Effect Of Different Pulse Shapes Research Articles

Effect of different pulse shapes on the laser welding of aluminum and copper

The Nd: YAG laser is utilized to weld 1060 aluminum (Al) and 110 copper (Cu) with a thickness of 0.4 mm. The effect of different pulse shapes on the microstructure, mechanical and electrical properties of Al-Cu lap joints are investigated by using of the optical microscopy, scanning electron microscope (SEM), tensile test device and micro-resistance tester, respectively. This investigation provided a detailed understanding of how the different pulse shapes influence the metal mixing and the formation of intermetallic compounds (IMCs). The results indicate that the pulse shape with an initial preheating phase improved the laser absorption efficiency. Additionally, this pulse shape resulted in less dissimilar metal mixing compared to the pulse shape that maintained the maximum power throughout. Furthermore, the pulse shape in which the laser power was linearly increased and then maintained at maximum power reduced the formation of IMCs at the joint interface. As a result, the joint exhibited mechanical strengths up to 92 % of the Al base material and similar electrical conductivity. The study provides theoretical guidance on how to utilize pulse shape modulation in laser welding to achieve optimal mechanical and electrical properties in typical joints between Al tabs and Cu busbars.

Pulsation curves strengthen the high gradient magnetic separation process: Experimental study and simulation explanation

The pulsating slurry high gradient magnetic separator (PHGMS) has been widely used for the separation of feebly magnetic materials. As the main competing force, pulsating slurry effectively overcomes matrix blockage and affects the buildup behavior of particles. At present, the used pulse shape in PHGMS constitutes a sinusoidal harmonic vertical motion in which the duration and intensity of the impulsion and suction strokes are similar. However, other pulsation profiles, such as, trapezoidal shape and saw-tooth shape pulses, can also be obtained depending on the stratification mechanism. There is little literature to focus on how pulse shape influences the performance of PHGMS. The change of curve could be a method worth exploring to improve the separation. In this paper, the asymmetry pulsating curves are obtained by switching the velocity of the step motor during one cycle. Then, the single-wire experiments, single-wire 2D numerical simulation and multi-wires experiments are presented to indicate the effect of different pulse shapes. In single-wire experiments, compared with the traditional sinusoidal harmonic curve, the asymmetry pulsating curves have a higher grade, finer particle buildup, but lower accumulation volume. The curves of the rapid downward stroke and slow upward stroke are better than the inverse movement curve in asymmetry pulsation. The results of separating the up and downstream accumulations on the magnetized wire and numerical simulation reveal that these effects can be attributed to the direction of net force and vortex strengthening. The trajectory simulation of multi-component obtains a similar result with single-wire experiments to confirm the superiority of rapid downward stroke and slow upward stroke in selectivity. However, in multi-wires experiments, due to the matrix blockage the curves of rapid upward stroke and slow upward stroke show the greater potential advantages in both grade and weight compared with other curves at condition of high feed velocity.

Modeling Nonperturbative Field-Driven Vibronic Dynamics: Selective State Preparation and Nonlinear Spectroscopy.

The partially linearized density matrix formalism for nonadiabatic dynamics is adapted to incorporate a classical external electromagentic field into the system Hamiltonian. This advancement encompasses the possibility of describing field-driven dynamics and computing a variety of linear and nonlinear spectroscopic signals beyond the perturbative limit. The capabilities of the developed approach are demonstrated on a simple two-state vibronic model coupled to a bath, for which we (a) perform an exhaustive search in the field parameter space for optimal state preparation and (b) compute time-resolved transient absorption spectroscopy to monitor the effect of different pulse shapes on measurable experimental signals. While no restrictions on the form of the field have to be assumed, we focus here on Gaussian shaped (linearly) chirped pulses.

Quantum multimode treatment of light scattering by an atom in a waveguide

We present a full multimode treatment of the interaction of the quantized radiation field with a single two-level atom in a one-dimensional waveguide configuration. Starting with an incident pulse consisting of an arbitrary (finite) number of photons in a general initial state, we derive the equations of motion and a closed-form expression for the shape of the pulse after its interaction with the atom. We then specialize our results to the two-photon case where a number of analytical results can be derived, for both unidirectional and bidirectional systems. We study the effects of different pulse shapes, the manifestations of the entangled, so-called bound state of the two photons, single- and two-photon detection probabilities, and provide simple approximate results for the strong-coupling (or adiabatic, or long-pulse) regime. We also discuss the requirements for a true unidirectional setup, and the application of such a setup to photon sorting proposed by Witthaut, Lukin, and S\o{}rensen [Europhys. Lett. 97, 50007 (2012)].

