Pulsed Mode Operation Research Articles

Impact of HAN Ternary Propellant System Decomposition on Catalytic Sustainability

AbstractAqueous solution of Hydroxylammonium nitrate (HAN) in combination with a suitable fuel has been explored as a promising high performing green monopropellant in recent times. The current study primarily explores the effect of the addition of a fuel component into HAN solution on the sustainability of a recently developed catalyst which was examined for the only binary system consisting of HAN and water. The HAN ternary system examined was HAN: methanol: water in 70 : 15 : 15 (w/w) composition. The endurance of an ‘iridium over alumina’ catalyst and an indigenously developed cobalt doped ceria‐based catalyst was analysed using a batch reactor wherein a pressure rise during decomposition of propellant whilst a pulse mode operation was monitored. Catalysts were also characterized via SEM/EDS, XRD, and XPS to identify changes over the period of sequential injection in the batch reactor. Doped ceria catalyst was found to be far robust and resistant to any poisoning when compared to iridium catalyst at run time of the operation involving nearly 45 sequential injections of propellant over the catalyst.

Design and demonstration of a micro air-fed magnetoplasmadynamic thruster for small satellites

This paper developed and tested a micro air-fed magnetoplasmadynamic thruster for small satellites. The thruster is a type of miniaturized electric propulsion system designed base on conventional full scale magnetoplasmadynamic thruster that operates at hundreds of kilowatts power. The thruster is designed and tested using normal air as the propellant under the pulse operation mode on a calibrated micro-force measurement thruster stand. The experiments revealed that the thruster can generate a 34.534 μNs impulse bit with an average power input of 1.857 ± 0.0679 W and thrust to power ratio of 8.266 μN/W, and the specific impulse is calculated to be 2319 s with the thruster efficiency of 9.402%, which is quite competitive comparing with other solid-state and liquid-fed pulse-mode thrusters. This paper presents the design and test results for the thruster under a low power level as well as an analysis of its problems and limitations with corresponding future research and optimization directions noted at the end.

Bias stress instability in multilayered MoTe 2 field effect transistors under DC and pulse‐mode operation

Here, bias stress instability on multilayered MoTe2 field effect transistors (m-MoTe2 FETs) with encapsulation of hydrophobic polymers (cyclic transparent optical polymer) is systematically investigated under DC and pulse mode operation. During DC mode stress, the threshold voltage shift (ΔVth) under positive bias stress is at least three times larger than that of negative stress due to high hole barrier (∼0.57 eV), compared with electron barrier (∼0.18 eV). However, ΔVth in positive pulse mode stress is significantly reduced with decrease of a duty cycle, as compared with that of negative stress. With isolation from external gas ambient effects such as H2O and O2, shallow electron traps in multilayered MoTe2 field effect transistors are identified as one of strong candidates to cause bias polarity dependency on ΔVth in pulse mode. Moreover, recovery time for traps, involved during positive bias stress, is six times faster than that of negative stress, substantiating that shallow electron traps and their fast detrapping are one of key origins. In practice, optimisation of pulse mode operation via bipolar switching can be potentially utilised for minimisation of device instability during the operation of multilayered MoTe2 field effect transistors devices and their circuits.

Hardware Self-Organizing Map Based on Digital Frequency-Locked Loop and Triangular Neighborhood Function

This paper proposes a unique hardware architecture for a self-organizing map (SOM) that mimics the biological brain by using pulse mode operation. In the proposed SOM, vector elements are given as in the form of frequency modulated signals, and digital frequency-locked loops (DFLLs) in neurons handle the computations of the vector elements. The SOM is trained by unsupervised learning, where the winner neuron that has the nearest weight vector is found first. In the proposed SOM, the winner neuron is found by counting cycle slips between the signals that carry input and weight vectors. After the winner neuron is found, weight vectors selected by a neighborhood function are updated toward the input vector. Triangular neighborhood function that is implemented by using an attenuating enable signal for the DFLLs, is employed. To evaluate the proposed SOM and its building components, VHDL simulations and experiments using an FPGA were conducted. Compared to the previous work, the operation speed and learning capability were significantly improved. Novelty of the proposed architecture is it uniquely uses a pulse-based operation that mimics the biological brain, and it was verified that unsupervised learning can be realized with neurons communicating with each other using frequency modulated pulse signals.

Safety Review and Perspectives of Transcranial Focused Ultrasound Brain Stimulation.

