A wireless electric field sensor for measuring an electrical potential treatment chair is proposed. Research on the treatment effects of the electric field generated by high-voltage (HV) electrodes at low frequencies, in this case, 50 or 60 Hz, has been conducted. However, most studies have only provided the value of the voltage applied to the HV electrodes, not the electric field generated by those. Therefore, it is necessary to provide the value of the electric field to verify the treatment effects. Because the electric field by the chair is too high to be measured by conventional sensors, it is necessary to develop a sensor that can adaptively measure the low and high electric field. The proposed sensor has an adaptive voltage gain that relies on digital potentiometers, which exert control for the proper gain depending on the field strength. Using a capacitive dipole probe, the electric field generated by the HV electrodes applied the voltage of 7.2 kV at 60 Hz was measured at diverse distances. It was found that the electric field was measured from 1.3 to 45.5 kV/m. For wireless notification, the sensor is equipped with a Wi-Fi module in a microcontroller unit.

This paper presents a curved-retrodirective beamforming system for improving microwave power transmission efficiency in the Fresnel region. Since microwave power transmission in the far-field region has very low efficiency, studies on the Fresnel region are being actively conducted. In these studies, a retrodirective beamforming (RDB) technique is popular. The RDB system with a sub-array structure was a realistic structure that reduced system complexity. However, the transmission efficiency is lowered because the beamwidth of the transmitter antenna element is narrow. To solve this problem, this paper proposes a curved-retrodirective beamforming system that can focus the microwave power on the receiver. The proposed system uses the peak gain of the transmitter antenna element by using tilted beams to improve transmission efficiency. The system design method that can maximize the transmission efficiency is also presented depending on the given conditions such as transmission distance, characteristics of the transmitter and receiver antenna. The simulation showed a reduction in power leakage compared to the conventional system. The fabrication and measurement validated the efficiency improvement of the proposed system for IoT devices in the Fresnel region.

Distance-based impedance matching networks for a tunable high frequency (HF) system are presented in this paper for the improved performance. The transmitting antenna for a HF system with an operating frequency of 13.56 MHz consists of a two-turn loop and three channel impedance matching networks corresponding to the distance of the receiving antenna. Each impedance matching network maximizes the system performance such as uniform power efficiency and reading range at specific distance between a transmitting and a receiving antenna. By controlling the distance-based matching networks, the power efficiency of the proposed antenna improves by up to 89% compared to the conventional antenna system with the fixed matching (FM) condition for distances, and the reliable reading range according to the impedance matching conditions is also increased. The proposed technique is applicable for near field communication (NFC), radio frequency identification (RFID), or wireless power transfer (WPT) devices.

Due to the convenience of using electronic devices, contactless energy transfer (CET) systems have garnered interest in various fields of industry. In this paper, a new design approach that uses antiparallel resonant loops for CET systems is presented. Forward and reverse loops forming an antiparallel resonant structure stabilize the transfer efficiency and therefore prevent it from dramatic distance-related changes, a phenomenon that can occur in CET systems with nonradiative methods (or resonant methods). This paper proposes frequency-insensitive antiparallel resonant loops and the optimal design of these loops for uniform transfer efficiency according to the distance. The proposed technique achieves frequency variation that is one-sixth that of conventional unidirectional loops, thus improving the power efficiency to a maximum of 87%. The improved performance of data transmissions for near-field communication is also verified.

A wireless electric field sensor for measuring an electrical potential treatment chair is proposed. Research on the treatment effects of the electric field generated by high-voltage (HV) electrodes at low frequencies, in this case, 50 or 60 Hz, has been conducted. However, most studies have only provided the value of the voltage applied to the HV electrodes, not the electric field generated by those. Therefore, it is necessary to provide the value of the electric field to verify the treatment effects. Because the electric field by the chair is too high to be measured by conventional sensors, it is necessary to develop a sensor that can adaptively measure the low and high electric field. The proposed sensor has an adaptive voltage gain that relies on digital potentiometers, which exert control for the proper gain depending on the field strength. Using a capacitive dipole probe, the electric field generated by the HV electrodes applied the voltage of 7.2 kV at 60 Hz was measured at diverse distances. It was found that the electric field was measured from 1.3 to 45.5 kV/m. For wireless notification, the sensor is equipped with a Wi-Fi module in a microcontroller unit.

This paper presents a curved-retrodirective beamforming system for improving microwave power transmission efficiency in the Fresnel region. Since microwave power transmission in the far-field region has very low efficiency, studies on the Fresnel region are being actively conducted. In these studies, a retrodirective beamforming (RDB) technique is popular. The RDB system with a sub-array structure was a realistic structure that reduced system complexity. However, the transmission efficiency is lowered because the beamwidth of the transmitter antenna element is narrow. To solve this problem, this paper proposes a curved-retrodirective beamforming system that can focus the microwave power on the receiver. The proposed system uses the peak gain of the transmitter antenna element by using tilted beams to improve transmission efficiency. The system design method that can maximize the transmission efficiency is also presented depending on the given conditions such as transmission distance, characteristics of the transmitter and receiver antenna. The simulation showed a reduction in power leakage compared to the conventional system. The fabrication and measurement validated the efficiency improvement of the proposed system for IoT devices in the Fresnel region.

