Pulse Modulation Research Articles

HIGH-VOLTAGE MODULATOR FOR ION LINAC INJECTOR WITH SMOOTH PULSE DURATION CONTROL

The ion linear accelerators stable operation essentially depends on the ion injector. To ensure maximum capture of the ion beam injected into the accelerating structure, the injector must be able to adjust the beam parameters. The paper describes the developed new injector power supply system, built on modern assemblies, which allows smoothly changing the modulator pulse duration in the range of 300…2000 µs. The analysis was carried out and the shortcomings of the previous systems were eliminated. The expected increase in the accelerated ion beam current is 15…20%. Related results include a decrease in the parasitic load capacitances of pulsed devices, a reduction in size, and the rejection of high-voltage isolation transformers, which increases the reliability of the accelerator.

Synchronisation of linear accelerator for fruit irradiation with FPGA-based system

Linear accelerator (LINAC) has been broadly used in various applications in recent years. For instance, the LINAC can produce X-rays and high-energy electrons, which are utilised in radiation therapy for medical purposes and also applied to fruit steriliser for exportation. At present, the prototype of the 6 MeV LINAC for fruit irradiation by using a magnetron radio frequency (RF) source has been developed at Synchrotron Light Research Institute (SLRI) in Nakhon Ratchasima, Thailand. The LINAC consists of several key sub-systems such as pulsed modulators both for electron gun and magnetron used to power the LINAC, magnetic guidance and beam diagnostic systems. All these have been integrated and worked in proper function to reach a proper and stable RF acceleration. Therefore, a timing system is required with well synchronisation for precise transfer of the clock and reference trigs to each sub-system. Furthermore, the low-cost in-house synchronous equipment has been built here for domestic researchers when they would like to apply this system to their work in the future; consequently, the FPGA-based system for real-time synchronisation has been created to achieve the sequences of the LINAC timing system. In this design, the Zybo Z7 development board from the Xilinx Zynq-7000 family is chosen, which integrates the programmable logic (PL) and processing system (PS) in the same chip. The experimental results are presented by the LINAC operation with synchronisation between a precise time and various delay times on both pulsed modulators, which the synchronous technique with accurate time demonstrates excellent performances leading to stable X-ray radiation for fruit irradiation with synchronous operation between the electron gun and magnetron.

Development of a pulse modulated sub-radio frequency power supply for atmospheric pressure plasma devices.

The effect of pulse-modulated sub-RF range (100 kHz-1MHz) excitation on atmospheric pressure argon plasma jet characteristics is studied. For this, a suitable power supply is developed, offering a sub-µs rise time with control of different parameters, such as voltage amplitude, pulse modulation frequency in the range of 1-30kHz, and an oscillation frequency of ∼520kHz, which can affect the plasma behavior. Plasma characteristics, such as reactive species generation, ionic composition, plasma plume length, and gas temperature, are evaluated qualitatively and quantitatively by employing diagnostics such as optical emission spectroscopy, molecular beam mass spectrometry, and optical imaging. Experimental observations indicate that the gas temperature of the plasma jet and plume length increase with the applied voltage for all pulse modulation frequencies, with a maximum value of ∼(325 ± 2K) and a maximum length of ∼(23 ± 3mm), respectively, at 30kHz and 9 kVpp. The emission intensities of OH• and O• lines show an incremental behavior with the applied voltage across all pulse modulation frequencies. The relative yield of different positive (OH+, O+, etc.) and negative (OH-, O-, etc.) ions also increases with the applied voltage for all pulse modulation frequencies with maximum values of ∼(7.6%, 9.9%) and (3.9%, 9.4%), respectively; these are relatively close to RF excited ionic concentrations reported previously. Attaining a high plasma length and species yield signify the features of both kHz and RF atmospheric plasmas. This study offers significant insights and flexibility into exploring the impact of different RF frequency regimes on plasma characteristics.

