High DC Field Research Articles

Microwave susceptibility analysis of ultrafast moment dynamics in a multicore magnetic nanoparticle system

Room-temperature magnetization dynamics of multicore magnetic nanoparticles often account for intrinsic dipolar magnetism to behave as a single macrospin at low-frequency regime. Either magnetic particle imaging or hyperthermia benefits from the resulting superparamagnetism in terms of nonlinear magnetization response and relaxation losses at frequencies where the rotation of magnetic moments dominates over Brownian motion for a given sinusoidal field. For this situation, spontaneous thermal relaxation (in the absence of external fields) of each composing particle moment within the cluster is critical to define effective Néel time constant and may intersect with ferromagnetic resonance (FMR) at GHz range. Here, we performed broadband AC susceptometry on both immobilized single-core and multicore iron-oxide nanoparticles up to 26.5GHz under DC bias fields. For each solid sample, we confirmed FMR frequency, where large single-core nanoparticle systems demonstrated typical resonance blueshift as DC field increased. Interestingly, high DC field induced the secondary satellite peak in the imaginary part of AC susceptibility spectra for the case of multicore nanoparticle systems. We further highlighted that a synchronous precession of the polarized macrospins under nonuniform effective fields was responsible for splitting FMR peaks at nearby microwave frequencies. Upon curve fitting of the field-dependent FMR frequency spectra, the Landau-Lifshitz-Gilbert-Kittel model later elaborates on the complex moment dynamics of multicore nanoparticle systems in correlation with distribution functions. Published by the American Physical Society 2024

Dielectric Behavior of Cellulosic Insulating Paper Subjected to a Combined AC and DC Electric Field

The effect of high dc-fields on the ac-dielectric response was studied in cellulosic insulating papers. Measurements of the complex permittivity were carried out in a frequency range from several Hz to 1 MHz with a custom-made dielectric test setup. Non-impregnated and oil-impregnated papers were investigated at different water contents. The real and imaginary components of the complex permittivity increased considerably at lower frequencies when a high dc-field was applied simultaneously. The increase depended on the water content of the paper and on the amplitude of the applied electric field. It is suggested that ionic motions in hydrated cellulose caused by a high dc-field had an effect on the complex permittivity in a frequency range determined by the time constants of movements of ionic species.

Electrical Tree Initiation and Growth in LDPE Under Negative HVDC Superimposed With AC Ripples

Understanding the role of power quality in the aging of HVdc cable systems is critical to the reliable connection of offshore renewable energy sources, and hence global ambitions to reduce carbon emissions. This work investigates electrical treeing with a needle-plane geometry in low-density polyethylene (LDPE) under a high negative dc voltage superimposed with ac ripples (−60 kV dc ± 7 kV ac). Tree initiation showed behavior similar to that widely reported under pure power frequencies. Subsequent tree growth, however, was observed to be confined in a smaller area with limited length and width than seen under pure ac voltages, even after long periods of voltage application. Traditional 2-D imaging showed overlapped tree channels which developed to cover the whole area within the tree outline. A distinguishing tree shape resulted, which we have named a “slim bouquet” shape. The volume rendering from X-ray computed tomography (XCT) showed the structure had a 3-D fractal dimension greater than 2, considerably larger than its 2-D representation. PD signals during the growth had wing-like phase-resolved partial discharge (PRPD) clusters and signal phase concentrations between 10°–45° appeared after hours of growth. There was a comb-like appearance in maximum partial discharge (PD) magnitude variation, which is typical in pure high negative dc fields. Consideration is given to both space charge distribution controlled by high dc fields and continuous degradation by ac fields to explain the slim bouquet tree formation.

