Ionization Sensor Research Articles

Impact Ionization Induced by Accelerated Photoelectrons for Wide-Range and Highly Sensitive Detection of Volatile Organic Compounds at Room Temperature.

Ionization-based volatile organic compound (VOC) sensors that use photons or electrons operating at room temperature have attracted considerable attention as a promising alternative to conventional metal oxide-based sensors that require high temperature for sensing function. However, the photoionization sensors cannot ionize many gas species for their limited photon energy, and field emission-based ionization sensors that rely on the breakdown voltage of specific gas species in a pure state may not tell different concentration. This work demonstrates the detection of VOCs using impact ionization induced by accelerated photoelectrons. Although the photoelectrons emitted by relatively low photon energy typically have insufficient kinetic energy to cause impact ionization, in this approach, they are accelerated between microgap electrodes to enhance their kinetic energy such that the impact ionization of VOCs can be achieved. The demonstrated gas sensor sensitively detects toluene concentration in a wide range from 1000 ppm to 100 ppb with fast response and recovery time at room temperature. Additionally, diverse VOC species including benzene, p-xylene, and even acetylene with high ionization energy can be detected. The proposed method could be a viable solution for VOC sensors with low cost, scalable producibility, and high performance.

A novel miniature planar gas ionization sensor based on selective growth of ZnO nanowires

In this study, a novel planar MEMS-based gas ionization sensor based on the field ionization of zinc oxide nanowires is reported. Selective and seedless ZnO nanowires have been grown directly on gold electrodes by low-cost and low-temperature hydrothermal method. Low operating voltage with fast response and recovery times have been achieved for detecting Argon, Helium, Air + %32 RH, Nitrogen, Dry Air, Oxygen, and Carbon dioxide at ambient temperature in atmospheric pressure. Sharp tips of ZnO nanowires reduce the gas breakdown voltage of different gases as shown for Helium and Argon to about 115 V, 85 V respectively due to their local electric field enhancement characteristic. Furthermore, an excellent semi linear response (about 80 V decrease in breakdown voltage) was observed by introducing 250 ppm of NH3 to pure N2 in 4 stages from 0 ppm to 1000 ppm as ammonia gas sensor. In addition, ZnO nanowires protect high conductive Au cathode and anode against sputtering and deformation due to their superior physical, chemical and mechanical properties.

ИССЛЕДОВАНИЕ ОСОБЕННОСТЕЙ СГОРАНИЯ В КАМЕРЕ СГОРАНИЯ ПЕРЕМЕННОГО ОБЪЕМА

The paper covers the study of special aspects of the application of ionization sensors intended for determining the characteristics of flame propagation (flame propagation velocity and the width of chemical combustion reactions area) in the variable volume combustion chamber. The review of contemporary methods of study of the process of hydrocarbon fuel combustion in piston engines showed the perspectivity of ionization sensors application. On a single-cylinder engine, the authors experimentally obtained and studied the main parameters of fuel combustion using the specially developed ionization sensors designed for identifying the characteristics of flame propagation when changing temperature, pressure, turbulence, and the combustion chamber volume in a wide range within several milliseconds. The variance of ion current, flame propagation turbulent velocity and the width of combustion chemical reactions area are determined depending on the fuel-air mixture composition when changing its physical and chemical properties due to the addition of hydrogen. It is shown that the change in the flame propagation turbulent velocity when adding hydrogen is caused by the increase in its normal component, and the width of turbulent combustion area is linearly related to the ion current value and its variance reflects the intensity of chemical combustion reactions. It is identified that despite the change in the excess air factor, the hydrogen concentration in fuel, and the engine speed rate, the linear dependence of flame width on the flame propagation turbulent velocity in the second combustion phase remains: the velocity increase corresponds to the flame width narrowing.

