Ionization Sensor Research Articles

Application of sculptured Mn conical (Spiral+helical) thin films for monitoring N2-CO and N2-CO2 gas mixtures: Gas ionization and field emission sensors

This study deals with the design and fabrication of Mn sculptured conical (spiral + helical) thin films as electrodes for the detection of gas mixtures of different percentages (N2-CO and N2-CO2) in a gas ionization and field emission face to face sensor. The electrodes were produced using oblique angle deposition (OAD) technique. X-ray diffraction (XRD), atomic force microscopy (AFM) and field emission electron microscopy (FESEM) as well as energy dispersive x-ray spectroscopy (EDS) confirmed crystallography, morphology and elemental composition of materials of the designed samples. The sharp tip of the nano-helices were aimed to act as an electric field enhancer by applying voltage. The results indicated that Paschen's law is not applicable for inter-electrodes gaps less than 15 μm at pressures higher than 250 mbar where the field emission process becomes the dominant reaction. Enhanced selectivity and sensitivity were obtained for CO, CO2 and their mixtures with N2 gas at lower concentrations and shorter inter-electrodes gaps (<100 μm). The ionization energies of different ionization channel reactions of N2, CO and particularly CO2 in the gas mixtures were used to explain the behavior of Paschen's curves in different pressure ranges. Highest sensitivity of the sensor was obtained for inter-electrodes gaps of less than 100 μm. Comparison of the results with the published literature showed better performance of the present sensors relative to previously reported works.

Gas Chromatography-Head Space-Flame Ionization Sensor based assessment of four residuary solvents in rivaroxaban bulk medication

In this research we established a new GC-HS-FID (Gas Chromatography-Head Space-Flame Ionization Sensor) process for concurrent assessment of methanol (MTL), ethyl acetate (ETL), triethyl amine (TTL), and dichloromethane (DRM) in rivaroxaban (RVN) bulk medication. MTL, ETL, TTL and DRM were separated using DB 624 column (3.0 μm thickness film, 75 m length x 0.53 mm internal diameter). The proposed GC-HS-FID method was authenticated for MTL, ETL, TTL and DRM analysis in RVN sample following ICH guidelines. A good linearity was gained over a range of solvents concentration 750.32 to 4501.94 ppm (MTL), 1249.67 to 7498.04 ppm (ETL), 1246.2 to 7477.17 ppm (TTL) and 150.92 to 905.54 ppm (DRM). The precision, specificity, accuracy, robustness data were documented in the within the acceptable limits. The GC-HS-FID process method can be regularly exploited for the intent of MTL, ETL, TTL and DRM analysis in RVN samples.

MOVE-III: A CubeSat for the detection of sub-millimetre space debris and meteoroids in Low Earth Orbit

The Munich Orbital Verification Experiment (MOVE) is a CubeSat student project housed at the Scientific Workgroup for Rocketry and Spaceflight at the Technical University of Munich. MOVE-III is the fourth CubeSat under development, and the first 6U mission of the MOVE project that will carry a dedicated scientific payload in orbit. The mission aims at acquiring in-situ observations of sub-millimetre space debris and meteoroids in Low Earth Orbit, with the objective of compiling a dataset of flux, as well as object mass and velocity measurements that can be used for the validation of the small object estimates of space debris models and support further studies related to the characterisation of the space environment. The MOVE-III CubeSat employs the MOVE-BEYOND platform and is planned to carry three Debris Density Retrieval and Analysis (DEDRA) plasma ionization sensors. The Preliminary Design Review has been completed in early 2022, with the next milestone being the Critical Design Review, planned for 2023. The paper elaborates on the scientific objectives of the mission and the expected data products, provides an overview of the detector operation principle and presents the overall system architecture, the platform configuration and the subsystem interaction. Considerations on the debris mitigation aspects of the mission are additionally discussed.

