Pulse Density Research Articles

ПОСЛІДОВНІ РЕЗОНАНСНІ ІНВЕРТОРИ З МОДУЛЬНОЮ СТРУКТУРОЮ ДЛЯ ВИСОКОЧАСТОТНИХ УСТАНОВОК ІНДУКЦІЙНОГО НАГРІВАННЯ

Research results of induction heating transistor high - frequency series resonant inverters with modular structure on the base of parallel – series connection are presented in the paper. Pulse density modulation is used to regulate the output current of the inverter. It is shown that the use of the out-of-phase inverter modules control allows reducing the amplitude pulsation of the output current amplitude, which is especially important under low quality of the output resonant circuit and a wide range of load parameters. A mathematical model of the series resonant voltage inverter with a modular structure is presented; it allows the calculation of output current under different parameters of pulse density modulation. References 7, tables 2, figures 5.

Load-Adaptive Resonant Frequency-Tuned $\Delta$–$\Sigma$ Pulse Density Modulation for Class-D ZVS High-Frequency Inverter-Based Inductive Wireless Power Transfer

This article presents a resonant frequency tuning (RFT) delta–sigma ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta$</tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Sigma$</tex-math></inline-formula> ) signal-transformed pulse density modulation (PDM) class-D converter for inductive power transfer (IPT) applications. The proposed power controller provides a load-adaptive pulse modulation by tuning a zero phase angle and peak-power frequency, i.e., resonant frequency in the primary-side high-frequency inverter. The switching frequency is regulated in accordance with the variations of the load and coupling coefficient between the transmitting (Tx) and receiving (Rx) coils. The output power is controlled by the RFT- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta$</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Sigma$</tex-math></inline-formula> PDM, which is effective for reducing a low-frequency oscillation (subharmonics); thereby, the high-efficiency power transmission can be attained. The essential performances of the proposed IPT power controller are demonstrated in an experiment of a 400 W–500 kHz of prototype, whereby the feasibility is clarified from a practical point of view.

Load Independent Constant Current and Constant Voltage Control of LCC-Series Compensated Wireless EV Charger

In this article, load-independent constant current/voltage control operations of an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> -Series compensated wireless electrical vehicle (EV) chargers are presented. The parameters of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> -Series compensation topology are designed based on load-independent zero phase angle and soft switching operation in the constant current charging operation. Then, the load independent soft switching conditions are achieved for constant voltage charging operation with a semibridgeless active rectifier using pulse density modulation control. Thus, high efficiency power transfer to the load is performed during the entire charging period. The wireless communication is not needed to achieve the output voltage regulation in the proposed EV charging system. The soft switching operations of the switches on the primary and the secondary side are achieved in a wide load range. The performance of the proposed charging system is validated by a prototype. At the full load condition, the output voltage of the system is regulated at 210 V while the output current is 5 A. The maximum efficiency is measured 93.8% at 1 kW output power with 150 mm air gap. The efficiency performance of the system is also evaluated based on the misalignment conditions.

Analytical model for extracting optical properties from absorptance of femtosecond-laser structured hyperdoped silicon

We set up an analytical optical model to emulate the absorptance spectra of light scattering, sulfur-hyperdoped silicon that we fabricate by using femtosecond laser pulses. The model allows us to distinguish between contributions to the absolute sub-bandgap absorptance from the path length enhancement of photons due to laser-induced surface roughness, on the one hand, and from the actual hyperdoped layer, on the other hand. Both effects are quantified via the two free parameters of the model. By varying the laser fluence and the areal pulse density, we create a range from almost planar to heavily structured hyperdoped Si samples that we show to behave almost like a Lambertian scatterer. The optical depth a1, i.e., the product of the absorption coefficient close to the Si bandgap energy and the effective thickness of the hyperdoped layer, scales with the surface area enhancement, which we identify as the main driving force for large sub-bandgap absorptances of this material type. It reaches maximum values of nearly a1 = 0.4, which refers to an absolute absorptance of 82% at a wavelength of 1450 nm. We furthermore discuss, quantify, and reduce possible error sources when determining the absorptance of such optically rough, hyperdoped samples with a spectrophotometer.

Influence of Industrial Metakaolin Waste on Autoclaved Fiber Cement Properties Changes in Standard Fire Environment.

