Microsecond Pulses Research Articles

A 100 kV, 50Hz repetitive high-voltage pulse lifetime test platform.

The pulse lifetime characteristics of solid materials have been widely concerned in the field of pulse power technology. In this paper, a repetitive high-voltage pulse lifetime test platform for the pulse lifetime test of insulation materials is set up. The platform contains a closed magnetic-core transformer and a sample cavity. The transformer insulated by transformer oil was stably operated at the 100 kV/50Hz mode with maximum rise time of 45 µs. The sample cavity insulated by SF6 gas includes a gas switch with an amplitude jitter less than 3% at the 50Hz mode. The platform has advantages of high efficiency and reliability. First, it can generate three kinds of different pulses simultaneously, which satisfied the insulation test requirements under different pulse conditions. The first kind of the generated pulse is a sinusoidal pulse with an amplitude of 100 kV when the gas switch keeps open. The second one is a unipolar microsecond pulse when the gas switch closes. The last one is a nanosecond pulse generated by secondary capacitor discharge. Second, long-time operation of the platform including the pulse transformer is realized. The platform was stably operated for more than 20 × 106 pulses at the 50 Hz/100 kV mode for pulse lifetime tests of solid pulse forming lines and other solid materials.

Novel IPOx Architecture for High-Voltage Microsecond Pulse Power Supply Using Energy Efficiency and Stability Model Design Method

The high-voltage microsecond pulse power supply (HV-MPPS) is a key power input device for the study and application of plasma discharge. The energy-storage-based high-voltage pulse power supply outputs microsecond pulsewidths to obtain high-power, ultra-high voltage, and fast front-end output pulses, which are suitable for most plasma discharge applications. However, with the increasing output power requirement of the HV-MPPS, the traditional energy storage type architecture will increase dramatically in volume and weight with lower output efficiency and lower reliability, so it will not be able to achieve optimal electrical performance in plasma discharge applications. This article proposes a design method of energy efficiency and stability model based on the system architecture of IPOx (input parallel output x), where “x” means the output terminal can be in parallel (IPOP) or series (IPOS), in the application field of low-temperature plasma dielectric barrier discharge (DBD) discharge. The optimal multimodule connection mode and the number of modules can be calculated and designed easily according to different DBD electrode structures using energy efficiency and stability model design method. Finally, the proposed energy efficiency and stability model is verified by comparing the electrical experimental results and discharge status photographs of two type DBD electrodes with the 2/3/4 modules IPOx system platform.

Abstract P814: Complex Movement Representations of Mouse Motor Cortex After Experimental Stroke

Stroke injury and incomplete long-term stroke recovery remain key health issues in the United States and world-wide. We seek to help identify cellular dysfunction of the motor cortex after stroke, and its possible circuit remodeling during stroke recovery, since this structure is heavily implicated in this biology. We propose to measure evoked motor responses during long-train intracortical microstimulation (LT-ICMS) of motor cortex in the mouse as a method to identify the functional organization of this structure and plasticity following experimental stroke that relates to functional recovery. This work is one of the first to use LT-ICMS in mice after experimental stroke and it is employed in this study because it evokes complex, multi-joint forelimb movements that may match the temporal activity patterns of motor cortical cells during volitional movement and relate to skilled motor behavior. Permanent stroke injury is induced here using photothrombotic occlusion of the distal middle cerebral artery (MCAo) using Rose Bengal dye and green laser photostimulation. Skilled motor behavior is tested using the single pellet reaching task. Each mouse completes 30 days of post-injury or sham-injury single pellet reaching that is followed by an evaluation of cortical forelimb movement representation using LT-ICMS and then histological testing of lesion size and location. LT-ICMS is delivered as 500 millisecond trains of biphasic 200 microsecond pulses (delivered at 333 Hz) via a platinum/iridium microelectrode. The microelectrode is applied to test sites across the motor cortex (354 micron spacing) that are each at a depth of 800 microns. Evoked movements to LT-ICMS are quantified using high-speed video kinematic tracking of the forelimb. Experimental blind conditions are maintained until study completion. Statistics are then used to relate outcomes of behavioral reaching, LT-ICMS, and lesion characteristics. Collectively, the goal of this project is to understand whether (and how) complex movement representations derived by LT-ICMS change during stroke recovery in order to guide rehabilitative and interventional stroke therapies.