(Digital Presentation) Biosensors – Researching at the Crossroads of Engineering and the Sciences

It has been a pleasure and honor to know Dr. Landheer for more than three decades and to have collaborated with him. In this invited presentation, I will focus on one aspect of our collaboration – the topic of Biosensors – which was our last research collaboration. In the list of references [1-15], I provide all publications we collaborated on since 1986.Biosensors are increasingly used in environmental applications, especially for water quality monitoring. This is because the availability of safe drinking water is fundamental to our good health. However, as water resources get increasingly stressed, ensuring a safe water supply and effective water treatment becomes increasingly important. In addition, waterborne illnesses are a significant public health problem. At the same time, current monitoring of microbiological contamination of water currently is time-consuming, laboratory based, and frequently compromises the timeliness of health advisory warnings even when contamination is found. Therefore, rapid detection of unsafe water can contribute greatly to mitigating the morbidity and mortality associated with waterborne diseases due to microbiological contaminants. Fortunately, the research community has shown increasing interest in the development of microtechnology-based sensors for the detection and identification of the bio-contaminants. These sensing systems use the same fabrication technology that has enabled the drastic lowering of cost, exponential increase in complexity of electronic chips and widespread availability of computing resources. In this presentation, we will discuss a low-cost, electrical, label-free microfabricated biosensor that we have been developing for pathogen detection related to water quality and also for ubiquitous-healthcare applications. The use of nano-dimensions devices to create futuristic nano-biosensors for both environmental and health applications will be introduced. And we will also describe our ongoing work to create highly integrated and parallel detection systems by integrating the sensor, the processing electronics and the pre-processing stages on the same cheap substrate. Finally, the success of such a low-cost, highly integrated sensing system demands a convergence of expertise from various engineering disciplines, the physical and life sciences as well as public health. References D Landheer et al, “Bioaffinity Sensors Based on MOS Field—Effect Transistors,” in Semiconductor Device-Based Sensors for Gas, Chemical, and Biomedical Applications, Eds. Ren, Pearton, Taylor & Francis Books, Boca Raton, 215-265, 2010.MW Shinwari, et al, Microfabricated Reference Electrodes and their Biosensing Applications, Sensors, Vol. 10(3), pp. 1679-1715, 2010.MW Shinwari, MJ Deen, D Landheer, “Study of the Electrolyte-Insulator-Semiconductor Field-Effect Transistor with Applications in Biosensor Design,” Microelectronics Reliability, Vol. 47(12), pp. 2025-2057, 2007.D Landheer, et al, Calculation of the Response of Field-Effect Transistors to Charged Biological Molecules, IEEE Sensors Journal, Vol. 7, 1233-1242, 2007.WH Jiang, et al, Post-processing of Commercial CMOS Chips for the Fabrication of DNA Bio-FET Sensor Arrays, Proceedings of MRS Symposium - Fall Meeting, 6 pages, 2006.Bioelectronics, Biointerfaces, and Biomedical Applications 2, Eds., D Landheer, R. Bashir, M. Deen, C. Kranz, C. Liu, M. Madou, A. Offenhaeusser, R. Schasfoort, ECS Transactions, Vol. 3, Issue 26, 2006.MJ Deen, et al, Noise Considerations in Field-Effect Biosensors, Journal Applied Physics, Vol. 100, #074703, 8 pages, 2006.MJ Deen, et al, High Sensitivity Detection of Biological Species via the Field-Effect, Proceedings of the IEEE ICCDCS, Playa del Carmen, Mexico, pp. 381-385, 2006.D Landheer, et al, Model for the Field-Effect from Layers of Biological Macromolecules on the Gates of Metal-Oxide-Semiconductor Transistors, Journal Applied Physics, Vol. 98, # 044701, 2005.Silicon Nitride and Silicon Dioxide Thin Insulating Films, Eds., R.E. Sah, MJ Deen, D Landheer, K.B. Sundaram, W.D. Brown, D. Misra, ECS Proceedings PV-03, 636 pages 2003.Silicon Nitride and Silicon Dioxide Thin Insulating Films, Eds., K.B. Sundaram, MJ Deen, D Landheer, W.D. Brown, D. Misra, M.D. Allendorf, R.E. Sah, ECS Proceedings Volume PV 2001-7, 2001.MJ Deen, et al, Low Frequency Noise in Cadmium Selenide Thin-Film Transistors, Applied Physics Letters, Vol. 77(14), pp. 2234-2236, 2000.MJ Deen, et al, Low Frequency Noise in CdSe Thin-Film Transistors, ESSDERC 2000, Cork, Ireland, pp. 592-595, 2000.MJ Deen, et al, NbN Thin Films Reactively Sputtered with a High Field DC Magnetron, Journal of Vacuum Science and Technology A, Vol. 6(4), pp. 2299-2303, 1988.MJ Deen, et al, The Effect of the Deposition Rate on the Properties of DC Magnetron Sputtered NbN Thin Films, Bull Am Phys Soc., Vol. 32(3), p. 646, 1987.