TVOC - Revisited

TVOC (total volatile organic compounds) has been used as a sum parameter in indoor air sciences for over 40years. In the beginning, individual VOC concentrations determined by gas chromatography were simply added together. However, several methods for calculating TVOC have become established over time. To understand the manifold definitions of TVOC, one must trace the history of indoor air sciences and analytical chemistry. Therefore, in this work, the original approaches of TVOC are searched and explained. A detailed description of the measurement methods is followed by a critical evaluation of the various TVOC values and their possible applications. The aim is to give the reader a deeper understanding of TVOC in order to use this parameter correctly and to be able to better assess published results. In addition, related sum values such as TSVOC and TVVOC are also addressed. A milestone was the analytical definition of VOCs and TVOC in 1997. A list of VOCs that should at least be considered when calculating TVOC was also provided. This list represented the status at that time, is no longer up-to-date and is being updated by a European working group as part of a harmonization process. However, there is still confusion about the exact definition and reasonable application of TVOC. The signals of other sum parameters, measured with photoacoustics, flame ionization, photoionization or electrochemical sensors, are also often given under the term TVOC. It was recognized early that TVOC is not a toxicologically based parameter and is therefore only suitable for a limited number of screening purposes. Consequently, TVOC cannot be used in connection with health-related and odor-related issues. Nevertheless, such references are repeatedly made, which has led to controversial scientific discussions and even court decisions in Germany about the correct and improper use of TVOC.

Assessment of gas chromatography methodology approach for the trace evaluation of carcinogenic impurity, methyl chloride, in trimetazidine dihydrochloride

A simple and robust head space/gas chromatography with flame ionisation sensor (HS/GC/FIS) approach for the trace evaluation of carcinogenic impurity, methyl chloride, in trimetazidine dihydrochloride (TRD) drug ingredient and its formulation is described. This HS/GC/FIS approach was based on separation and analysis of CH3Cl content on DB-624 [75.0m - length, 0.53mm - internal diameter, 3.0μm - film thickness] column using nitrogen as carrier gas flowing through the column at 3mL/min stream rate. Detection of eluted CH3Cl was accomplished with flame ionization sensor at a set temperature of 260̊C. The optimised HS/GC/FIS methodological approach was thoroughly validated, demonstrating that it was linear with range of 5.0ppm to 1508.4ppm, sensitive with detection limit of 1.65ppm and quantification limit of 5.01ppm, reproducible with RSD values of 2.10-2.35%, accurate with recoveries of 81.9-99.0%, robust with percent variation of 7.5-12.22% with respect to changes in oven temperature, injector temperature, detector temperature and practical for regular TRD quality control. The findings revealed that with this optimised HS/GC/FIS methodological approach, the trace amounts of carcinogenic impurity (methyl chloride) in TRD drug ingredient and formulation could be successfully measured.

The Influence of Air Humidity on the Output Signal from an Ionization Smoke Detector in the Presence of Soot Nanoparticles

In 2019, the European Committee for Standardization (CEN) initiated work on the preparation of a strategy for air quality monitoring at workplaces. The aim was to determine the concentrations of nano-objects and their aggregates and agglomerates (NOAA) by means of direct measurements using low-cost sensors. There is a growing need for low-cost devices that can continuously monitor the concentrations of nanoparticles, and that can be installed where nanoparticles are used or created spontaneously. In search of such a device, in this study, a smoke detector with an ionization sensor was tested. The aim of the research was to investigate the response of the analog output signal with respect to changes in environmental parameters such as the relative humidity of air. The research was conducted in controlled laboratory conditions, and the results confirmed that an ionization detector could be used to measure the concentrations of nanoaerosols. The modified smoke detector detected soot particles smaller than 100 nm. The linear regression line was calculated for the relative humidity dataset and had a slope coefficient of −1.214 × 10−4; thus, the value of the output signal was constant during the experiment. The dependence on air temperature was approximated by a second-degree curve, with a slope coefficient of −8.113 × 10−2. Air humidity affected aerosol concentrations, which may be related to surface modification of nanoparticles.