Feasibility Study of Microsecond Pulsed Microwave Ablation Using a Minimally Invasive Antenna

In this study we established the feasibility of producing localized ablation zones using microsecond pulsed microwave ablation (MWA) as an alternative to conventional continuous wave (CW) MWA. We verified that a thin floating-sleeve dipole ablation probe can withstand pulsed power delivery with peak powers as high as 25 kW, with pulse widths on the order of 1 us. We conducted MWA experiments in egg white using CW and pulsed modes of operation and found that ablation zones achieved via pulsed MWA are comparable in dimension to those created via CW MWA when the average power and procedure duration are equivalent. Finally, we performed pulsed MWA experiments in bovine liver and confirmed that pulsed MWA consistently produces large, localized ablation zones and temperatures that exceed 100{\deg}C. Establishing the feasibility of pulsed MWA opens the opportunity for developing a coupled MWA treatment and imaging system using pulsed MWA and microwave-induced thermoacoustic signals for real-time monitoring of MWA.

Space low earth orbit environment simulator for ground testing materials and devices

The design and operation of an experimental installation are described, used for simulating those factors that most greatly affect the properties of materials and microelectronic devices in conditions of the near Earth (Low Earth Orbit) environment. The simulator apparatus is in the form of a cylindrical metal vacuum chamber constructed and mounted to the electron accelerator facility of the Center for the Advancement of Natural Discoveries using Light Emission Synchrotron Research Institute (Armenia) which allows the production of accelerated electrons with the following parameters: ultra-short pulse duration (τ = 4·10−13 s), electron energy 3.5 MeV, pulse current intensity 60 A/cm2, pulse frequency 12 Hz. A comparison may be made with conventional electron accelerators, which employ micro-second pulse duration, and a far lower current intensity of 2∙10−3 A/cm2. Thus, the specific features of this installation enable the simulation of ultra-fast processes as occur in cosmic space or under other extreme conditions. Here, we present the initial results obtained, concerning the influence of high-density electron irradiation on the behavior of the electro-physical properties of silicon crystals. Peculiarities and differences are presented between the results obtained from silicon crystals irradiated by electrons with an energy of 3.5 MeV and a pulse duration of τ = 4·10−13 s, and those from silicon samples irradiated with 7.5 MeV or 50 MeV energy electrons, using conventional electron accelerators.

Microsecond Laser Texturing of an Aerospace Grade Aluminum Alloy to Synthesize Superhydrophobic, Anti-Water Clogging Surfaces

Traditionally superhydrophobic surfaces are prepared by applying liquid repellant organic coatings or nano-based coatings. These superhydrophobic coatings are prone to wear and can be easily damaged by abrasion and cleaning. Recently researchers are switching interest to more efficient and promising technology of pulse laser texturing for engineering sub-micron topographies to have superhydrophobic surfaces. In this research, the micro-second Laser Pulses are used to feature sub-micron textures on titanium nitride coated aluminum and polished aluminum surfaces in order to achieve the water contact angle greater than 150°. Titanium nitride coated aluminum surface with scan line separation of 50 µm shows superior hydrophobicity having a water contact angle of 156º. These superhydrophobic aluminum surfaces have applications for anti-water clogging and anti-corrosion use.

Laser drilling of banknote substrates

In banknote production, several security features are introduced into banknotes, including perforation of organic substrates like paper, polymer or their composites. This paper describes a comparative study about efficiency and quality aspects of laser drilling processes of organic substrates with different laser systems. The substrates investigated are cotton-based paper, Guardian™ (Biaxially Oriented Polypropylene) and two composite substrates composed of cotton paper and polymer (Durasafe™ and Hybrid™). The used laser wavelengths are 515 nm, 1060/1070 nm and 2940 nm. Laser systems with pulse durations covering the ultra-short pulse regime (ps), nanosecond pulses (ns) and microsecond pulses (µs) were used. This article gives an overview of this topic, deals with the tasks and challenges in this special field of laser manufacturing and compares different laser systems with respect to drilling quality and energy specific volume.

