Flat Probe Research Articles

Investigation of the attenuation of the fluxes of the low-energy plasma component of electric rocket engines by the ventilation holes of the unpressurized instrument compartment of the spacecraft

The results of an experimental study of the attenuation of the fluxes of the low-energy component of the plasma formed during the operation of electric propulsion engines (ERE), ventilation holes (VH) of the non-sealed equipment compartment (NSEC) of the spacecraft (SC) are presented. Authors studied the attenuation of plasma fluxes by standard VHs made in honeycomb panels that form the NSEC. A Hall-effect engine of the SPT-70 type was used as a plasma source. The experiment consisted of measuring the plasma concentration at the inlet and outlet of the VH. The concentration at the inlet was measured with a flat Langmuir probe, and at the outlet with a Faraday probe, which allows collecting all ions passing through the VH. The aim of the work was to study the weakening of the fluxes of the lowenergy component of the EJE plasma when passing through the VH in the honeycomb-nels that form the NSEC. Based on the experimental data, a semi-empirical model was constructed that describes the dependence of the attenuation coefficient of plasma flows on the geometric parameters of the vent-holes. It has been established that a vent-holes of this design attenuates the plasma flows by 102 ... 104 times. The largest contribution to the weakening of plasma fluxes is made by the honeycomb filler, which is due to the recombination of ions during their collision with the channel walls. Taking into account the attenuation of the fluxes of the low-energy component of the plasma of electric rocket engines by ventilation holes is a key stage in assessing the effect of plasma on the power on-board equipment of spacecraft and should be used by spacecraft developers when analyzing the resistance to this factor.

Elaboration of novel and comprehensive protocols toward determination of textural properties and other sensorial attributes of canning peach fruit.

Peach (Prunus persica) products are destined for fresh consumption or are being consumed after processing in various forms. Despite its huge economic importance, no standardized protocols to define sensorial attributes and mechanical properties of canned peaches exist. Thus, the aim of the current study was dual and included the setting up of a list of sensorial descriptors and the elaboration of a toolkit to evaluate the textural properties of canned peaches using large deformation mechanical testing. A standardized vocabulary ("consensus language") was initially developed toward the determination and quantification of 15 sensorial attributes through a descriptive quantitative analysis (QDA) approach. Textural properties were additionally evaluated with a TA-XT Plus texture analyzer by applying three discrete large deformation tests [(a) puncture test with a flat cylindrical probe; (b) texture profile analysis (TPA) with a flat compression plunger; and (c) Kramer shear test (KST) cell with a bladed fixture]; that is, a total of nine textural properties, namely, "puncture firmness" (individual halves), "Kramer" hardness (applied in a complex mixture of peach slices), "TPA" hardness (central section of halves), fracturability, consistency, cohesiveness, springiness, chewiness, and total hardness were assessed. We hereby present novel protocols that encompass the comprehensive determination of sensorial and textural properties. The established protocols, providing complementary information, are readily applicable to the canning industry in setting up qualitative tests to determine product shelf life as well as to assist on going breeding programs for the evaluation of new candidate clingstone cultivars destined for canning purposes.

Using a conductive sphere as a probe to characterize the sensitivity of soft piezoresistive films

AbstractFlexible piezoresistive films, such as, carbon black/polydimethylsiloxane (C‐PDMS) composites, are often used as skin analogs and integrated into complex array sensors for tactile sensing. The uniformity of the sensor characteristics heavily depends on the homogeneity of the composite. Therefore, the ability to locally characterize a film that will be integrated into a complex force sensor could be critical. Here, a method to characterize the local sensitivity of flexible piezoresistive films is presented. Using a conductive sphere, which was chosen over a flat probe to eliminate misalignment issues, the surface of a thin film composite is indented to characterize the change in resistivity in terms of average strain. Experiments were performed with 15 and 18 wt% carbon black C‐PDMS films of varying thickness. The contact radius of the probe with the piezoresistive film was estimated using the Johnson‐Roberts‐Kendall contact theory. Theoretical contact area estimates were found to agree with contact radius measurements carried out using optically transparent PDMS films observed through an optical microscope. Results show that C‐PDMS with 15 wt% carbon black exhibit a higher rate if change of resistivity and gauge factor than films of same thickness with 18 wt% carbon black. On the other hand, thicker films exhibit higher gauge factors for the two tested carbon black contents. Tests carried out at multiple locations yielded consistent sensitivity values, making these types of composites suitable for array type force sensors.

