Low Pressure Range Research Articles

Simple measurement of the pressure dependence of density for fatty acid esters.

A simple variable-volume method using a polytetrafluoroethylene capsule as a sample cell was applied to measure the pressure dependence of liquid density (ρ). The method was applied to 2-ethylhexyl benzoate at 313, 333, and 353K, and the reproducibility of its volume change was confirmed at pressures of up to 400 MPa. A correction term for the apparatus was also estimated. The uncertainty in the high-pressure ρ measurements was estimated to be ∼±1%. Using the developed method, the ρ values of methyl laurate at pressures of up to 400 MPa at 313 and 333K, as well as those of methyl linoleate at pressures of up to 400 MPa at 313, 333, and 353K, were measured. The results were in good agreement with the literature values in the low-pressure range. The proposed method enables the determination of the high-pressure ρ of liquids with greater ease than previously possible.

High-pressure phases of BaCN[formula omitted] explored using a genetic algorithm

Nitrogen-containing polymers have attracted considerable research attention for their application to high energy density materials, where the energy is internally stored in their triple bonds. In this regard, it is intriguing to examine whether such polymerized phases appear in the high-pressure phase of metal carbodiimide MCN2, which have been synthesized recently. However, very few studies have investigated crystal structures up to 10/15 GPa in experiments/simulations. In this work, we adopted a structure search based on genetic algorithm coupled with ab initio electronic structure calculations to investigate possible crystal structures that may appear in the high-pressure phase of BaCN2. Furthermore, we reproduced the previously reported crystal structures in the lower pressure range ∼6GPa. With confirmed reliability of its predictive capability, we used the genetic search and predicted a polymerized phase with Ima2 appearing at higher pressure above 42 GPa. The polymerized phase has a linear network structure of CN3 planar triangular units. It has been found that the anion site units CN2, which are close to each other under high pressure, form direct covalent bonds and stabilize the phase.

Formulation Analysis and Follow-Up Study of Differential MEMS Touch-Mode Sensor Utilizing Capacitive Vacuum Gauge Framework for Low-Pressure Measurements

Differential capacitance diaphragm gauges have become more popular in pressure measurements as they yield superior sensitivity and lesser non-linearity for pressure differential measurements. In addition, differential capacitance diaphragm gauges do not require a high vacuum reference cavity which reduces their manufacturing complexity. Efficient analysis for modelling differential capacitance diaphragm gauges is thus increasingly becoming vital due to their innumerable use cases. The higher sensitivity of circular diaphragm for the same side length in comparison to square diaphragm makes it ideal for sensor design. In this work, a complete formulation for analysis of differential capacitive vacuum gauge with the circular diaphragm in normal and touch mode operation has been presented for the low-pressure range of (1 to 1500 pascals). A comprehensive study of sensor parameters like capacitance, diaphragm deflection, capacitive and mechanical sensitivity has been formulated to aid the choice of sensor characteristics. Computationally complex methods have been used in the past for analysis of circular diaphragms. MATLAB and COMSOL have been used to compute and simulate results.

Development and characteristics study of compact Penning ion source

A compact-size Penning ion source with a small discharge volume (1.24 cm3) is developed. It consists of two concentric cylinders of different heights that act as cathodes and one hollow cylindrical anode. A homogeneous magnetic field is achieved within the discharge volume with geometrical optimization of the ion source. As a result, dense plasma is generated at low discharge power. The dynamics of the pulse mode discharge at low pulse width and frequency of anode voltage are studied. A high discharge (hundreds of amperes) current pulse with low delay time and fast rise time is recorded. The ion source is equally efficient to operate in continuous as well as pulse modes of ionization for various gases. It is operated in a wide range of low pressure at low anode voltage. An extraction system is designed to extract ions efficiently in the axial direction at a variable extraction voltage. The beam current of 200 µA in continuous mode and 6 A fast pulse in the pulsed mode of discharge have been measured. Variable beam current can be extracted with variable extraction voltage for any potential application.