Ultrasound is an important theragnostic modality in modern medicine. Technical advancement of both acoustic focusing and transcranial delivery have enabled administration of ultrasound waves to localized brain areas with few millimeters of spatial specificity and penetration depth sufficient to reach the thalamus. Transcranial focused ultrasound (tFUS) given at a low acoustic intensity has been shown to increase or suppress the excitability of region-specific brain areas. The neuromodulatory effects can outlast the sonication, suggesting the possibility of inducing neural plasticity needed for neurorehabilitation. Increasing numbers of studies have shown the efficacy and excellent safety profile of the technique, yet comparisons among the safety-related parameters have not been compiled. This review aims to provide safety information and perspectives of tFUS brain stimulation. First, the acoustic parameters most relevant to thermal/mechanical tissue damage are discussed along with regulated parameters for existing ultrasound therapies/diagnostic imaging. Subsequently, the parameters used in studies of large animals, non-human primates, and humans are surveyed and summarized in terms of the acoustic intensity and the mechanical index. The pulse-mode operation and the use of low ultrasound frequency for tFUS-mediated brain stimulation warrant the establishment of new safety guidelines/recommendations for the use of the technique among healthy volunteers, with additional cautionary requirements for its clinical translation.

Characterization of neutron emission during pulse mode of low output electronic neutron generator

The paper deals with the characterization of the neutron output during operation the neutron generator in the pulsing mode. The characterization is performed by a cadmium covered He-3 detector. First, the adequacy of a cadmium covered He-3 detector to study the pulsed mode operation of neutron generator is assessed using Monte Carlo simulations in MCNP6 code. Second, the pulsing mode operation of the D-D P-385 Thermo Fisher Scientific neutron generator with a maximal neutron output of 7 x 106 n/s is studied. The study shows the dependence of neutron emission and pulse shapes on the frequency, duty factor, high voltage and beam current.

Design of the interaction cavity extending to the nonlinear taper for a 10 kw, W-band gyrotron

ABSTRACT In this paper, the design of an interaction structure for a 10-kW, W-band gyrotron is presented. The beam voltage and beam current are chosen as 30 kV and 1 A, respectively. The mode of interaction was chosen as TE6,2. A parametric design code and a gyro large-signal analysis (LSA) code were developed. The computational steps are discussed in brief. The LSA was done using the in-house developed code and the Gyro-K code. The results of these two codes were found to be in good agreement. The design of the nonlinear taper (NLT) was also carried out. Based on Ohmic loss, the power dissipated in the cavity was estimated. A novel cooling arrangement was proposed with two concentric cylindrical jackets around the cavity. The computational fluid dynamics (CFD) analysis was done using the software FloEFD. Steady-state analysis for the CW mode of operation and the transient analysis for the pulsed mode of operation were carried out for various flow-rates of the coolant.

A 10-W X-Band Class-F High-Power Amplifier in a 0.25-μm GaAs pHEMT Technology

In this article, a design methodology is presented to realize integrated class-F high-power amplifiers (HPAs). A harmonic-control network (HCN) is proposed to present short- and open-circuit impedances to each transistor employed in the output stage of the HPA at 2f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and 3f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> frequencies. The HCN absorbs the parasitic capacitance of the transistor and lends itself to be absorbed in the matching and power combiner networks, reducing the die area of the HPA. A proof-of-concept 9.7-10.3-GHz class-F HPA was designed and implemented in a 0.25-μm GaAs pHEMT technology with VDD of 6 V. The designed HPA consists of two amplifying stages, and its output stage includes 16 transistors in parallel to provide 39-40-dBm output power. The class-F HPA achieves a 10-W output power and a peak power added efficiency (PAE) of 63% for pulsed-mode operation with a pulse repetition frequency (PRF) of 1 kHz and a duty cycle of 10%. The measured peak output power and PAE in the continuous-wave (CW) operation are 9.3 W and 58%, respectively.

Detection of Transient Junction Temperature Characteristics of High Power IGBT

In this paper, Insulated Gate Bipolar Transistor (IGBT), which is the most widely used full-control power electronic device, is taken as the research object. Under the special working mode of short-time intermittent pulse, with the increase of conduction current, the chip junction temperature of high-power IGBT will rise sharply and fluctuate greatly, causing the operating characteristics of the device to be greatly affected by temperature. The commonly used method of measuring the bottom plate shell temperature with thermocouples and then estimating the steady junction temperature can no longer meet the demand. Firstly, the fluctuation characteristics of junction temperature of high-power IGBT are analyzed. Then, a high-speed infrared thermal imaging device is used to carry out real-time junction temperature detection. The distribution and rising process of instantaneous junction temperature on the chip surface are obtained, which further verifies the correctness of theoretical analysis. The research has important guiding significance for IGBT application design under short-time intermittent pulse operation mode, and also has certain reference value for general operation mode.

