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Détails du magazine
Format
Magazine
eISSN
2255-8896
Première publication
18 Mar 2008
Période de publication
6 fois par an
Langues
Anglais

Chercher

Volume 59 (2022): Edition 1 (February 2022)

Détails du magazine
Format
Magazine
eISSN
2255-8896
Première publication
18 Mar 2008
Période de publication
6 fois par an
Langues
Anglais

Chercher

6 Articles
Accès libre

Evaluation of Received Signal Power Level and Throughput Depending on Distance to Transmitter in Testbed for Automotive WLAN IEEE 802.11ac Communication Network

Publié en ligne: 02 Feb 2022
Pages: 3 - 12

Résumé

Abstract

WLAN IEEE 802.11ac is one of the wireless network technologies that can be used for ITS (Intelligent Transport Systems) needs, in particular for providing vehicle passengers with access to the data transmission network. To evaluate the performance of such automotive wireless access networks, it is necessary to perform experimental measurements. By conducting the throughput measurements in WLAN-based automotive communications testbed, it has been observed that the throughput of the communication channel decreases and the received signal becomes weaker as the vehicle moves away from the wireless access point. The aim of the research is to verify theoretically whether there is a correlation between the received signal power level and the throughput of the communication channel depending on the distance to the transmitter. To calculate the received signal power depending on the distance to the transmitter, a log-normal signal propagation model can be used, which takes into account random signal fluctuations that are described by the Nakagami distribution. Further, based on the obtained results, Shannon’s theorem can be used to calculate the maximum theoretical throughput of the communication channel. The analysis of the obtained results shows that a correlation exists between the received signal power level and the throughput of the communication channel depending on the distance to the transmitter. The performed theoretical calculations justify the experimentally obtained results.

Mots clés

  • Experimental results
  • IEEE 802.11ac
  • received signal power level
  • theoretical Nakagami distribution
  • throughput
Accès libre

Solar Microwave Emission Associated with Coronal Mass Ejections (CME)

Publié en ligne: 02 Feb 2022
Pages: 13 - 20

Résumé

Abstract

The connection between Coronal Mass Ejections (CME) and radio burst has been discovered especially at lower frequencies (< 2 GHz). The aim of the study is to investigate possible connection between CMEs and variability of radio brightenings at 37 GHz (8 mm) within the time frame of four days. The millimetre radio observations have been made on RT-14 radio telescope at Metsähovi Radio Observatory of Aalto University, Finland. In addition, 11.2 GHz (2.7 cm) total solar flux information is included in the analysis. The radio observations were made between March 2011 and September 2017, totally including 24 events. The results demonstrate that in most of the cases the radio brightening intensity achieves its maximum before CME occurs. Time of 11.2 GHz intensity appearance matches with time of CME appearance with difference of two to three hours. However, in most cases a maximum of 11.2 GHz intensity appears before CMEs. The study investigates a possibility of predicting CME appearance based on milli- and centimetre radio observations. The study also proposes a scenario connection between CMEs and solar microwave events.

Mots clés

  • Coronal Mass Ejection (CME)
  • radio telescope
  • solar activity
  • solar radio brightening
Accès libre

The Relation Between Photoconductivity Threshold and Open-Circuit Voltage in Organic Solar Cells

Publié en ligne: 02 Feb 2022
Pages: 21 - 29

Résumé

Abstract

Most of the solar cell parameters (short-circuit current, fill factor, power conversion efficiency) can only be determined by creating and measuring the solar cell. However, there is an empirical relation that links energy level values of the materials in the active layer to an open-circuit voltage (Uoc) of the solar cell. Due to a variety of possible methods used to determine energy level values and the dispersion of obtained results, this estimate is not always correct. Even if correct energy level values are obtained for separate materials, energy level shift takes place at the interfaces when two materials are mixed. That is why a simple and reliable experimental method for Uoc estimation is required. Usually, photoconductivity is used to obtain the energy gap between molecule ionization energy and electron affinity of a single material. When two materials are mixed, direct charge transfer from donor to acceptor molecule can be observed. The threshold energy (ECT) shows the real difference between donor molecule ionization energy and acceptor molecule electron affinity. This difference should correspond to the Uoc. The present study makes the comparison between the open-circuit voltage estimated from material energy level values, the obtained ECT values for various donor:acceptor systems, and the real Uoc obtained from solar cell measurements. Strong correlation between ECT and Uoc is obtained and the photoconductivity measurements can be used in the estimation of Uoc.

