Low Pulse Width Research Articles

Effect of Pulse Width in Pulsed Nd:YAG Dissimilar Laser Welding of Austenitic Stainless Steel (304 L) and Carbon Steel (st37)

In the recent development of the automobile, power generation and petrochemical industries the application of dissimilar welds are gaining importance. In the present work, pulsed Nd:YAG laser welding of austenitic stainless steel (304 L) and carbon steel (st37) of 1.4 mm thickness for butt joint configuration have been investigated for automotive industries. The effect of pulsed width on weld bead width (top bead width (TBW) and bottom bead width (BBW), depth of penetration (DOP) and heat affected zone (HAZ) and fusion zone area have been studied. The microstructure characterization of the fusion zone, HAZ and base metals have been compared at varying pulse width using optical microscope. DOP decreases with increase in pulse width beyond 5 ms and fusion zone area decreases with increase in pulse width. Bottom weld bead width decreases with increase in pulse width and HAZ width of st37 side decreases with increase in pulse width. The mechanical properties such as microhardness and tensile strength of the welded joints at varying pulse width have been investigated. Ultimate tensile strength of all the welded joint at different pulse width was equal to the base metal st37 and fracture location was away from the fusion zone. The average microhardness of the fusion zone decreases with increase in pulse width due to the presence of martensite at low pulse width.

Optical delay in photorefractive SBN:61 and SBN:61:Ce via two-wave mixing : A theoretical study

The slowing down of light in photorefractive SBN:61 and SBN:61:CeO₂ as a function of input pulse width via two wave mixing is presented theoretically. Optical delay has been found to vary from 0.106 s to 4.411 s in SBN: 61 and from 0.212 s to 6.852 s in SBN:61:CeO₂ on varying the pulse width from 0.25 s to 7 s respectively. Cerium doping resulted in enhancement of optical delay at low pulse width. At higher pulse width optical delay was stabilized.

Fragmentación dirigida a discontinuidades preferentes: un nuevo concepto en endolitotricia con láser Holmium:YAG

IntroductionThere are currently 3holmium laser, YAG (Ho:YAG) endolithotripsy procedures that are considered basic (fragmentation, pulverisation, “pop-corn” technique). We present the technique of fragmentation targeted at preferred discontinuities (FTPD), a new concept of endolithotripsy by Ho:YAG laser. Material and methodsThe FTPD technique is based on the selective application of energy (targeting a specific preselected point) to an area that is visually prone to the formation of a fracture line or preferred discontinuity (conditioned by the anisotropy of the urolithiasis). The ideal energy regimen (setting) is a high range of working energy (2-3J) with a very low frequency range (5-8Hz) and short pulse width. Between January 2015 to February 2017, the FTPD technique was used in 37 procedures (7 NLP, 16 RIRS, 12 URS, 2 cystolithotomies), with a Ho:YAG laser (Lumenis Pulse 120H®, Tel-Aviv, Israel). Maximum power used: 24W (3J/8Hz) with fibres of 365μ and 273μ (URS, RIRS), and 32W (4J/8Hz) with fibres of 550μ (NLP, cystolithotomy). ResultsStrategic improvement was achieved in all cases using the TFPD technique to continue the endolithotripsy or remove fragments. No complications were recorded after the use of this method. ConclusionsFTPD can be considered a complementary option in combination with the basic methods of fragmentation and pulverisation. In our experience, it constitutes significant progress in optimising the performance of Ho:YAG laser endolithotripsy.

A 1.55 μW Bio-Impedance Measurement System for Implantable Cardiac Pacemakers in 0.18 μm CMOS.

This paper presents an implantable bio-impedance measurement system for cardiac pacemakers. The fully integrated system features a low power analog front-end and pulse width modulated output. The bio-impedance readout benefits from voltage to time conversion to achieve a very low power consumption for wirelessly transmitting the data outside the body. The proposed IC is fabricated in a 0.18 μm CMOS process and is capable of measuring the bio-impedance at 2 kHz over a wide dynamic range from to with accuracy and maximum current injection while consuming just from a 1 V supply.

