Chopped Pulses Research Articles

Effect of pulse configuration on the reactive deposition of TiN coatings using HiPIMS

In this work, TiN coatings are deposited using three different series of pulse configurations. Each series consisted of a single pulse of 90 μs, chopped into 2-, 3-, and 6-pulse sequences, where the short delay time between the sequential chopped pulses have been varied from 10 to 300 μs. This allows control of the intensity of the target peak current, which in turn affects the deposition rate and mechanical properties of the growing coatings. Results show that changing the pulse configuration resulted in a deposition rate comprised between 4.4 and 5.2 μm/h. The change observed in deposition rate can be attributed to several phenomena known to reduce the deposition rate. This includes gas rarefaction, self-sputtering, target poisoning, and power loss resulting from the increase in circuit impedance when power is switched on and off during the pulsing process. It was shown that strategic selection of the pulse configuration plays a crucial role in mitigating the negative impact of these phenomena which opens up favorable conditions for a substantial enhancement in the deposition rate. In fact, the proper choice of pulse configuration can result in an enhanced deposition rate of up to 12.3 % compared to the conventional single pulse case. An overall slight increase in the average hardness from 18.7 GPa to 19.8 and 22 GPa for the 2-, 3-, and 6-pulse series respectively, while no noticeable structural changes were observed.

An Electrical Stimulator IC with Chopped Pulse based Active Charge Balancing for Neural Interface Applications

In this paper, a current-mode neural stimulator integrated circuit (IC) using novel active charge balancing technique is presented. The charge balancing technique proposed in this work is based on chopped pulse waveform, where the number of chopped pulses generated in the anodic phase is controlled accurately in order to limit the amount of residual potential at the electrode. In addition, a quick automatic electrode shorting process follows the active charge balancing phase to further discharge to a negligible residual voltage level in every stimulation cycle, ensuring a safe and long-term operation. Both symmetric and asymmetric stimulation pulse waveforms can be selected to provide wide flexibility for various stimulation environment. The stimulator IC designed using 0.18-μm standard CMOS process achieves 12.3 V of voltage compliance and can deliver 1 mA of maximum stimulation current with 5-bit resolution and high linearity. All circuit functions are integrated on-chip without external components, and the fabricated chip consumes only 0.095 mm² of active die area.

Non-intrusive laser-induced breakdown spectroscopy in flammable mixtures via limiting inverse-bremsstrahlung photon absorption

For the purpose of employing laser-induced breakdown spectroscopy (LIBS), nanosecond laser pulses (6 ns FWHM) from a standard Q-switched Nd:YAG laser (2nd harmonic) are modulated or chopped—using a novel method utilizing a variable air-pressure optical cell—to limit the inverse-Bremsstrahlung photon absorption process occurring in the breakdown plasma. The resulting plasma does not ignite flammable mixtures, but plasma emission is sufficiently strong to enable the characterization of reactants without strong perturbation (i.e., no ignition or shock wave results from the breakdown plasma). Two strong atomic emission lines, H (656 nm) and N II (568 nm), are chosen to find correlations between the plasma emission spectrum and the fuel concentration; plasma emission is captured after a delay of 20 ns with a gate width of 60 ns, the time over which there are well defined emission peaks. The chopped laser pulse is created within the pressurized optical cell with an initial breakdown plasma, by focusing the beam in high-pressure air. The pulse width of the laser beam transmitted through the cell is dependent on the cell pressure, and for this work, a pulse duration of approximately 600 ps was derived from the cell operated at a pressure of 10 bar. The chopped pulses were used for LIBS, and a 2D concentration distribution of a stoichiometric methane-air flow in ambient air were recorded without combustion reactions initiated by the laser-induced plasma.

Comparison of the efficiency of chopped and non-rectangular electrical stimulus waveforms in activating small vagus nerve fibers

BackgroundIn the context of morbid obesity, vagus nerve stimulation could be used to control gastric function targeting the small afferent B-fibers and C-fibers. Compared to large A-fibers, activation thresholds of these small efferent fibers are 10 to 100 times greater, inducing technical constraints and possible nerve damages. Although rectangular waveform is commonly used in nerve stimulation, recent modeling and experimental studies suggest that non-rectangular waveforms could reduced the charge injected by the stimulator. New methodThe objective of the present study is to evaluate the charge injection of complex waveforms such as the ramp, quarter sine and chopped pulses in the context of vagus nerve stimulation. We performed in-vivo study on the porcine abdominal vagus nerves and evaluated charge injection at activation thresholds. A modeling study was performed to further extent the results obtained in-vivo. Comparison with existing methodCompared to the rectangular pulse, the ramp and quarter sine waveforms activated gastric fibers with the lowest charge injection: −23.2% and −30.1% respectively. The efficacy of chopped pulses is questioned through the consideration of the strength-duration curve. ConclusionContinuous ramp and quarter sine waveforms effectively activate small diameter fibers. These pulse shapes may be considered for long-term vagus nerve stimulation. The results predicted by computational models were qualitatively consistent with experiments. This suggested the relevance of using modeling in the context of complex waveforms prior to future in-vivo tests.

