristic electric field levels were conducted. Commercial electronic liquid FC-40 was used to prevent the setup from dielectric breakdown under a high electric field. Weibull strength distribution was used to interpret the mechanical strength data. The data showed that the strength levels of the PZT tested under OC (open circuit) in air and in FC-40 were almost the same. It was further revealed that, for the studied cases, the effect of loading history on the biaxial flexural strength of the PZT was significant in −EC, but not in OC or zero field as well as 4EC. An asymmetric “V” curve was observed for the characteristic strength-electric field graph, and the bottom of “V” curve was located near the negative coercive field. Microscopic analysis showed that surface-located volume-distributed flaws were the strength limiter and responsible for the failure of the tested PZT under electromechanical loadings.

Long-term exposure to mobile communication radiation: an analysis of time-variability of electric field level in GSM900 downlink channels

Interest for knowing long-term human exposure levels due to mobile communications has increased in the last years. It has been shown that short-term exposure assessment made under standard procedural restrictions is not reliable when it comes to conclusions on long-term exposure levels. The present work is the result of a several week analysis of time variability of electric field level inside traffic and control channels of the GSM900 mobile communication downlink band and it indicates that a temporal model to allow future predictions of exposure on the long run is obtainable. Collecting, processing and statistically analysing the data provide expression of the maximum and weighted field strengths and their evolution in time. Specific electromagnetic footprints of the channels have been extracted, differentiations between their characteristics have been emphasised and practical advice is provided, with the scope of contributing to the development of reliable procedures for long-term exposure assessment.

On the Use of Antenna Diversity Measurements for Mobile DVB-T Performance Assessment

A novel measurement method based on antenna diversity principle is proposed for mobile digital video broadcasting-terrestrial (DVB-T) performance assessment. The method relies on an integrated measurement station and follows a measurement procedure that allows the direct comparison of A/V video signal quality and the respective electric field levels on a geo-referenced basis. The results of a wide measurement campaign performed in the urban area of Bolzano not only allow the validation of the method but also outline the necessity to enhance the practical application of the common link budget model, which predicts the minimum median field strength in a target area, as a function of the specific combining technique used at the receiver side.

A compact dielectric elastomer tubular actuator for refreshable Braille displays

Electroactive polymer actuators stimulated by appropriate levels of electric field are particularly attractive for human-assist devices such as Braille. The development of a full page refreshable Braille display is very important for the integration of the visually impaired into the new era of communication. In this paper, development of a compact dielectric elastomer actuator suitable for Braille application is reported. The actuators are fabricated from commercially available silicone tubes. The tube has been rendered mechanically anisotropic through asymmetric levels of applied pretension in circumferential and axial directions in order to direct the actuation strain in the axial direction of the actuator. Key performance parameters, such as displacement, force, and response time of the actuator are investigated. The test results demonstrate the potential of the compact, lightweight, and low cost dielectric elastomer as actuators for a refreshable full page Braille display.

Magnetic Field–Temperature Phase Diagram of the Ferro-quadrupolar State and Crystal Electric Field Effect in UCu2Sn

The ternary uranium compound UCu 2 Sn shows a ferro-quadrupolar transition at T Q = 16 K originating from the ordering of the non-Kramers doublet Γ 5 ground state. To investigate the magnetic field–temperature phase diagram of the ferro-quadrupolar state in UCu 2 Sn, we measured elastic modulus C 66 at magnetic fields of up to 14 T. We found an anisotropic field dependence of T Q ( H ) in H ∥[\bar12\bar10], [0001], and [01\bar10]. We optimized the crystal electric field level scheme using C 66 under fields, magnetic susceptibility, and electronic entropy. The quadrupolar phase diagram is well reproduced by the obtained level scheme.

Mechanisms behind positive streamers and their distinct propagation modes in transformer oil

