Ultra-high Speed Camera Research Articles

Ground experimental study of the electron density of plasma sheath reduced by pulsed discharge

Abstract A plasma sheath will be generated around the hypersonic vehicle during reentry, where a large number of electrons will significantly affect the propagation of EM waves, resulting in the phenomenon of communication blackout. This paper proposes a method of reducing the electron density of reentry vehicle plasma sheath by pulsed discharge. Experiments were conducted in a high-speed plasma wind tunnel to study the effects and scope of pulsed discharge on the plasma sheath electron density using an ultrahigh-speed camera and microwave diagnostic system. The experimental results show that the application of pulsed discharge resulted in the formation of a light intensity attenuation region measuring 14 × 19 × 4 cm around the discharge area, with an attenuation degree ranging from 30% to 58%. The microwave diagnostic results indicate that after the actuator discharge, the electron density of the plasma sheath within a 4 cm height above the vehicle wall is significantly reduced compared to before the actuator discharge, with a maximum reduction of approximately 86%. These results demonstrate that this method has significant effects on reducing plasma sheath electron density. Furthermore, the low power consumption, load, and space requirements suggest that it has potential for practical applications.

Preliminary study of the electrospray DPE peculiarities from the liquid surface in the presence of the CSWs

The Ultrasonic Electric Propulsion (UEP) system is a cutting-edge propulsion technology that is mostly used on platforms for small satellites (less than 10 kg). The characteristics of droplet partial emissions (DPEs) in the UEP system are investigated using a high-speed imaging technique (an ultra-high speed camera (NAC HX-6) and a long-distance microscope) in this work. The experiments demonstrate that there are a few partial emission modes, including left-side emission, double-side emission, and right-side emission, that are present in the droplet emission process of the UEP system. These modes are primarily caused by the partial formation of capillary standing waves (CSWs) on the emission surface of the ultrasonic nozzle. The emission rate for single- and double-sided emissions varies at different times, indicating that there are different CSWs engaged in droplet emission due to variations in the liquid film thickness and charge state of the liquid cones. Additionally, as the droplets emit continuously, a raised area on the emission surface appears, with several droplets emitting there as a result of charge accumulation. Additionally, photos of the CSWs with emitting droplets are obtained, which highlights the CSWs’ distinctive wave morphology.

Observation of Oblique Laser-Supported Detonation Wave Propagating in Atmospheric Air

Elucidation of the propagation velocity of a laser-supported detonation (LSD) wave and its propagation mechanism is necessary for various engineering applications. This study was conducted to observe an oblique laser-supported detonation wave off the laser axis. The relation between the local laser intensity and detonation-wave propagation velocity was investigated. For this purpose, the time-space distribution of the laser intensity was measured precisely. The change of the LSD wavefront shape was visualized using an ultrahigh-speed camera. The relation between the local laser intensity and the propagation velocity of the oblique LSD wave measured off the laser axis was found to be identical to the relation between the local laser intensity and the detonation propagation velocity at the laser axis.

Ultrahigh-speed imaging for high-impact concrete deformation analysis in pre- and post-cracking stages.

The evaluation of high-speed camera image sequence analysis results in concrete material testing under high-impact loading necessitates the consideration of the effect of the image quality on the measurement accuracy and thus on the potential of the geometric measurements derived from the image sequences. In this contribution, we evaluate the application potential of three ultrahigh-speed cameras with frame rates up to 10Mfps to analyze the deformation of concrete specimens before and after main crack formation in bending and compression tests. Specifically, we evaluate the Kirana 7M and Shimadzu HPV-X2 cameras with ISIS sensor architecture, and the Phantom TMX 7510 camera with BSI CMOS sensor technology. Three-point bending tests and split-Hopkinson pressure bar tests are performed on 160×40×40m m 3 cuboids and on 80mm long, 50mm diameter cylinders. Prior to main crack formation, the displacement vector field represents the specimen deformation, with higher values indicating the position where main cracks will initiate and propagate. Deformations of 80µm in 54µs for a bending test and of 154µm in 36.67µs for a compression test could be measured. The main cracks are then detected using displacement vector field discontinuity analysis techniques, and their evolution is followed to estimate the crack propagation velocity. Average velocities in bending tests between 603 and 854m/s have been determined over a time interval up to 40µs. An investigation of the camera sensor operation of the three optical devices is presented to assess their suitability for deformation analysis. Laboratory tests and real experimental results show that the quality of the propagation vector field, the crack detection, and the crack tip tracking are obviously affected by the image quality, but more significantly by the spatial and temporal resolution due to the small relative step deformations.