Dynamics of the Spatial Structure of a Microsecond Pulsed Barrier Discharge Initiated in Atmospheric Pressure Air in the Point–Plane Geometry at Different Polarities of Feed Voltage

The evolution of a microsecond pulsed barrier discharge initiated in atmospheric pressure air in the point–plane electrode geometry has been investigated using streak camera photorecording and shadow photography with micrometer resolution and nanosecond exposure. It has been shown that the discharge develops in series and its structure evolves both within a series and from series to series. It has been found that, irrespective of the polarity of a feed voltage pulse, the discharge develops from the point electrode, having the form of a set of many micrometer-diameter channels. At the late stage, the discharge consists of a number of glowing microstructured channels, which occupy the space between the point and barrier and deviate from the point axis, and many faint channels radially propagating over the surface of the barrier. Numerical parameters of the structured have been obtained.

Microsecond Pulsed Electric Fields: An Effective Way to Selectively Target and Radiosensitize Medulloblastoma Cancer Stem Cells

Cancer stem cells constitute an endless reserve for the maintenance and progression of tumors, and they could be the reason for conventional therapy failure. New therapeutic strategies are necessary to specifically target them. In this context, microsecond pulsed electric fields have been selected to expose D283Med cells, a human medulloblastoma cell line resulted to be rich in cancer stem cells, and normal human astrocytes. We analyzed invitro different endpoints at different times after microsecond pulsed electric field exposure, such as permeabilization, reactive oxygen species generation, cell viability/proliferation, cell cycle, and clonogenicity, as well as the expression of different genes involved in cell cycle, apoptosis, and senescence. Furthermore, the response of D283Med cells exposed to microsecond pulsed electric fields was validated invivo in a heterotopic mouse xenograft model. Our invitro results showed that a specific pulse protocol (ie, 0.3 MV/m, 40 μs, 5 pulses) was able to induce irreversible membrane permeabilization and apoptosis exclusively in medulloblastoma cancer stem cells. In the surviving cells, reactive oxygen species generation was observed, together with a transitory G2/M cell-cycle arrest with a senescence-associated phenotype via the upregulation of GADD45A. Invivo results, after pulsed electric field exposure, demonstrated a significant tumor volume reduction with no eradication of tumor mass. In conjunction, we verified the efficacy of electric pulse pre-exposure followed by ionizing irradiation invivo to enable complete inhibition of tumor growth. Our data reveal novel therapeutic options for the targeting of medulloblastoma cancer stem cells, indicating nonionizing pulsed electric field pre-exposure as an effective means to overcome the radioresistance of cancer stem cells.

Use of bursts of 1.54-μm microsecond laser pulses for cataract destruction

The possibility of using bursts of microsecond pulses of an Yb,Er : glass laser (λ = 1.54 μm) for cataract destruction was investigated experimentally in vitro for the first time. The energy in a laser pulse was limited from below by the eye lens destruction threshold and from above by the radiation resistance of the input end face of the radiation-supplying fibre. The energy of a burst consisting of three microsecond laser pulses, separated by time intervals of 850 μs, was 255 ± 15 mJ, and the burst repetition rate was 15 Hz. The hydroacoustic signal, generated after each burst pulse in the water around the lens, contained two components. The first occurred immediately after the laser pulse transmission, and the second was delayed by 250 to 350 μs. The amplitude of the second component of the hydroacoustic signal exceeded the amplitude of the first component and was maximum (50.0 ± 8.0 MPa) for the signal induced by the second pulse in the burst. The efficiency of cataract destruction by microsecond-pulse bursts generated by an Yb,Er : glass laser was found to depend on the lens nucleus density, to exceed significantly the efficiency of cataract destruction by single microsecond pulses of this laser, and to be comparable with the efficiency of eye lens destruction by a 1.44-μm Nd : YAG laser.

Физические процессы в канале распространения импульсов СО2-лазера при генерации электрических и магнитных полей

The mechanisms of generation of electric and magnetic fields during the propagation of microsecond pulses of a CO2 laser in the atmosphere over long paths are considered. The range of radiated waves selected for research is substantiated. The power of the source required for the realization of the pre-breakdown and breakdown modes of interaction of radiation with the medium is estimated. The dependence of the observed signals on the conditions of radiation propagation is investigated. Comparison of theoretical estimates and results of outdoorexperiments is carried out.