Low-Voltage Gas Field Ionization Tunneling Sensor Using Silicon Nanostructures

In this paper, we report the design and characteristics of a field-ionization gas sensor based on freestanding silicon nano structures. Silicon nanostructures fabricated using a three-step chemical/electrochemical technique on silicon wafer were placed between two parallel plates separated by a small gap. The sensor works based on the field ionization tunneling effect. For the first time, it is shown that silicon nanostructures can be used for the purpose. The device was tested for Ar, N2, O2, and He gases in a pressure range of $0.01 torr. The device demonstrated a distinctive $I$ – $V$ curve and the ionization voltages for the considered gases. Detected breakdown voltages were much lower than those reported in the literature for gas ionization sensors based on metallic nanowires.

Nuclear-recoil energy scale in CDMS II silicon dark-matter detectors

The Cryogenic Dark Matter Search (CDMS II) experiment aims to detect dark matter particles that elastically scatter from nuclei in semiconductor detectors. The resulting nuclear-recoil energy depositions are detected by ionization and phonon sensors. Neutrons produce a similar spectrum of low-energy nuclear recoils in such detectors, while most other backgrounds produce electron recoils. The absolute energy scale for nuclear recoils is necessary to interpret results correctly. The energy scale can be determined in CDMS II silicon detectors using neutrons incident from a broad-spectrum 252Cf source, taking advantage of a prominent resonance in the neutron elastic scattering cross section of silicon at a recoil (neutron) energy near 20 (182)keV. Results indicate that the phonon collection efficiency for nuclear recoils is 4.8−0.9+0.7% lower than for electron recoils of the same energy. Comparisons of the ionization signals for nuclear recoils to those measured previously by other groups at higher electric fields indicate that the ionization collection efficiency for CDMS II silicon detectors operated at ∼4V/cm is consistent with 100% for nuclear recoils below 20keV and gradually decreases for larger energies to ∼75% at 100keV. The impact of these measurements on previously published CDMS II silicon results is small.

Selective Detection of NO and NO₂ with CNTs-Based Ionization Sensor Array.

The accurate detection of NOx is an important issue, because nitrogen oxides are not only environmental pollutants, but also harm to human health. An array composed of two carbon nanotubes (CNTs)-based ionization sensors with different separations is proposed for NO and NO2 selective detection. The experimental results indicate that the CNTs-based ionization sensor has an intrinsic, monotonically decreasing response to NO or NO2. The sensor with 80 µm separations and 100 µm separations exhibited the highest sensitivity of −0.11 nA/ppm to 300 ppm NO and −0.49 nA /ppm to 70 ppm NO2, respectively. Although the effect of the NO2 concentration on the NO response is much stronger than that of NO on NO2, the array of these two sensors still exhibits the ability to simultaneously detect the concentrations of NO and NO2 in a gas mixture without component separation.

A tripolar-electrode ionization gas sensor using a carbon nanotube cathode for NO detection

Nitric oxide accounts for more than 95% of the total NOX emission from power plants, which is a major air pollutant. Therefore, it is imperative to accurately detect NO for environmental protection. A tripolar-electrode ionization sensor with a carbon nanotube (CNT) cathode is proposed for NO detection. The non-self-sustaining discharge state and the tripolar-electrode configuration ensures a long nanotube life, which ensures a good stability and fast response of the sensor. Experimental results demonstrate that the tripolar-electrode ionization sensor with 120 µm separations has an intrinsic monotonously decreasing response to NO and exhibits a fast response time of 7 s and recovery time of 8 s. More consumption of the two metastable states N2(A3 ∑ u+) and N2(aʹ1 ∑ u+) of N2 with the increasing of NO concentration is responsible for this. The tripolar-electrode ionization sensor also shows excellent long-term stability of at least one month due to the long CNT life. In addition, the weak effect of SO2 introduction on NO response indicates a good selectivity of the sensor to NO.

