Flat-top Waveform Research Articles

Dynamic range enhancement for the sensing signals of peak-saturated fiber Bragg grating spectra.

Fiber Bragg grating (FBG) sensors applying time-delay interrogators with wavelength swept lasers (WSLs) are popular for their great potentials in high sensing resolution and power budget. In these systems, well-calibrated WSLs with reduced wavelength nonlinearity and jitter are critical for the sensing performance. However, high-performance WSLs are expensive and could significantly increase the cost of the systems. The overall cost may be reduced by maximally sharing each WSL with multiple sensing FBGs through mechanisms like power splitting, which distribute the WSL signal into multiple independently operated serial FBG chains. Under such scenarios, the sensing processing unit (SPU) of each serial FBG chain must be synchronized with the WSL for correctly estimating the FBGs' respective spectra from the signal return time delays. We previously propose a self-synchronized scheme relying on the dual-polarity spectrum signal, which reduces the synchronization labor. The dual-polarity signal has a wider dynamic range, which may limit the system response speed or accuracy, considering the amplifiers' responses or the analog-to-digital converters' (ADCs') quantization noise. In this Letter, we apply peak-saturated FBG spectra for the sensors to increase the receivers' equivalent dynamic range. The flattop waveforms of the saturated peaks result in uncertainty for the peak positions. An artificial neutral network (ANN)-based method is further studied to enhance the peak detection accuracy. We show an ∼88% receiver dynamic range improvement with an inaccuracy reduction of about a half compared to the filter-and-maximum-readout (FMR) method.

A Flat-Top Single-Ended Resonant Converter With Low Switch Voltage Stress

This paper proposes a flat-top single-ended resonant converter (SERC) for wireless charger with the merit of low switch voltage stress, by introducing a parallel LC network in series with the primary switch. A characteristics analysis of the proposed SERC is performed in time domain, obtaining the ZVS condition, power transfer capacity expression and the time requirement to achieve an ideal voltage cancelling. Due to the injected third harmonic, the voltage waveform of the switch can be shaped into a near trapezoid or a saddle shape. From the perspective of waveform superposition, we derive the conditions for the minimum switch voltage stress and the flat-top waveform of switch voltage. Finally, a 1900W prototype is built to verify the theoretical analysis. The experimental results show that the proposed converter achieved a flat-top switch voltage waveform and the voltage stress of 2.12 times the input voltage at full load, compared to that of 2.65 times the input voltage for the conventional one. Besides, the maximum efficiency is also increased to 93.33% from 92.32%.

Uniform-density Bose-Einstein condensates of the Gross-Pitaevskii equationfound by solving the inverse problem for the confining potential.

In this work, we study the existence and stability of constant density (flat-top) solutions to the Gross-Pitaevskii equation(GPE) in confining potentials. These are constructed by using the "inverse problem" approach which corresponds to the identification of confining potentials that make flat-top waveforms exact solutions to the GPE. In the one-dimensional case, the exact solution is the sum of stationary kink and antikink solutions, and in the overlapping region, the density is constant. In higher spatial dimensions, the exact solutions are generalizations of this wave function. In the absence of self-interactions, the confining potential is similar to a smoothed-out finite square well with minima also at the edges. When self-interactions are added, terms proportional to ±gψ^{*}ψ and ±gM with M representing the mass or number of particles in Bose-Einstein condensates get added to the confining potential and total energy, respectively. In the realm of stability analysis, we find (linearly) stable solutions in the case with repulsive self-interactions which also are stable to self-similar deformations. For attractive interactions, however, the minima at the edges of the potential get deeper and a barrier in the center forms as we increase the norm. This leads to instabilities at a critical value of M. Comparing the stability criteria from Derrick's theorem with Bogoliubov-de Gennes (BdG) analysis stability results, we find that both predict stability for repulsive self-interactions and instability at a critical mass M for attractive interactions. However, the numerical analysis gives a much lower critical mass. This is due to the emergence of symmetry-breaking instabilities that were detected by the BdG analysis and violate the symmetry x→-x assumed by Derrick's theorem.