Интервально-импульсная модуляция сверхширокополосных хаотических радиоимпульсов: теория и эксперимент

An approach to reduce the negative impact of multipath signal propagation (interpulse interference) in a wireless communication channel has been proposed. Pulse-interval modulation of chaotic radio pulses allows to increase the time interval between pulses without reducing the average bitrate. The possibility of using this method in ultra-wideband microwave channels with multipath propagation is demonstrated. The noise immunity of the AWGN channel has been studied. An experimental implementation of the method is described.

Design of High-Frequency Fast-Rise Pulse Modulators for Lifetime Testing of Dielectrics

Design of High-Frequency Fast-Rise Pulse Modulators for Lifetime Testing of Dielectrics

Correlated-photon-pair generation via SFWM in tapered optical fibers with femtosecond laser pump

Spontaneous four-wave mixing (SFWM) in optical micro-/nanofibers is studied theoretically and experimentally. Joint spectral intensity of the biphoton field generated via SFWM under excitation of femtosecond laser pulses is measured and calculated considering self-phase modulation of the pump pulses and SFWM throughout the tapered fibers. In comparison with the previous study (Shukhin et al 2020 Phys. Rev. A 101 053822), replacing picosecond pump by a femtosecond one with the same average power makes it possible to increase the photon pair generation rate tenfold.

A novel textile drying technique via pulsed vacuum method

Drying is a time-consuming and energy-intensive process linked to environmental thermodynamic properties. Conventional methods often use high temperatures for long durations, potentially harming textiles. This article introduces an innovative vacuum textile drying technique utilizing pressure pulsation. Experimental validation reveals that pulsed vacuum drying (PVD) accelerates drying rates and lowers operational temperatures for cotton samples. Compared to constant vacuum drying, PVD achieves a 23% faster reduction to 5% moisture content while maintaining quality. PVD reduces drying temperature from 80 to 60 °C for the same drying time at atmospheric pressure. This article presents a numerical model to analyze fabric drying properties. Simulation results align with experimental results, with deviations in a range of 10 °C for critical temperatures and 2% for moisture content and drying time. The experimental and computational results helped to identify dryer performance key variables: chamber pressure, temperature, and vacuum pulse modulation. A series of experiments reveal optimized vacuum modulation that enhances average drying rate and minimizes drying time.

Broadband Cross-Polarization to Half-Integer Quadrupolar Nuclei: Wideline Static NMR Spectroscopy.

Cross-polarization (CP) is a technique commonly used for the signal enhancement of NMR spectra; however, applications to quadrupolar nuclei have heretofore been limited due to a number of problems, including poor spin-locking efficiency, inconvenient relaxation times, and reduced CP efficiencies over broad spectral bandwidths─this is unfortunate, since they constitute 73% of NMR-active nuclei in the periodic table. The Broadband Adiabatic Inversion CP (BRAIN-CP) pulse sequence has proven useful for the signal enhancement of wideline and ultra-wideline (i.e., 250 kHz to several MHz in breadth) powder patterns arising from stationary samples; however, a comprehensive investigation of its application to half-integer quadrupolar nuclei (HIQN) is currently lacking. Herein, we present theoretical and experimental considerations for applying BRAIN-CP to acquire central-transition (CT, +1/2 ↔ -1/2) powder patterns of HIQN. Consideration is given to parameters crucial to the success of the experiment, such as the Hartmann-Hahn (HH) matching conditions and the phase modulation of the contact pulse. Modifications to the BRAIN-CP sequence such as flip-back (FB) pulses and ramped contact pulses applied to the 1H spins are used for the reduction of experimental times and increased CP bandwidth capabilities, respectively. Spectra for a series of quadrupolar nuclei with broad CT powder patterns, including 35Cl (S = 3/2), 55Mn (S = 5/2), 59Co (S = 7/2), and 93Nb (S = 9/2), are acquired via direct excitation (CPMG and WCPMG) and indirect excitation (CP/CPMG and BRAIN-CP) methods. We demonstrate that proper implementation of the sequence can enable 1H-S broadband CP over a bandwidth of 1 MHz, which to the best of our knowledge is the largest CP bandwidth reported to date. Finally, we establish the basic principles necessary for simplified optimization and execution of the BRAIN-CP pulse sequence for a wide range of HIQNs.