(Invited) Metal Oxide Decorated Porous Silicon Interfaces for Sensor Applications: The Question of Water Interaction, Stability, Platform Diversity, Sensitivity, and Selectivity

Key parameters of a metal oxide nanostructure modified porous silicon (PSi) template that can affect the development and performance of PSi-based sensors are considered1. The importance of pore selection and direct in-situ nitrogen functionalization are discussed. Metal oxide (MOx , MxO, x≥1) nanostructured island sites, deposited to select, well defined and reproducible micron sized p and n-type silicon pores (0.7–1.5 µ diameter) provide sensitivity and selectivity as they facilitate rapid “Fickian” analyte diffusion to these highly active sites. The metal oxide nanoparticles are trapped by a thin nanopored wall covering preventing their sintering at elevated temperatures. Variable sensitivities of the metal oxide nanostructured sites are well predicted within the recently developed Inverse Hard/Soft-Acid/Base (IHSAB) model. Ready nitrogen functionalization can further provide the conversion of the decorating metal oxides and an oxidized PSi interface from hydrophilic to hydrophobic character. The decrease in water interaction provides enhanced stability. Selectivity in the measurement of multiple gases is possible with a combination of nanostructure based detection matrices, p and n-type charge carrier variation, time dependent diffusion response, and pore structure influenced sensitivity as the range of variable responses is dominated by the molecular electronic structure of the nanostructured island sites as evaluated using the IHSAB concept. Fast Fourier Transfer techniques (pulsed mode operation) can facilitate low analyte consumption and higher analyte selectivity, and provide the ability to assess false positive signals. A new Fermi distribution–based adsorption isotherm is superior to other isotherms in modeling the PSi system. AIMS Electronics and Electrical Engineering, 4(1): 87-113,2020 DOI: 10.3934/ElectrEng.2020.1.87

RF commissioning of the compact energy recovery linac superconducting cavities in pulse mode

At the KEK compact energy recovery linac (cERL), a new beam line to produce radioisotopes (RIs) was constructed. To increase the beam energy for RI production, we proposed to switch the operation mode from continuous-wave mode to pulse mode. The first commissioning test of the cERL superconducting radio frequency (RF) cavities operated in pulse mode was therefore carried out. The RF pulse pattern for each cavity was carefully selected according to the corresponding cavity’s loaded Q and the capabilities of the power sources. A modified feedforward table was applied to reduce the peak reflected power at the power coupler. In addition, a filling on resonance approach that aims to reduce the required incident power during the filling time due to the existence of the Lorentz force detuning was adopted. The slow drift of the pulse-to-pulse detuning on the flat top of an RF pulse was successfully compensated for by a piezo feedback system. In this paper, we present the results related to the cERL pulse mode operation. The measured RF stabilities and beam energy stability in the cERL beam commissioning are presented as well.

Synthesis of antibacterial composite coating containing nanocapsules in an atmospheric pressure plasma

Antibacterial coating is an important strategy preventing bacterial colonization and biofilm formation. One-step synthesis of nanocapsule-containing antibacterial coatings with controlled release of Ag+ ions was achieved in the current work by aerosol-assisted atmospheric pressure plasma deposition. The experimental parameters of deposition including the discharge power, silver nitrate concentration, aerosol flow rate, continuous and pulsed mode of operation were studied in order to analyze their effects on surface morphology and chemical composition of the coating. Formation of nanocapsules embedded in the polymeric coating was observed. A core-shell structure was found for nanocapsule with silver in the core and polymer in the shell. Antibacterial coatings on polyethylene terephthalate film were studied in terms of Ag+ ion release, antibacterial properties against Escherichia coli and Staphylococcus aureus, and cytotoxicity with murine fibroblasts. Two-phase release kinetics of Ag+ ions was observed as initially a short-term burst release followed by a long-term slow release. It was revealed that high antibacterial efficiency of the coatings deposited on polyethylene terephthalate films can be coupled with low cytotoxicity. These biocompatible antibacterial coatings are very promising in different fields including biological applications.

Microsecond pulse-mode operation of a micro-integrated high-power external-cavity tapered diode laser at 808 nm.