On-Line Measurement Method for Diameter and Roundness Error of Balls

This paper presents an on-line measurement method for the diameter and roundness error of balls. An easy-installation rotary scanning system, which integrates the principles of the diameter and the roundness measurements, is constructed. The rotary scanning system consists of a rotary stage, a linear stage, and two sensors with a flat probe. Two sensors are initially installed on the linear stage and contact each other. The outputs of two sensors are reset to zero at first. The ball is then mounted on the rotary stage and positioned between two flat probes. The variations of the diameter and the roundness error of the ball at each angular position can be directly recorded by two sensors when the ball is rotated by the rotary stage. Substituting the outputs of two sensors into the proposed mathematical models, the diameter and roundness error can be evaluated. The effects of the alignment error induced by the spindle error of the rotary stage and the titling error and the eccentric error of the ball on the measurement accuracy can be self-separated in the proposed on-line measurement method. A series of experiments are carried out to verify the effectiveness and the capability of the proposed on-line measurement method and the designed rotary scanning system. The designed system is easy to construct both in the laboratory environment and the factory field.

A method for measuring plasma parameters and dielectric film thickness by analyzing transient voltages for deposition plasma processing monitoring

An electrical method is proposed to measure the dielectric film thickness, electron temperature, and plasma density for deposition plasmas. In this method, a square voltage is applied to a flat probe coated with a dielectric film, and the transient voltage of a series capacitor connected to the probe is measured. The thickness of the dielectric film is obtained from the transient voltage because the applied voltage is divided across the dielectric film and the series capacitor. The deposited dielectric film causes a change in transient voltage of the series capacitor. A circuit model with a nonlinear sheath, a series capacitor, and the dielectric films is suggested to obtain plasma density and electron temperature. The time response of transient voltage is related to plasma density, electron temperature and total capacitance of the series capacitor and the dielectric film. Two square voltages with different amplitudes were applied to measure plasma density and electron temperature. Experiments were conducted in inductively coupled plasma. Various capacitors were used to replace the dielectric films, and a flat probe coated with Al2O3 was used to verify the measurement of dielectric film thickness, showing the high accuracy of our method. In addition, the electron temperature from our method is in good agreement with that from electron energy distribution functions, and the plasma density is in good agreement with that from orbital motion limited theory. Therefore, this method would be useful for monitoring plasma parameters and deposited film thickness in industrial plasma processing.

Slag Formation during Entrained Flow Gasification: Calcium-Rich Bark Fuel with KHCO3 Additive

Slag property management is of utmost importance for successful operation of entrained flow gasifiers. The present study investigates the influence of potassium introduced as KHCO3 on the ash and slag formation of softwood bark, a calcium-rich fuel, during entrained flow gasification. The bark contained only minor mineral inclusions causing the ash composition to be dominated by calcium and potassium. Wood bark with and without KHCO3 additive was gasified between 850 and 1400 °C at O2 stoichiometric ratio (λ) 0.6. The ash particles collided with a flat impact probe inside the hot reactor at particle impact angles set to 90°, 60°, and 30°. The reactor and probe allowed long-distance microscope data collection close to the probe surface. Particle deposition was optically monitored and resulting deposits were analyzed by SEM-EDS and XRD. Thermodynamic equilibrium and viscosity calculations were used to assist interpretation of experimental results. The predicted temperature window for liquid carbonate formation was experimentally verified, but the melt fraction of the deposit was too low to cause efficient flow and removal of ash from the probe under the prevailing experimental conditions. At higher temperatures, spherical particles indicated lower ash melting temperatures than expected from the bulk ash composition, and a detailed mechanism was proposed.

Investigation of acoustic and geometric effects on the sonoreactor performance.