Research on Distributed Measurement and Control System Based on FlexRay Bus

With the purpose of the design problem of electromagnetic launch distributed measurement and control system, this paper proposes a design method of scalable large-scale distributed interconnected measurement and control system based on FlexRay bus. The task execution time deviation of each node in the distributed system, including phase deviation and frequency deviation, is reduced by using the macro tick generation process and clock synchronization process to achieve task synchronization in the distributed system. The synchronization of timing generation is realized based on the universal clock technology. When the timing interval is zero, the pulse power units are guaranteed to be close to the ideal full synchronization, thus ensuring that the released energy during transmission is close to the design value. In the state of adjustable timing, when the pulse power supply module conducts pulse discharge, the trigger discharge times of the modules are set according to the load needs. The flat top, sawtooth, and other characteristic current waveforms are adjusted accurately. At the same time, a combined multi-level protection structure based on hardware and software is realized. The verification results show that the distributed electromagnetic launch measurement and control system implemented in this paper can meet the high efficiency, fast and continuous launch target.

Optimization of a Controlled- Z Gate with Data-Driven Gradient-Ascent Pulse Engineering in a Superconducting-Qubit System

The experimental optimization of a two-qubit controlled-Z (CZ) gate is realized following two different data-driven gradient ascent pulse engineering (GRAPE) protocols in the aim of optimizing the gate operator and the output quantum state, respectively. For both GRAPE protocols, the key computation of gradients utilizes mixed information of the input Z-control pulse and the experimental measurement. With an imperfect initial pulse in a flattop waveform, our experimental implementation shows that the CZ gate is quickly improved and the gate fidelities subject to the two optimized pulses are around 99%. Our experimental study confirms the applicability of the data-driven GRAPE protocols in the problem of the gate optimization.

A compact electron beam driver based on the annular parallel-plate pulse forming lines

A compact electron beam driver based on an annular parallel-plate pulse forming line (APPPFL) was presented in this paper. Compared with the traditional system, the characteristics of compactness and flat-top waveform output have been achieved by using APPPFLs, which can generate a high voltage quasirectangular pulse up to 20 kV with a width of 60 ns, a rising edge of 10 ns at a lower matched load with an impedance of 1.25 Ω. The key part of the driver is the Marx generator, which consists of 37 stages, each of the stages consisting of an APPPFL, a gas spark switch, two charging inductors, and a nylon insulator that provides insulation between two stages as well as mechanical support. The generator is charged synchronously with positive and negative voltages to reduce the difficulty of the insulation design. When the APPPFL of each stage was charged up to ±20 kV, the output voltage and current of the electron beam driver are 680 kV and 15 kA at a 46 Ω planar diode load, respectively, and the power of the output electron beam is 10 GW. The repetition frequency operation of the electron beam driver has also been investigated.

Analysis of optical arbitrary waveform generation based on time-domain synthesis in a dual-parallel Mach–Zehnder modulator

A photonic-assisted microwave arbitrary waveform generator is theoretically analyzed and verified by simulation. The basic principle of the generator is synthesis of optical field envelops. By using a sinusoidal signal to modulate a CW via a dual-parallel Mach–Zehnder (DP-MZM), square-shaped waveforms are directly generated firstly, whose envelops or harmonic power ratios are able to be modified by changing the RF driving voltage. When two identical square-shaped pulses with harmonics power ratio (9:1) between the 1st- and the 3rd-order components suffer a differential envelope phase shift (π/2), the superposition of these envelops contributes to a triangular-shaped waveform. Similarly, we generate flat-top waveform and Gaussian waveforms by properly setting the bias drifts of DP-MZM, time delay of the tunable time delay line, and modulation index. As DP-MZM is a key component in our proposal, we discuss the influence of the bias drifts on the generated waveforms, which make the scheme more practical.

Comparison of Simulated Sonic Boom in Stratified Atmosphere with Flight Test Measurements

A method for predicting sonic boom waveforms emanating from a vehicle flying at supersonic speed is presented and compared to flight-test data. The prediction is achieved through three main steps: searching for the position of the sound source along the flight path, predicting the near-field waveform by a combination of computational fluid dynamics simulations on structured and unstructured meshes, and propagating this waveform to the far field by a numerical solver of the augmented Burgers equation. It is shown that this framework successfully predicts sonic boom signatures observed during the large-scale first phase of the drop test for simplified evaluation of the nonsymmetrically distributed sonic boom field test recently conducted by our research group at the Japan Aerospace Exploration Agency for both conventional waves and lower-amplitude flattop waveforms.

Experiments of a 100 kV-level pulse generator based on metal-oxide varistor.