Deep ablation and LIBS depth elemental profiling by combining nano- and microsecond laser pulses

A combination of nano- and microsecond pulses has been suggested for LIBS elemental profiling beyond 1 mm depth for metal coatings. Deep laser ablation and LIBS measurements have been compared for different laser pulse temporal shapes: single and double nanosecond pulses, free-run pulse and combined micro-nanosecond pulse. The deepest laser crater was produced by free-run pulse but plasma emissivity fell dramatically within the first few laser shots. Both single nanosecond pulse and double nanosecond pulse ablation provided crater with depth less than 0.6 mm which is not enough for a typical cladded coating thickness measurements. Nano- and microsecond laser pulses coupling resulted in deep crater formation (> 1.5 mm) but LIBS spectra with good signal-to-noise ratio can be still captured. The feasibility of LIBS depth profiling by coupled nano- (first) and microsecond (second) pulses has been demonstrated for 0.8–1.2 mm thick superalloy coatings measurements.

The effect of modulated electric field on characteristic of SDBD‐like plasma jet for surface modification

AbstractIn this paper, the dynamics and flow behaviour of an atmospheric argon plasma jet was studied in the new nozzle structure similar to the surface dielectric barrier discharge (SDBD) using the Schlieren imaging method. The effect of plasma jet driven by repetitive high‐voltage microsecond pulses with low‐frequency sinusoidal bias was measured qualitatively in a single mirror Schlieren optical system. The enhancement of plasma jet length and cross‐section of plasma jet with surface in this condition is due to highly turbulent flow of argon plasma jet in this structure. This study revealed the important role of SDBD structure and modulated electric field on the behaviour of plasma jet in a high diameter nozzle. In practice, this technique allows us to increase the jet length of the nozzle output to 5 cm and under these conditions, the diameter of the plasma jet cross‐section is increased to 8 mm, without increasing the electrical power consumption. Eventually, the hydrophilicity of the surface is also measured by the contact angle of a water droplet that decreases from 78° to 8° after surface treatment, implying we were able to reach a super‐hydrophilic surface with this plasma jet structure.

The Modification Mechanism of Nano-Liquids on Streamer Morphology and Breakdown Strength under Microsecond Pulse

In liquid mediums, whether the breakdown strength can be greatly improved after introducing the nano-particles has been widely investigated, however, there has been no scientific consensus on the modification mechanism of this anomalous phenomenon. In this paper, we first experimentally measured the streamer morphology and breakdown strength in pure transformer oil, TiO2 nano-liquids and Al2O3 nano-liquids under microsecond pulse. The results demonstrated that there are significant differences in streamer morphology between pure transformer oil and nano-liquids, as the streamers in pure transformer oil exhibit thick bush-like qualities, while in nano-liquids they exhibit tree-like qualities. Moreover, the breakdown voltage results show that the breakdown strength of transformer oil is improved after nano-modification, and the TiO2 nano-liquids and Al2O3 nano-liquids have nearly the same optimal volume fraction. The results of the analysis indicate that the modification mechanism of nano-particles is significantly linked to the trapped electrons process. Specifically, the addition of nano-particles can affect the electrons’ density and thus affect the breakdown process and streamer morphology.

Formation of diamond nanostructures from graphite using 10 W fibre laser

The high activation energy required for graphite–diamond transition limits its applicability in novel areas. To exploit fully the multifunctional properties of diamond in diverse fields, there is a necessity to explore more efficient ways for its synthesis. In this study, we have demonstrated a new approach for nanodiamonds formation by employing a commercially available low power 10 W continuous-wave fibre laser. The laser system is modulated to generate the high-pressure high temperature environment necessary for the phase conversion of graphite to diamond. The microsecond pulse duration combined with liquid confinement effect on plasma provide scope for a lower rate of supercooling, which restricts the epitaxial growth of the crystals. The sample is characterized by X-ray powder diffraction, transmission electron microscope and Raman spectroscopy, confirming the presence of different types of nanodiamonds including newly discovered n-diamond. The process offers many important advantages like scalable process, non-catalyst-based eco-friendly and cost-effective synthesis of metastable nanodiamonds. The results demonstrate the effectuality of inexpensive commercial lasers towards attaining the localized extreme environment necessary for direct phase conversion of diamond materials.

Electrochemotherapy Using Doxorubicin and Nanosecond Electric Field Pulses: A Pilot in Vivo Study.