Investigation on effect of semiconducting screen on space charge behaviour of polypropylene‐based polymers for HVDC cables

High voltage direct current (HVDC) power transmission cable is critical for realising sustainability through renewable energy revolution. Eco-friendly thermoplastic polypropylene (PP)-based polymers/nanocomposites are regarded as promising candidates for replacing current thermoset crosslinked polyethylene (XLPE) cables. As an essential component of the extruded HVDC cable for improving conductor/insulation interface and suppressing charge injection to insulation at high DC electrical stresses, developing semiconducting (SC) screens that are compatible with PP-based insulation is of similar importance but has not been well studied yet. This work aims at designing PP-based semiconducting screens and investigating space charge behaviours of SC/PP/SC sandwich specimen to unfold the effect of semiconducting materials, bonding methods, applied DC electric field, and temperature on charge injection, accumulation, transportation, and dissipation in PP-based insulation. Although conventional thermal, mechanical, and low field electrical characterisations demonstrated that all of the developed semiconducting materials meet the performance criteria of commercial semiconducting materials, their space charge and local electric field distribution varied significantly at high DC fields. Compared with the traditional non-bonded configuration used at lab-scale, charge injection was enhanced in hot-pressed SC/PP/SC samples with tightly bonded interfaces, which better reflects the real situation in extruded cables. High temperature further intensified charge injections. Besides, our results also revealed that high temperature and electric field strongly influence charge mobilities and consequently their distribution and local electric field in PP-based insulations.

Phase coexistence and grain size effects on the functional properties of BaTiO3 ceramics

The functional properties of a series of BaTiO3 ceramics, having grain sizes ranging from 75 nm to 2.25 μm, with polymorph coexistence around room temperature are presented. Large temperature ranges of phase coexistence were detected through structural analyses, with no apparent size effect on the extension of co-existence domain, while the transition temperatures vary with grain size. Permittivity values are among the highest reported and the typical maximum around 1 μm grain size is confirmed by low field measurements and sub-switching Rayleigh analysis. An interesting feature not reported elsewhere is the persistence of permittivity maximum above Curie temperature and under high dc field at saturation, where domain walls contribution is minimal, raising questions about the largely accepted interpretation concerning the domain walls role on permittivity maximum. The planar defects in the starting powders give rise to extended strained defects in the ceramics, impacting their functional properties and multi-phase character.

Dielectric polymer nanocomposites: Past advances and future prospects in electrical insulation perspective

AbstractPolymeric materials enjoy widespread acceptance among electrical insulation design engineers due to their multi‐functional attributes (e.g., excellent dielectric properties, high strength to weight ratio, and ease of molding). However, charge accumulation at the high DC field, poor discharge resistance, low thermal conductivity, limited‐service temperature range, and inadequate stiffness have proven to be severe obstructions to far‐reaching utilization of these materials. To ensure the reliability of today's electrical power systems, novel dielectric materials with enhanced functionalities are essential. An idea that originated under the name of polymer nanocomposites (PNCs) is supposed to provide a viable solution to the challenges mentioned earlier. PNCs are made by mixing a small quantity of nanometer‐sized fillers into a polymer matrix and dispersing them uniformly. To effectively use PNCs in electrical insulation for power apparatus, extensive research into the physical and chemical phenomena associated with these new materials is required. This article aims to provide a comprehensive review of previous research on dielectric PNCs, including synthesis, electrical and nonelectrical characterization, and attendant issues from an electrical insulation standpoint.