Production and correlation of reactive oxygen and nitrogen species in gas- and liquid-phase generated by helium plasma jets under different pulse widths

In this paper, we present the effects of the pulse width (PW) on the plasma jet's discharge characteristics, particularly focusing on the production and correlation of the reactive oxygen and nitrogen species (RONS) in gas- and liquid-phase. It is found that the length of plasma jet plume first increases before the PW of 10 μs, then gradually decreases and finally almost remains unchanged beyond 150 μs. The plasma bullet disappears after the falling edge of the voltage pulse at low PW, while it terminates far ahead of the falling edge of voltage pulse at high PW. This is mainly attributed to accumulation of space charges that lead to weakening of the reduced electric field with an increase of PW from low to high. More important, it is found that the excited reactive species, the positive and negative ions from plasma jet, and the concentrations of NO2– and NO3– in deionized water exposed to plasma jet also display the first increasing and then decreasing change trend with increase of PW, while the concentration of H2O2 in water almost displays the linearly increasing trend. This mainly results from the formation of the H3O+ and HO2–, as well as their ion water clusters that can produce more OH radicals to be converted into H2O2, while the NO2– and NO3– in gas phase can transport into water and exist most stably in water. The water cluster formation at gas-liquid interface is an important key process that can affect the chemical nature and dose of aqueous RONS in water; this is beneficial for understanding how the RONS are formed in liquid-phase.

The Role of Ti Buffer Layer Thickness on the Resistive Switching Properties of Hafnium Oxide-Based Resistive Switching Memories.

Ti/HfOx-based resistive random access memory (RRAM) has been extensively investigated as an emerging nonvolatile memory (NVM) candidate due to its excellent memory performance and CMOS process compatibility. Although the importance of the role of the Ti buffer layer is well recognized, detailed understanding about the nature of Ti thickness-dependent asymmetric switching is still missing. To realize this, the present work addresses the effects of Ti buffer layer thickness on the switching properties of TiN/Ti/HfOx/TiN 1T1R RRAM. Consequently, we have demonstrated a simple strategy to regulate the FORMING voltage, leakage current, memory window, and decrease the operation current, etc. by varying the thickness of the Ti layer on the HfOx dielectrics. Accordingly, controllable and reliable bipolar, complementary, and reverse bipolar resistive switching (BRS, CRS, and R-BRS) properties have been demonstrated. This work also provides the direction to avoid unwanted CRS properties during the first RESET operation by decreasing the FORMING voltage. Furthermore, the memory device shows good nonvolatility at ∼1 μA programming current by selecting a proper thickness of Ti buffer layer. To achieve reliable BRS properties for low power application, the operation current has been further optimized, whereas the memory device shows pulse endurance of more than 7 million cycles at a low pulse width of 50 ns and excellent data retention properties of more than 40 h at 150 °C measurement temperature.

A Low Frequency PWM Based Multilevel DC-Link Inverter with Cascaded Sources

This paper presents a novel Cascaded Sources Multilevel DC Link (CSMLDCL) configuration to an H-bridge inverter, which effectively reduces the number of components to achieve a preferred voltage level. The CSMLDCL topology provides a dc output voltage with the shape of a staircase approximating the rectified shape of a desired sinusoidal wave. A set of area equalization based low frequency Pulse Width Modulation (PWM) techniques suitable for multi-level inverters is suggested. The objective of the new switching strategies is to lower the Total Harmonic Distortion (THD) apart from minimizing the switching losses. Simulation and experimental results of a seven-level inverter are included to illustrate the operating principle and highlight the merits of the proposed strategy.