Equation of state remeasurements for aluminum and copper under low-impact loading

In this work, the Hugoniot equation of state for aluminum and copper under low-impact loading was measured by using the plane impact technique and laser Doppler velocimetry. The linear relationship between shock wave velocity and particle velocity was fitted by a least squares method, with D=5.28114+1.306(17)us for an Al pressure range from 2.5 to 13.9 GPa and D=3.9386+1.484(14)us for Cu at 5.7–47.5 GPa. The linear fitting correlation coefficient was greater than 0.99, which was better than the previous experimental data. The results demonstrate that the Doppler pin system has great advantages for measuring the Hugoniot EoS at low shock pressure compared with the electric pin technique The experimental data obtained in this work extend to a lower pressure range. This can provide more accurate Mie–Grüneisen EoS of Al and Cu under low shock pressure.

Comparative Study of the Adsorption of 1- and 2-Propanol on Ice by Means of Grand Canonical Monte Carlo Simulations

In this paper, we use Grand Canonical Monte Carlo simulations to compare the adsorption characteristics of two propanol isomers (1- and 2-propanol) on crystalline ice, at the temperature of 227 K (i.e., typical of the Earth’s troposphere), for which experimental data are available in the literature. The adsorption isotherms simulated for these two isomers show a very good agreement with the reported experimental data, giving thus confidence in the two interaction potential models used in the calculations. The results of the simulations thus nicely support the experimental conclusion that 2-propanol is preferentially adsorbed on ice with respect to 1-propanol, at least in the low pressure range where only a few molecules are trapped by the ice surface. The accuracy of the approach used, as tested here in tropospheric conditions, opens the way for its use in modeling studies also relevant to astrophysical context.

Flexible and Wearable Capacitive Pressure Sensor for Monitoring Heart Parameters

The increase in global average life expectancy over the past century has been largely attributed to medical science developments. In this study, we demonstrate a polymer-based capacitive pressure sensor for measuring heart rate and pulse pressure signal. The fabricated sensor has been characterized to evaluate its performance and to verify its repeatability and precision. It is observed that the sensor works in the range of 0 – 8 kPa pressure range and is suitable for measuring the pulse pressure. This sensor has a high sensitivity of 7.11 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> in the low-pressure range of 0 to 8 kPa. Further, the sensor demonstrated a considerable amount of repeatability with an error less than 6% in consecutive measurements. Moreover, the sensor demonstrated the use of a wearable, flexible piezo-capacitive pressure sensor for pulse pressure monitoring. The wrist pulse was used as the stimulus for the experimental characterization of the sensor, and health markers related to the measured response were also discussed.

Diffusion Coefficient and Absorption of Carbonyl Sulfide in 1-Hexyl-3-methylimidazolium Bis (Trifluoromethyl) Sulfonylimide ([hmim][Tf2N

The solubility of carbonyl sulfide (COS) and also the diffusion coefficients of COS, carbon dioxide, and hydrogen sulfide were experimentally investigated in 1-hexyl-3-methylimidazolium bis(trifluoromethyl) sulfonylimide ([hmim][Tf2N]). The solubility was measured using a static apparatus, and the acid gas diffusivity was obtained by monitoring pressure drop with low initial pressure via the so-called semi-infinite volume method. All experimental absorption trials were carried out in the range of low and medium pressures and temperatures from (313.15 to 353.15) K. Furthermore, all diffusion coefficient experiments were determined at a temperature from (313.15 to 333.15) K and low pressure to some extent to be acceptable in the semi-infinite volume approach. The experimental results were correlated using the Shiflett and Yokozeki versions of the Redlich–Kwong equation of state. In addition, Henry’s law constants and the thermodynamic properties of dissolution at infinite dilution were calculated and discussed.

Coordination Changes in Densified Aluminate Glass upon Compression up to 65 GPa: A View from Solid-State Nuclear Magnetic Resonance.

