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Radio frequency (RF) energy harvesting system scavenges energy from electromagnetic waves and supplies power wirelessly enabling the usage of zero-energy sensors or devices. Frequency band of the electromagnetic wave is an important parameter for energy harvesting systems. In this study, simultaneous multiband RF energy harvesting systems are analyzed both theoretically and experimentally for zero-energy devices. An advanced measurement system, which consists of an RF energy harvesting circuit, universal software radio peripherals (USRPs), and other equipment, is established to obtain received power and charging time samples for Industrial, scientific, and medical (ISM) and Global system for mobile communications (GSM) radio bands. The effects of each band and their different combinations on the charging time as well as the conversion parameter are thoroughly investigated for RF energy harvesting. According to a real-life communication scenario, the outage probabilities of wireless zero-energy sensors are presented. It is demonstrated in this study that the use of multiband frequencies in energy harvesting, in addition to the low-power requirement, increases the feasibility of zero-energy devices. [ABSTRACT FROM AUTHOR]

One of the most important, albeit ignored, issues in the process of curriculum implementation is teachers' beliefs; indeed, this is a vital issue since their beliefs about teaching and learning will in part govern their actions in the classroom. There is a substantial body of the literature that highlights how teachers' beliefs are important when ensuring that science education reforms are successfully carried out. Therefore, it is important to explore the beliefs of teachers and teacher candidates to support them in adapting these beliefs to be in accord with the goals of the reform. This paper presents the results of an investigation into the nature of preservice science teachers' (PSTs) beliefs about teaching, the congruency of their beliefs about teaching, their actual classroom practices, and the potential role of their early experiences as learners in shaping their beliefs and classroom practices. At the outset of the study, there were 13 PSTs. Among them, four were recruited for the study by purposive sampling. They were all in the final year of their 4-year teacher education programme and will be able to teach middle school science classes after graduation. This study employed a basic qualitative research method. The primary methods of data collection in this study were: 1) initial interviews to select participants in a purposeful manner; 2) classroom observation of each PST to identify how they taught science; and 3) final interviews with each PST to explore their beliefs about science teaching and their past experiences. We found that the PSTs who chose to participate in this study hold student-centred teaching beliefs while performing teacher-centred science teaching practices. The result was interesting in that the PSTs' teaching practices closely resemble those of their early science teachers. [ABSTRACT FROM AUTHOR]

In this study, charging time in RF energy harvesting systems is measured and statistically analyzed. The measurement system is carried out using an RF energy harvesting circuit, transmitters as RF sources, a patch antenna and other auxiliary devices. The RF power signals generated by single, double and triple RF sources are collected wirelessly by the RF energy harvesting circuit at distances from 1 to 5 m at the interval of 0.5 m. Measurement samples for the charging time are recorded and then evaluated. Test of normality using Kolmogorov–Smirnov shows that the measurement samples of the single, double and triple RF sources are not in a normal distribution. Based on Spearman's rho correlation coefficient, it is detected that there is no strong correlation among the measurement samples at different distances for each RF source. Additionally, it is observed that received power distributions of the RF sources match the charging time values. Based on the experimental results, charging time models are proposed for the single, double and triple RF sources. As a result, it is determined that there is a good match between the proposed models and the charging time values. [ABSTRACT FROM AUTHOR]