An investigation was conducted on the influence that industrial metakaolin waste (IMW) has on the properties of autoclaved fiber cement composition (FCC) samples. FCC samples were made from fiber cement plate’s typical components using the same proportions. In samples, IMW was used instead of cement in 10%, 20%, 30% proportions and in 50%, 100% proportions instead of ground quartz. Differential thermal analysis (DTG), thermogravimetric analysis (TGA), ultrasound pulse velocity (UPV), density, porosity and optical microscope (OM) research methods were used to identify the micro and macrostructure of samples. Mechanical properties were evaluated using flexural and compressive strength research methods. It was established that IMW was used instead of cement in fiber cement composition samples up to 10% and in fiber cement composition samples instead of ground quartz forms density microstructure structure because of Al-rich tobermorite. As a result, the flexural and compressive strength increased. Samples with higher content of IMW instead of cement had unreacted IMW and a less dense microstructure. In this case, flexural and compressive strength decreased. All FCC samples were fired in a standard fire curve (ISO 842) for 30 min. Samples of mechanical properties were established by doing flexural and compressive strength tests, and which results showed the same trends.

A 32-MHz, 34-μW Temperature-Compensated RC Oscillator Using Pulse Density Modulated Resistors

Highly stable on-chip frequency references offer the possibility of replacing crystal oscillators in many cost-and form-factor-constrained applications. However, achieving good frequency stability in a power-efficient manner across process, voltage, and temperature variations possess many design challenges. This article describes these challenges and presents a method for improving the integrated RC oscillator’s frequency accuracy by overcoming them. We show that the impact of resistor temperature coefficient (TC) on the accuracy of output frequency can be mitigated by using a parallel combination of two switched resistors that are digitally controlled by pulse-density modulated sequences. By trimming at only two temperatures, a prototype frequency-locked loop (FLL)-based 32-MHz oscillator fabricated in a 65-nm CMOS process achieves an inaccuracy of 530 ppm (8.4 ppm/°C), 80-ppm/V voltage sensitivity, 2.5-ppm Allan deviation, and 1- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> /MHz power efficiency.

Investigation on Performance of Various Power Control Strategies with Bifilar Coil for Induction Surface Melting Application

In recent years, induction heating applications assisted by electronic power control have been very appealing. For melting applications, induction heating is widely used as it seems to be appropriate and provides higher efficiency, zero pollutants, non-contamination of material, etc. in comparison with conventional heating. The conventional variable frequency control scheme is not sufficient for melting applications because of its high switching loss, low efficiency, and lower heat rate. A superlative control technique is required to control the output power smoothly, for a high heating rate with minimum power loss, and to lower the number of components. In this paper, a capacitorless self-resonating bifilar coil is proposed for induction surface melting applications. The performance of the system in terms of modular losses, heat rate, and efficiency is analyzed for various power methods such as pulse duty cycle control, phase shift control, pulse density modulation control, and asymmetric duty cycle control. An experimental validation is performed for the 1 kW prototype, and the heating rate, efficiency, and modular losses are calculated. The control technique is digitally validated using a PIC16F877A microcontroller with 30 kHz switching frequency. The temperature distribution is analyzed using a FLIR thermal imager. Among the tested methods, pulse density modulation-based control provides smooth and varied power control from 0% to 100% with minimum modular losses. The efficiency of the system is 89% at a rated output power and is greater than 85% for pulse density modulation control with a fast heating rate.

PDM-Based Feedforward Power Compensation for FMPSK Communication in WPT Systems

A wireless power transfer (WPT) system usually needs dual-side cooperated control for efficiency optimization and power regulation, and requires wireless communication between the transmitter and the receiver. Phase shift keying (PSK) communication is a good choice for WPT systems because of its advantages of high security and low hardware cost. However, the converter phase modulation required by the PSK communication causes output power and voltage fluctuations. In this brief, we analyze the relationship between the phase modulation depth and the output fluctuation amplitude. Then we propose a pulse density modulation-based feedforward power compensation method to compensate the fluctuations caused by the PSK communication. Experimental results show that the proposed power compensator can suppress the output voltage fluctuations to an insignificant level without a large output filter capacitor. The proposed method overcomes the main drawback of the PSK communication in WPT systems.

Design of wireless voice transmission system based on nRF52833

This article chooses pulse density modulation, 2.4GHZ radio frequency, I2S bus nRF52833 chip as the central processing unit to develop the wireless audio transmission system. And carry on the theoretical design and analysis to the hardware module and software module of the whole system, and test the RF distance and power consumption, as well as the audio delay and fidelity, basically realise the design of the wireless voice transmission system based on nRF52833.