Development of a Fire Smoke Detector that Satisfies the UL 268 (7th Edition) Fire Sensitivity Tests

In this study, we developed a multi-sensor fire detector that satisfies the revised requirements of the cooking nuisance test, polyurethane foam fire test, and polyurethane foam smoldering smoke test of UL 268, and the special program, UL 268 (7th edition), at the Underwriters Laboratories (UL) headquarters in Northbrook, Illinois, United States. The fire detection algorithm was confirmed using the "Research Preliminary Test" program. Our fire detector was evaluated in a dark room with a smoke detector consisting of photoelectric, carbon monoxide, and ionization sensors, and was mounted on a board. In addition, the upper case of the detector is designed to have sufficient space on its top and side surfaces to allow the flow of air and combustion gases. As a result, in the polyurethane foam fire test, the detector triggered an alarm (within 3 min) before the smoke concentration reached 5%/ft (after 3-4 min); thus, satisfying the requirements of the UL 268 polyurethane foam fire test. In the polyurethane foam smoldering smoke test, the detector was operated for 22-26 min before the smoke concentration reached 12%/ft (after 26 min), thus satisfying the requirements of the UL 268 polyurethane foam smoldering smoke test. Lastly, in the cooking nuisance test, the detector was operated for 16-18 min before the smoke concentration reached 1.5%/ft (after 16 min), thus satisfying the requirements of the UL 268 cooking nuisance test. It can be concluded that the results of this study will be useful for the developers of similar products who want to obtain UL certification in the future.

Determination of the Concentration of Ultrafine Aerosol Using an Ionization Sensor.

As public awareness of the threats related to ultrafine aerosols increases, there is a growing need for inexpensive, real-time exposure assessment devices. In this work, the well-established technology used in the smoke detector with a radioactive source was tested in laboratory conditions to check its suitability for determining the number concentration of the ultrafine aerosol. It has been shown that the sensor output changes linearly with the change of diesel soot concentration in the range up to 8.3 × 105 particles cm−3. The sensor has also been shown to be able to detect rapid changes in aerosol concentration. Empirical equations describing the influence of air velocity, temperature, relative humidity, and pressure on the sensor output were determined. The collected results confirm that the ionization sensor can be used to assess ultrafine aerosol exposure, although additional engineering work is required to increase the resolution of the output signal measurement and to compensate for the effects of weather conditions. The presented method can be used for concentration monitoring and risk assessment in environmental engineering, materials engineering, cosmetics industry, textiles, sports, chemical, mining, energy, etc.

Structural characteristics and application of Mn oblique nano-rod thin films as electrodes in gas ionization and field emission sensor

In this work, the performance of a face-to-face gas sensor based on Mn nano-rod thin films with different heights as both electrodes is reported. Paschen’s law and departure from Paschen’s law are studied. The electrodes were fabricated on Ti/Si(400) substrates. The dynamic performance of the sensor was studied at 0.1–1000 mbar gas pressures for gap sizes between 3 and 200 µm for N2, air and CO gases. It was observed that the Paschen’s law is satisfied when the gap size is greater than 10 µm, but at less than this gap size deviation from the Paschen’s law occurs. Results showed that the aspect ratio of the nano-rod directly influences the breakdown voltage. A pronounced resolution for selectivity of the sensor under different conditions of the measurements was obtained, which improved with gas pressure. Comparison of the results with the published works showed higher sensitivity (except those of Chahshouri et al. (Chahshouri et al. in JMM. 30:075001, 2020) for 20 and 100 μm gaps distances) for the three gases studied.

Temperature Compensation With Highly Integrated Ionization Sensor Array Used in Simultaneous Detection of Mixed Gases

On-line detection of fault characteristic gases released by the insulation oil of transformers is developed as a scientific basis for estimating explosion accidents. However, the performance of most gas sensors, such as H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensors, is usually affected by temperature, and there exists large detection error when the temperature of transformer oil changes in operation. And the existing temperature compensation methods suffer from problems such as low integration, large volume, and high costs. Herein, a sensor array based on three triple-electrode sensors with carbon nanotubes was fabricated. Each of the three sensors has three vertically stacked electrodes with various interelectrode distances. The first and second sensors were used to detect H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , respectively, and the third sensor was used to measure temperature. All the detection mechanisms are based on the dependence of discharge current on gas concentration and temperature. The sensor array could detect H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixture and temperature due to the exponential function between the output currents and electrode separations. The proposed sensor exhibited low relative and repeatability error values less than 5.1% and 4.9%, respectively, and displayed humidity compensation potential like temperature. High integration makes the sensor array superior among the other mechanism sensors.