Investigation of the efficiency of the shape of chopped pulses using earthworm model.

In neural electrical stimulation, limiting the charge delivered during a stimulus pulse is essential to avoid nerve tissue damage and to save power. Previous experimental and modeling studies indicated that waveforms such as non-rectangular continuous pulses or rectangular chopped pulse were able to improve stimulation efficiency. The goal of this study is to evaluate if non-rectangular chopped pulses such as quarter sine and ramp are more charge efficient than rectangular chopped pulse. We performed in vivo study on 17 lumbricus terrestris and compared the charge per stimulating phase needed to activate lateral giant fibers (LGF) and medial giant fiber (MGF) using chopped non-rectangular pulses and rectangular pulse, varying stimulation duration parameters. Results indicated that non rectangular chopped pulses activated MGF and LGF with less charge than rectangular chopped pulses. For MGF (respectively LGF), the gain of charge was up to 33.9\% (resp. 17.8\%) using chopped ramp, and up to 22.8\% (resp. 18.1\%) using chopped quarter sine.

A Multichannel High-Frequency Power-Isolated Neural Stimulator With Crosstalk Reduction.

In neuroprostheses applications requiring simultaneous stimulations on a multielectrode array, electric crosstalk, the spatial interaction between electric fields from various electrodes is a major limitation to the performance of multichannel stimulation. This paper presents a multichannel stimulator design that combines high-frequency current stimulation (using biphasic charge-balanced chopped pulse profile) with a switched-capacitor power isolation method. The approach minimizes crosstalk and is particularly suitable for fully integrated realization. A stimulator fabricated in a 0.6 μm CMOS high-voltage technology is presented. It is used to implement a multichannel, high-frequency, power-isolated stimulator. Crosstalk reduction is demonstrated with electrodes in physiological media while the efficacy of the high-frequency stimulator chip is proven in vivo. The stimulator provides fully independent operation on multiple channels and full flexibility in the design of neural modulation protocols.

Thermal Lens Phenomenon Studied by the Z-Scan Technique: Measurement of the Thermal Conductivity of Highly Absorbing Colloidal Solutions

We discuss the thermal lens phenomenon in high-absorbing colloidal systems, studied by using the Z-scan technique. The characteristics of the experimental setup to avoid undesirable effects are presented, in particular when pulsed laser beam is used. We show that a cumulative effect may appear in the experiment with chopped laser beams and compromise the results obtained with this technique. This artefact is more significative when colloidal suspensions are investigated. These materials have different characteristic times of heat and mass diffusion, which must be carefully considered to choose the appropriate time interval for the laser pulse and the time between pulses. Two experimental cases with a chopped laser beam, with and without a shutter, are discussed. The sample employed is a magnetic colloidal suspension (a ferrofluid). This sample has magnetic nanoparticles electrically charged in an aqueous solution with free ions and counter ions. Besides the thermal lens effect, charge and mass diffusion may take place when the sample is illuminated by the Gaussian beam, which imposes a thermal gradient on it. The results show that, with the experimental setup without a shutter, the sample does not achieve a complete relaxation between two laser pulses. This generates a measurable cumulative effect after the sample is illuminated during a relatively long period of time. A time modulation with longer time interval between chopped pulses allows the complete relaxation of the sample. This procedure is important for the correct analysis of the thermal lens effect. Reliable values of the thermal conductivity of the sample in different temperatures are obtained and discussed.

Einzel lens chopper and behavior of the chopped beam in the KEK digital accelerator

The KEK digital accelerator (KEK-DA), which is a small-scale rapid-cycle induction synchrotron (IS), has commenced operation. A permanent magnet $x$-band electron cyclotron resonance ion source serves as the KEK-DA ion source and delivers various ions. A new Einzel lens beam chopper has been developed to provide the necessary pulse width of a few microseconds. The chopper is implemented by applying a rectangular pulse voltage generated by a solid-state Marx generator to the middle electrode of the Einzel lens. Momentum modulation at the bunch head and tail resulting from chopping in longitudinal direction has been observed. This intrinsic property of the chopped pulse has been clearly observed in a long drift (a free run in the circular ring) in KEK-DA.

Effect of Pump Intensity on Slowing Down of Light in ${\rm Ce{:}BaTiO}_{3}$ Crystal via Degenerate Two-Wave Mixing Using Chopped Pulses

The slowing down of light in Ce:BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> at room temperature via degenerate two-wave mixing for chopped pulses is reported. Delay of 0.9 ms is observed for chopped pulses of duration 8 ms, corresponding to a group velocity of 5.5 m/s. Effect of pulse width of signal beam and pump intensity onto the slowing down action of light in the crystal is studied. The building up and decay time of photo grating is also recorded as a function of pump beam intensity.

Quasi-elastic measurements using neutron spin flippers

A method for low-resolution quasi-elastic measurements using commonly available components on a polarized neutron beam reflectometer is demonstrated. By amplitude modulation of the current in a neutron spin flipper placed between the neutron beam polarizer and polarization analyzer, the intensity of the neutron beam illuminating a sample is similarly modulated (or chopped). We show that the intensity contrast between subsequent chopped pulses is dramatically reduced by a sample that changes neutron velocity.