Theoretical analyses of magnetoelectric effects for magnetostrictive/radial mode piezoelectric transformer composite under dual ac stress and magnetic field modulation

Magnetoelectric (ME) composite based on the converse magnetoelectric (CME) effect is promising for the high sensitivity dc and low-frequency magnetic field detection application, however, the performance is restricted by the stress modulation ability of piezoelectric phases and the narrow bandwidth. This work presents a nonlinear equivalent circuit model to design a new ME composite consisting of magnetostrictive layers/radial mode piezoelectric transformer/magnetostrictive layers under dual ac magnetic field and stress modulation. The theoretical model is based on the nonlinear constitutive relationships of magnetostrictive material, motion equation with imperfect interface condition, and improved ME equivalent circuit. This model cannot only predict the resonant ME effects of electrically modulated ME composite under the dual ac stress and magnetic field drive, but can also predict the conventional CME and mutual inductance effects separately. Specifically, the theoretical prediction indicates that with negligible extra power consumption, the dual modulated ME composite provides higher dc and low-frequency magnetic field sensitivity with frequency conversion method and significantly wider bandwidth compared to the conventional CME effect. Such theoretical predictions are further verified by the experimental results of Metglas/piezoelectric transformer/Metglas and Terfenol-D/piezoelectric transformer/Terfenol-D laminate. The theoretical study plays a guiding role in designing the new ME magnetometer with low power consumption, high sensitivity, and wide bandwidth.

Ambient Pressure Ion Funnel: Concepts, Simulations, and Analytical Performance.

In mass spectrometry (MS), a major loss of ions can readily occur during their transfer from atmospheric pressure to a lower pressure, which limits performance. Here, we report an ion funnel that can be used to effectively focus ions at ambient pressure (∼777 Torr) to significantly enhance performance in electrospray ionization (ESI) MS. For seven singly charged test ions (m/z 124-1131), the ambient pressure ion funnel (APIF) is demonstrated to improve ion abundances, sensitivity, and detection limits by up to factors of ∼17, ∼16, and ∼3, respectively, compared to the operation of conventional ESI-MS. Simulated ion trajectories were used to rationalize the enhanced performance of the APIF, which is attributed primarily to using a relatively high RF field amplitude to radially confine ions, a high DC field, and a wide exit ring electrode. The effective focusing of ions at ambient pressures should be beneficial in the future for improving the performance of (i) additional methods that ionize molecules at atmospheric pressure, (ii) ambient pressure ion mobility-based instruments, and (iii) high flow rate liquid chromatography mass spectrometry platforms.

Accelerated Degradation of IGBTs Due to High Gate Voltage at Various Temperature Environments

In this study, degradation phenomena due to gate bias stress at elevated temperature for the reliability test of punch-through IGBTs, which are widely used in DC circuit systems for automotive applications, were investigated. For the reliability tests of various temperatures, 4000 times temperature cycle stress was applied in IGBTs between −40°C and 200°C to accelerate the degradation process using the wide range temperature. And the delamination of the passivation layer and the metal layer in IGBTs was observed using the scan acoustic microscopy. In addition, the positive bias stress with 48 V at elevated temperature of 150°C for 60 min was applied to the gate, the threshold voltage increased up to 6.07 V due to charge trapping at gate oxide. We also compared the recovery of the devices, but the IGBTs that stressed with high DC field and elevated temperature slowed down the recovery process after 24 hours without reverse voltage. This work was focused to find the device recovery considering real conditions. Therefore, the various temperature stress and high electric field stress are important in the reliability test for IGBTs, it was reported the IGBT degradation process and failure symptoms using the accelerated and various reliability tests.

Johari-Goldstein relaxation in glass electrets

We investigate the dielectric response in the glass-electret state of two dipolar glass-forming materials. This unusual polar glassy state of matter is produced when a dipolar liquid is supercooled under the influence of a high electric dc field, which leads to partial orientational order of the molecules carrying a dipole moment. Investigation of the prepared glass-electrets by using low-field dielectric spectroscopy reveals a clear modification of their dielectric response in the regime of the Johari-Goldstein beta-relaxation, pointing to a small but significant increase of its relaxation strength compared to the normal glass. We discuss the implications of this finding for the still controversial microscopic interpretation of the Johari-Goldstein relaxation, an inherent property of glassy matter.