In this work, three design configurations of a sonoreactor are considered under various operating conditions, and the acoustic characteristics during water sonication are investigated while using an immersed-type ultrasonic flat transducer probe in a sonoreactor model. Numerical models are also developed to simulate the sonication process, and they are successfully validated and compared with available data in the literature. Several sets of numerical investigations are conducted using the finite-element method and solved by the computational acoustics module in the COMSOL Multiphysics. The effects of the acoustical and geometrical parameters are investigated, analyzed, and reported, including the ultrasonic frequency, acoustic intensity, and scaling-up the reactor. The present study includes a parametric investigation examining the change of the ultrasonic frequency, intensity, and probe immersion depth on the performance. The results of the parametric study show that the highest cavitation energy corresponds to the maximum magnitude of negative pressure that takes place in the range of 60-80kHz. The cavitation energy analyses are conducted under the conditions of 20kHz of frequency and at 36W input power. It is found that the cavitation energy of 15.87W could produce 2.98×10-10 mol/J of sonochemical efficiency. In addition, the effect of altering the transducer probe depth changes the acoustic pressure field insignificantly. Furthermore, a recommendation is made to improve the sonochemical efficiency by introducing more considerable ultrasound input power while operating the sonoreactor at an ultrasonic frequency lower than 60kHz. The results presented in this paper provide a comprehensive assessment of different sonoreactors and the feasibility of scaling-up their production rate.

Compression test of soft gellan gels using a soft machine equipped with a transparent artificial tongue

A soft machine system (texture analyzer equipped with an artificial tongue) was developed to analyze the occurrence of fractures in soft food gels compressed between the tongue and hard palate. Artificial tongues were newly designed with a modulus similar to that of a somewhat tense human tongue, using transparent urethane gels. A model of soft foods that are easy or difficult to crush with the tongue was prepared using gellan gums at different concentrations. A piece of gellan gum gel was uniaxially compressed on an artificial tongue with the flat probe of a texture analyzer. The food gel and artificial tongue were deformed, leading to the fracturing of food gels alone. During compression-induced fracture, the softer food gels exhibited a lower force, lower displacement, and lower true stress than the harder gels on all artificial tongues. The fracture probability of gellan gels was lower for the combination of harder food gels and softer artificial tongues, as softer materials can deform to a larger extent. Fracture displacement of food gels was increased as the modulus of the artificial tongue decreased; however, the fracture force did not differ significantly. These results suggest that an artificial tongue with elastic modulus values similar to those of the actual human tongue is suitable for determining the fracture behavior of foods during compression between the tongue and hard palate.

An atomically flat single–crystalline gold film thermometer on mica to study energy (heat) exchange at the nano–scale

There is a great interest in the scientific community to perform calorimetry on samples having mass in the nanogram range. A detailed knowledge of the energy (heat) exchange in the fast growing family of micro– and nano–systems could provide valuable information about the chemistry and physics at the nano–scale. The possibility to have an atomically flat thermal probe represents an added value, because it provides the unique opportunity to perform Scanning Probe Microscopy (SPM) together with calorimetry. Here we report the fabrication, characterization, and calibration of atomically flat, single–crystalline gold film thermometers on mica substrate. Gold re–crystallization has been obtained, and successively the thermometer surface has been studied by Low Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy (STM). The thermometer calibration demonstrates a heat exchange coefficient of 2.1×10-7 W/K and a performance about 10 times better than previous sensors based on Si substrates. The experimental setup allows the simultaneous investigation of heat exchange and surface physics on the same sample.

Study of the transition from self-organised to homogeneous plasma distribution in chromium HiPIMS discharge

The self-organised plasma patterns, known as spokes or ionisation zones in magnetron sputtering discharges, were observed in a wide range of power densities, from low power direct current magnetron sputtering (dcMS) discharge to high power impulse magnetron sputtering (HiPIMS) discharge. For some target materials and non-reactive gases, it was observed that at very high power densities (>) the plasma exhibits a transition from a regime where spokes are observed to a homogeneous plasma regime. In this contribution, we present a comparison of plasma properties: plasma emission (optical emission spectroscopy) and flux of argon and chromium ions (mass spectrometry), measured both in the spoke regime and in the homogeneous plasma regime, aimed to expand the understanding of the plasma transition between the two modes. A simple biased flat probe was used to distinguish between the spoke regime and the homogeneous plasma regime. It was found that the flux of multiply charged ions (Ar2+ , Cr2+ , Cr3+ , Cr4+) increases abruptly at the transition between the spoke regime and the homogeneous plasma regime. Similarly, the emission from Cr+ ions exhibits a strong increase of about 50% when the plasma torus becomes homogeneous. These observations are interpreted as an increase in electron temperature and a change in the electron heating mode, from a combination of secondary electron heating and Ohmic heating towards pure Ohmic heating. The transition to the homogeneous plasma regime and pure Ohmic heating is only observed in non-reactive HiPIMS discharges for target atoms with the second ionisation potential higher than the first ionisation potential of Ar (15.76 eV), and a self-sputter yield larger than 1.

