Effect of oxygen on the electrical conductivity of Pt-contacted α-Ga2O2/ε(κ)-Ga2O3 MSM structures on patterned sapphire substrates

Electrical conductivity and gas sensitivity of α-Ga2O2/ ε(κ)-Ga2O3 structures were measured for oxygen concentrations ranging from 2 % to 100 % and temperatures ranging from 25 °C to 220 °C. It was found that the oxygen sensitivity of the structures depended on the donor dopant concentration. The alpha -Ga _{2}O_{3}/arepsilon ( kappa )-Ga 2 O 3 structures doped with sim 1.5 imes 10^{17} cm −3 of Sn showed high sensitivity to O 2 in the temperature range from 180 °C to 220 °C and at the bias voltage below 7.5 V. This effect can be attributed to the chemisorption of oxygen molecules on the surface of structures, which reduces energy barriers between ε(κ)-Ga2O3 grains

Low-resistivity gas sensors based on the In2O3-Ga2O3 mixed compounds films

The effect of H2, NH3, CO, CH4, O2 and NO2 on the electroconductive properties of the In2O3-Ga2O3 mixed compounds films obtained by the halide vapor phase epitaxy was studied. In the temperature range of 150–550 °C In2O3-Ga2O3 films are characterized by high responses, high speed of operation when exposed to H2, NH3, CO and O2. A qualitative mechanism of gas sensitivity for the In2O3-Ga2O3 mixed compounds films to gases was proposed. The gas-sensitive characteristics of In2O3, κ(ε)-Ga2O3 and In2O3-Ga2O3 films were compared. The advantage of the In2O3-Ga2O3 mixed compounds films compared with Ga2O3 and In2O3 films is a low base electrical resistivity with a relatively high gas sensitivity

Improving the energy efficiency of a LoRaWAN by a UAV-based gateway

Abstract The Internet of Things (IoT) devices and applications are spreading all over around us to become the cardiovascular infrastructure for the data of the cyber-physical systems of the future. The implementation of a reliable collection of telemetry data within various application domains, including medicine, safety, and security, industry, smart cities, or environmental monitoring, to name just a few, is among the major challenges still to be solved. Importantly, many of the use cases imply a huge geographic area span or operation in remote areas with limited infrastructure availability and poor reachability. To address these scenarios in this paper, we propose a combination of the two technologies the Low Power Wide Area Network (LPWAN) and the Unmanned Aerial Vehicles (UAVs). Specifically, we study the energy utility and the communication performance of introducing a UAV-based GW into an LPWAN based on the LoRaWAN technology. The results of our simulations show that a UAV-based GW enables to reduce the mean energy consumption for communication in the network by up to 59%. Depending on the UAV speed, the communication performance in terms of the packet delivery ratio can either increase or decrease by several percentage points

Wireless power transfer from unmanned aerial vehicle to low-power wide area network nodes:performance and business prospects for LoRaWAN

Abstract Supported by the remarkable progress across many technological domains, the Internet of Things (IoT) ecosystem demonstrates steady growth over the few past years. This growth enables a number of new exciting applications. Nonetheless, hardly one can say today that the utility of the IoT is used to its full potential. This fact is especially notable for the monitoring applications deployed in remote areas. To address the needs of these use cases, in the article we propose a solution based on the combination of three key technologies: the low-power wide area networks, the unmanned aerial vehicles, and the wireless power transfer. In the article, we first detail the novel concept of a wireless power transfer-enabled unmanned aerial vehicle employed to charge the LoRaWAN sensor nodes. Then, via extensive simulations and analysis of an illustrative LoRaWAN application, we investigate both technical and, notably, business performance indicators, and compare them against the ones for a baseline scenario with no unmanned aerial vehicle. Our results illustratively demonstrate that in the long-term perspective, the inclusion of a wireless power transfer-enabled drone may drastically reduce the system’s operating expenses. At the very same time, our results highlight the limits, bottlenecks, and trade-offs related to the proposed concept, thus providing the basis and calling for further investigation

Method of assigning spreading factor to improve the scalability of the LoRaWAN wide area network