Deciphering the structural evolution in irreversibly densified oxide glasses is crucial for fabricating functional glasses with tunable properties and elucidating the nature of pressure-induced anomalous plastic deformation in glasses. High-resolution NMR spectroscopy quantifies atomic-level structural information on densified glasses; however, its application is limited to the low-pressure range due to technical challenges. Here, we report the first high-resolution NMR spectra of oxide glass compressed by diamond anvil cells at room temperature, extending the pressure record of such studies from 24 to 65 GPa. The results constrain the densification path through coordination transformation of Al cations. Based on a statistical thermodynamic model, the stepwise changes in the Al fractions of oxide glasses and the effects of network polymerization on the densification paths are quantified. These results extend the knowledge on densification of the previously unattainable pressure conditions and contribute to understanding the origin of mechanical strengthening of the glasses.

Pressure Sensors Combining Porous Electrodes and Electrospun Nanofiber-Based Ionic Membranes

It is one of the most urgent development directions and crucial challenges for flexible pressure sensors to have both characteristics of high sensitivity and wide measuring range. To address this challenging problem, this paper proposes an innovative, convenient, and industrially scalable capacitive pressure sensor that combines porous electrodes and electrospun nano ionic membranes with surface microstructure. The advantage of this sensor is that nano ionic nanofiber membranes are directly prepared on porous conductive fabrics by electrospinning with high reliability and good repeatability. The prepared dielectric layer of the sensor is in complete contact with the electrode, which effectively eliminates the uncertainty of air gap interference in traditional packaging methods. The sensing mechanism of the designed sensor is also persuasively revealed by finite-element and theoretical analysis in this paper. First, the porosity of both the conductive fabric and dielectric layer expands the measurement range. Second, the surface microstructure of the nano ion membrane increases the effective contact area between the dielectric layers when external pressure is applied to the sensor, thus increasing the conduction path of the ions. The increase of the ionizing degree under pressure leads to the change of the interface capacitance. These make the sensor have high sensitivity in the wide measurement range. The designed sensor exhibits a sensitivity of up to 1254.5 kPa–1 over a low-pressure measurement range of 0–10 kPa, providing an amazingly wide measurement range of 0–800 kPa, with an extremely high sensitivity of 128.1 kPa–1 over the entire measurement range. The designed sensor illustrates both a fairly fast response time of 10 ms and a relaxation time of 16 ms, in addition to the durability of up to 3000 cycles. The above exceptional performance demonstrates its remarkable potential applications in smart wearable devices and pneumatic pressure monitoring.

Capacitive Sensors with Hybrid Dielectric Structures and High Sensitivity over a Wide Pressure Range for Monitoring Biosignals

Various dielectrics with porous structures or high dielectric constants have been designed to improve the sensitivity of capacitive pressure sensors (CPSs), but this strategy has only been effective for the low-pressure range. Here, a hierarchical gradient hybrid dielectric, composed of low-permittivity (low-k) polydimethylsiloxane (PDMS) foam with low Young's modulus (low-E) and high-permittivity (high-k) MWCNT/PDMS foam with high Young's modulus (high-E), is designed to develop a CPS for monitoring biosignals over a wide force range. The foam-like structure with hybrid permittivity (low-k + high-k) is facilitated to improve the sensitivity, while the hierarchical structure with gradient Young's modulus (low-E + high-E) contributes to broadening the pressure sensing range. With the hierarchical gradient hybrid structure, the flexible pressure sensor achieves an enhanced sensitivity of 2.155 kPa-1, a wide pressure range (up to 500 kPa), a minimum detection limit (50 Pa), and an excellent durability (>2500 cycles). As a demonstration, a venous thrombosis simulation and smart insole system are established to monitor venous blood clots and plantar pressures, respectively, which reveal potential applications in wearable medicine, sports health prediction, athlete training, and sports equipment design.