Noncontact diagnostics of remote anisotropic plasmas

A new noncontact method for diagnostics of nonequilibrium plasma that integrates technologies of optical-and-magnetic technique of the Hanley effect and those of probe investigations is proposed. The method mentioned has been experimentally tested in plasmas with cardinally dissimilar structure of the electron velocity distribution function. As a model plasma object the positive column of glow discharge has been studied and as a distant object a short low-voltage beam discharge. The following potentialities of this method were illustrated, viz. in the distant object the complete electron velocity distribution function was determined and the diagram of electron pressure angular anisotropy was constructed. Verification of the method accuracy was carried out using the technique of flat single-sided probe.

Structure of the Wall Sheath in a Gas-Discharge Plasma for an Arbitrary Orientation of a Flat Probe Relative to the Electric Field in the Plasma

We investigate the structure of the wall sheath of a gas discharge near a flat surface at a negative potential for high mean electron energy. It is shown that in the conditions where the mean energy of ions in the plasma is much lower than the mean electron energy, the parameters of the wall sheath weakly depend on the mutual orientation of the normal to the surface and the electric field in the plasma for an arbitrary ratio of the Debye radius to the ion mean free path relative to the resonant charge exchange process. It is found that for inert gases (He, Ar) for ratio E/P of the electric field to pressure exceeding 10 V/(cm Torr) in the plasma, the disregard of ionization in the perturbed wall sheath can lead to substantial errors in the calculation of its parameters. It is shown that the ionization leads to an increase in the electric field in the wall sheath and, as a consequence, to an increase in the mean velocity of ions at the boundary between the quasi-neutral presheath and the part of the perturbed wall sheath in which quasi-neutrality is substantially violated. The parameters of the wall sheath where quasi-neutrality is significantly violated depend on the ionization rate much less strongly than the corresponding parameters of the quasi-neutral presheath. We have determined the relation for concentration of charged particles in the unperturbed plasma from the ion saturation current considering the actual ion energy distribution function in the plasma as well as ionization in the presheath and the part of the perturbed wall sheath in which quasi-neutrality is violated significantly.

Magnetocardiography with a 16-channel fiber-coupled single-cell Rb optically pumped magnetometer

We have constructed a low-cost, portable, high-sensitivity 16-channel optically pumped magnetometer (OPM), operating in the spin-exchange relaxation-free regime, and demonstrated its applications in magnetocardiography (MCG). The decrease in the cost of sensors by an order of magnitude is achieved by the 16-channel operation realized in a single module using a single large flat pancake rubidium vapor cell, broad pump and probe laser beams, and a 16-channel photodiode array. The OPM is also based on a fiber-coupled nearly parallel-beam configuration to facilitate multichannel design and make the system portable. For human MCG experiments, the 16-channel OPM which includes optical components is placed inside a wooden enclosure for laser safety. The enclosure is set on a nonmagnetic table inside a magnetically shielded room, while the lasers and electronics are placed outside the shielding room, to avoid magnetic noise. We show that the 16-channel OPM enables simultaneous imaging of human cardiac activity on a large area of the chest in a single scan. The multichannel capability will accelerate clinical MCG imaging to reduce the procedure time and patient fatigue.