Design and engineering of ionization gas sensor based on Mn nano-flower sculptured thin film as cathode and a stainless steel ball as anode

In this work a field ionization gas sensor based on 3-fold symmetry Mn nano-flower sculptured thin film as cathode and a stainless steel ball (SSB) as anode is used. The breakdown voltage of the system was studied for nitrogen, oxygen, argon, air and carbon mono-oxide gases. Investigations for these gases at different distances between anode and cathode (40, 100 and 200 μm), anode (SSB) diameter sizes of 2, 6 and 10 mm and different gas pressures (0.2–1000 mbar) confirmed Paschen’s Law. Results for different anode sizes showed that by decreasing the ball size at high pressures the breakdown voltage decreased, while at low pressures the opposite behavior was observed. For pd values (mbar cm) between 0.025 and 0.2 mbarcm and for different gases studied in this work a good gas selectivity was obtained. Lower breakdown voltages at medium gas pressures are obtained when comparison is made with the published data for different materials (i.e., CNT, Cu, Au, Ag and ZnO) and designs. The effective secondary emission coefficient of Mn nano-flowers and the ratio of the probability of secondary electron emission of Mn to that of other types of cathodes made of different materials showed higher values. These results suggest that Mn can act as a good material in ionization sensors and the nano-sculptured structure designed and engineered in this work can enhance the sensor’s performance.Nano-structure and morphology of the produced samples were obtained by field emission electron microscope (FESEM) and atomic force microscope (AFM) analyses.

The electrical conductivity of the flame front, as a characteristic of the rate of heat release and composition of gas fuel in SI engines

The paper considers the possibility of using the electrical conductivity of the flame front as a characteristic of the rate of heat release and composition of gas fuel in a SI engines. Based on the analysis of the experimental data, the dependences of the parameters of the electrical conductivity of the flame front on the rate of heat release are obtained with the variation of the chemical activity of the gas fuel in a SI engines. The influence of the composition of the mixture and the effect of the amount of added hydrogen on the increase in the rate of heat release and, consequently, on the increase in the electrical conductivity of the flame. The obtained dependences will allow to increase the efficiency and reduce the toxicity of the SI engines operation during the regulation of the working process by ionization sensors.

Experimental Investigation of Ionization Sensors Under Shock Tube Stagnation Conditions

Recently, there has been a growing interest in studies concerning ionization sensors for aerospace applications, power generation, and fundamental research. In aerospace research, they have been used for studies of shock and detonation waves. Two key features of these sensors are their short response time, of the order of microseconds, and the fact that they are activated when exposed to high temperature air. In this sense, the present paper describes the development of an ionization sensor to be used in shock tube facilities. The sensor consists of 2 thorium-tungsten electrodes insulated by ceramic, with a stainless steel adapter for proper mounting, as well as 2 copper seal rings. An electrical circuit was also built with 2 main purposes: to provide the electrodes with a sufficient large voltage difference in order to ease ionization of the air and to assure a short time response of the sensor. The tests were carried out in a shock tube with the objective of observing the response of the sensor under stagnation conditions. For that, we chose initial driven pressures of 1.0; 1.2 and 1.5 kgf/cm², with a constant driver pressure equal to 70 kgf/cm². We analyzed the response of the sensor as a function of the initial driven pressure, stagnation temperature, and density. For the studied conditions, the results showed that the mean amplitude of the ionization

Fabrication of Gas Ionization Sensor to Recognize Gases and Measure Pressure and Humidity

Single Ionic gas sensor (IGS) was fabricated to measure pressure, humidity and recognizes the gases. Anodic method was used to create TiO2 nanotubes (TNTs) (with internal diameter from 45 to 90 nm) on the surfaces of pure Ti and Ti-6Al-7Nb alloy. Covered surface with TNTs was operated as negative electrode to build high localized electric field and minimize breakdown voltage (Vbd). The distance between the electrodes was fixed at 60 μm. Local electric field enhancement β factor was calculated by Fowler–Nordheim plot. Its value was 857 for anodized Ti (ATi). After annealing at 800 °C; TNTs on pure Ti surface transformed to parallel rods with diameters (from 95 to 550 nm). But on alloy surface, TNTs were transformed to protrusions. Sensitivity of measuring pressure for anodized samples decreased with increasing mean free path of testing gases. For all gases; there was increment in Vbd with pressure increasing. For each gas there was specific Vbd at definite pressure and humidity; this value represented a “fingerprint” for each gas recognized it from other gases. Sensitivity of humidity for both anodized and annealed IGSs increased with increasing of relative humidity (%RH). (Vbd, Humidity) curve was approximately linear for annealed Ti and its alloy.