Mass spectrometry analyzes to highlight differences between short and long HiPIMS discharges

This study investigates the understanding of the impact on the pulse width duration (30 and 100μs) regarding the plasma dynamic of an HiPIMS discharge by investigating time-resolved and time-integrated ion energy distribution functions. In order to establish an objective comparison, the cathode voltage and the mean power were kept constant at −600V and 7Wcm−2, respectively. Time average measurements revealed that for a pulse as long as 100μs, the ion flux at the substrate is mostly composed of argon ions (18% higher). Instead, for a lower pulse width of 30μs, the ions flux at the substrate seems to be dominated by chromium ions (up to 7%). Furthermore, the huge difference between these discharges resides in the lowest energy part of the IEDFs of singly charged chromium ions where the intensity is actually more important in short HiPIMS pulse. Our results reveal that long HiPiMS pulses are characterized by a longer rarefaction effect close to the chromium target vicinity as compared to shorter pulses. In order to explain these phenomena, time-resolved measurements were carried out and highlighted the fact that low energy ions cannot escape the cathode environment due to the applied high voltage acting as a low-energy ions trap. Current characteristics can be correlated to time-resolved ions fluxes measurements and support this explanation. These findings may help the community to find out that working with shorter pulses (tON≤100μs) can have an important benefit to improve the material properties of most common thin films, but also to enhance the adhesion of coatings on substrates by a metallic pre-treatment.

Natural Balancing of the Neutral Point Potential of a Three-Level Inverter with Improved Firefly Algorithm

Modern power systems driven by high-power converters have become inevitable in view of the ever increasing demand for electric power. The total power loss can be reduced by limiting the switching losses in such power converters; increased power efficiency can thus be achieved. A reduced switching frequency that is less than a few hundreds of hertz is applied to power converters that produce output waveforms with high distortion. Selective harmonic elimination pulse width modulation (SHEPWM) is an optimized low switching frequency pulse width modulation method that is based on offline estimation. This method can pre-program the harmonic profile of the output waveform over a range of modulation indices to eliminate low-order harmonics. In this paper, a SHEPWM scheme for three-phase three-leg neutral point clamped inverter is proposed. Aside from eliminating the selected harmonics, the DC capacitor voltages at the DC bus are also balanced because of the symmetrical pulse pattern over a quarter cycle of the period. The technique utilized in the estimation of switching angles involves the firefly algorithm (FA). Compared with other techniques, FA is more robust and entails less computation time. Simulation in the MATLAB/SIMULINK environment and experimental verification in the very large scale integration platform with Spartan 6A DSP are performed to prove the validity of the proposed technique.

Dual mode modulation method for the full‐bridge converter operating in a wide input voltage range

To improve the efficiency of full-bridge converter operating under wide input voltage conditions, this Letter proposes a dual mode modulation method. The full-bridge converter is controlled by phase-shifted mode at low input voltage and asymmetric pulse width modulation mode at high input voltage. The proposed method can reduce power loss, voltage stress of rectifier and output filter requirement. A 500-W full bridge converter with a 160 to 400 V input voltage range is built to confirm the validity of the proposed dual mode method.

An Efficient High Voltage Level Shifter using Coupling Capacitor for a High Side Buck Converter

We propose an efficient high voltage level shifter for a high side Buck converter driving a light-emitting diode (LED) lamp. The proposed circuit is comprised of a low voltage pulse width modulation (PWM) signal driver, a coupling capacitor, a resistor, and a diode. The proposed method uses a property of a PWM signal. The property is that the signal repeatedly transits between a low and high level at a certain frequency. A low voltage PWM signal is boosted to a high voltage PWM signal through a coupling capacitor using the property of the PWM signal, and the boosted high voltage PWM signal drives a p-channel metal oxide semiconductor (PMOS) transistor on the high side Buck converter. Experimental results show that the proposed level shifter boosts a low voltage (0 to 20 V) PWM signal at 125 kHz to a high voltage (370 to 380 V) PWM signal with a duty ratio of up to 0.9941.