We investigate microsecond pulse-mode operation of a micro-integrated high-power diode laser based on volume Bragg grating external-cavity feedback around 808 nm. The laser system contains a tapered amplifier consisting of a ridge-waveguide section and a tapered section with separated electrical contacts. Thus, the diode laser system can be pulsed by modulating the injected current either to the ridge waveguide section (IRW) or to the tapered amplifier section (ITA). With a trigger signal of a 50 µs pulse width and a 10 kHz repetition rate, comparing the modulation depth, peak output power, beam propagation factor, and spectral bandwidth, we conclude that the pulse-mode operation achieved by modulating the ITA gives better results than by modulating the IRW due to the decreased thermal effect. At a constant IRW of 0.2 A and a modulated ITA of 6.0 A, 4.3 W of peak output power is obtained with an emission spectral bandwidth with an upper bound of 0.2 nm, and a beam propagation factor in the slow axis, Mslow2, of 2.6 (1/e2). The modulation depth is almost 100%. The results show that the tapered diode laser system may be a good candidate for microsecond pulse-mode solid-state lasers.

Development of vacuum compatible, multi-mode operation light source

Light sources are used extensively at various stages of development and characterization of an electro-optical (EO) payload like Cartosat, HySIS, Microsat etc. These sources are required to characterize many critical parameters of EO payload like photo response non uniformity (PRNU), noise performance, saturation radiance etc. Currently integrating sphere with quartz tungsten halogen (QTH) lamp is widely used for payload characterization. These lamp sources generally operate in continuous mode in clean room environment and thermo-vacuum. In case of high resolution payloads, time-delay and integration (TDI) detectors are used to improve signal collection. For characterization and testing of such payloads multi-mode (pulsed and continuous) light source (switching at kHz rate in synchronization with payload electronics) with specific spectral range is required. Pulse mode operation requirement cannot be met using QTH lamps. To cater to such need a LED based indigenous source has been developed. This paper delineates circuit design and implementation of driver and characteristics of the source is also discussed. Proposed source is capable to synchronize and operate in multi-mode with external clock pulse with high achieved linearity (>99%) and high stability (>99%) in vacuum condition.

Optimization and kinetic study of ultrasound assisted deep eutectic solvent based extraction: A greener route for extraction of curcuminoids from Curcuma longa

The use of deep eutectic solvents (DESs) as a new extraction medium is a step towards the development of green and sustainable technology. In the present study, nine DESs based on choline chloride acids, alcohols, and sugar were screened to study the extraction of curcuminoids from Curcuma longa L. Choline chloride and lactic acid DES at 1:1 M ratio gave the maximum extent of extraction. Further, DES based extraction was intensified using ultrasound. The impact of various process parameters such as % (v/v) water in DES, % (w/v) solid loading, particle size, ultrasound power intensity, and pulse mode operation of ultrasound was studied. The maximum curcuminoids yield of 77.13 mg/g was achieved using ultrasound assisted DES (UA-DES) based extraction in 20% water content DES at 5% solid loading and 0.355 mm particle size with 70.8 W/cm2 power intensity and 60% (6 sec ON and 4 sec OFF) duty cycle at 30 ± 2 °C in 20 min of irradiation time. Kinetics of UA-DES extraction was explained using Peleg’s model and concluded that it is compatible with the experimental data. Additionally, anti-solvent (water) precipitation technique was applied, which resulted in 41.97% recovery of curcuminoids with 82.22% purity from UA-DES extract in 8 h of incubation at 0 °C. The comparison was made between conventional Soxhlet, batch, DES and UA-DES based processes on the basis of yield, time, solvent requirement, temperature, energy consumption, and process cost. The developed UA-DES based extraction can be an efficient, cost effective, and green alternative to conventional solvent extraction for curcuminoids.

A 40 μW–30 mW generated power, 280 Ω–1.68 kΩ load resistance CMOS controllable constant-power source for thermally-based sensor applications

A controllable constant-power source in 0.35 μm CMOS technology is presented in this paper. It is based on the resistive mirror method, and suitable for thermally-based sensor applications. Two versions have been developed and fabricated: a high-voltage design with a single supply of 10 V, and a low-voltage design with a single supply of 3.6 V. The measured results for the high voltage (low voltage) design are the following: a generated power dynamic range of 57.5 dB (52.4 dB), a load resistance dynamic range of 15.6 dB (12 dB), a voltage efficiency of 0.7 (0.61), and a relative error of the generated power less than 1.8% (1.8%). The temperature compensation of the controllable constant-power source has been performed for the temperature range 0 °C ≤ T ≤ 50 °C. The stability test has been carried out using a resistive load in pulse mode operation confirming that the stability of the proposed controllable constant-power source is not dependent on either the load resistance or the generated power.