Development of a DC Motor Speed Control System Based on PID

In the field of motion control systems, motor speed control plays a pivotal role. Various control algorithms and methods have been developed for this purpose, and one of the earliest strategies to emerge was analog control. Over time, it has evolved into a typical control structure with convenient parameter tuning capable of meeting general control requirements. This design is based on digital control algorithms, with the ST89C52 microcontroller as the control core. It generates pulse-width modulation (PWM) pulses controlled by a digital algorithm to regulate the speed of direct circuit (DC) motors. Additionally, it utilizes a photoelectric sensor to convert motor speed into pulse frequency, which is fed back to the microcontroller, thereby achieving closed-loop speed control and eliminating static speed errors.

Quadrupole Electromagnetic Linear Positioning System (QELPS):

In linear motion systems, including linear motors and actuators, precise and controlled linear motion is provided for various applications. However, they have several drawbacks: high costs, complexity, limited stroke length, high energy consumption, speed limitations, heat generation, noise and vibration, limited load capacity, environmental considerations, and integration challenges. High costs are especially significant for applications requiring high precision. The components' complexity and additional control electronics can increase maintenance and trouble-shooting requirements. Ensuring accurate and efficient operation necessitates regular maintenance. The limitation in stroke length, determined by the drive's size and guide length, can pose challenges for applications requiring long strokes. High energy consumption can be a concern, and speed limitations may be challenging. Managing heat generation is crucial to prevent component damage. Noise and vibration can be problematic, particularly in quiet applications. Integration challenges can arise when dealing with complex systems or automation processes. To overcome some of these drawbacks, an innovative coil configuration design for linear positioning system applications is proposed. The proposed design focuses on the Quadrupole Electromagnetic linear Positioning System (QELPS), comprising four coils generating a uniform electromagnetic field to produce a Lorentz force on the slider. The QELPS design is meticulously crafted using 3D modeling in ANSYS software, and the magnetic characteristics indicate the potential for scaling this model to different levels. The power circuit of the QELPS is simulated using ANSYS Simplorer and incorporates silicon-controlled rectifiers (SCR) and a pulse width modulation (PWM) pulse generator. The design achieves a force of 27.6 newtons with the paper presenting current and force plots in comprehensive detail. Furthermore, an interactive design algorithm is introduced, facilitating the customization of this model for various linear track dimensions. This research aims to advance linear drive technology and enhance linear motion applications by developing this new coil configuration design and harnessing the Quadrupole Electromagnetic System.

A π-polarized 1084 nm laser with pump pulse modulation based on Nd:MgO:LiNbO3 crystal

A π-polarized （π-pol） 1084 nm laser based on Nd:MgO:LiNbO3 crystal under modulation pulsed pumping mode was demonstrated. The anisotropic Nd:MgO:LiNbO3 slab crystal was end-pumped by a pulsed laser diode (LD) with a different duty cycle for experiments. The dual-wavelength fundamental laser emission range was effectively controlled within a certain pump peak power interval, and the unmatched polarized fundamental laser is completely suppressed when the duty cycle is 20 % and below. At a repetition frequency of 5 Hz and pulse width of 40 ms, the π-pol 1084 nm fundamental laser with a maximum average output power of 1.396 W in the whole pump range was obtained, and the single pulse energy was 279.2 mJ.