Mots clés

  • Energy levels
  • direct charge transfer
  • open-circuit voltage
  • organic materials
  • organic solar cells
  • photoconductivity
Accès libre

Morphology Influence on Wettability and Wetting Dynamics of ZnO Nanostructure Arrays

Publié en ligne: 02 Feb 2022
Pages: 30 - 43

Résumé

Abstract

Changes in nanostructure morphology and size may result in very different surface wettability. In this research, the impact of different morphological parameters on the wetting dynamics of ZnO nanostructured layers is studied. Six different morphologies are chosen to determine the specific wetting processes of ZnO nanostructures: nanoneedles, small diameter rods, large diameter rods, nanotubes, nanoplates, and plain thin films. Wetting dynamics is investigated using conventional sessile drop technique and a novel approach based on electrochemical impedance spectroscopy. The results show that the surface of nanostructured ZnO thin films exhibits both hydrophilic and hydrophobic wetting behaviour, depending on nanostructure form, size, and orientation. ZnO nanostructure arrays are a promising platform for electrochemical and optical sensing in aqueous solutions. The full and effective use of the sensor working surface can be ensured only under the condition of complete wetting of the nanostructured layer. Therefore, it is important to take into account the peculiarities of the wetting process of a specific morphology of nanostructures.

Mots clés

  • Electrochemical impedance spectroscopy
  • nanostructures
  • water contact angle
  • wettability
  • ZnO
Accès libre

Investigation of Power Efficiency Changes in DWDM Systems Replacing Erbium-Doped Amplifiers By Semiconductor Optical Amplifiers

Publié en ligne: 02 Feb 2022
Pages: 44 - 52

Résumé

Abstract

To evaluate potential utilization of semiconductor optical amplifiers (SOAs) as a wideband amplification alternative to erbium doped fibre amplifiers (EDFAs) in dense wavelength division multiplexed (DWDM) coherent systems, the authors discuss changes in power consumption levels required for a single bit transmission. The research evaluates the power efficiency parameter for WDM transmission systems using both amplification schemes – EDFAs that utilise standard C-band and SOAs assuming 75 nm amplification spectral band. The power efficiency levels have been estimated for five transmission spans with maximal distance of 640 km. The standard 50 GHz channel spacing has been chosen for both system configurations to allocate 100 Gbps dual-polarization quadrature phase shift keying (DP-QPSK) optical signals. The simulation schemes are described along with the critical parameters, derived from the recent relevant studies that should be taken into account considering usage of SOAs as in-line amplifiers.

Mots clés

  • Coherent SOA-amplified transmission systems
  • DWDM systems
  • phase modulation formats
  • power efficiency
  • semiconductor optical amplifier
  • SOA as in-line amplifiers
Accès libre

The Least-Cost Optimization of PV-Station DC/AC Equipment Using Battery Energy Storage System

Publié en ligne: 02 Feb 2022
Pages: 53 - 62

Résumé

Abstract

The auction allocation of state support quotas for renewable generation implementation that will change the existing incentive for their development by providing “green” tariffs to producers is based on competitive selection of the power plant projects with the least cost of electricity generation. The competitive advantage of solar photovoltaic power plant (PV stations) projects can be done by deciding what kind of equipment can provide the minimum cost of electricity generation during the period of operation. In the article, there is improvement of non-linear mathematical least-cost optimization model of the structure of PV-station equipment using DC coupled battery energy storage system (BESS) to store the excess electricity of photovoltaic modules (PV modules), which is lost on inverters when they are overloaded during the hours of the highest intensity of solar radiation. The article presents the modelling results of overall operation of PV station with fixed power of PV modules, as well as determines optimal power of inverter equipment and battery capacity. The model calculations have shown that when the DC equipment costs of the PV station are reduced by almost 62 % and DC equipment costs of BESS are reduced by 86.7 % of the actual value in 2020 at the power of 10 MW PV modules, the optimal power of inverter equipment decreases from 7.08 to 6.29 MW, and the storage capacity increases from 0.22 to 2.51 MWh. The use of BESS allows accumulating the amount of electricity produced by PV modules, which is lost with limitation on inverters, while the cost of their joint electricity production is decreased by 0.42 %.