Analysis of MIMO Band-Limited DS-CDMA Systems in the Presence of Multitone Jamming Over Generalized-$K$ Fading Channels

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, we study the effects of different pulse shapes on the bit-error-rate (BER) performance of a space-time transmit diversity scheme for band-limited direct-sequence code-division multiple-access (DS-CDMA) systems in the presence of multitone jamming (MTJ) over generalized-<formula formulatype="inline"><tex Notation="TeX">$K$</tex> </formula> fading channels. We consider a space-time system with two transmitter and multiple receiver antennas. Two types of band-limited pulse shapes, namely, spectrum raised cosine (SRC) and Beaulieu–Tan–Damen (BTD) pulses, are considered in the BER performance of the conventional matched-filter receiver, the decorrelator receiver, and the minimum-mean-square-error (MMSE) receiver. Numerical results show that the system with BTD pulse outperforms the system with SRC pulse, and the MMSE receiver gives the best BER performance among the three receivers considered. </para>

Pulse shapes for optimized two-photon laser scanning microscopy

A numerical model describing the effect of different pulse shapes on the probability of two-photon absorption for two-photon laser scanning microscopy (2PLSM) is reported. Despite the commercial preference for sech2 pulses, this pulse shape does not provide the best performance. The presented model reveals that a square or parabolic pulse shape is preferable and shows that applications of such pulse shapes can improve the probability of two-photon absorption by up to 50% to facilitate improved 2PLSM.

Metal release in a stainless steel Pulsed Electric Field (PEF) system: Part I. Effect of different pulse shapes; theory and experimental method

Liquid pumpable food is mostly pasteurised by heat treatment. In the last decennia there is an increasing interest in so-called Pulsed Electric Field (PEF) treatment. During this treatment food is pumped between two metal electrodes and exposed to short high electric field pulses, typical 2–4 kV·mm − 1 during 1–10 μs. During this treatment the stainless steel electrodes are in direct contact with the food product. Associated with the charge that has to be exchanged at the interface of electrode and food, electrode material may be transferred from electrode to food. This transfer of material may cause serious electrode corrosion and adds metals to the food. The magnitude of material transfer depends on many factors such as current magnitude, pulse duration, pulse shape and fluid constitution. In this contribution the effect of three different mono-polar pulse shapes on treatment chamber corrosion is investigated. Experiments are carried out in an aqueous sodium chloride solution. The experiments showed that due to PEF treatment dissolved metals are present in the liquid. The four main elements of stainless steel, iron, chromium, nickel and manganese, have been considered in particular. These elements could only be detected in the liquid when it was repeatedly exposed to a Pulsed Electric Field treatment, which was realised by repeatedly circulating. From the experiments a relationship between dissolved metals in sodium chloride and the transferred charge is derived. With these values an upper limit for dissolved metals caused by PEF treatment can be defined. Industrial relevance This paper investigated the metal release in a stainless steel Pulsed Electric Field (PEF) system by considering the effect of three different pulse shapes. The theory and experimental method are given in detail. Also a relationship between dissolved metals and the transferred charge is derived. The author proposed to use mono-polar Pulse Forming Network (PFN) topologies with a transformer or parallel inductor instead of more complex symmetrical bi-polar topologies.

Impact Resistance Modeling of Hybrid Laminated Composites

This paper discusses the analytical and numerical results for the impact responses of two types of plates with equal areal weights: hybrid laminated composite plates and homogeneous metallic plates. The loadings and the boundary conditions for the two types of plates are the same, and an impact load was applied at the center of each plate. An analytical solution based on Fourier expansion was developed to obtain the impact responses of the plates. The finite element method (FEM) was used to perform numerical analyses to verify the analytical solutions. The response patterns from the results were compared and a preliminary conclusion made on the impact resistance ratio between the hybrid laminates with proper interfacial bonding and that of equivalent homogeneous metallic plates. The effect of different shapes of pulse on the laminated composites was also examined. Three loading cases were considered, each being a function of time. The effect of different pulse shapes on the impact response was evaluated. Finally, a solution based on shear deformation theory was developed, and the comparison between classical plate theory results and shear deformation theory results indicates that for the problem examined classical plate theory predicts relatively accurate results.

Calculation of the efficiencies and phase shifts associated with an adiabatic transfer atom interferometer

We have performed calculations to assess the phase shifts and efficiency of an adiabatic transfer process using orthogonal linearly and circularly polarized laser beams of the same frequency. By using this type of adiabatic transfer as the `optical' elements of an atom interferometer, atoms can be kept in a magnetically insensitive state for the majority of the time, thus reducing the phase shifts associated with magnetic fields. We have looked at the effect of different pulse shapes, family momenta and the relative peak intensities of the laser beams. We find that the best compromise between transfer efficiency and accumulated phase shift occurs when the linearly polarized laser beam has a lower peak intensity than that of the circular beam.

A new gas-filled trigger tube for logical functions

The tube has been designed with a view to large-scale mechanized production with the least possible handling and this has affected the mechanical form and electrical characteristics. A study of its basic operation has led to a new way of presenting its characteristics, enabling the equipment designer to calculate more exactly the requirements for ignition and extinction. In particular, the build-up of current between trigger and cathode after the application of an overvoltage has been studied, and from the results are derived the requirements for pulse ignition of the tube and the effect of different pulse shapes. The requirements for extinction of the anode-cathode discharge either by an externally produced pulse or in a self-extinguishing circuit are also discussed.