Structure optimization of carbon nanotube ionization sensor based on fluid model

Compared with the traditional ionization sensor, triple electrode ionization gas sensor based on carbon nanotubes features excellent performances of small size and low operation voltage, and plays an important role in developing smart grids and the ubiquitous Internet of Things. However, they exhibit the disadvantages of small collecting current and low sensitivity, and need to be optimized in structure. Based on the Townsend discharge mechanism and three governing equations of particle mass conservation, electron energy conservation and Poisson equations, a two-dimensional plasma discharge fluid simulation model of the sensor is established by using the COMSOL Multiphysics software. According to gas composition, component concentration, structure of the sensor and voltage applied to the electrodes, we determine the chemical reaction, reaction rate coefficient, field control equation, initial values and boundary conditions. In order to calculate the interior distribution of charged particles inside the boundary, the inter-electrode space region is meshed. Initial values of mesh are set, such as a dense mesh of nano-meter length around the electrode having micro-nano structure, and a rough mesh of micro-meter length in the other region of inter-electrode space. The initial values of time-step are set for each mesh grid, and the discharge model of each mesh grid is numerically solved by the finite volume method. The three linkage governing equations are discretized and calculated iteratively in time and space, and the mesh values and time-steps are adjusted to make the results converged. The electrostatic field distribution and the average collecting current density of the eight kinds of sensors are obtained in the background gas of nitrogen. The optimal sensor structure is obtained by comparing the electric field intensities and current densities under different structure parameters. The eight kinds of the sensors are prepared for experimentally verifying the optimization method. The optimal structure of the 7# sensor has the highest collecting current density in the eight kind structures, which is consistent with the simulation results, and proves the feasibility of the structure optimization method proposed in the paper. Based on the optimal structure, the sensors, respectively with the electrode spacings of 100 and 120 μm, are fabricated, and the response characteristics of NO/SO&lt;sub&gt;2&lt;/sub&gt; mixture gas are obtained. Compared with other technologies, the sensor with optimal structure exhibits 1－2 orders of sensitivity higher than the others. The optimized triple electrode ionization sensor based on carbon nanotubes exhibits many potential applications.

Система автоматичного контролю факелу горіння під час спалювання газу у виробництві деревинностружкових плит

The article presents the results of research on the creation of a system of automatic control of the combustion torch in a gas burner during the production of particle board. The analysis of the existing control systems of the flame during the combustion of gas in hot water and steam boilers, which are used in the production of board materials based on wood waste as heat generators. It is shown that systems based on ionization and photoelectric sensors are used to control the presence of a combustion torch. The combustion torch control system based on the ionization sensor has a significant disadvantage - the sensitive element of the sensor (electrode) during operation is in a high temperature zone, so the electrode gradually burns out, over time the ionization sensor loses sensitivity and stops working. Therefore, it must be replaced frequently, which requires additional time and money. In addition, the torch control system may malfunction when the ionization sensor, the electrodes of which have burned out, fails. The system based on photoelectric sensors has no such disadvantages. The paper also analyzes modern methods and means of controlling the combustion torch in order to reduce energy consumption. The analysis of the existing methods, devices, sensors allowed to choose the method and technical means of control of the flare in the gas burner during the production of particle board.