Mots clés

  • BESS
  • DC/AC overloading
  • levelized daily cost of electricity
  • nonlinear modelling
  • optimization
  • PV station
6 Articles
Accès libre

Evaluation of Received Signal Power Level and Throughput Depending on Distance to Transmitter in Testbed for Automotive WLAN IEEE 802.11ac Communication Network

Publié en ligne: 02 Feb 2022
Pages: 3 - 12

Résumé

Abstract

WLAN IEEE 802.11ac is one of the wireless network technologies that can be used for ITS (Intelligent Transport Systems) needs, in particular for providing vehicle passengers with access to the data transmission network. To evaluate the performance of such automotive wireless access networks, it is necessary to perform experimental measurements. By conducting the throughput measurements in WLAN-based automotive communications testbed, it has been observed that the throughput of the communication channel decreases and the received signal becomes weaker as the vehicle moves away from the wireless access point. The aim of the research is to verify theoretically whether there is a correlation between the received signal power level and the throughput of the communication channel depending on the distance to the transmitter. To calculate the received signal power depending on the distance to the transmitter, a log-normal signal propagation model can be used, which takes into account random signal fluctuations that are described by the Nakagami distribution. Further, based on the obtained results, Shannon’s theorem can be used to calculate the maximum theoretical throughput of the communication channel. The analysis of the obtained results shows that a correlation exists between the received signal power level and the throughput of the communication channel depending on the distance to the transmitter. The performed theoretical calculations justify the experimentally obtained results.

Mots clés

  • Experimental results
  • IEEE 802.11ac
  • received signal power level
  • theoretical Nakagami distribution
  • throughput
Accès libre

Solar Microwave Emission Associated with Coronal Mass Ejections (CME)

Publié en ligne: 02 Feb 2022
Pages: 13 - 20

Résumé

Abstract

The connection between Coronal Mass Ejections (CME) and radio burst has been discovered especially at lower frequencies (< 2 GHz). The aim of the study is to investigate possible connection between CMEs and variability of radio brightenings at 37 GHz (8 mm) within the time frame of four days. The millimetre radio observations have been made on RT-14 radio telescope at Metsähovi Radio Observatory of Aalto University, Finland. In addition, 11.2 GHz (2.7 cm) total solar flux information is included in the analysis. The radio observations were made between March 2011 and September 2017, totally including 24 events. The results demonstrate that in most of the cases the radio brightening intensity achieves its maximum before CME occurs. Time of 11.2 GHz intensity appearance matches with time of CME appearance with difference of two to three hours. However, in most cases a maximum of 11.2 GHz intensity appears before CMEs. The study investigates a possibility of predicting CME appearance based on milli- and centimetre radio observations. The study also proposes a scenario connection between CMEs and solar microwave events.

Mots clés

  • Coronal Mass Ejection (CME)
  • radio telescope
  • solar activity
  • solar radio brightening
Accès libre

The Relation Between Photoconductivity Threshold and Open-Circuit Voltage in Organic Solar Cells

Publié en ligne: 02 Feb 2022
Pages: 21 - 29

Résumé

Abstract

Most of the solar cell parameters (short-circuit current, fill factor, power conversion efficiency) can only be determined by creating and measuring the solar cell. However, there is an empirical relation that links energy level values of the materials in the active layer to an open-circuit voltage (Uoc) of the solar cell. Due to a variety of possible methods used to determine energy level values and the dispersion of obtained results, this estimate is not always correct. Even if correct energy level values are obtained for separate materials, energy level shift takes place at the interfaces when two materials are mixed. That is why a simple and reliable experimental method for Uoc estimation is required. Usually, photoconductivity is used to obtain the energy gap between molecule ionization energy and electron affinity of a single material. When two materials are mixed, direct charge transfer from donor to acceptor molecule can be observed. The threshold energy (ECT) shows the real difference between donor molecule ionization energy and acceptor molecule electron affinity. This difference should correspond to the Uoc. The present study makes the comparison between the open-circuit voltage estimated from material energy level values, the obtained ECT values for various donor:acceptor systems, and the real Uoc obtained from solar cell measurements. Strong correlation between ECT and Uoc is obtained and the photoconductivity measurements can be used in the estimation of Uoc.