High cycle fatigue life improvement of superferritic stainless steel by laser shock peening without coating

The excellent mechanical properties, high thermal conductivity and corrosion resistance combined with moderate cost make superferritic stainless steels (SFSS) commercially attractive. Though these steels are finding increase uses in many applications where fatigue loadings are applied, few studies are devoted to study this theme. Even fewer works aim to investigate the fatigue improvement by surface treatments. Laser shock peening without coating (LSPwC), is a surface modification technology using high-energy laser with no absorbent coating that increases the fatigue life in many alloys. However, though LSPwC in SFSS UNS44600 has reported to produce beneficial compression residual stresses (CRSs) and strain-hardening surface layer, it also causes intergranular corrosion which avoids the improvement of low fatigue life (LCF). Thus, attempting to discern if this result remains in the HCF regimen, the present paper is focused on studying the influence of LSPwC on the high cycle life (HCF) of SFSS UNS S44600. The results showed that LSPwC enhances the HCF of SFSS UNS S44600, being the fatigue life improvement more pronounced with higher pulse density. This can be rationalized considering the main role of the induced CRS in slowing occurrence and growth of crack in corroded grains on HCF regimen. The examination of fracture surface by scanning electron microscopy (SEM) substantiates these fatigue results.

СИСТЕМА ЦИФРОВОГО ФАЗОВОГО АВТОМАТИЧНОГО ПІДСТРОЮВАННЯ ЧАСТОТИ РЕЗОНАНСНОГО ІНВЕРТОРА НАПРУГИ

The digital phase-locked loop (PLL) system for the resonant voltage inverter with pulse density modulation of induction heating installations is developed. The proposed system for frequency determination uses the feedback signal on the collector-emitter (drain-source) voltage of the inverter transistors and on the output current of the inverter, and stores this frequency on the interval of zero output voltage. A study of the PLL system in different operating modes when changing the load parameters is presented. References 8, figures 6, table 1.

Investigation of fracture mechanics, physical and dynamic properties of UHPCs containing PVA, glass and steel fibers

Fracture energy, non-destructive testing, some physical and mechanical tests and microstructural investigations were performed on 18-month 0.7 V%, 1.3 V% and 2.0 V% PVA fiber, glass fiber (GF) and steel fiber (SF) reinforced Ultra High Performance Concretes (UHPCs). Fracture test was performed on Single Edge Notched Beams (SENB) to investigate fracture energy, dissipated energy, flexural strength, crack resistance index (CRI), and flexibility index (FI) of UHPCs. Dynamic modulus of elasticity and damping ratios of the UHPCs were calculated by performing resonance frequency tests on the SENB samples by ASTM C215 standard. In addition, compressive strength, static modulus of elasticity, electrical resistivity, ultrasonic pulse velocity (UPV), Leeb hardness, Schmidt hammer, and density tests were also performed on the cylindrical samples. Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-Ray (EDX) analyzes were performed to examine the interaction between the UHPC matrix and different fibers. Among all the mixtures, an exceptionally positive effect of SFs on the all mechanical properties of the UHPCs was observed. Dynamic test results showed that the increase in fiber ratio increased the damping ratio of UHPCs irrespective of fiber type. The UPV and electrical resistivity results offered promising results regarding the internal structure of UHPCs.

Development of a portable laser peening device and its effect on the fatigue properties of HT780 butt-welded joints

Laser peening (LP) is a well-established technique for introducing compressive residual stress (RS) near the surface of metal components, to improve their high-cycle fatigue properties. The authors have developed a compact LP device with a thumb-sized Nd:YAG microchip laser mounted on a collaborative robot arm. The device was applied to 9-mm-thick HT780 high-strength steel plate samples with irradiated pulse energies of 7.5−8.0 mJ, spot sizes of 0.42−0.58 mm and pulse densities of 100−1,600 pulses/mm2. X-ray diffraction showed that the maximum compressive RS was over 500 MPa near the surface, and the LP effect reached a depth of approximately 0.1 mm from the surface. Butt-welded HT780 samples were laser-peened with a pulse energy of 7.7 mJ, spot size of 0.49 mm and pulse density of 800 pulses/mm2. Then, the samples were subjected to a uniaxial fatigue test with a stress ratio of 0.1. The results showed that the fatigue strength at 107 cycles was improved by at least 50 MPa, comparable to the improvement attained by LP in a previous study with a pulse energy of 200 mJ from a conventional Nd:YAG laser.