Finland and Singapore are both top-performing countries in international assessments such as PISA. Finland has been consistently one of the high-achievers regarding not only students' literacy levels but also educational equity. Similarly, Singapore has continuously shown outstanding performance in PISA. It outperformed all the other participants in all three literacy domains in PISA 2015. We believe exploring the factors affecting students' science literacy in these two top-performing countries will provide the low-performing countries with a useful guideline. In this regard, we aim to build models including the student and school-level factors associated with the students' science literacy in Finland and Singapore using PISA 2015 data. We conduct Hierarchical Linear Modeling to create these models. The sample includes 5882 students in Finland and 6115 students in Singapore. The resulting models explain about 43% and 40% of the within-school variance while they explain 62% and 71% of the between-school variance in science literacy in Finland and Singapore respectively. At the student level, students' enjoyment and interest in science are the most influential predictors of science literacy while at the school level, schools' economic, social, and cultural status is by far the most powerful predictor of science literacy in both Finland and Singapore. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) energy harvesting as an alternative energy source is an emerging technology that supplies energy for low power wireless devices. In this study, the impacts of RF sources, antenna gains, output power levels and path losses on charging times of an RF energy harvesting system were measured and analyzed in detail. An advanced measurement system that consisted of RF sources used as signal generators, dipole and patch antennas, an RF energy harvesting circuit and the other auxiliary devices were installed for acquiring measurement samples. The generated RF power signals in continuous wave mode at 915 MHz carrier frequency were collected wirelessly by the RF energy harvesting circuit for different antenna gains and output power levels at distances from 20 to 50 cm at the interval of 5 cm. The measurement samples were analyzed statistically. According to the measurement results, it was determined that double RF sources, 6.1 dBi antenna gain and 17 dBm output power level reduced the charging times by 63.09%, 59.24% and 46.41% on average, respectively. [ABSTRACT FROM AUTHOR]

Radio-frequency (RF) energy harvesting is a promising technology that obtains energy from electromagnetic waves. As an alternative energy source, this modern technology can provide power wirelessly enabling the practical use of battery-free devices and it is also expected to be widely used in future applications. Many studies have examined the effects of different modulation techniques on power or efficiency in RF energy-harvesting systems. In this article, the effects of different modulation techniques, such as amplitude shift keying (ASK), quadrature amplitude modulation (QAM), phase-shift keying (PSK), and frequency shift keying (FSK) on charging time, were measured and theoretically analyzed in detail. The measurement system was designed using a signal generator, an RF energy-harvesting circuit, and other auxiliary devices. The signal generator produced four different modulated signals as transmit power signals from 1 to 10 dBm at the interval of 1 dBm, and then, the RF energy-harvesting circuit was fed with these power signals. According to the measurement results, four different modulation techniques charged the RF energy-harvesting circuit at different times. It was observed that the 4-ASK modulation technique had the shortest charging time in the range of 1–10 dBm when comparing to QAM, PSK, and FSK modulation techniques, and thus, it was evaluated to be the most suitable modulation technique for the RF energy-harvesting system among these modulation techniques in terms of charging time. [ABSTRACT FROM AUTHOR]

In this study, an analogy has been developed to teach students electric circuits in a more concrete way. A connection between the elements of electric circuits and the characters in the Little Red Riding Hood story has been established to teach how simple electric circuits work. In addition to the similarities in the story, we have indicated where the analogy between the analogue concept (Little Red Riding Hood) and the target concept (simple electric circuits) breaks down, and suggested several ways to address any misconceptions that might arise during the implementation. [ABSTRACT FROM AUTHOR]

Radio-frequency (RF) energy harvesting is a promising technology that obtains energy from electromagnetic waves. As an alternative energy source, this modern technology can provide power wirelessly enabling the practical use of battery-free devices and it is also expected to be widely used in future applications. Many studies have examined the effects of different modulation techniques on power or efficiency in RF energy-harvesting systems. In this article, the effects of different modulation techniques, such as amplitude shift keying (ASK), quadrature amplitude modulation (QAM), phase-shift keying (PSK), and frequency shift keying (FSK) on charging time, were measured and theoretically analyzed in detail. The measurement system was designed using a signal generator, an RF energy-harvesting circuit, and other auxiliary devices. The signal generator produced four different modulated signals as transmit power signals from 1 to 10 dBm at the interval of 1 dBm, and then, the RF energy-harvesting circuit was fed with these power signals. According to the measurement results, four different modulation techniques charged the RF energy-harvesting circuit at different times. It was observed that the 4-ASK modulation technique had the shortest charging time in the range of 1–10 dBm when comparing to QAM, PSK, and FSK modulation techniques, and thus, it was evaluated to be the most suitable modulation technique for the RF energy-harvesting system among these modulation techniques in terms of charging time. [ABSTRACT FROM AUTHOR]