ИССЛЕДОВАНИЕ ВЗАИМОСВЯЗИ ТОКА ИОНИЗАЦИИ И МАКСИМАЛЬНОГО ИНДИКАТОРНОГО ДАВЛЕНИЯ ПРИ СГОРАНИИ БЕНЗОВОЗДУШНОЙ СМЕСИ, ОБОГАЩЕННОЙ ВОДОРОДОМ

Ion current occurring in the result of chemical reactions of hydrocarbon fuel combustion is called the chemi-ionization current. The analysis of the research works displayed that the chemi-ionization current value can characterize the intensity and velocity of chemical reactions of burning in the combustion chamber of a piston engine, and therefore, the efficiency of heat generation during the combustion in the internal combustion engine. The paper shows that the study of the interrelationship of ion current and indicated combustion pressure determining, to the greatest extent, the workflow efficiency is the critical task, especially for gasoline engines with hydrogen transfer. The goal of the paper is to analyze the dependence of indicated combustion pressure and ion current under various initial conditions of fuel-air mixture combustion. Based on the experimental studies carried out on the single-cylinder motor unit UIT-85, the authors obtained data on the ion current occurring on the ionization sensor electrode remote from the ignition spark plug in the result of the flame front passing through it. Using the Kistler’s piezoelectric pressure sensor combined with the ignition spark plug, the authors created the indicator diagrams. The paper presents the data on the processing of the ion current peaks and the indicated pressure and the diagrams of their dependence on the mixture composition under various initial conditions. As the result of the study, the authors presented the diagram of the interrelationship of maxima of indicated pressure and ion current when varying the mixture composition at various crankshaft speeds, mass fraction of hydrogen added to the fuel-air mixture, compression and two angles of ignition advance.

Influence of fluctuation velocity on the electric conductivity of hydrocarbon flames

The feasibility of using ionization sensor for the investigation and diagnosis of the fuel combustion process in piston power plants with spark ignition is substantiated. It is shown that in order to expand the functions and increase the reliability of operation and signal processing accuracy of the ionization sensor it is necessary to know the impact of the flame fluctuating velocity on the latter. Based on the analysis of published data and in-house research a mechanism of the effect of fluctuation velocity on the electrical conductivity of hydrocarbon flame is proposed, estimated by the value of ion current. A formula for calculating the ion current is proposed, which includes the fluctuation velocity, the flame temperature and the concentration of carbon particles in the fuel. For methane-air flame, it was revealed that for U' 8 m/s an increase of ion current is observed, which is due to increased flame temperature and concentration of carbonaceous fuel particles in the zone of chemical reactions of the flame. When U' 8 m/s the ion current decreases due to the growth of heat consumption for heating the incoming fuel in the flame front, directly proportional to the fluctuation velocity. The results can be used to predict and monitor characteristics of turbulence in the combustion chambers of power plants with the aid of the ionization sensor.

Using the phenomenon of electrical conduction of flame of non-homogeneous air-fuel mixture in design and development of combustion chamber

The use of ionization sensors for the study and diagnosis of the combustion process in gas-turbine power plants is substantiated in the paper. The review of literature data and in-house research show that thermionic emission of electrons from incandescent carbon particles plays a decisive role in the mechanism of ionization of flame sprayed in a stream of liquid hydrocarbon fuels. It is shown that as liquid fuel is injected into the circulation area of a bluff body the area of maximum concentration of electrons that determine the conduction current is located in the circulation area. When liquid fuel is injected in the flame holder the zone of maximum electron density is located in the zone between the recirculation mixing zone and the slipstream. It was found experimentally that the distance between the region of maximum electron density and the stabilizer base is determined by the quantity of the fuel sprayed, the initial temperature, the flow turbulence and the gas flow rate. The results can be used to predict and monitor the characteristics of turbulent flame in combustion chambers of power plants with the help of ionization sensors. They also make it possible to create a system of continuous monitoring and control of ignition and combustion processes ensuring minimum concentration of toxic emissions in the exhaust combustion products.