Advanced Stabilization Methods of Plasma Devices for Plasma-Based Acceleration

Towards the next generation of compact plasma-based accelerators, useful in several fields, such as basic research, medicine and industrial applications, a great effort is required to control the plasma creation, the necessity of producing a time-jitter free channel, and its stability namely uniformity and reproducibility. In this Letter, we describe an experimental campaign adopting a gas-filled discharge-capillary where the plasma and its generation are stabilized by triggering its ignition with an external laser pulse or an innovative technique based on the primary dark current (DC) in the accelerating structure of a linear accelerator (LINAC). The results show an efficient stabilization of the discharge pulse and plasma density with both pre-ionizing methods turning the plasma device into a symmetrical stable accelerating environment, especially when the external voltage is lowered near the breakdown value of the gas. The development of tens of centimeter long capillaries is enabled and, in turn, longer acceleration lengths can be adopted in a wide range of plasma-based acceleration experiments.

Effect of varied unmanned aerial vehicle laser scanning pulse density on accurately quantifying forest structure

ABSTRACT Airborne laser scanning (ALS) is increasingly used to estimate various forest characteristics. Technological improvements in unmanned aerial vehicles (UAVs) and drone laser scanning (DLS) sensors have permitted the acquisition of high pulse density datasets. There is an assumption that higher pulse densities yield greater accuracies in estimating forest characteristics. In this study, we investigated the effect of pulse density (.25, .5, 1, 5, 10, 50, 100 and 300 pulses m−2) on the ability to delineate individual tree crowns (ITCs) and estimate ITC height and crown horizontal diameter, in addition to plot-level leaf area index (LAI). The current study took place in an experimentally varied Pinus taeda L. forest, which included three stem densities: (i) 618; (ii) 1236; and (iii) 1853 trees per hectare (TPH). ITCs were classified directly from the DLS point cloud for each of the pulse densities. The correct delineation of ITCs relative to field tree-coordinates was relatively consistent (±5%) for pulse densities of 5 to 300 pulses m−2. ITC delineation accuracy decreased with lower pulse densities. Planting stem density did impact ITC delineation accuracy. Higher pulse densities, plots with 618 TPH correctly classified ~88% of ITCs, and plots with the 1853 TPH correctly classified ~50% of ITCs. Estimates of tree height were largely unaffected by changes in tree density. Root mean square error (RMSE) for tree height varied from .5 to 2.5 m at pulse densities of 300 to .25 pulses m−2, respectively. Estimates of crown horizontal diameter varied with regard to both pulse and stem density from 1.2 (300 ppm−2 and 1853 TPH) to 4.2 m (.25 ppm−2 and 618 TPH). RMSE varied among stem densities from .6 to 1.2 m as pulse density decreased. There was significant difference in ITC delineation accuracy, particularly when considering stem density, and the estimates of tree height and crown horizontal diameter among the DLS pulse densities used. The accuracy of predicted LAI was largely unaffected by changes in pulse density, when pulse density was above .5 pulses m−2. There was little or no difference in estimates of LAI at these pulse densities. Our results suggest that low-density DLS data may be capable of estimating plot-level forest metrics reliably in some situations, however once the analysis scale is reduced to the individual-tree-level, the influence of pulse density is more substantial. The results here provide guidance to forest managers who must balance metric estimation accuracy and price when planning new ALS or DLS acquisitions.

Pulse density modulation control-based multi-load handling three leg inverter for cooking applications

PurposeInduction heating applications aided by power electronic control have become very attractive in the recent past. For cooking applications, power electronics circuits are very suitable to feed power to multi loads with an appropriate control technique. The purpose of this paper is to develop a three leg inverter to feed power to three loads simultaneously and independently.Design/methodology/approachPulse density modulation control technique is used to control the output power independently with constant switching frequency.FindingsMulti-load handling converter with independent power control is achieved with reduced number of switching devices (two switches/per load) with simple control strategy.Originality/valueThe proposed system is simulated in MATLAB/Simulink, and the thermal analysis is carried out in COMSOL multi-physics software. The hardware realisation is performed for a 1 kW prototype with 20 kHz switching frequency and 10 kHz pulse density modulation frequency. PIC16F877A microcontroller is used to validate the experimental results for various values of control signals (DPDM). The simulation and experimental results are in good agreement and validates the developed system.

A study to assess the efficacy of fractional carbon dioxide laser with topical platelet-rich plasma in the treatment of androgenetic alopecia.