This paper introduces the development and experiments of a 100 kV-level pulse generator based on a metal-oxide varistor (MOV). MOV has a high energy handling capacity and nonlinear voltage-current (V-I) characteristics, which makes it useful for high voltage pulse shaping. Circuit simulations based on the measured voltage-current characteristics of MOV verified the shaping concept and showed that a circuit containing a two-section pulse forming network (PFN) will result in better defined square pulse than a simple L-C discharging circuit. A reduced-scale experiment was carried out and the result agreed well with simulation prediction. Then a 100 kV-level pulse generator with multiple MOVs in a stack and a two-section pulse forming network (PFN) was experimented. A pulse with a voltage amplitude of 90 kV, rise time of about 50 ns, pulse width of 500 ns, and flat top of about 400 ns was obtained with a water dummy load of 50 Ω. The results reveal that the combination of PFN and MOV is a practical way to generate high voltage pulses with better flat top waveforms, and the load voltage is stable even if the load's impedance varies. Such pulse generator can be applied in many fields such as surface treatment, corona plasma generation, industrial dedusting, and medical disinfection.

Effects of cell-driving jitters on the output voltage of magnetically insulated induction voltage adders

Based on a 12-cell transmission line code model, the effects of cell-driving jitters on the output voltage (both the rise time and the flat-top waveform) of magnetically insulated induction voltage adders (MIVAs) were analyzed in detail. Simulation results show that the rise time (0.1–0.9) of the MIVA output voltage is a function of $\sigma $ (the standard deviation of the cell-driving jitters) when N (the number of cells connected in series for an MIVA) is small. When cell-driving jitters follow a normal probability distribution, the rise time of the output voltages also accord well with normal distributions. Parameters of these distributions are analytically deduced and presented. For any experimental shot, there is a fiducial probability that the rise time falls into the analytic solution range (within a certain error range). With the same error range, the fiducial probability decreases as $\sigma $ increases, while probabilities that the rise time are higher or lower than this range increase synchronously. Simulation results also indicate that cell-driving jitters have fewer effects on the flat-top peak of the MIVA output voltage. However, a series of ripple voltages is added on the flat-top waveform, and the average peak of these ripple voltages increases as $\sigma $ increases.

Effect of Low-Boom Waveform on Focus Boom Using Lossy Nonlinear Tricomi Analysis

Focus boom occurs when a flight vehicle accelerates or maneuvers at supersonic speed. Its overpressure is typically more than three times greater than that of a cruise boom. As a result, future supersonic transports are likely to face restrictions on their flight conditions. To investigate ways to alleviate this problem, this paper presents the effects of the focusing of several sonic boom signatures. So-called low-boom waveforms have promising characteristics, not only in cruise but also in transition flight phases including acceleration from Mach 1. Computations of the focused waveform for several accelerations at a constant altitude reveal that the low-boom ramp and flattop waveforms show strong reductions of the peak overpressure and perceived level measured on the ground track of the aircraft. Acceleration strongly impacts on the size of the noise exposure footprint of the focus boom, whereas the peak overpressure and the metric are not sensitive. Also shown is the importance of applying the low-boom concept to not only the front but also the rear section of the boom signature.

Photonic arbitrary waveform generator based on Taylor synthesis method.

Arbitrary waveform generation has been widely used in optical communication, radar system and many other applications. We propose and experimentally demonstrate a silicon-on-insulator (SOI) on chip optical arbitrary waveform generator, which is based on Taylor synthesis method. In our scheme, a Gaussian pulse is launched to some cascaded microrings to obtain first-, second- and third-order differentiations. By controlling amplitude and phase of the initial pulse and successive differentiations, we can realize an arbitrary waveform generator according to Taylor expansion. We obtain several typical waveforms such as square waveform, triangular waveform, flat-top waveform, sawtooth waveform, Gaussian waveform and so on. Unlike other schemes based on Fourier synthesis or frequency-to-time mapping, our scheme is based on Taylor synthesis method. Our scheme does not require any spectral disperser or large dispersion, which are difficult to fabricate on chip. Our scheme is compact and capable for integration with electronics.

Microring-based reconfigurable optical pulse shaper

Based on the amplitude and phase-shift characteristics of microring (MR) resonator, a novel reconfigurable optical pulse shaping approach is proposed. By adjusting the variable attenuators to set the proper relative weights, a transform-limited Gaussian input optical pulse can be shaped into flat-top waveform or triangular waveform flexibly. In contrast to the conventional pulse shaping method, only positive real relative weights are used in the proposed pulse shaper, which not only facilitates the reconfigurable adjustment, but also is robust to the wavelength detuning and temporal duration variations of the input pulse.