A Flexible Pressure Sensor Based on Silicon Nanomembrane

With advances in new materials and technologies, there has been increasing research focused on flexible sensors. However, in most flexible pressure sensors made using new materials, it is challenging to achieve high detection sensitivity across a wide pressure range. Although traditional silicon-based sensors have good performance, they are not formable and, because of their rigidity and brittleness, they are not suitable for fitting with soft human skin, which limits their application in wearable devices to collect various signals. Silicon nanomembranes are ultra-thin, flexible materials with excellent piezoresistive properties, and they can be applied in various fields, such as in soft robots and flexible devices. In this study, we developed a flexible pressure sensor based on the use of silicon nanomembranes (with a thickness of only 340 nm) as piezoresistive units, which were transferred onto a flexible polydimethylsiloxane (PDMS) substrate. The flexible pressure sensor operated normally in the range of 0-200 kPa, and the sensitivity of the sensor reached 0.0185 kPa-1 in the low-pressure range of 0-5 kPa. In the high-pressure range of 5-200 kPa, the sensitivity of the sensor was maintained at 0.0023 kPa-1. The proposed sensor exhibited a fast response and excellent long-term stability and could recognize human movements, such as the bending of fingers and wrist joints, while maintaining a stable output. Thus, the developed flexible pressure sensor has promising applications in body monitoring and wearable devices.

Dynamic modelling and analysis of MEMS-based low-pressure range capacitive sensors for biomedical applications

Sensitivity and linearity are promising parameters for MEMS (Microelectromechanical system) based Capacitive pressure sensors (CPS). This study discusses the basic principle, classification of the sensing mechanism and recent trends for improving the sensitivity. The review includes mathematical analysis and dynamic modelling on various parameters like deflection, and capacitance. In addition, this comprehensive study also discusses capacitive pressure sensors of different structures/shapes with their advantages and limitations. MEMS-based Capacitive pressure sensors have attracted research interest in recent years for various potential applications in the field of biological, industrial, microphones, touch screens etc. This article deals with different substrates and membrane materials for the sensor along with fabrication methodology. Existing technologies for MEMS-based Capacitive pressure sensor faces common challenges which are discussed here. Advancements in MEMS sensing technology and attractive feature of state of the art in MEMS-based low-range capacitive pressure sensors make use of it in medical applications like BP, IOP and ICP are discussed in detail. Finally, the main finding of this study shows the square shape CPS gives maximum deflection up to the range of 10 kPa.

Design, optimization, and analysis of a human-machine compatibility upper extremity exoskeleton rehabilitation robot

For rehabilitation therapy robots, the movement range, and comfort of rehabilitation are crucial to the patient’s training and recovery and are also key factors in the design and performance evaluation of rehabilitation robots. In this paper, a highly harmonized upper extremity rehabilitation robot was proposed based on the human-machine coupling system model. Meanwhile, the shoulder joint structure of the rehabilitation robot was optimized to study the workspace range of this robot, the workspace of the upper extremity rehabilitation robot was fitted based on kinematic equations and the workspace volume size for different shoulder joint angles was analyzed. Finally, the upper extremity exoskeleton rehabilitation robot prototype was used to conduct the movement range tracking experiment and human-machine compatibility experiment in healthy volunteers to verify the rehabilitation training range and movement comfort of the rehabilitation robot. The experimental results show that when the optimized upper extremity exoskeleton rehabilitation robot was used to move in the coronal plane and sagittal plane of the human body, the overlaps of the movement range of the upper extremity wrist point W and the movement range of the healthy person was 97.23% and 97.66%, respectively, while the human-machine interaction force generated during the movement was mainly concentrated in the range of 0–10 kPa, which belongs to the low-pressure range of human-machine interaction. Therefore, this upper extremity rehabilitation robot can increase the movement range of patients’ upper extremities and improve the comfort of rehabilitation training.