Comprehensive modeling and analysis is presented for the charge generation, recombination, attachment, and transport of positive ions, negative ions, and electrons in transformer oil between a positive high voltage sharp needle electrode and a large spherical ground electrode. Case studies show that a key mechanism in streamer development is field ionization, which is the direct ionization of molecules due to action of the electric field. Due to the high mobility electrons, which are about 1 × 105 times more mobile than the positive ions, the newly generated electrons quickly exit the high field ionization zone towards the anode leading to the development of a net positive space charge peak which subsequently creates an electric field enhancement in the oil. The process is driven by the applied high voltage creating temporally dynamic space charge and electric field distributions that develop an ionizing wave that drives streamer development. The pre-breakdown modeling and analysis elucidates the development of different streamer modes in transformer oil. In particular, the analysis focuses on mechanisms driving filamentary fast mode streamers discussed in the literature. The results demonstrate that streamer modes arise in transformer oil due to the ionization of different families of hydrocarbon molecules (i.e., aromatic, naphthenic, and paraffinic) at increasing electric field levels (or applied voltages). Ionization of the low concentration aromatic molecules in transformer oil, that generally have lower ionization energies than naphthenic/paraffinic molecules, leads to the propagation of streamers with velocities on the order of 1 km/s. As the applied voltage is increased, the ionization of the main hydrocarbon molecules in transformer oil, high concentration naphthenic/paraffinic molecules, dominates producing high electric field levels and space charge at the streamer tip. This results in the propagation of a very fast streamer with velocities on the order of 10 km/s. Furthermore, these streamers have protrusion spacing in the approximate range of 20-100 μm in ~36 ns like those of electrohydrodynamic instability of charged jets that may be the origin of streamer branching. A preliminary model based on earlier electrohydrodynamic stability analysis is presented that predicts protrusion spacing in the approximate range of 7-30 μm with growth rate 2.5-5 μs.

In situ LTE exposure of the general public: Characterization and extrapolation

In situ radiofrequency (RF) exposure of the different RF sources is characterized in Reading, United Kingdom, and an extrapolation method to estimate worst-case long-term evolution (LTE) exposure is proposed. All electric field levels satisfy the International Commission on Non-Ionizing Radiation Protection (ICNIRP) reference levels with a maximal total electric field value of 4.5 V/m. The total values are dominated by frequency modulation (FM). Exposure levels for LTE of 0.2 V/m on average and 0.5 V/m maximally are obtained. Contributions of LTE to the total exposure are limited to 0.4% on average. Exposure ratios from 0.8% (LTE) to 12.5% (FM) are obtained. An extrapolation method is proposed and validated to assess the worst-case LTE exposure. For this method, the reference signal (RS) and secondary synchronization signal (S-SYNC) are measured and extrapolated to the worst-case value using an extrapolation factor. The influence of the traffic load and output power of the base station on in situ RS and S-SYNC signals are lower than 1 dB for all power and traffic load settings, showing that these signals can be used for the extrapolation method. The maximal extrapolated field value for LTE exposure equals 1.9 V/m, which is 32 times below the ICNIRP reference levels for electric fields.

Measurement of Leaked High-Frequency Burst Electric Field and EMI Evaluation for Cardiac Pacemaker in Fusion Facility

In this study, we measured the time variation of burst electric fields leaked from a heating device in the ion cyclotron range of high-frequency in an experimental fusion facility, and analyzed their statistical characteristics such as the amplitude probability distribution (APD) and crossing rate distribution (CRD). As a result, we found that the variation of the leaked electric field level is very irregular, far from the normal distribution. Moreover, the leaked electric field variation with time may reach 400 times in one second to cross its mode value. Although so, the maximum electric field intensity itself is much smaller than the ICNIRP safety guideline. In addition, we also evaluated the possibility of electromagnetic interference to an implanted cardiac pacemaker in the measured electromagnetic environment. We found that even in the worst case the interference voltage induced in the output of the pacemaker sensing circuit does still not exceed the threshold for a malfunction.

Single Die Multiple 600 V Power Diodes With Deep Trench Terminations and Isolation

This paper presents a new concept for low cost and high reliability monolithic integration of vertical power devices. The concept relies on the creation of deep trench terminations on the edge of the device, thus allowing to avoid 3 D peak surface electric field levels whereas complete insulation of the integrated power devices sharing the same backside contact electrode is guaranteed. Simulation results show that the stress of the electric field can be further reduced by introducing an angle on the trench termination walls. Power diodes in the range of 600 V with 87° wall angles of the 100-μm deep trench terminations are fabricated to demonstrate the feasibility and the effectiveness of the concept. The multidiode devices were experimentally tested under static and dynamic practical conditions. The fabricated prototypes fulfilled the initial design electrical specifications considering the breakdown voltage rating and demonstrated an excellent functional behavior. The implementation of the multidiode device into an interleaved converter is presented in this paper.