Kinetics of Ions Emitted From Nanosecond-Pulsed Laser-Generated Plasma in Broad Range of the Laser Fluence

Carbon plasma was produced by irradiating a graphite target with nanosecond-pulsed Nd:YAG laser beam in the broad range of the laser fluence (25– $2196\,\,\text {J}\cdot \text {cm}^{-2}$ ). A time resolving flat Langmuir probe was used to record the carbon ion pulses. For the investigated range of laser fluence, approximately three orders of magnitude increase in total ion charge (0.03– $2.74~\mu \text{C}$ ) and peak ion energy (4–492 eV) was observed. The ion pulses were deconvoluted using Coulomb–Boltzmann-shifted time function to estimate the number of ion charge states and ion energy of various charge states. The number of available ions charge states in the plasma was found to gradually increase with the laser fluence and C6+ was observed only at the laser fluence of $2196\,\,\text {J}\cdot \text {cm}^{-2}$ . At a given laser fluence, peak energies of the ions are proportional to their charge state. The observed correlation between ions charge state and ions energy points toward the definite electrostatic acceleration mechanism. The equivalent ion accelerating potential was estimated for various values of the laser fluence and compared with the available literature data. These findings are quite useful for the development of laser plasma-based ion sources.

A study of cryosurgery of lung cancer using Modified Legendre wavelet Galerkin method

In this paper, we have developed a new mathematical model describing bio-heat transfer during cryosurgery of lung cancer. The lung tissue cooled by a flat probe whose temperature decreases linearly with time. The freezing process occurs in three stages and the whole region is divided into solid, mushy and liquid region. The heat released in the mushy region is considered as discontinuous heat generation. The model is an initial-boundary value problem of the hyperbolic partial differential equation in stage 1 and moving boundary value problem of parabolic partial differential equations in stage 2 and 3. The method of the solution consists of four-step procedure as transformation of problem in dimensionless form, the problem of hyperbolic partial differential equation converted into ordinary matrix differential equation and the moving boundary problem of parabolic partial differential equations converted into moving boundary problem of ordinary matrix differential equations by using finite differences in space, transferring the problem into the generalized system of Sylvester equations by using Legendre wavelet Galerkin method and the solution of the generalized system of Sylvester equation are solved by using Bartels-Stewart algorithm of generalized inverse. The whole analysis is presented in dimensionless form. The effect of cryoprobe rate on temperature distribution and the effect of Stefan number on moving layer thickness is discussed in detail.

Equilibrium and Out-of-Equilibrium Adherence of Hydrogels against Polymer Brushes

At low pH, underwater adherence between poly(N,N-dimethylacrylamide) hydrogels and poly(acrylic acid) brushes is due to the formation of multiple hydrogen bonds. The effect of the key parameters controlling the formation of these interactions (contact time and composition of the hydrogel) was investigated with a contact mechanics test using a flat probe. We specifically quantified the difference in adherence observed between the gel and the brush as gels were in their preparation state or in their equilibrated state. The progressive swelling to equilibrium of the gels results (for a fixed contact time) in a significant decrease in adherence even in the case of relatively low dilution factors. This adherence loss was attributed to the slowdown of the kinetics of formation of multiple H-bond interactions as the gel approached its equilibrated state. In both equilibrated and nonequilibrated conditions the energy of adherence scaled with the polymer concentration, independent of the cross-linking density of t...

Investigating the mechanical and optical properties of thin PDMS film by flat-punched indentation

We investigated mechanical and optical properties of a thin polydimethylsiloxane (PDMS) film through a flat-punched indentation experiment and a finite element simulation. A microscopic imaging method was used to measure the compressive strain of thin PDMS films, and its corresponding bulk refractive index (RI) was estimated using the relation between density and refractive index. A total internal reflection (TIR) experiment was conducted to estimate the local RI values near the bottom surface of PDMS film. We obtained the correlations between force and indentation displacement in thin PDMS films (10–70 micron). Stress-strain curves present the non-linear deformation of PDMS film with the instantaneous modulus depending on the load and the thickness. Poisson's ratio of PDMS film is estimated by fitting with Yang's asymptotic solution and is inversely proportional to the aspect ratio between the radius of the flat punch probe and the film thickness. RI of PDMS film increases with the decreasing film thickness as well as the increasing load. The bulk RI was increased up to 1.476 by the compressing load while the bottom-surface RI was increased only up to 1.435. This difference is explained qualitatively through the localized stress-strain distribution from finite element analysis. An inhomogeneous stress-strain distribution is observed in the simulation with lower strain at the bottom of the film, corresponding to experiment. A lower strain leads to lower local density resulting in a lower refractive index. Our research provides fundamental insights into the correlation between mechanical and optical properties of thin polymer films.