The Humidity-Induced Sensitivity Amplification Effect in an Ionization Gas Sensor With Silicon Nanostructures

This letter reports a significantly amplified response towards organic and inorganic target gases induced by a small variation of humidity for an ionization sensor, which is based on silicon hybrid micro-nanostructures. By introducing Si nanowire arrays using metal-assisted chemical etching, a boosted dynamic range could be achieved with increasing relative humidity read from I-V characteristics. With dry air as carrier gas, the 5000-ppm ethanol vapor sample of 60% relative humidity showed almost two magnitude higher response and signal-to-noise ratio than those of dry ethanol vapor. This humidity amplification effect brought by micro-needle array -Si nanowires hierarchical structure renders the devices especially suitable for working under highly humid environments with optimal performance.

Ionization Gas Sensor using Suspended Carbon Nanotube Beams.

An ionization sensor based on suspended carbon nanotubes (CNTs) was presented. A suspended CNT beam was fabricated by a low-temperature surface micromachining process using SU8 photoresist as the sacrificial layer. Application of a bias to the CNT beam generated very high non-linear electric fields near the tips of individual CNTs sufficient to ionize target gas molecules and initiate a breakdown current. The sensing mechanism of the CNT ionization sensor was discussed. The sensor response was tested in air, nitrogen, argon, and helium ambients. Each gas demonstrated a unique breakdown signature. Further, the sensor was tested with gaseous mixtures. The sensor exhibited good long-term stability and had comparable performance to other reported CNT-based ionization sensors in literature, which use high-temperature vapor deposition methods to grow CNTs. The sensor notably allowed for lower ionization voltages due to its reduced ionization gap size.

CNT-based sensor array for selective and steady detection of SO2 and NO

The accurate detection of NO and SO2 emitted from fossil fuel power plants is critical for realizing the real-time control of clean combustion systems and environmental protection. An array of two CNT-based ionization sensors with different electrode separations is used to detect NO and SO2 in flue gas. The responses of each sensor show a monotone decreasing response, and are obviously separated but almost parallel. The decreasing response is attributed to strong consumption of N2(A3∑u+) and N2(a'1∑u+) in collision with SO2 or NO. And the separated and parallel responses in gas mixture indicates a good selectivity and the ability to simultaneously detect SO2 and NO concentrations with no other means. In addition, the array also have excellent long-term stability due to its non-self-sustaining discharge, which reducing the damage of CNTs caused by electrical breakdown. And the sensor has a fast response and recovery times of 8 s and 7 s, respectively.

The use of ionization sensors to study the combustion process in spark ignition engines

The article discusses the use of ionization sensors to study the combustion process in spark ignition engines. The results of an experimental study of the combustion process when operating both on gasoline and gas fuel are presented. Correlating dependences are obtained, which show the possibility of diagnosing the combustion process by the ion current of chemionization. The relationship between the amplitude of the ion current and the composition of the mixture, the speed of flame propagation, and the maximum pressure in the cylinder of the engine is revealed.

Advances in gas ionization sensors based on nanostructured materials: a review

In this review article collection of summary of research works related to gas ionization sensors based on nanostructured materials is attempted. Among physical gas sensors, gas ionization sensor is used to identify gases based on breakdown of ionized gases as each gas has a unique breakdown voltage. The sensor is generally, made of two parallel electrodes separated by a narrow gap. Nanostructures, usually metallic or semiconducting, in from of nanowires/nanorods are places between the two plates. These structures act as electric field amplifiers to enhance the electric field intensity to reduce the breakdown voltages of the gases. Numerous investigations revealed that type of materials and their physical properties play important roles in the sensor characteristics and their operations. Identifying materials to optimize the strength of electric field and generate large field enhancement is a crucial step towards this application. Carbon nanotubes were among the first candidates to utilize in these structures and in fact, they were used to prove the principle of the device. The very first developed sensor showed that using carbon nanotubes between the two parallel plates of the sensor reduces the required applied voltages to ionize gases up to one order of magnitude. Since 2003 many studies are done to improve the performance and physical properties like sensitivity, selectivity, durability and stability of the device by incorporating various materials in form of nanowires/nanorods inside the device structure. In this work, first the fundamental structure of gas ionization sensor and the theory of their operations like field emission, field ionization and quantum tunneling phenomena are presented. Then, related research works reported in the literature are summarized. This review article is partitioned based on the materials used in the structure of the device as they play the most effective role in their performances. It is started with studies on devices based on carbon nanotubes, and then those used metallic nanowires followed by works done using semiconductor nanostructure to develop the device. The review started from the oldest articles in each category carried on to the most recent published works. All essential parameters effecting the structures and operations of the reported devices including their pros and cons are discussed.