Experimental Investigation of Blast‐Induced Crack Propagation Based on Digital Image Correlation Analysis

Blasting is widely used in civil and mining engineering projects, with the side effect of introducing damage to the remaining rock. The damage can be differentiated from the cracks in the remaining rock, which increases the concerns of safety and requirements for rock support. In situ study of crack development remains complicated and costly; therefore, small‐scale blasting experiments are a viable alternative for a detailed investigation of the crack propagation behavior. To fill the gap, this study examined a small‐scale blasting test by investigating the velocity of the cracks implementing the digital image correlation (DIC) technique and avoiding contact methods such as strain gauges. An ultra‐high‐speed camera (UHSC) was used to record the blasting test in a single blasthole rock‐like sample with a PETN cord. The experimental design underwent calibration until achieving the configuration of the equipment while ensuring the safety distance. The developed experimental methodology was tested successfully capturing the crack behavior. The analysis outcomes showed that the raw UHSC data needed to be preprocessed to enhance the tracking of cracks with the DIC method. The findings of the DIC data analysis indicated a fluctuation in the propagation velocity along the cracks (889–1129 m/s), revealing that the proposed methodology positively contributes to the propagation behavior of using the DIC method to track the blast‐induced cracks.

Analysis of lithotripsy efficiency and stone retropulsion displacement according to pulse characteristics of Ho: YAG laser with Moses effect.

Compared to the conventional Ho: YAG laser, a Ho: YAG laser device has been reported that has a Moses effect to reduce stone retropulsion and increase lithotripsy efficiency. The principle of this equipment is to convert a single laser pulse into two pulses. Most studies on such lasers are limited to lithotripsy efficiency and the prevention of stone retropulsion; studies according to each pulse condition have not been performed. Therefore, the purpose of this study was to quantify the bubble shape, lithotripsy efficiency, and stone retropulsion displacement in a ureteral phantom according to the modulation of the first pulse characteristics of the Moses effect laser under conditions that maintained the total energy and repetition rate. In this study, a Ho: YAG laser system (Holinwon Pro, Wontech Inc., Korea) with an emission wavelength of 2.10 μm and a Moses effect was used. To verify the Moses effect based on the changes in the pulse, a water tank was fabricated, and the ureteral phantom was manufactured in a structure that could be easily installed in the water tank. Additionally, a spherical artificial stone in the ureteral phantom was prepared by mixing calcined gypsum (Cacinated Gypsum) and water at a ratio of 3:1. In the ureteral phantom, a high-speed camera (FASTCAM NOVA S12, Photron Inc.) and visible light were used to record pulse-dependent image analysis of bubbles and stone retropulsion. After mounting the artificial stone in the ureteral phantom, the pulse duration and energy of the first pulse of the Moses effect laser were varied; 30 laser shots for 3 s at a repetition rate of 10 Hz were applied to quantify the lithotripsy efficiency and stone retropulsion displacement, and the experimental values were compared. The fragmentation efficiency was confirmed by measuring the mass before and after the laser pulse application, the original position of the stone retropulsion displacement, and the distance moved. The minimum value of stone retropulsion displacement appeared when the pulse duration of the first pulse was 300 μs, the pulse energy was 100 mJ, and the value was approximately 0.28 mm. The highest fragmentation efficiency was observed under the same conditions, and the mass loss of the artificial stone at that time was approximately 3.7 mg. Quantitative indices, such as lithotripsy efficiency and stone retropulsion displacement, were confirmed using ultrahigh-speed cameras to determine the effect of the first pulse energy and duration of the Ho: YAG laser with the Moses effect on stone removal. It was confirmed that the longer the duration of the primary pulse and the lower the energy, the higher the fragmentation efficiency. In this study, the possibility of manufacturing a laser with an optimal stone-removal effect was confirmed according to the first-pulse condition of the laser with the Moses effect.

Research on the influence of grain size of CuCr contact on the characteristics of cathode spot and cathode surface erosion in vacuum arc

CuCr alloy is widely used in vacuum interrupters. The characteristics of cathode spot and erosion of cathode surface directly affects the lifetime and breaking capacity of vacuum interrupter. In order to control the cathode spot and crater, two types of contacts with different Cr phase size were used in this paper. The vacuum arc breaking experiments were conducted. The cathode spot images were recorded by ultra high speed camera and craters were measured by Scanning Electron Microscope and Profiler. It was found that the smaller the Cr phase size, the higher the expansion velocity of cathode spots, the larger the number of cathode spot, the smaller the cathode spot size and the lower the current carried by each cathode spot. The reduction of Cr phase size helps to improve the uniform distribution of cathode spots on the contact surface. Besides, the smaller Cr phase size leads to the decrease of radius and depth of crater. For CuCr contacts, thermal diffusion process was analyzed and there is a significant difference in the thermal diffusivity between Cu and Cr. The Cr phase uniformly distributed in Cu prevents the thermal diffusion process which reduces the size of crater and the erosion of cathode surface.