Passive Q-Switching of an All-Fiber Laser Using WS <sub>2</sub>-Deposited Optical Fiber Taper

Abstract: We demonstrate the passive Q-switching operation of an erbium-doped fiberlaser using a few-layer WS 2 -based saturable absorber with evanescent field interaction.WS 2 flakes have been synthesized via a liquid-phase exfoliation method, and an opticalfiber taper was selected as a light-material template that causes to achieve a long inter-action length of the evanescent wave. Subsequently, the prepared solution was opticallydeposited around the 3-mm interaction length of the fabricated optical fiber taper with a5- m waist diameter. The proposed Q-switched fiber laser based on the WS 2 -depositedfiber taper saturable absorber could generate stable output pulses at 1565 nm, with apulsewidth ranging from 1.3 to 3 s and a repetition rate of 33–108 kHz.Index Terms: Tungsten disulfide, nonlinear optical materials, saturable absorber,Q-switched fiber laser. 1. Introduction Q-switched fiber lasers have attracted great attention owning to the relatively large pulse energyat relatively low repetition rates and pulse width of the scale from microsecond to nanosecond.These short pulsed lasers have extensive applications in material processing, telecommunica-tions, medicine, and sensing [1]. Q-switched pulses can be obtained via active or passiveQ-switching techniques. Passively Q-switched lasers have several advantages such as sim-plicity, compactness, and low cost compared to that of active techniques which require anactive optical component such as electro-optic or acousto-optic modulators [2].Passive Q-switched technique of lasers based on saturable absorber (SA) is the well-knownand most effective method to achieve Q-switching operation which has been widely investigated.In the past few decades, researchers investigated various kinds of SA materials, including toxicdye materials [3], semiconductor saturable absorber mirrors (SESAMs) [4], carbon nanotubes(CNTs) [5], and graphene [6], [7]. Although the SESAMs are very mature and commercialized,

Evaluation of laser drilling of holes in thermal barrier coated superalloys

Laser drilling of precise holes in thermal barrier coated Ni based superalloys has been studied. The interplay between various hole geometrical features such as hole shape, taper, barrelling, undercut, etc. and laser parameters such as pulse energy, pulse width and pulse repetition rate have been examined. The hole diameters are seen to follow a linear dependence on the incoming laser power densities for pulse width up to 2·0 ms. However, such a linear dependence was not observed for a pulse width of 3·0 ms. It was found that high pulse energy and short pulse width (high power density) gave crack free recast layer, whereas low pulse energy and longer pulse width (low power density) gave microcracks in the heat affected layer of superalloy. The significant barrelling observed in IN718 material at low power density values is due to multiple reflection of the incident beam from the cavity in combination with plasma formation at the evaporation front and trapping of the incident radiation causing excessive heating in that region.

An Experimental Investigation for Optimization of Ytterbium Fiber Laser Parameter during Machining of Al/5 Wt%Al2O3-MMC

This paper presents experimental investigation into the influence of machining parameters of Ytterbium fiber laser during machining of Al/5 wt%Al2O3-MMC. The response surface methodology (RSM) is used to achieve optimum responses i.e. minimum tapering and maximum material removal rate. A comprehensive mathematical model for correlating the interactive and second-order influences of Ytterbium fiber laser machining parameters such as laser power, modulation frequency, gas pressure, wait time, pulse width on metal removal rate and tapering phenomena has been developed for achieving controlled over fiber laser machining process. Test results reveal that the MRR is high at 15 bar gas pressure and 0.1s wait time. MRR is less at moderate gas pressure and moderate wait time. The gas pressure and pulse width both have great effect on taper. At low gas pressure i.e. 15 bar and low pulse width i.e.75% of duty cycle the taper is minimum.

Multi-mode bipolar resistance switching in CuxO films

Electric pulse induced resistance change has been studied in the CuxO binary oxide systems for application to resistive random access memory. Binary transition metal oxides have typically shown unipolar switching, however, this has led to resistance states that have been somewhat erratic. We address here bipolar resistance switching (regular and reversed polarity) in thin film CuxO samples. I-V measurements at different temperatures showed strong evidence for a metallic bulk filament formation under application of an initial forming electric pulse. After forming, Set and Reset states can be controlled by changing positive and negative pulse amplitudes, but show two distinct resistance change regions: (i) resistance states from 20 Ω to 40 Ω with reversed polarity; and (ii) resistance states from 150 Ω to 8,000 Ω with regular polarity. A highly stable reversed polarity bipolar switching regime under application of low amplitude pulses and pulse width of 200 nsec is achieved, and a model for the switching mechanisms based on Cu+ ion motion in the interface region between the metallic filament and the top electrode is developed.