Metal Decoration and Magnetic Field Effect on the Electrical Breakdown Voltage for ZnO Nanorods Gas Ionization Sensor

ZnO nanorod arrays with sharp tips were synthesized via chemical vapor deposition and utilized as the anode for gas ionization sensor. The effects of metal (Mn, Ni81Fe19 and Au) decoration and magnetic field on the electrical breakdown voltage were studied. Compared with the bare ZnO nanorod, metal decorated ZnO nanorod arrays in the magnetic field can effectively reduce the breakdown voltage for the air to 20 V. The possible mechanism is that metal decoration produces small size protuberance on the surface of ZnO nanorods and then enhances the electrical field near the tips. The magnetic field exerts action on the motion of the electron and therefore increases electron impact ionization efficiency and second electron emission efficiency.

Experimental research into the influence of two­spark ignition on the deflagration to detonation transition process in a detonation tube

The paper reports a study into the initiation of detonation in pulse detonation engines. The chosen direction to resolve this issue is the use of detonation tubes with multifocal ignition. We applied two spark discharges as a source of ignition, which ignited synchronously. The spark discharges were ignited at a distance, which provided for the intensive gas-dynamic interaction between the discharges. The interaction implied a collision between shock waves generated by the spark discharges. As a result, the growth in temperature of gas was ensured in the region between spark intervals, due to a collision between the oncoming shock waves.The influence of dual spark ignition on the time and length of the section where deflagration transfers into detonation along a detonation tube was studied by comparing the transition parameters for cases of single-spark and dual spark ignition all other conditions for research being equal. The study involved a detonation tube with a length of 2.3 m and an inner diameter of 22 mm. Spark plugs were located at the closed end of the tube. We applied a stoichiometric mixture of propane with oxygen, diluted with nitrogen by 50 % at the initial pressure in the mixture equal to 50 kPa. To register the time of propagation of the flame front and to measure the process rate, the tube was equipped with 22 ionization sensors. Distance between the sources of ignition was 6 mm. Length of the discharge interval at each source of ignition was 2.5 mm. Sources of ignition in the form of spark plugs were connected to high-voltage units with a total discharge energy of 3.3 J.The results of our study helped establish a reduction in the distance of deflagration to detonation transition by 1.6…2 times, and in the time of transition ‒ from 3.9 ms to 1.2 ms for the case of the transition from single-spark to dual spark ignition.The results obtained could be used when designing ignition systems for pulse detonation engines.

Combustion Ionization for Detection of Misfire, Knock, and Sporadic Preignition in a Gasoline Direct Injection Engine

Detection of combustion-related phenomena such as misfire, knock, and sporadic preignition is very important for the development of electronic controls needed for the gasoline direct injection engines to meet the production goals in power, fuel economy, and low emissions. This paper applies several types of combustion ionization sensors, and a pressure transducer that directly senses the in-cylinder combustion, and the knock sensor which is an accelerometer that detects the impact of combustion on engine structure vibration. Experimental investigations were conducted on a turbocharged four-cylinder gasoline direct injection engine under operating conditions that produce the above phenomena. One of the cylinders is instrumented with a piezo quartz pressure transducer, MSFI (multi-sensing fuel injector), a stand-alone ion current probe, and a spark plug applied to act as an ion current sensor. A comparison is made between the capabilities of the pressure transducer, ion current sensors, and the knock sensor in detecting the above phenomena. The signals from in-cylinder combustion sensors give more accurate information about combustion than the knock sensor. As far as the feasibility and cost of their application in production vehicles, the spark plug sensor and MSFI appear to be the most favorable, followed by the stand-alone mounted sensor which is an addition to the engine.