The motion and distribution characteristics of cathode spot and its influence on plasma parameters

Cathode spots and plasma are the key factors affecting the breaking capacity of vacuum switches. In order to analyze the motion and distribution characteristics of cathode spot and its influence on plasmas, the experiments of cathode spot observation and plasma diagnosis were conducted in this paper. The cathode spot images were captured by ultra high-speed camera. Based on the continuous spectrum theory, the electron density was measured by the colorimetric thermometry. According to the cathode spot images and method of cathode spot recognition, the parameters of cathode spots including number, size and current were obtained. The changes of these parameters with arcing time and current amplitude were analyzed. The dependence of the cathode spots average size on spot current and spot expansion velocity was discussed. The axial and radial distributions of electron density were obtained which is related to the cathode spot distribution on the cathode surface. The significant fluctuation in the radial direction for electron density was observed.

The influence of gadolinium concentration on the twin propagation rate in magnesium alloys

Ultra-high-speed camera (UHSC) imaging was used for the study of the influence of gadolinium (Gd) content on the longitudinal growth of twins in Mg-Gd binary alloys. The results clearly indicate that the twin propagation rate is of the order of 101 m/s and slows down with increasing Gd concentration. Concurrent molecular dynamics (MD) simulations reveal that the presence of Gd atoms enhances the formation of stacking faults (SFs), which hinder twin propagation as effectively as twin boundary pinning by Gd solutes. As a result, the twin tip exhibits intermittent motion at the microscopic level.

Dynamic characteristics of cathode spots during expansion process in a vacuum arc

Cathode spot is the source of plasma and metal vapor which affects the breaking capacity of vacuum circuit breakers. In this paper, the cup-shaped axial magnetic field contacts were used and the images of cathode spots were obtained by an ultra high-speed camera in the experiment. The dynamic characteristics of cathode spots during expansion process in vacuum arc were investigated. Under the conditions of different current amplitudes, different distributions of cathode spots were observed. During the expansion process of cathode spot, there are group spots and individual spots. The group spot only occurs in the cold electrode. The electrons emission characteristics of cathode spot as a function of temperature and electric field was calculated. The formation of group spot is related to the current and electron emission of cathode spot. The cathode spots were identified by Matlab. It was found that the variation of number of cathode spots is consistent with the current. However, at different stages, the reasons for the increase in the number of cathode spots are different, such as the increase in the area of cathode spots in the initial arcing stage and the splitting of cathode spot. It was observed that the cathode spots are not completely evenly distributed on the cathode surface. The farther away from the center of the contact, the longer the distance between the cathode spots. It is mainly effected by the transverse magnetic field (TMF) which is generated by the arc column. The closer to the contact edge, the higher the TMF at the cathode spot and the higher the expansion velocity of cathode spot.

Optical fiber tip damage by sparks in holmium:YAG laser lithotripsy

Laser lithotripsy disintegrates urinary stones using laser pulses delivered to the stone via an optical fiber. The fiber tip is frequently damaged during the procedure, but the mechanism of damage is not understood. Here we show that the free-running long-pulse (>150 μs) infrared holmium:YAG lasers that currently are most often used for laser lithotripsy can produce sparks and shock waves, which is an unexpected result as the optical breakdown is typically observed with more powerful Q-switched lasers. We used an ultrahigh-speed camera Shimadzu HPV-X2 at frame rate up to 10 million frames per second to record single laser pulses with 242-μm glass-core-diameter fibers in contact with whole surgically retrieved urinary stones, BegoStones, and hydroxyapatite-coated glass slides in air and water. Fiber-tip damage occurred even without cavitation and was greater at 1.0 J than at 0.6 J (p = 0.010). No fiber-tip damage occurred without sparks (1.0 J, 500 pulses, water). Shock waves produced by sparks and subsequent collapses of vapor bubbles could break optical fiber tip in a single laser pulse. These observations suggest that the previously unappreciated optical breakdown with the free-running holmium:YAG lasers can be responsible for fiber-tip damage in laser procedures. [Work supported by NIDDK of NIH under award R43DK129104.]