Owing to the inadequate response to and limitations of the approved medications for androgenetic alopecia, novel therapies are warranted to enhance outcomes. The objective of this paper is to ascertain the effectiveness of fractional carbon dioxide laser followed by platelet-rich plasma application on hair regrowth and to compare the two laser settings. Seven participants were enrolled in this half-head pilot study based on different laser pulse energy and density values (12 mJ, 800 spots/cm2 and 22 mJ, 400 spots/cm2). Ten treatment sessions were performed every 2 weeks with 12-week follow-up. The evaluation methods were based on hair density from standardized phototrichograms, global photographic assessment, and patient satisfaction. Significantly increased total and terminal hair densities were observed during treatment in both groups as compared with baselines. The mean total hair density has weekly increased significantly with high pulse energy (1.42 hair/cm2) as compared to low pulse energy (1.04 hair/cm2) throughout the study period (p = 0.023; 4.89 hair/cm2). Global photographs and patient satisfaction scores demonstrated improvement, but only the latter showed statistical significance (p = 0.029). The average pain intensity scores were not different between the groups (p = 0.760) all over the procedure. The adverse events were minor and well tolerated. This synergistic treatment remarkably leads to hair restoration and high patient satisfaction. The parameters of 22-mJ beam energy with 400 spots/cm2 density are appropriate and superior to 12-mJ beam energy with 800 spots/cm2. Albeit higher energy, no more pain is indicated in the high pulse energy group. Trial registration number (TRN): TCTR20180619004, Thai Clinical Trials Registry (TCTR) since 2018-05-15 13:39:48.

Investigation of type I modifications in fused silica for recording phase diffractive optical elements by femtosecond laser

In this paper we demonstrate the application of direct laser writing technology for writing phase diffractive optical elements under a glass surface. This technology is based on writing refractive index change modifications in volume of transparent materials. Different parameters were studied to determine the type of modifications: pulse repetition rate, pulse energy, pulse density, focusing depth and polarization. The modulation of the refractive index change of these modifications was investigated by using two different methods: Bragg gratings method and Michelson interferometer method. Further development was made to form 1D and 2D gratings and even more difficult elements such as Fresnel lens. It has been observed that the diffraction efficiency of the Bragg gratings was up to 97 %, ∼ 96 % for 1D gratings, 75 % for 2D gratings and 64 % for the Fresnel lens.

Diagnostic of laser wakefield acceleration with ultra – Short laser pulse by using SMILEI PIC code

• Generation of high energy beam with LWFA is the most efficient and low in cost as compared with conventional accelerator. • In LWFA, we firstly performed this acceleration with the combination of up ramp and down ramp density region. • We firstly performed the work related with production of high energy beam with self-injected electrons. • We firstly performed the work with ultra – short laser pulse and polygonal plasma density profile for LWFA. High-energy particle beam is used to probe the local or long range structure and properties of materials. Particle accelerators are also used in material science to understand radiation damage, particularly in studies of structural material to be applied in fusion power generator and satellites. Laser Wakefield Acceleration (LWFA) is a promising technique to build compact and powerful particle accelerators for generating multi-GeV electron beams. The efficient coupling of laser energy with plasma is very important to generate high energy electrons, which is the subject to optimum laser and plasma profiles. In this article, we have used high intensity ultra-short laser pulse and a polygon plasma density profile to analyse the behaviour of LWFA in the bubble regime, which corresponds to the evacuation of plasma electrons in the wake of the laser pulse. Many electrons get self-injected in this wakefield and get accelerated behind the laser pulse up to very high energies, producing high energy beam useful for material processing along with their other applications. We have diagnosed some parameters such as electron density variation, wakefield magnitude and energy spectrum of the electrons accelerated in this mechanism.

A 0.5-mm2 Solar Cell-Powered Biofuel Cell-Input Biosensing System With LED Driving for Stand-Alone RF-Less Continuous Glucose Monitoring Contact Lens

This letter presents the first solar cell (SC)-powered biofuel cell (BFC)-input biosensing system with pulse interval modulation (PIM) and pulse density modulation (PDM) LED driving capability for continuous glucose monitoring (CGM) contact lenses featuring stand-alone RF-less operation. Power supply from on-lens SCs can eliminate the necessity of wireless power delivery, and LED implementation can eliminate the necessity of wireless communication. By employing the BFC-input approach instead of using a power-hungry potentiostat, powering and sensing components are separated, which reduces the power budget from SCs. The measured power of 28/144 nW at the PIM/PDM mode with a 0.31/0.39-V supply voltage can be managed by the on-lens SCs, enabling a fully stand-alone on-lens operation under office-room ambient light whose typical illumination intensity is 800–1600 lx.