Laser-induced grayscale patterning in TeO x thin films

Grayscale patterns have been widely studied and applied in many fields. In this paper, grayscale patterns with precise grayscale changes are fabricated on TeO x thin film by laser pulse with respective wavelengths of 635 and 405 nm. Two obvious changes according to the different grayscale level emerge as laser energy increases. The first change is from invisible to white-grayscale with low laser pulse width between 2 ns and 50 ns. After a transient period with laser pulse width between 48 ns and 55 ns, the grayscale in the second change becomes darker and darker following the laser pulse width increases from 56 ns to 250 ns. The mechanism of the grayscale change is partly explained and verified by TEM, which involves the agglomeration and segregation of Te, crystallization and recrystallization after melting of Te and TeO 2, and ablation of TeO x , wherein different mechanism is dominant in each stage. We can obtain grayscale patterns with precise grayscale changes to meet specific requirements by controlling the parameters precisely.

Nanocrystalline Diamond Synthesized in Graphite Suspension by Pulsed Laser Irradiation

Cycled water suspension of fine graphite powders was irradiated by a Nd:YAG pulsed laser with low energy density and long pulse width. Transmission Electron Microscopy (TEM) results indicated diamond particles with cubic structure were obtained, and the size of the diamond particles was about 5 nm. The mechanism of the diamond formation was investigated; it was found that graphite powders were molten by laser irradiation and diamond formed through a nucleation‐growth process.

Landau–Lifshitz–Gilbert study of the effect of pulse width on spin-transfer torque magnetization switching

We studied the effect of a current pulse width on current-induced magnetization switching in magnetic tunnel junctions based on a macrospin model of the free layer. We performed finite temperature Langevin simulations of the Landau–Lifshitz–Gilbert–Slonczewski equation with an additional spin-torque term. By evaluating the switching current density, we obtained the diagram in the plane of the critical current density and the pulse width at 300 K. As the pulse width increased, we observed an adiabatic regime in the shorter pulse widths, an intermediate crossover regime, and a thermally activated regime in long pulse widths. We found that the easy-plane anisotropy field shifts the crossover pulse width to the lower pulse width, suggesting that the reversed region is enhanced by controlling the device shape. Our results are consistent with those of recent experiments over the pulse widths ranging from 10−1 to 105 ns.

Analysis of Pacing/Defibrillator Lead Failure Using Device Diagnostics and Pacing Maneuvers

Patients with Medtronic Sprint Fidelis (Medtronic Inc., Minneapolis, MN, USA) lead failures present with oversensing, resulting in pacing inhibition and inappropriate shocks. We present a case of lead noise from the right ventricular (RV) ring conductor, resulting in multiple inappropriate shocks with subsequent pacing inhibition and syncope. RV pacing lead impedance at no point exceeded 1,000 ohms. We found that increased noise and oversensing was more likely to be induced when pacing at higher pulse widths. RV pacing outputs at lower pulse widths may decrease susceptibility to noise generation and prove an effective temporizing measure in pacing-dependent patients.

Statistical analysis of recast formation in laser drilled acute blind holes in CMSX-4 nickel superalloy

The present study investigates the effects of four controllable variables on the metallurgy and drilling velocity of laser percussion drilled acute (30° to surface) blind holes in 2 mm thick flat pieces of nickel superalloy—CMSX-4 material. Design of experiment and statistical modelling were used in the experimental study to understand parameter interactions. Pulse energy, pulse width, pulse frequency and gas pressure were chosen as the independent process variables. The response surface method was used to develop the models for each of the responses: physical characteristics of wall and bottom recast layer and drilling velocity (function of material removal rate). A central composite design was chosen as it offered the most economical number of experiments for the required information. The significant process factors in each model were identified based on the analysis of variance and the models were checked by complete residual analysis. It was found that high pulse energy and short pulse width gave the maximum drilling velocity and lowest recast layer thickness at the hole bottom, whereas low pulse energy and short pulse width minimised the wall recast layer thickness.