Study on Townsend first ionization coefficient in a streamer filament of the pulsed electric discharge in water

Streamers in water usually consist of several weakly ionized gaseous filaments. It is important to understand the ionization and excitation processes occurring in a streamer filament. In this paper, we studied the Townsend first ionization coefficient α in a streamer filament. The emission images of streamers in water were acquired by using an ultra-high speed camera system. Based on the emission images, it was found that the luminance of a streamer filament decreased exponentially as the distance increased from the anode tip. The Townsend first ionization coefficient in the streamer filament in water was then estimated by the emission profile method. It was found that the Townsend first ionization coefficient in a streamer filament was 5.3 cm−1 on average and did not depend on the water conductivity or the applied voltage of interest in the present paper. The Townsend first ionization coefficient estimated by the emission profile method is in agreement with that deduced from the electron density profile of the streamer filament in water, indicating that the emission profile method for measuring the Townsend first ionization coefficient can be applicable to the streamers in water. We also estimated the reduced Townsend first ionization coefficient α/N in a streamer filament in water and found that the obtained value for α/N was four orders of magnitude lower than those obtained from the glow discharge in low pressure water vapor, but at least ten orders of magnitude greater than those predicted by the empirical formulas.

Hybrid interferometric diagnostic for the refractive index measurement across nearly discrete shock waves

The measurement of high temperature gas properties is key for characterizing high speed flows. Nearly discrete changes in density across shock waves, in particular, are difficult to resolve through traditional fringe-counting interferometric methods. Existing techniques for estimating large fringe jumps are either resolution limited or require specialized window configurations. In this Letter, we describe a unique hybrid interferometric technique that combines narrowband fringes for high resolution and broadband fringes as an absolute reference to measure changes in refractive index with a resolution of up to 7 × 10−8 across nearly discrete index changes of up to 1.5 × 10−4. By capturing fringes with an ultrahigh-speed camera, the refractive index changes across discrete shock fronts can be estimated inside a shock tube with high accuracy and time resolution. First, a novel hybrid calibration method for tracking finite fringes is discussed. Next, this technique is used to measure the post-initial-shock refractive indices for Mach 2.7 to 4.2 flows (pressures from 90.4 to 228.4 kPa). Results are then compared with theoretical values showing agreement within 2%.

Bionic technology analyzed precisely

AbstractComplex fundamental research is necessary to realize future visions such as robotic humanoids with artificial joints and muscles. The Max Plank Institute for Intelligent Systems (MPI‐IS) in Stuttgart, Germany, has dedicated itself to this research using a Phantom ultrahigh speed (UHS) camera for precise observation and versatile analysis of these complex processes.

Bionic technology analyzed precisely

PhotonicsViewsVolume 19, Issue 4 p. 59-61 Machine VisionFree Access Bionic technology analyzed precisely Ultrahigh-speed camera used in complex fundamental research First published: 01 September 2022 https://doi.org/10.1002/phvs.202270416AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract Complex fundamental research is necessary to realize future visions such as robotic humanoids with artificial joints and muscles. The Max Plank Institute for Intelligent Systems (MPI-IS) in Stuttgart, Germany, has dedicated itself to this research using a Phantom ultrahigh speed (UHS) camera for precise observation and versatile analysis of these complex processes. Volume19, Issue4August/September 2022Pages 59-61 RelatedInformation

Experimental investigation on the velocity of cathode spots in a vacuum arc with high di/dt

With the development of DC transmission and aerospace technology, the demands on the breaking capacity of vacuum circuit breakers (VCBs) under high condition are getting higher and higher. The breaking capacity of VCBs is determined by cathode spots, which provide electrons and metal vapor to maintain the arc. In this paper, the experiments of cathode spot observation were carried out based on the detachable vacuum interrupter and the cup-shaped axial magnetic field contacts. The images of cathode spot distribution were obtained by an ultra high-speed camera. In the initial expansion stage of arcing, it was discovered that the distribution of cathode spots is ring-shaped and symmetrical. The initial expansion velocity of cathode spot ring is approximately proportional to the value of and is independent of frequency. During the whole arcing process, the expansion velocity of cathode spot ring rises first and then drops with arcing time. The effects of the magnetic field and metal vapor density on the expansion process of cathode spot were analyzed. Based on the experimental conditions and results, the values of magnetic field and metal vapor density were calculated which can reasonably explain the variation of expansion velocity of cathode spot.