Switched capacitor based 7-level and 9-level multilevel inverters with single DC source and reduced voltage stress

This paper proposes two different switched capacitor based Multilevel Inverter topologies having single dc voltage source. One of the proposed MLIs is a seven-level structure whereas the other circuit successfully generates a nine-level output voltage. The special features of the seven-level topology consist of reduced number of circuit elements, lower voltage stress on switches, and boosted output voltage. The nine-level MLI having unity gain also possess the reduced switch count along with lower value of switch voltage stress. Fundamental frequency based Nearest Level Control modulation and Level-Shifted Pulse Width Modulation have been used for generating the required voltage levels. Successful implementation of the proposed MLI circuits has been done with the help of a laboratory prototype and its results are presented and explained in the paper to show its practical suitability. Other type of analysis include loss analysis which has been done in PLECS software. From this analysis, the efficiency has been estimated. A comparative analysis of both the proposed structures has been carried out with some other similar topologies on different performance parameters. From the analysis and comparison, it is evident that the proposed MLIs are better than some of the existing topologies and can be used for industrial applications.

φ-OTDR Based on Orthogonal Frequency-Division Multiplexing Time Sequence Pulse Modulation

φ-OTDR Based on Orthogonal Frequency-Division Multiplexing Time Sequence Pulse Modulation

Synaptic transistor based on PVK mixed with oxadiazole and its logic gate application

Because of the simplicity of device integration, high energy efficiency, and the ability to achieve robust neuromorphic calculation, the explore of artificial synaptic devices has attracted extensive attention. In this work, an electronic synaptic organic transistor based on a mixture of p-type polymer and n-type small molecule semiconductor colloids by spin coating was designed to achieve synaptic plasticity. Typical synaptic behavior, including excitatory postsynaptic current and paired-pulse facilitation, is simulated using electrical impulse stimulation. In addition, the transition from short-term plasticity to long-term plasticity were realized by adjusting input pulse operation. More importantly, the logic function of “AND” and “NAND” gate is designed and realized based on the operability of organic transistor pulse modulation. Our work offers a new approach for the exploitation of organic multifunctional neuromorphic electronic devices.

Development of a 40-kV Pulse Modulator and Experiment With Industrial Odor Removal Using Nonthermal Plasma

Development of a 40-kV Pulse Modulator and Experiment With Industrial Odor Removal Using Nonthermal Plasma

A Hybrid Weight Quantization Strategy for Memristive Neural Networks

Due to the ability to store data and process information, the memristor-based neuromorphic system has attracted extensive attention. Its efficient parallel computing approach allows it to implement neural networks in hardware. However, due to the limitation of the range of memristor conductance, it is difficult to represent high-precision weights in memristive neural network. During the off-chip learning, it is crucial to find an efficient weight quantization scheme and map it to the memristor array. Therefore, a hybrid weight quantization strategy that combines uniform and non-uniform quantization is proposed to overcome these problems. Specifically, the curve fitting of pulse modulation for tantalum oxide-based memristor is carried out, and the mapping rules of weights are proposed to simplify the process of reading verification. Furthermore, the hybrid quantization strategy is proposed and applied to a multilayer perceptron and a convolutional neural network, respectively. The effectiveness and robustness of the hybrid quantization scheme are verified in the MNIST dataset. Experiments show that the proposed hybrid quantization scheme can achieve 99.26% accuracy at 4 bits and tolerate 20% noise interference. The simulation results in this paper also provide an effective solution for the hardware implementation of memristive neural networks.

The hybrid pulse amplitude width modulation scheme: high efficiency technique for dimmable VLC systems

Abstract Visible-light communications (VLC) is an environmentally friendly optical wireless communication (OWC) technology that operates in the 400–800 THz frequency band. It is currently a critical technology for 5G and 6G wireless indoor applications due to its high data rates, low latency, and superior reliability. Intensity modulated direct detection (IM/DD) is widely used in VLC systems. A channel modulation scheme is designed using L-level pulse modulation techniques such as on–off keying (OOK), amplitude modulation (PAM), position modulation (PPM), and the width modulation (PWM). We introduce a novel hybrid modulation scheme n-M-PAWM based on both PAM and PWM schemes to improve throughput and significantly increase power and spectrum efficiency in VLC communication systems. The performance of our proposed hybrid n-M-PAWM scheme is studied in several aspects, including the number of transmitted bits per symbol, average BER, information rate ratio (IRR), PAPR, bandwidth, and power requirement. In an extremely noisy VLC system, the proposed 2-M-PAWM modulation outperforms both PPWM and PAPM modulation schemes due to its better BER performances. Additionally, we examine the performance of the VLC system in terms of spectral efficiency (SE) using our proposed PAWM-based dimming control system by varying the number of pulses transmitted during one symbol period. We demonstrate through simulation results that our PAWM-based dimming control system performs significantly better compared to the other pulse modulation schemes. All results of this research show that our proposed hybrid PAWM modulation scheme has high potential for VLC technology in indoor and noisy environments.