Flexible Atmospheric-Pressure Gas Ionization Sensors with Horizontally Aligned Carbon Nanotube Electrodes

Flexible Atmospheric-Pressure Gas Ionization Sensors with Horizontally Aligned Carbon Nanotube Electrodes

Sensorized buoy for oil spill early detection

The Sea is often a fragile environment to be protected against possible pollutants. In this context, the present work contributes to its safeguard by proposing a new buoy equipped with advanced sensors for the detection of oil spills. In particular, the buoy is provided with various sensors for the evaluation of both meteorological and marine parameters (e.g. waves, wind, temperature), and chemical/physical data acquired by an electronic nose system specifically designed for the detection of hydrocarbons. The electronic nose is composed of a flow chamber, a chamber equipped with photo ionization sensors, pumps and valves for air inlet and outlet, and a low-cost electronic board. The designed system samples the air above the water and produces data that are processed through two artificial neural networks allowing for a classification of detected hydrocarbons and overall pollution level. Suitable network interfaces and a connector toward a Marine Information System (MIS) allow both for real-time data visualization and for long-term assessment of water quality.

MEMS gas ionization sensor with palladium nanostructures for use at ambient pressure

A microfabricated gas ionization sensor with integrated field enhancing silicon- palladium nanostructures is presented. The sensor can be used to determine the ambient gas by its specific breakdown voltage. Technological details of the fabrication and the assembly of the sensor are presented too.

An enhanced gas ionization sensor from Y-doped vertically aligned conductive ZnO nanorods

A stable and highly sensitive gas ionization sensor (GIS) constructed from vertically aligned, conductive yttrium–doped ZnO nanorod (YZO NR) arrays is demonstrated. The conductive YZO NRs are synthesized using a facile one-pot hydrothermal method. At higher Y/Zn molar ratio, the aspect ratio of the YZO NRs is increased from 11 to 25. Doping with yttrium atoms decreases the electrical resistivity of ZnO NRs more than 100 fold. GIS measurements reveal a 6-fold enhancement in the sensitivity accompanied with a significant reduction in breakdown voltage from the highly conductive YZO NRs. Direct correlations between the resistivity of the NRs and GIS characteristics are established.

Influence of the initiation energy on development of hydrogen–air mixtures combustion in large spherical volumes

We investigate the influence of the initiation energy on the development of burning in hydrogen–air mixtures with an hydrogen content of 7–31% (volume). We initiated the mixtures in the center of the spherical reaction volume, 7–40 m3 in size, by energies from 1 J up to 4600 J. The reaction volume was bordered by a thin rubber envelope and located inside the 910 m3 spherical explosion chamber. We registered the flame front movement by means of the ionization sensors, the video camera, and the high-speed video camera.

Micro-structured electron accelerator for the mobile gas ionization sensor technology

Abstract. Mobile and economically priced gas monitoring and warning systems will become increasingly important for civil security, such as in fire brigade operations in undefined hazardous environments (Daum et al., 2006). Normally, photoionization detectors (PIDs) are used for the detection of gases. Hereby, the principle is based upon the ionization of the measured gas by photons, which are generated by a high-energetic gas discharge lamp with energy of 10–11 eV. Besides the detrimental unspecific gas detection because of the ionization of all gases with ionization potential (IP) below the provided photon energy, sensors also have a short lifetime combined with a high cost (http://www.intlsensor.com/pdf/photoionization.pdf). This can be remedied by the concept of an electronic supported photoionization detector (ePID; Zimmer et al., 2012) consisting of a durable UV-LED with an above-positioned electron accelerator chip manufactured on a glass substrate by planar technology. Photoelectrons are extracted by UV illumination out of the bottom electrode and will be accelerated to an energy matching the ionization potential of the gas by a downstream acceleration grid. Thereby, the stable honeycomb-structured grid acts as a porous separator between the evacuated electron acceleration path due to nm scaling and the ionization area of the detector. To enhance the emitting area yielding a higher photoelectron current, the grid structure almost levitates, realized by the use of compatible planar technological processes such as reactive ion etching (RIE) and isotropic wet etching of sacrificial layers, which will be explained in detail in this paper. Furthermore, the tunability of the grid's acceleration voltage would enable a substance-specific determination of the gas composition, where the ionization of the analytes is clearly performed by photoelectrons instead of photons.