Ultra-high speed holographic shape and displacement measurements in the hearing sciences

The auditory system of mammals enables the perception of sound from our surrounding world. Containing some of the smallest bones in the body, the ear transduces complex acoustic signals with high-temporal sensitivity to complex mechanical vibrations with magnitudes as small as tens of picometers. Measurements of the shape and acoustically induced motions of different components of the ear are essential if we are to expand our understanding of hearing mechanisms, and also provide quantitative information for the development of numerical ear models that can be used to improve hearing protection, clinical diagnosis, and repair of damaged or diseased ears.We are developing digital holographic methods and instrumentation using an ultra-high speed camera to measure shape and acoustically-induced motions in the middle ear. Specifically we study the eardrum, the first structure of the middle ear which initializes the acoustic-mechanical transduction of sound for hearing. Our measurement system is capable of performing holographic measurement at rates up to 2.1 M frames per second. Two shape measurement modalities had previously been implemented into our holographic systems: (1) a multi-wavelength method with a wavelength tunable laser; and (2) a multi-angle illumination method with a single wavelength laser. In this paper, we present a third method using a miniaturized fringe projection system with a microelectromechanical system (MEMS) mirror. Further, we optimize the processing of large data sets of holographic displacement measurements using a vectorized Pearson's correlation algorithm. We validate and compare the shape and displacement measurements of our methodologies using a National Institute of Standards and Technology (NIST) traceable gauge and sound-activated latex membranes and human eardrums.

Experimental study on dynamic notch fracture toughness of V-notched rock specimens under impact loads

In this study, the dynamic notch fracture toughness of V-notched rock specimens was investigated. V-notched semicircular bend specimens made of a medium-grained granitic rock called Fangshan granite were subjected to tests using a split Hopkinson pressure bar (SHPB) system combined with an ultrahigh-speed camera. First, an empirical formula was derived using dimensional analysis to calculate the fracture parameters of sharp V-notches, and the dynamic notch fracture toughness was calculated using dynamic forces obtained from the SHPB tests and the empirical formula. Second, full-field displacement fields generated during the dynamic fracture process were measured using the digital image correlation (DIC) method, and the notch fracture toughness was extracted using the displacement fields at the V-notch tip. Third, the experimental results obtained using the empirical formula were compared with the DIC results and subsequently validated using a modified mean stress criterion. The proposed methods have significant applications in the fracture assessment of rock structures weakened by notches.

Comparative study of plume characteristics of polymeric propellants filled with different oxides for laser-electric hybrid thruster

Laser-electric hybrid thrusters have attracted increasing attention as a new concept for space propulsion systems because of their low weight, high propulsion performance, and controllable thrust. When the thruster works, the laser-ablation plasma induced by the laser irradiation of a solid target is additionally accelerated by electrical means in the discharge chamber, generating thrust. Therefore, a stable and continuous ablation plume is required to ensure the subsequent electromagnetic acceleration process. This study compared and analyzed the plume characteristics of polymeric propellants doped with different oxides under the same operating conditions. The plume images were examined using an ultrahigh-speed camera, and the plume length, expanding velocity, plume area, and normalized intensity distribution were collected from the plume images based on the image processing method. The results illustrated that the CuO dopant contributed to the rapid, stable, and massive formation of the ablation plume, and VO2 could make the plume have a certain distance from the ablation surface, and then reduce the particle reflux deposition effect to a certain extent. It was also found that the samples doped with CuO, NiO, and Fe2O3 generated a micro cluster with a duration of about 0.5 ms at the beginning of ablation, while the sample doped with VO2 did not generate such a cluster. There were two regions of high-intensity light in the plumes of the samples doped with CuO and VO2. Furthermore, the plume areas of the samples doped with NiO, VO2, and Fe2O3 experienced a quiescence of approximately 2 ms before rapid growth, while that of CuO continued to increase steadily.

Microbubble generation with rapid dissolution of ammonia (NH3)-hydrogen (H2) mixed gas fed from a nozzle into water

Because of their useful characteristics, microbubbles attracted much interest in industry and medicine. In this study, we developed a novel method of generating microbubbles through the chemical absorption of ammonia (NH3). By using an ultrahigh-speed camera, consecutive images of bubble formation were captured, and the microbubble generation mechanism was investigated. The effects of the gas flow rate and ammonia concentration in the liquid phase on the size of the microbubbles were examined. The hydrogen (H2) gas flow rate was found not to demonstrate a significant effect on the bubble diameter. The diameter of the microbubbles increased as the superficial velocity of the gas mixture (NH3 – H2) decreased.