Specific heat studies of RCu 2Si 2 (R=Tb, Ho) and RCu 2Ge 2 (R=Gd, Tb) compounds

Magnetic properties of RCu 2Si 2 (R=Tb, Ho) and RCu 2Ge 2 (R=Gd, Tb), crystallizing with the tetragonal ThCr 2Si 2-type crystal structure, were investigated by means of magnetic and calorimetric measurements. All compounds exhibit antiferromagnetic ordering below T N equal to 11.2 K for TbCu 2Si 2, 5.3 K for HoCu 2Si 2, 12.0 K for GdCu 2Ge 2 and 12.5 K for TbCu 2Ge 2. At temperatures of T t = 8.5 K for TbCu 2Si 2 and 9.8 K for TbCu 2Ge 2 additional phase transitions were observed. Apart from the investigation on magnetic phase transitions, magnetic contributions to the specific heat were analyzed in terms of Schottky effect. The corresponding crystal electric field (CEF) level splitting schemes were calculated. Moreover, the phononic characteristic temperatures were estimated.

Flash‐Sinterforging of Nanograin Zirconia: Field Assisted Sintering and Superplasticity

We report on the influence of a uniaxial applied stress on flash‐sintering and field assisted superplastic behavior of cylindrical powder preforms of 3 mol% tetragonal‐stabilized zirconia. The experiments use the sinterforging method, where, in addition to pressure, a dc electrical field is applied by metal electrodes sandwiched between the push‐rods and the specimen. The axial and radial strains in the experiment provide simultaneous measurement of the time‐dependent densification and shear strains. Large effects of the electric field on sintering and superplasticity are observed. We see flash‐sintering which is characterized by a threshold level of temperature and electric field. With higher applied fields, the sample sinters at a lower furnace temperature. Surprisingly, the applied stress further lowers this critical temperature: a sample, which sinters at 915°C under a stress of 1.5 MPa, densifies at only 850°C when the stress is raised to 12 MPa. This stress induced reduction in sintering temperature maybe related to the additional electrical fields generated within the specimen by the electro‐chemo‐mechanical mechanism described by Pannikkat and Raj [Acta Mater., 47 (1999) 3423]. Remarkably, we also show that the sample deforms in pure shear to 30% strain in just a few seconds at anomalously low temperatures. The specimen temperature was measured with a pyrometer, during the flash sintering, as a check on Joule heating. A reading of 1000°C–1100°C was obtained, up to 200° above the furnace temperature. This temperature is still too low to explain the sintering in just a few seconds. It is suggested that the electric field can nucleate a defect avalanche that enhances diffusion kinetics not by changing the activation energy but by increasing the pre‐exponential factor for the diffusion coefficient, noting that the pre‐exponential factor depends on concentration of defects, and not upon their mobility.

The coupling constant polarizability and hyperpolarizabilty of 1J(NH) in N-methylacetamide, and its application for the multipole spin-spin coupling constant polarizability/reaction field approach to solvation

We present a benchmark study of a combined multipole spin-spin coupling constant (SSCC) polarizability/reaction field (MJP/RF) approach to the calculation of both specific and bulk solvation effects on SSCCs of solvated molecules. The MJP/RF scheme is defined by an expansion of the SSCCs of the solvated molecule in terms of coupling constant dipole and quadrupole polarizabilities and hyperpolarizabilities derived from single molecule ab initio calculations. The solvent electric field and electric field gradient are calculated based on data derived from molecular dynamics (MD) simulations thereby accounting for solute-solvent dynamical effects. The MJP/RF method is benchmarked against polarizable QM/MM calculations for the one-bond N-H coupling constant in N-methylacetamide. The best agreement between the MJP/RF and QM/MM approaches is found by truncating the electric field expansion in the MJP/RF approach at the linear electric field level. In addition, we investigate the sensitivity of the results due to the choice of one-electron basis set in the ab initio calculations of the coupling constant (hyper-)polarizabilities and find that they are affected by the basis set in a way similar to the coupling constants themselves.

Physical and chemical characteristics of waste activated sludge treated with electric field

This study investigates the physical and chemical characteristics of sludge treated with controlled levels of electric field. The results indicated that the potential gradient and contact time strongly influenced the physical and chemical characteristics of sludge. Based on the settling velocity measurements, a potential gradient of 6 V/cm with a treatment time of 10 min is recommended as an optimal condition for improving sludge settling. For sludge disintegration, applying a higher potential gradient and a longer treatment time to the sludge are more efficient than applying lower levels. The results of the experiments presented here show that an electric field not only disintegrates sludge and destroys microbial cells but also removes and solubilizes organic substances. Possible mechanisms of electric field treatment are also discussed.