Characterization of the Ion Beam Current Density of the RF Ion Source with Flat and Convex Extraction Systems

The characterization of ion beam current density distribution and beam uniformity is crucial for improving broad-beam ion source technologies. The design of the broad ion beam extraction system directly affects these two parameters, therefore, depending on the application, the design and geometry of the source is changed. In this study, the effect of the presence or the absence of a neutralization process on the ion beam density was investigated. Also, the effect of the probe bias on the ion beam current measurement was evaluated. Eventually, using a flat probe, the ion beam profiles obtained from the extraction system of the ion source (Model RFIS 60, ACECR, Iran) were measured at energies from 300 eV to 1000 eV and compared in terms of current and uniformity of the ion beam in the absence of the neutralizer. In these experiments, screen and accelerator grids with different geometries (flat and convex grids) were used for comparison purposes. According to the obtained results, the flat grids generate a higher current density while the convex grids generate a more uniform beam. Therefore, each of these grid geometries can be suitable depending on the desired application.

Investigation of non-saphenous veins in C0S patients.

C0S patients have symptoms of chronic venous disorders (CVDs), though an anatomical or pathophysiological explanation is lacking. C0 and C1 classified lower limbs can present with valve incompetence from the second to sixth generation of tributaries of saphenous veins despite the absence of a detectable saphenous truncal reflux. We hypothesized that C0S venous symptoms could stem from the second to sixth generation of saphenous tributaries and small veins that are not connected to the saphenous system. The aim was to explore these veins in C0S subjects and compare them with asymptomatic C0A subjects. This was an open, controlled study enrolling 36 subjects, where C0S patients (N.=18) were compared with asymptomatic C0A subjects (N.=18). The VAS (visual analog scale) was used to assess leg pain. Veins were assessed using B-flow ultrasound (valve anatomy), continuous-wave (CW) Doppler (flow patterns), biomicroscopy (visualization of nutritional vessels), laser Doppler flowmetry (quantify supine microvascular perfusion) and quantitative digital photo-plethysmography (PPG) (measuring post-exercise venous refilling time [VRT]). There were no significant differences between C0S and C0A subjects in terms of microvascular perfusion (laser-Doppler), nutritional vessels (biomicroscopy) and VRT (PPG). B-flow ultrasound was unable to acquire sufficient data in second generation saphenous tributaries. However, the CW Doppler identified two different flow patterns: uni- and bidirectional. Bidirectional flow was significantly (P=0.05) higher in C0S versus C0A patients. CW Doppler, using a flat high-sensitivity probe, revealed the presence of a bidirectional flow that was significantly (P=0.05) higher in C0S than in control patients, suggesting the presence of reflux in non axial veins. These data give a new perspective on the management of C0S patients.

The Structure Design and Simulation of Ultrasonic Inspection Instrument for Inside Pressurized Pipe Elbows

Elbows in pressure pipes are important parts which may become serious corrosion locations. Ultrasonic detection is a main technique for pipe inner inspection, and the use of traditional ultrasound and phased array technique for in-line inspection are advanced, long-term interesting and known by researchers. Several devices were invented for inside pipeline inspection and suitable to some extent such as detecting long-distance pipelines. However, elbows especially tight elbows are still difficult to implement inner detection or travelling. To obtain good effect in detecting elbows, the inner inspection technique was investigated. Spherical and flat cylindrical probe holder structures were proposed to ensure the ability to pass through elbows, while the spherical holder has many conventional probes in its shell with a uniform distribution. The flat cylindrical probe structures are suitable for phased array ultrasonic technique to form a convex array. CIVA simulation was conducted and the focal effects were analyzed. Comparing with detecting precision and manufacture process, the phased array technique was chosen, and the elbow inspection experiments were carried out. The ultrasonic system was taken by a robot to travel through the elbow, and the experimental data were used to verify the applicability of the ultrasonic inspection technique.