Abstract In modern world Low Power Wide Area Network (LPWAN) technologies have become the key enabler for a sheer diversity of the Internet of Things (IoT) applications involving massive deployment of resource-limited devices. In this paper we address the problem of improving the network scalability for one of the most widely used today licensee-free-band LPWAN technologies, named LoRaWAN. We show that the conventional method for assigning the spreading factor (SF) parameter to the devices in a LoRaWAN network, which effectively minimizes the consumption of individual devices, has some drawbacks when this comes to the scalability of the network as whole. Therefore, in this paper we propose another method of assigning the SFs to the nodes, which improves the probability of data delivery in an LPWAN at a cost of minor increase of the devices’ consumption. The results of the conducted simulations confirm and characterize the utility of the proposed method

Electrocatalytic multicomponent transformation of cyclic 1,3-diketones, isatins, and malononitrile : facile and convenient way to functionalized spirocyclic (5,6,7,8-tetrahydro-4H-chromene)-4,3′-oxindole system

An electrochemically induced catalytic multicomponent transformation of cyclic 1,3-diketones, isatins, and malononitrile in alcohols in an undivided cell in the presence of sodium bromide as an electrolyte results in the formation of spirooxindoles with fused functionalized 5,6,7,8-tetrahydro-4H-chromene system in 83-98% yields. The application of this efficient electrocatalytic method to the formation of medicinally relevant spirocyclic (4H-chromene)-4,3′-oxindoles is beneficial from the viewpoint of diversity-oriented large-scale processes and represents novel, facile, and environmentally benign synthetic concept for multicomponent reaction strategy

Effect of ambient humidity on the electrical conductivity of polymorphic Ga2O3 structures

The effect of ambient humidity on the electrical conductivity of α-Ga2O3 and α-Ga2O3/ε-Ga2O3 is investigated. Polymorphic epitaxial Ga2O3 layers are deposited by the method of chloride vapor-phase epitaxy on sapphire substrates. The contacts are made of Pt and Pt/Ti. It is discovered that the I–V characteristics of the Pt/α-Ga2O3/Pt and Pt/Ti/α-Ga2O3/ε-Ga2O3/Ti/Pt structures have a high sensitivity to atmospheric humidity in the temperature range of 25–100°C. It is found that the effect of water vapor on the I–V characteristics is reversible, and the most significant current changes in the samples are observed at a relative humidity of RH ≥ 60%. As the temperature rises, the effect of atmospheric humidity on the I–V characteristics decreases and disappears at temperatures of T > 100°C. The experimental results obtained are explained within the framework of the Grotthuss mechanism

Hydrogen sensors based on Pt/α-Ga2O3:Sn/Pt structures

Gas sensing properties of Schottky metal-semiconductor-metal (MSM) structures based on α-Ga2O3 epitaxial films with Pt contacts are investigated. The electrical conductivity of the MSM structures exposed to H2, O2, CO, NO, CH4 and NH3 gases in the temperature range of 25–500 °C is studied. The structures show a very high sensitivity to H2. It is found that Pt contacts and the Sn doping level play a key role in determining the hydrogen sensing properties of Pt/α-Ga2O3:Sn/Pt MSM structures. The sensitivity to H2 is attributed to a modulation of the Schottky barrier height at the interface between Pt and α-Ga2O3:Sn

Effect of oxygen on the Gas-sensitive properties of α-Ga2O3/ε-Ga2O3 structures

Miniature O2 sensors with low energy consumption are of practical interest for the chemical and metallurgical industries, development of systems for analyzing the performance of internal combustion engines and as functional elements of artificial lung ventilation devices. The requirements for miniaturization, high sensitivity, speed and relative cheapness are satisfied by O2 sensors based on β-Ga2O3. The chemical and thermal stability of β-Ga2O3 allows developing gas sensors with extremely high operating temperatures of 400-1100 °C ensuring high reproducibility of their characteristics and high speed of operation. In turn, the high operating temperatures of O2 β-Ga2O3 sensors are their drawback causing high energy consumption