Impact ionizations in amorphous semiconductors and insulators; Se, Ge2Sb2Te5 and SiO2

It is known that impact ionizations occur in amorphous materials such as Se and SiO2 under exposures to high dc fields, pulsed-laser exposures, and high-energy radiations. These processes have been explored from different perspectives, including avalanche carrier multiplications, laser fabrications, and x-ray detections. The present work tries to clarify the relations between such phenomena. Characteristic differences of the ionizations in crystalline and non-crystalline forms are also considered. Among recent topics, specifically interesting is the laser excitation that can produce intense light pulses with the duration between femto- and nano-second ranges, which cover collision times governing impact ionization and electron-lattice interactions. For SiO2, we can connect the collision times with related mean free paths estimated from dc studies. By contrast, optical studies are still insufficient for chalcogenides, except for amorphous Ge2Sb2Te5 films.

Combined Characterization of Free-Moving Particles in HVDC-GIS Using UHF PD, High-Speed Imaging, and Pulse-Sequence Analysis

Reliable operation of high-voltage equipment depends on defect-free HV insulation systems. However, defects in the insulation can lead to partial discharge (PD) activity. PD measurement has been shown to be a useful tool for evaluating the condition of high voltage components including gas-insulated switchgear (GIS). This work focuses on characterizing the motion and PD signal behavior of free-moving particles in an experimental GIS arrangement under high dc field stress. For this purpose, the particle geometry, material composition, and amplitude of the applied negative dc voltage are varied. PD signals are measured using a broadband ultra-high-frequency (UHF) sensor and recorded in the time domain. The UHF signal is used to trigger a synchronized high-speed camera in order to observe the correlation between particle motion and UHF PD pulse activity. Certain unique combinations of UHF pulse repetition rates and signal amplitudes in the time domain are observed that depended on and were correlated with particles’ motion. These are evaluated by means of pulse sequence analysis, whose significant clusters enable estimation of particle motion. In particular, particle motion with small hopping amplitudes on the negative electrode—known as “firefly”—is differentiated with high accuracy.

A parallel co-wound no-insulation REBCO pancake coil for improving charging delays

High-Tc superconducting coils wound by REBCO coated conductors with no turn-to-turn insulation have been widely used for high-field DC magnets, due to the fact that they have a higher engineering current density and can be self-protective during a quench. One long-lasting problem of no-insulation (NI) coils is the charging delay due to low characteristic resistance. In this paper, the authors propose the structure of a parallel co-wound NI pancake coil. Unlike a traditional NI pancake coil which is wound by a single tape, in the new design multiple NI tapes are co-wound. From a circuit point of view, the tapes are connected in parallel. It is discovered that the charging delay of the NI coil can be substantially reduced by the parallel co-wound method. The mechanism is that the inductance of a coil is proportional to the square of the number turns which is inversely proportional to the number of co-wound layers, whereas the characteristic resistance is nearly irrelevant to the number of layers, therefore the coil’s time constant can be considerably reduced. The new design could also further increase the engineering current density of a magnet due to the independent current transporting of co-wound layers, which will be investigated in future work.

Charge transport and accumulation in clay-containing LDPE nanocomposites

This paper discusses the charge transport and accumulation in clay-containing LDPE (low density polyethylene) nanocomposites. LDPE is shown to host charges of both polarities in the form of homo and heterocharge when subjected to high electric fields. The addition of nanoclays has been shown to always increase the high field DC conductivity of the nanocomposites. This is shown to actually work in favor of the ability of the material to prevent the accumulation of space charge by slowly, but persistently, allowing space charges to flow across the insulation wall. However, in severe conditions of a combined high electric field and high temperature, the current flow exceeds a threshold where massive injected charges negatively impact the charge profile and the electric field distribution is greatly distorted.