Generation of Controllable High Energy Nanosecond Flat-Top Waveform Based on Brillouin Amplification

We propose a method based on Brillouin amplification, which reshapes the Gaussian pulse generated from a $Q$ -switched laser into the flat-top waveform. The numerical simulations show that the reshaped waveform depends on Stokes pulse width and energy, and optimum conditions for a flat waveform are also investigated. It is demonstrated experimentally by the independent two-cell filled with FC-40 liquid. In the experiment, the flat-top waveform pulses with width from 9.1 to 13.3 ns and continuously adjustable energy from 90 to 210 mJ are obtained at the wavelength of 1064 nm. The pulses with flat-top waveform and high energy are achieved by injecting a small Stokes seed into the Brillouin amplifier, which is a novel method to obtain high-energy flat-top laser pulses.

Modeling Double Blumlein with Variable Duration and Polarity using Orcad PSpice

Double Blumlein generator is an excellent technique in generating high voltage short pulsed power with fast rise time signal. However properties of fixed pulse duration and polarity of Blumlein configuration limits the generator flexibility and efficiency. A modeling of double Blumlein with double switching configuration with controlled delay is proposed in this paper to solve the limitation problem. The circuit is modeled in PSpice environment and the result successfully showed double output pulse voltage of flat top square waveform with adjustable duration and polarity.

Versatile waveform generation using single-stage dual-drive Mach-Zehnder modulator

The generation of 10 GHz triangular, sawtooth, flat-top, sinusoidal and doublet waveforms based on the generation and manipulation of the frequency comb from a continuous-wave laser source by a single-stage dual-drive Mach-Zehnder modulator is experimentally demonstrated.

Investigation in discharge progress of a long pulse high power microwave-driven source

According to the experiment, we analyze the propagation process of the electromagnetic wave on the pulse forming line with water-dielectric, which is the long pulse high power microwave-driven source. And then an equivalent method of discharge process is put forward to study the cause of the flattop waveform distortion. We ind the relationship between the variation trend of the output flattop waveform and the voltage waveform on the pulse forming line, which is validated through the Pspice simulation. By adjusting the breakover time of laser triggered switch, we obtain an output pulse with a flattop of 60 ns, FWHM (full width of half maximum) of 150 ns and voltage amplitude of several hundred kV, showing the distinct improvement on the flattop waveform.

Traceability and Verification of Interharmonic Generators in Support of Low-Frequency Immunity Testing (IEC61000-4-13)

A description of the interference immunity testing of electrical products is given, and the need for traceable calibration methods of the associated testing generators is described. A presentation of three analysis techniques to verify the respective testing modes of immunity testing generators is given, together with typical uncertainties. A deconvolution method developed for the phase characterization of the analog-to-digital converter (ADC) used in this work is reported. A least squares algorithm for the piecewise analysis of the International Electrotechnical Committee (IEC) flat-top waveform is presented in the Appendix.

Single-turn extraction from a K110 AVF cyclotron by flat-top acceleration

Single-turn extraction from the Japan Atomic Energy Agency AVF cyclotron with a K number of 110 using a flat-top (FT) acceleration system has been achieved to reduce the energy spread of an ion beam for microbeam formation with energy up to hundreds of MeV and to increase extraction efficiency from the cyclotron. In order to generate a FT waveform voltage using the fifth-harmonic frequency on a dee electrode, a FT resonator was designed using MAFIA code to achieve downsizing and low power consumption. The FT resonator, coupled to the main resonator through a coupling capacitor, covered the full range of the fifth harmonic frequency from 55 to 110 MHz. Various ion beams, accelerated using different acceleration harmonic modes of h=1 and 2, such as 220 MeV (12)C(5+) (h=2), 260 MeV (20)Ne(7+) (h=2), and 45 MeV H(+) (h=1), were developed by FT acceleration. A clear turn separation of the beam bunches was successfully observed at the extraction region of the large-scale AVF cyclotron with number of revolutions greater than 200. As a result, high extraction efficiency (over 95%) from the cyclotron was achieved. Single-turn extraction was confirmed by counting the number of beam bunches out of the cyclotron for an injected beam pulsed by a beam chopping system in the injection line. The energy spread of the 260 MeV (20)Ne(7+) beam was measured using an analyzing magnet, and we verified a reduction in the energy spread from DeltaE/E=0.1% to 0.05% by single-turn extraction after FT acceleration.

Electro-optic Solc-type flat-top bandpass filter based on periodically poled lithium niobate

Based on the spectrum waveform similarity (SWS) rule we discovered in periodically poled lithium niobate (PPLN), a compact tunable flat-top bandpass filter is proposed theoretically, from which the bandwidth of the flat-top waveform can be obtained. For practical application, tunable flat-top filter can be easily achieved by selecting appropriate electric field along the transverse direction of PPLN. The tolerance analysis for this kind of tunable flat-top bandpass filter is also presented.