Using High-Frequency Pulsed Supersonic Microjets to Control Resonant High-Speed Cavity Flows

A novel actuator concept is evaluated in a series of active flow control experiments on a resonant high-speed cavity flow. The actuator generates pulsed supersonic microjets by using the resonance of an impinging microjet source, and with smart materials incorporated into its design, the actuator’s resonant frequency can be actively controlled. The actuator was designed such that its resonant frequency would lie within the range of predicted cavity resonance. Results from Mach 1.5 flow over a cavity of length are presented, and the actuator’s performance is evaluated across three modes of operation: pulsed, active pulsed, and steady. In the active pulsed mode, the smart materials are used to actively vary the actuator’s resonant frequency, enabling frequency modulation of the actuator’s output. When the actuator operates in both pulsed modes, the amplitude of the dominant peak in the cavity’s unsteady pressure spectra is reduced by as much as 7 dB. However, steady microjet injection yields more effective control. The dominant peak is substantially attenuated (by 25 dB) in this mode of operation. The effectiveness of the steady mode is attributed to higher momentum flux that can be attained in contrast to the pulsed modes of operation.

Influence of air atmosphere on electrical characteristics of p-type MoTe2 FETs under DC and pulsed mode operation

Herein, ambient effects on electrical characteristics of p-type MoTe2 FETs under DC and pulse mode measurements were systematically investigated. As a result of reduced hole concentration in a high vacuum condition, threshold voltage increased as compared to air condition. Moreover, reduction of charge trapping and scattering in vacuum condition leads to electrical performance improvement such as contact resistance, mobility, and interface trap density. Pulsed I-V measurement and CYTOP passivation was additionally introduced to investigate into intrinsic ambient effects by excluding external issues near interface and top channel region. Lastly, temperature dependent mobility variation was examined to validate scattering mechanism in the channel of MoTe2 FETs.

Thermal focal length determination of a laser crystal by modulating the pump source

A simple method for determining the thermal focal length of a laser crystal is developed only by modulating the pump source to the pulse operation mode. The maximum output energy of a laser pulse is initially measured with the modulated pump source at 1 Hz repetition rate, where the thermal effects are negligible. Therefore, the beam waist of the resonator mode is equal to that of the pump laser beam, and a relationship between the energy and cavity waist is deduced. Then, the output energies at different repetition rates of the pump source are measured and the corresponding cavity waist sizes are calculated using the above relationship. Eventually, the thermal focal length of the laser crystal is directly determined by using a formula for the cavity mode radius of the resonator with an internal lens. The present method paves the way to determine the thermal focal length for different laser crystals and hence appropriate laser resonator cavity can be designed for higher energy with good beam quality.

Avalanche leds based on nanostructured silicon for optical interconnections

The paper analyzes the parameters of silicon avalanche LEDs and their use for electron-optical signal transmission systems. The advantages of silicon avalanche LEDs are shown, among which high speed and compatibility with silicon technology should be highlighted. Experimental avalanche LEDs based on nanostructured silicon were fabricated and studied. The results of controlling the electroluminescence spectrum of avalanche LEDs due to the choice of production conditions to form nanostructured silicon are presented. It was found that the temperature of the substrate during the deposition of the surface nanocomposite aluminum + silicon film affected the size of the formed silicon nanoparticles determining the spectral characteristics of avalanche LEDs. This allows shifting the maximum of their emission spectrum to a shorter wavelength region of the visible range due to the forming of smaller silicon nanoparticles. The authors have developed an optical interconnection system consisting of avalanche LEDs based on nanostructured silicon and a microchannel silicon wafer used to transmit a light signal. The study of various operating modes of the developed optoelectronic system was performed and an increase in the efficiency of optocouple based on avalanche LEDs to 0.2% due to the pulsed operating mode was achieved. It is shown that the efficiency of the optocouple increases with LED current and it is the pulsed mode of its operation that is characterized by the maximum current, which is due to more efficient removal of Joule heat in the intervals between pulses, ensuring stable operation of the entire system. The results obtained open up new opportunities for the development of optical interconnections between silicon chips and silicon optoelectronics in general.