One of the most important research areas searches for new sources of energy and for the highest efficiency from existing energy sources. Radio frequency (RF) energy harvesting is a promising alternative to obtain energy for wireless devices directly from RF energy sources in the environment. In this paper, we provide a broad overview of the main blocks of RF energy harvesting systems, which are the wireless transmission medium, the antenna and impedance matching circuit, the rectifier, the voltage multiplier, and the energy storage device or load. The characteristics of these blocks directly affect the performance of an RF energy harvesting system. We mainly focus on the ratio of output and input powers at each block, named as the conversion efficiency and the impedance matching efficiency, which determines the overall efficiency of system. We present detailed information about the system parameters. Thus, we characterize an RF energy harvesting system, which makes the design of system possible to obtain the maximum efficiency and correspondingly the maximum output power, providing the necessary insight about the design of RF energy harvesting systems. • A broad overview of main blocks of RF energy harvesting systems. • Characteristic of circuits affecting the performance of RF energy harvesting. • Overall efficiency of RF energy harvesting systems. • Necessary insight about the design of RF energy harvesting systems. [ABSTRACT FROM AUTHOR]

In this study, radiofrequency electromagnetic field exposure levels were measured as mobile on the main streets of Diyarbakır during a week. The measurements were carried out using high precision spectrum analyzer with an isotropic antenna mounted on the top of a car. With this mobile measurement, large areas were measured in a short time and information about characteristics of electromagnetic environment was obtained quickly. Measurement results showed that measurement values were not in normal distribution and variances between independent variables were not homogeneous. According to Spearman’s rho correlation coefficient, there was no strong correlation between measurement days. In terms of mean electric field values, contribution of each band to total band was arranged as UMTS DL, GSM900 DL, GSM1800 DL, TV4-5, FM, and TV3 band, respectively. It was determined that all measurement values were below the reference levels of the International Commission on Non-Ionizing Radiation Protection. [ABSTRACT FROM AUTHOR]

International Commission on Non-Ionizing Radiation Protection (ICNIRP) accepted by many countries as well as Turkey is a commission which determines reference levels for general public and occupational exposure to electromagnetic fields and has intensive works on these issues. ICNIRP has published separately a low frequency band (0-100 kHz) and a high frequency band (100 kHz-300 GHz) guidelines which investigate the biological and potential health hazard effects of electric, magnetic and electromagnetic fields. In this study, measurements of low frequency electric and magnetic fields were taken in 30 different locations in the city center of Diyarbakir. Some locations exceeding the reference levels for general public exposure specified by ICNIRP were determined in the measurements of low frequency electric and magnetic fields and then some assessments were made about them. Low frequency electric and magnetic field meter device which is named EHP- 50C was used in the measurements. The measurement results were calculated as an average value of 6 minute measurements. In addition, under a high voltage power line during 60 minutes, electric and magnetic field intensity values were recorded in the same manner. As a result of recordings, changes in the electric and magnetic field intensity values were observed, and then these changes were shown on the charts. [ABSTRACT FROM AUTHOR]

Exploration of the Red Planet is essential on the way through both human colonization and establishing a habitat on the planet. Due to the high costs of space missions, the use of distributed sensor networks has been investigated to make in situ explorations affordable. Along with this, the devices with ultralow-power receivers, which are called zero-energy (ZE) devices, can pave the way to further discoveries for the environment of Mars. This article focuses on wireless power transmission to provide the power required by ZE devices on the Martian surface. The main motivation of this study is to investigate whether conventional harvesters and communication units can supply the required power for a long distance. The numerical results show that it is possible to deliver power to ZE devices without utilizing any sophisticated hardware. In addition, the effects of pointing error and dust storms on harvesting performance are investigated. Comprehensive simulation results reveal that harvester selection and design should be done by considering propagation channel and transmitter characteristics. [ABSTRACT FROM AUTHOR]