Error performance analysis for chaotic pulse width position modulation in free space optical communication system

Abstract In this paper, a pulse time modulation method called chaotic pulse width position modulation (CPWPM) is studied for free space optical communication system. This is a digital modulation technique that combines pulse position modulation and pulse width modulation with chaos. In this scheme, the binary information is carried by both the position and width of the pulses, which are modulated by a chaotic signal. Hence, on a single pulse, two bits of information are encoded, which results in higher bit rates, better privacy, and larger effective bandwidth as compared to chaotic pulse position modulation (CPPM) and chaotic pulse width modulation (CPWM) techniques. Probability of error is investigated for different FSO scenarios, i.e., varying turbulence conditions and link lengths for CPWPM scheme. Finally, the performance of CPWPM-FSO system is compared with a commonly used differential chaos shift keying (DCSK) scheme. CPWPM-FSO system shows comparable results as DCSK-FSO system (for probability of error, P e = 10−4 average signal-to-noise ratio (SNR) required for DCSK and CPWPM scheme is 40 dB and 41 dB, respectively, for same length and system conditions), while data rate is doubled in latter, and this verifies the validity of using CPWPM in FSO communication system.

Сравнительный анализ математических описаний и методов широтно-импульсной модуляции

The article considers the mathematical description and comparison of the most common methods of pulse-width modulation (PWM) for a three-phase voltage inverter, namely vector PWM, PWM with third harmonic premodulation and classical PWM. In contrast to the classical mathematical description of PWM, a description is presented that is close to the implementation of modulation using modern microcontroller technology. The classic representation of PWM is based on comparing two signals. In this representation, the modulation pulse occurs at the moment when the modulating function is greater in value than the reference signal. When implementing PWM by a microcontroller, the pulse is placed within the period symmetrically with respect to the middle of the interval, while the pulse width is determined by the average value of the voltage modulating function. With a different mathematical description of PWM, the pulse is located differently within the modulation interval. There are presented the results of modeling and compares the mathematical descriptions of PWM methods according to the criterion of minimum dispersion of the current flowing in the load. As a result of the comparison, it was revealed that the same, differently described PWM algorithm gives different results. A comparison of vector PWM with a modified vector PWM was made. The modification consists in applying a dynamic pulse shift algorithm in such a way as to obtain a minimum of current dispersion in the load. Comparison of PWM methods was carried out at different frequencies of the reference signal; a static RL circuit was used as a load when simulating a three-phase voltage inverter. The results obtained allow us to recommend a pulse shift algorithm for implementing PWM in voltage inverters operating at relatively low PWM frequencies. Minimization of the current dispersion makes it possible to obtain improved energy and vibration-noise characteristics of the electric drive.

MODERNIZATION OF THE HELIUM ION ACCELERATOR MICROWAVE POWER SUPPLY SYSTEM

The high-voltage rectifier modernization, which is part of helium accelerator (PSS-4) high-frequency system, is described. The rectifier supplies the pulse modulator with direct current energy. The valves of the modulator used are mercury thyratrons. Modernization involves replacing thyratrons with semiconductor diodes. In the article, a comparative analysis of the parameters of thyratrons and diodes, which are supposed to be replaced by thyratrons, is carried out, and the expediency of such a replacement is substantiated.