Mots clés

  • Energy levels
  • direct charge transfer
  • open-circuit voltage
  • organic materials
  • organic solar cells
  • photoconductivity
Accès libre

Morphology Influence on Wettability and Wetting Dynamics of ZnO Nanostructure Arrays

Publié en ligne: 02 Feb 2022
Pages: 30 - 43

Résumé

Abstract

Changes in nanostructure morphology and size may result in very different surface wettability. In this research, the impact of different morphological parameters on the wetting dynamics of ZnO nanostructured layers is studied. Six different morphologies are chosen to determine the specific wetting processes of ZnO nanostructures: nanoneedles, small diameter rods, large diameter rods, nanotubes, nanoplates, and plain thin films. Wetting dynamics is investigated using conventional sessile drop technique and a novel approach based on electrochemical impedance spectroscopy. The results show that the surface of nanostructured ZnO thin films exhibits both hydrophilic and hydrophobic wetting behaviour, depending on nanostructure form, size, and orientation. ZnO nanostructure arrays are a promising platform for electrochemical and optical sensing in aqueous solutions. The full and effective use of the sensor working surface can be ensured only under the condition of complete wetting of the nanostructured layer. Therefore, it is important to take into account the peculiarities of the wetting process of a specific morphology of nanostructures.

Mots clés

  • Electrochemical impedance spectroscopy
  • nanostructures
  • water contact angle
  • wettability
  • ZnO
Accès libre

Investigation of Power Efficiency Changes in DWDM Systems Replacing Erbium-Doped Amplifiers By Semiconductor Optical Amplifiers

Publié en ligne: 02 Feb 2022
Pages: 44 - 52

Résumé

Abstract

To evaluate potential utilization of semiconductor optical amplifiers (SOAs) as a wideband amplification alternative to erbium doped fibre amplifiers (EDFAs) in dense wavelength division multiplexed (DWDM) coherent systems, the authors discuss changes in power consumption levels required for a single bit transmission. The research evaluates the power efficiency parameter for WDM transmission systems using both amplification schemes – EDFAs that utilise standard C-band and SOAs assuming 75 nm amplification spectral band. The power efficiency levels have been estimated for five transmission spans with maximal distance of 640 km. The standard 50 GHz channel spacing has been chosen for both system configurations to allocate 100 Gbps dual-polarization quadrature phase shift keying (DP-QPSK) optical signals. The simulation schemes are described along with the critical parameters, derived from the recent relevant studies that should be taken into account considering usage of SOAs as in-line amplifiers.

Mots clés

  • Coherent SOA-amplified transmission systems
  • DWDM systems
  • phase modulation formats
  • power efficiency
  • semiconductor optical amplifier
  • SOA as in-line amplifiers
Accès libre

The Least-Cost Optimization of PV-Station DC/AC Equipment Using Battery Energy Storage System

Publié en ligne: 02 Feb 2022
Pages: 53 - 62

Résumé

Abstract

The auction allocation of state support quotas for renewable generation implementation that will change the existing incentive for their development by providing “green” tariffs to producers is based on competitive selection of the power plant projects with the least cost of electricity generation. The competitive advantage of solar photovoltaic power plant (PV stations) projects can be done by deciding what kind of equipment can provide the minimum cost of electricity generation during the period of operation. In the article, there is improvement of non-linear mathematical least-cost optimization model of the structure of PV-station equipment using DC coupled battery energy storage system (BESS) to store the excess electricity of photovoltaic modules (PV modules), which is lost on inverters when they are overloaded during the hours of the highest intensity of solar radiation. The article presents the modelling results of overall operation of PV station with fixed power of PV modules, as well as determines optimal power of inverter equipment and battery capacity. The model calculations have shown that when the DC equipment costs of the PV station are reduced by almost 62 % and DC equipment costs of BESS are reduced by 86.7 % of the actual value in 2020 at the power of 10 MW PV modules, the optimal power of inverter equipment decreases from 7.08 to 6.29 MW, and the storage capacity increases from 0.22 to 2.51 MWh. The use of BESS allows accumulating the amount of electricity produced by PV modules, which is lost with limitation on inverters, while the cost of their joint electricity production is decreased by 0.42 %.

Mots clés

  • BESS
  • DC/AC overloading
  • levelized daily cost of electricity
  • nonlinear modelling
  • optimization
  • PV station

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