Pulsed electric field (PEF) is frequently used for intertumoral drug delivery resulting in a well-known anticancer treatment—electrochemotherapy. However, electrochemotherapy is associated with microsecond range of electrical pulses, while nanosecond range electrochemotherapy is almost non-existent. In this work, we analyzed the feasibility of nanosecond range pulse bursts for successful doxorubicin-based electrochemotherapy in vivo. The conventional microsecond (1.4 kV/cm × 100 µs × 8) procedure was compared to the nanosecond (3.5 kV/cm × 800 ns × 250) non-thermal PEF-based treatment. As a model, Sp2/0 tumors were developed. Additionally, basic current and voltage measurements were performed to detect the characteristic conductivity-dependent patterns and to serve as an indicator of successful tumor permeabilization both in the nano and microsecond pulse range. It was shown that nano-electrochemotherapy can be the logical evolution of the currently established European Standard Operating Procedures for Electrochemotherapy (ESOPE) protocols, offering better energy control and equivalent treatment efficacy.

Microsecond pulse gas–liquid discharges in atmospheric nitrogen and oxygen: Discharge mode, stability, and plasma characteristics

AbstractA plasma's working gas is a significant factor affecting their discharge characteristics and the induced chemistries during plasma–water interactions. However, the effects on the discharge mode and discharge stability have not been fully investigated. This study focuses on the discharge mode transition and stability with nitrogen and oxygen gases. Compared with the oxygen discharge, the nitrogen discharge remained stable over a larger voltage range and long duration time. A diffuse mode discharge had better stability and lower plasma activity for both nitrogen and oxygen gases, whereas a transient spark mode in nitrogen and filament mode in oxygen had lower stability but a higher plasma activity. This study improves the understanding of the physicochemical processes of plasma–water interactions.

Justification in Selection of Voltage Pulse Durations at the Electrochemical Dimensional Micromachining with Nano- and Microsecond Pulses

The work is devoted to justifying the selection of a rational range of voltage pulse duration on the basis of comparing the time of the anodic dissolution start with the time of the electric double layer’s charging during electrochemical dimensional micromachining. The range of short circuit times as the limit of the maximum voltage pulse duration is justified. The simulation of dimensional electrochemical micromachining using ultrashort voltage pulses without taking into account the changes in the properties of the interelectrode environment is performed on the assumption that the anodic dissolution is determined by the Butler–Volmer equation. The zones of the current density, which have varying influence on the process of the dimensional electrochemical micromachining, are revealed. An approach to the selection of an effective voltage pulse duration based on the analysis of the character of the time zones of the process is proposed.

Understanding nano-modification in liquid dielectric from coefficient of viscosity

The breakdown experiments were conducted on the castor oil and Midel 7131 nano-liquids under microsecond pulse. The breakdown strength of the castor oil nano-liquid with 1% volume fraction was over 50% higher than its base liquid, while the breakdown strength of the Midel 7131 nano-liquid with 0.3% volume fraction was 10% higher than its base liquid. A high viscosity base liquid would help increase the optimal volume fraction of the nano-particles because the nano-particles in a high viscosity liquid are harder to polymerize. This study proposed new ideas for the mechanism of nano-modification and extended the scope of liquid nano-modification.

Ultra-short pulse simulation for characterising oxide layer formation on stainless steel during μECM

Electrochemical machining is a controlled metal shaping process based on anodic dissolution performed by the electrode reactions. When pulse signals, in the micro-second or less range, are combined with a small inter-electrode gap, the process is referred to as Micro-Electro-Chemical machining or μECM. The application of using nano-second/micro second pulses for μECM for certain passivation metals can be very limited by the formation of an oxide layer that prohibits the penetration of ultra-short pulse durations due to the capacitive effect of the oxide layer. This paper will present findings from the development of a μECM numerical model that incorporates an advanced hybrid time stepping approach for representing nano-second pulse interactions with the physical phenomena of the electrolytic environment associated with μECM, thereby enabling the characterisation of the capacitive model of the formed oxide barrier layer. Experimental work was conducted using nano and micro-second pulses on the machining of 18CrNi8 and copper using NaNO3 electrolyte. The μECM simulation model contributed to quantifying the lack of faradic machining of 18CrNi8 that was experimentally observed. A particular solution, believed to be effective in breaking through the oxide film, is to directly pre-polarize the layer by super imposing a DC signal prior to the ultra-short pulses, such that its capacity has been already loaded when the short pulse signal is applied. However, too long of a DC signal application time can lead to machining damage. Through the development of an ultra-short pulse simulation model, this work has established, that we can numerically determine an optimal DC signal duration necessary to load the oxide layer just enough for facilitating anodic dissolution during physical μECM process, thus minimising machining damage.