Observation of current spikes caused by possible fast carrier transport through a low-density polyethylene sheet under high DC fields

The repetitive current spikes caused by possible fast carrier transport through a low-density polyethylene (LDPE) sheet under high DC fields from 0.1 to 2.0 MV/cm are simultaneously measured with space charge distributions. Although a constant dc voltage is applied to the sheet between a semi-conduction (SC) electrode and an Al-evaporated electrode, large current spikes of the order of 10−8 A are repeatedly superimposed onto the dc conduction current of the order of 10−10 A. Results of the space charge measurements indicate that the charge injection from the SC anode and the subsequent deep penetration into the LDPE bulk can be observed when the current spikes are repeatedly detected. In addition, we find that a phenolic antioxidant added into the LDPE has an inhibition effect not only on the space charge penetration but also on the repetitive current spikes. This finding suggests that the antioxidant additive produces a deep trapping site for fast-moving carriers.

Discharge characteristics in inhomogeneous fields under air flow

This research investigates the impact of high velocity air flow on Partial Discharge (PD) patterns generated in strongly inhomogeneous fields. In the laboratory, a needle plane electrode configuration was exposed to a high electrical DC-field and a laminar air flow up to 22 m/s. The needle was connected to a variable DC potential of up to 100 kV over a grounded plate in order to trigger different corona modes. The impact of the air flow on the space charges created in the vicinity of the electrode is evaluated by means of PD measurements in time domain. The results indicate that the wind increases the frequency and magnitude of partial discharges in the vicinity of the electrode due to an increased rate of space charge removal around the tip of the needle and in the gap. The positive polarity shows higher dependency on air flow compared to the negative polarity. It is shown that positive breakdown streamer corona can be extinguished if wind speeds of more than 14.3 m/s are applied to the electrode.

Polaron-mediated low-frequency dielectric anomaly in reduced LiNbO3:Ti

Measurements of the real and imaginary parts of the dielectric permittivity of reduced Ti-doped lithium niobate reveal a low-frequency dielectric relaxation as well as a strong increase in the conductivity compared to undoped samples. The low-frequency permittivity is increased by about an order of magnitude due to the relaxation. The analysis of the temperature-dependence of the relaxation frequency reveals a thermally activated behavior with an activation energy of Ea = 0.65 eV, which is in agreement with a transition between NbLi4+ small bound polarons and NbNb4+ free polarons. Both low-field ac conductivity and high-field dc conductivity indicate a Poole-Frenkel-type electron hopping mechanism between NbLi4+ sites at low temperature, turning into similar hopping between NbNb4+ at high temperatures.

Electrical characterization of extruded DC cable insulation — The challenge of scaling

HVDC cable technology with extruded insulation systems have been growing rapidly in the recent years. Different insulation concepts including crosslinked or thermoplastic polymers with or without particle fillers have been studied intensively. The DC conduction in the insulation systems is one of the most important mechanism in dielectric physics; therefore reliable and representative methods are needed to characterize it. In the development process of HVDC cables from small scale plaque sample experiments to full scale cable testing, high field DC conductivity measurement and space charge measurement with the pulsed electro-acoustic (PEA) method are common. These two methods provide two different views into the conduction physics in the insulation and provide different types of information. But both of these methods have their own drawbacks and limitations which are important to keep in mind when choosing measurement methods in different stages of the development process. Another important aspect is the inherent differences between the different types of test samples. Thin pressed plaque samples are easy to produce and require less complicated testing equipment than experimental cables but there are major differences which should not be ignored. In this paper, the principles, advantages and limitations of DC conductivity and PEA measurements on samples of different scales are described and their relevance to the evaluation process is discussed. Some of the less discussed challenges of these measurement methods on different objects are discussed in more details and recommendations are made for obtaining more useful results.

Measurements of high voltage DC fields in air

The global demand for electric power continues to increase in most countries but in particular in non-OECD (Organisation for Economic Cooperation and Development) countries [1]. Often the generation is located far from the consumers, and this requires transmission of electric power over long distances. For various reasons, high voltage direct current (HVDC) is often the preferred technology for these links [2]. To keep losses at a minimum, the voltage must be as high as possible, and this has stimulated the development of ultra-high voltage DC transmission. Over the last decade, 800 kV has been established as a new standard level for long transmission links [3].