Hollow Cathode Glow Discharge Initiation in a Fore-Vacuum Plasma–Cathode Electron Source

In this article, we present the results of a study on the initiation of a hollow cathode discharge in the electrode system of a fore-vacuum plasma–cathode electron source. It is shown that the development of the hollow cathode effect is facilitated by the back-streaming ion flux of the high-voltage glow discharge (HGD) that arises in the accelerating gap of the electron source. The effect of the type of operating gas and the cathode hollow geometry on the value of the initiating accelerating voltage, which ensures the HGD back-streaming ion flux, have been studied. It is proposed to use an auxiliary pulsed surface flashover discharge to trigger the hollow cathode discharge. The two methods used jointly provide a stable discharge initiation in the entire operating pressure range of the source, including the ultimately low-pressure range where the operation of the hollow cathode discharge in its low-voltage form is still stable.

Highly sensitive active-powering pressure sensor enabled by integration of double-rough surface hydrogel and flexible batteries

A conductive, elastic, and biocompatible hybrid network hydrogel was prepared by cross-linking of locust bean gum, polyvinyl alcohol, and carbon nanotubes, yielding a rough top surface and smooth bottom surface. The merging of the two pieces of hydrogel flat face to flat face forms a highly elastic hydrogel with double-rough surfaces. A piezoresistive sensor assembled with the double-rough surface hydrogel sandwiched between two carbon cloth electrodes exhibits a high sensitivity (20.5 kPa-1, 0-1kPa), a broad detection range (0.1–100 kPa) and a reliable response for 1000 cycles. The rough contact area between the hydrogels and the carbon cloth is found critical in achieving ultra-high sensitivities in the low-pressure range. Moreover, further monolithic integration of the sensor with a flexible solid-state zinc ion battery ensures the self-powering of the sensor for various human motions detection applications.

Metallization of hydrogen by intercalating ammonium ions in metal fcc lattices at lower pressure

Metallic hydrogen is capable of showing room temperature superconductivity, but its experimental syntheses are extremely hard. Therefore, it is desirable to reduce the synthesis pressure of metallic hydrogen by adding other chemical elements. However, for most hydrides, the metallization of hydrogen by “chemical precompression” to achieve high-temperature superconductivity still requires relatively high pressure, making experimental synthesis difficult. How to achieve high-temperature superconductivity in the lower-pressure range (≤50 GPa) is a key issue for realizing practical applications of superconducting materials. Toward this end, this work proposes a strategy for inserting ammonium ions in the fcc crystal of metals. High-throughput calculations of the periodic table reveal 12 elements that can form kinetically stable and superconducting hydrides at lower pressures, where the highest superconducting transition temperatures of AlN2H8, MgN2H8, and GaN2H8 can reach up to 118, 105, and 104 K. Pressure-induced bond length changes and charge transfer reveal the physical mechanism of high-temperature superconductivity, where the H atom continuously gains electrons leading to the transition of H+ ions to atomic H, facilitating metallization of hydrogen under less extreme high pressure. Our results also reveal two strong linear scalar relationships: one is the H-atom charge vs superconducting transition temperature, and the other is the first ionization energy vs the highest superconducting transition temperature. In addition, ZnN2H8, CdN2H8, and HgN2H8 were found to be superconductors at ambient pressure, and the presence of interstitial electrons suggests that they are also electrides, whose relatively low work functions (3.03, 2.78, and 3.05 eV) imply that they can be used as catalysts for nitrogen reduction reactions as well.

In situ Raman spectroscopic measurement of the 13C/12C ratio in CO2: Experimental calibrations on the effects of fluid pressure, temperature and composition