Automatic adjustment of chopping-modulated defibrillation pulses to patient transthoracic resistance

Defibrillation of the heart requires a high amplitude short duration current pulse to be passed through large electrodes placed on the patient's chest. The current meets a virtually active resistance, which can vary in the approximate range of 25 to 180 z. As the delivered current or energy depends on the resistance, several methods have been developed to reduce or compensate its influence. For example, pre-shock resistance has been measured by a high-frequency current and the current or energy set accordingly; measurements have been made from the initial tilt and the pulse durations adjusted; and pre-shock measurements have been made by a sub-shock pulse to generate an appropriately selected constant current. A method is proposed using high-frequency chopped biphasic pulses, with pulse-width and period modulation of the elementary pulses. Patient resistance is measured with the first elementary pulse and depending on its value a modulated waveform is generated, selected by a micro-controller from a preprogrammed set. Thus the selected energy is accurately delivered to the patient. In addition, this method allows the shaping of a desired mean patient current waveform, maintaining adequate charge balance between the two phases and securing an appropriate time course of the model-derived transmembrane potential.

Lidar profiling by long rectangular-like chopped laser pulses

A novel, simple method is developed and tested (experimentally and by simulations) for effective, high-resolution retrieving of time-resolved lidar profiles for long rectangular-like laser pulses with arbitrary shapes of their leading and trailing edges. Such pulses are typically created by chopping cw optical radiation. The processing algorithm is based on differentiation and iteration procedures and avoids the use of divisions or deconvolutions that are often responsible for some errors and increases in the noise. Comparisons with pulsed and pseudo-random noise modulation lidar methods are given. The method enables a simplification of the entire lidar hardware. No powerful pulsed supplies, high driving pulsed voltages, complicated optical modulations, etc. are required. It could be very attractive for high-resolution, wide-spectral-band lidar measurements in the atmosphere, ocean, etc., using arbitrary optical emitters, especially for closer distances. © 2000 Society of Photo-Optical Instrumentation Engineers.

パルスCO&lt;SUB&gt;2&lt;/SUB&gt;レーザーの生体作用に関する基礎研究

In order to achieve independent control of thermal damaged layer thickness and ablation depth (or volume), the effect of pulse shapes on CO2 laser ablation was experimentally and theoretically discussed. In the condition of 400W/cm2 in intensity and 2.8kJ/cm2 in total energy density, an independent control of thermal damaged layer thickness was achieved by a duty ratio control of chopped pulses from 0.5 to 0.04. In the above conditions, the ablation capability was remained constant. To explain and estimate these results, an ablation simulation model was discussed. Preliminary results of calculation showed excellent agreement on tendency by the duty ratio control. TEA pulsed laser beam was also used to discuss. The optimum energy density which of the maximum energy of for the ablation was found at 12J/cm2. The ablation hole with no thermal damaged layer thickness was revealed by TEA CO2 laser ablation.

Effects of some different pulse parameters on bladder inhibition and urethral closure during intravaginal electrical stimulation: an experimental study in the cat.

Intravaginal electrical stimulation (IVS) was used in the cat to induce bladder inhibition and urethral closure. The purpose of the study was to compare the efficacy of alternating constant-voltage pulses of different durations (0·1, 0·2, 0·5 and 5 ms) with that of chopped alternating pulses, each consisting of a train of five 0·5 ms pulses with 0·5 ms pauses between. The voltage requirement for an equal biological effect was lowest for the 5 ms alternating pulse, whereas the pulse power dissipation was lowest for the 0·1 ms pulse, about 10 per cent of that for the 5 ms pulse. If both voltage requirement and power dissipation are taken into account, the 0·5 ms pulse was considered the most appropriate compromise. The chopped pulse was the least efficient stimulus, since the threshold voltage was comparable to that of the 0·5 ms duration alternating pulse, implying a five times higher power dissipation. For bladder inhibition, the optimal stimulation frequency for alternating pulses was 10 Hz, both in terms of threshold voltage and power consumption. For urethral closure the voltage requirement was lowest at 50 Hz but 20 Hz was preferable in terms of power dissipation for an equal, although submaximal, effect.

High Current Traveling Wave Electron Linear Accelerators

The steady state and stored energy operational regimes of microwave electron linear accelerators are discussed with reference to high current capability. Avoidance of the beam blow-up pulse shortening phenomenon enables long pulse beam currents considerably greater than the maximum conversion efficiency value to be demonstrated. Heavy beam loading effects and choice of frequency are discussed with respect to this steady state operation, and it is shown that conversion efficiencies of greater than 90 per cent can be readily achieved. Stored energy considerations indicate that an increase in peak current of one or two orders of magnitude may be achieved for pulses of short duration with relatively conventional accelerator waveguides. Electron orbit theory including space charge effects for this transient condition is developed. Some experimental data obtained with a 10 Mev linear accelerator using a short pulse inflection system is presented. A concluding discussion deals with design criteria for stored energy operation in high power traveling waye structures and encourages further exploitation by providing higher current high potential sources capable of prebuncher or r-f chopped short pulse injection.