The carbon isotope (δ13C) signature of CO2 within fluid inclusions is of significance to investigate because it can be used to decipher the carbon source of geological fluids. Raman spectroscopy has been applied to determine the δ13C of pure CO2. However, whether this approach can be applied to natural inclusions with complex compositions remains unknown. Here we present Raman spectra of CO2 ± N2 ± CH4 systems with known 13C/12C ratio (0.01–1.12) at temperatures (T) of 21 °C and 40 °C and at pressures (P) ranging from 0.5 to 50 MPa. Peak areas and peak heights of the 13CO2 (∼1370 cm−1) and 12CO2 (∼1285 cm−1) bands were determined to calculate the Raman spectroscopic quantification factors (F- and G-factor ratio). The results show that the quantification factors vary significantly with rising pressure in the low pressure range (e.g., <10 MPa), especially for pure CO2 system. Different fluid systems are characterized by pressure dependences. Specifically, both F- and G-factor ratios for CO2 fluid with a low 13C/12C ratio (e.g., 0.01) are different from that with a high 13C/12C ratio (e.g., 0.13) under the same T-P conditions. Fluid temperature does not result in significant variation in F- or G-factor ratios at the investigated temperatures. Based on these calibrations, we suggest that fluid pressure and composition (x) are prerequisites for Raman spectroscopic measurements of the 13C/12C ratio of CO2. However, the 13CO2 (∼1370 cm−1) band for CO2 from natural fluid inclusions is characterized by low Raman intensity, resulting in large errors in calculated peak area and peak height. Thus, accurate determination of the 13C/12C ratio of fluid inclusion CO2 is not feasible for inclusions with low CO2 density. Nevertheless, this method can be applied to investigate the carbon isotope fractionation in 13C labelled hydrothermal experiments, where CO2 with high a 13C/12C ratio is produced.

Flexible pressure sensor based on graphene/PS microsphere/PDMS composite dielectric layer and activated carbon non-woven fabrics

• Fabrication of ultra-thin dielectric layers with surface microstructures and filler doping. • Offering new ideas for improving the sensitivity of flexible capacitive sensors. • Activated carbon non-woven fabrics are used to make flexible electrodes. • New dielectric layer fabrication process developed. • A number of dynamic tests have been completed using this sensor. With the widespread application of wearable devices, the demand for high-performance sensors has increased dramatically. This study proposes a novel capacitive sensor. By using polystyrene (PS) microspheres and the sacrificial layer method, the ultrathin dielectric layer with surface micro-dome structure and uniform graphene doping are fabricated. In addition, the activated carbon non-woven fabrics (ACNWF) electrode was prepared, and the device characteristics of the sensor were investigated. The sensor has a good capacitive response in a wide pressure range (0–150 kPa) and a sensitivity of 0.209 kPa −1 in the low-pressure range. The short response time (<25 ms) is suitable for real-time dynamic monitoring. Meanwhile, the sensor has good stability (3500 cycles) and performs well in mouse double-click, muscle contraction and arm swing. This sensor has great potential in wearable electronics and human-computer interaction.

Differential dose responses of transcranial focused ultrasound at brain regions indicate causal interactions

We have previously shown that focused ultrasound (FUS) pulses in low pressure range exerted bidirectional and brain state-dependent neuromodulation in the nonhuman primate somatosensory cortices by fMRI. Here we aim to gain insights about the proposed neuron selective modulation of FUS and probe feedforward versus feedback interactions by simultaneously quantifying the stimulus (FUS pressures: 925, 425, 250 kPa) and response (% BOLD fMRI changes) function at the targeted area 3a/3b and off-target cortical areas at 7T. In resting-state, lowered intensities of FUS resulted in decreased fMRI signal changes at the target area 3a/3b and off-target area 1/2, S2, MCC, insula and auditory cortex, and no signal difference in thalamic VPL and MD nuclei. In activated states, concurrent high-intensity FUS significantly enhanced touch-evoked signals in area 1/2. Medium- and low-intensity FUS significantly suppressed touch-evoked BOLD signals in all areas except in the auditory cortex, VPL and MD thalamic nuclei. Distinct state dependent and dose-response curves led us to hypothesize that FUS's neuromodulatory effects may be mediated through preferential activation of different populations of neurons. Area 3a/3b may have distinct causal feedforward and feedback interactions with Area 1/2, S2, MCC, insula, and VPL. FUS offers a noninvasive neural stimulation tool for dissecting brain circuits and probing causal functional connections.