Distance-based impedance matching networks for a tunable high frequency (HF) system are presented in this paper for the improved performance. The transmitting antenna for a HF system with an operating frequency of 13.56 MHz consists of a two-turn loop and three channel impedance matching networks corresponding to the distance of the receiving antenna. Each impedance matching network maximizes the system performance such as uniform power efficiency and reading range at specific distance between a transmitting and a receiving antenna. By controlling the distance-based matching networks, the power efficiency of the proposed antenna improves by up to 89% compared to the conventional antenna system with the fixed matching (FM) condition for distances, and the reliable reading range according to the impedance matching conditions is also increased. The proposed technique is applicable for near field communication (NFC), radio frequency identification (RFID), or wireless power transfer (WPT) devices.

Due to the convenience of using electronic devices, contactless energy transfer (CET) systems have garnered interest in various fields of industry. In this paper, a new design approach that uses antiparallel resonant loops for CET systems is presented. Forward and reverse loops forming an antiparallel resonant structure stabilize the transfer efficiency and therefore prevent it from dramatic distance-related changes, a phenomenon that can occur in CET systems with nonradiative methods (or resonant methods). This paper proposes frequency-insensitive antiparallel resonant loops and the optimal design of these loops for uniform transfer efficiency according to the distance. The proposed technique achieves frequency variation that is one-sixth that of conventional unidirectional loops, thus improving the power efficiency to a maximum of 87%. The improved performance of data transmissions for near-field communication is also verified.

Abstract Blue‐light‐emitting polymer (polyfluorene)/dielectric nanolayer nanocomposites were prepared by the solution intercalation method and employed in an electroluminescent (EL) device. Their photoluminescence (PL) and electroluminescence characteristics demonstrates that the interruption of interchain interaction in intercalated organic/inorganic hybrid systems reduces the low‐energy emission that results from keto‐defects. By reducing the probability that the excitons initially generated on the polyfluorenes will find keto‐defects, both the color purity and the luminescence stability were improved. Furthermore, the dielectric nanolayers have an aspect ratio of about five hundred, and therefore act as efficient exciton blocking layers and barriers to oxygen diffusion, producing a dramatic increase in the device stability. A nanocomposite device with a Li:Al alloy cathode gave a quantum efficiency of 1.0 %(ph/el), which corresponds to an approximate five times enhancement compared to the neat polymer device. The nanocomposite emitting layer is considered to have a pseudo‐multiple quantum well structure.

This paper presents a safe sensing scheme and radio frequency energy harvesting system (RFEHS) to monitor rail conditions for autonomous trains. Conventional sensing schemes expose trains on railroads to danger because trains must pass the rail to know its condition. The proposed sensing scheme gets rid of the danger and reduces the complexity of sensing processes and train systems because trains do not have to communicate directly with sensors. In this sensing scheme, the RFEHS receives dual polarization (DP) signal, which is all of the base station's polarizations so that the sensor operation gets more frequent. The harvesting capability of DP and linear polarization (LP) from a real base station is compared. To prove the feasibility of the proposed sensing scheme, the RF energy harvesting was conducted from a base station on the rail track. As a result, rail temperature data were obtained using DP-RFEHS in the proposed sensing scheme, which has low-complexity and is a safer solution for autonomous trains.

This paper presents a phase-offset adjustment method for sidelobe suppression in co-frequency multi-beam systems. The proposed method addresses the issue of minor lobe superposition, which arises when multiple co-frequency beams are radiated simultaneously, leading to increased sidelobe levels and degraded communication performance. By optimizing the phase offsets of each beam, the proposed technique effectively minimizes the vector sum of array factors in the sidelobe region without requiring additional hardware for amplitude control. Theoretical analysis explains the underlying principle and the algorithm used to adjust phase offsets, ensuring effective suppression of sidelobes. Experimental results obtained from an implemented S-band fully-connected multi-beam system validate the effectiveness of the proposed method, showing a significant reduction in sidelobe levels compared to conventional amplitude-only tapering techniques.

This communication proposes a method for rapid in-field estimation of the 3-D array factor (AF) of active phased array antennas (APAAs). The proposed system integrates a coupling probe into each antenna element and employs an equally-distributed combiner and electronic phase sweeping to reconstruct the in-field array factor (IAF) across hemispherical space without requiring far-field conditions or mechanical rotation. A mathematical model is developed to analyze the relationship between the AF and the IAF, including the impact of mutual coupling. To validate the proposed concept, an X-band 8 × 4 APAA is designed and implemented with the coupling probe structure. Simulations confirm that the IAF closely follows the AF behavior in both ideal and beam-shaped conditions, with correlation coefficients exceeding 0.86. In experiments conducted at 8.15 GHz, the measured IAF captures the mainlobe shape, sidelobe suppression, and beam distortions under various scenarios. Correlation values between IAFs and conventionally measured array patterns (APs) were found to be greater than 0.87 in all cases. These results demonstrate that the proposed method provides a compact and scalable solution for monitoring the APAA’s performance.

This paper presents a coverage estimation considering human body shadowing in a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$6.4 \times 6.4 \mathrm{m}$</tex> indoor environment using a fabricated 5 G mmWave phased array antenna. The measurements were conducted using an electrically steerable Tx <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$8 \times 8$</tex> phased array antenna positioned on the wall and ceiling, similar to a mmWave repeater, and a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Rx} 4 \times 4$</tex> array antenna with a beamwidth similar to that of the user's device. To evaluate communication performance, the Error Vector Magnitude (EVM) of 16-QAM modulation was measured when a human was positioned in the line-of-sight (LOS) path between the transmitter and receiver. Coverage estimation results indicate that, in the absence of human body shadowing, a wall-mounted Tx phased array antenna with a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pm 65^{\circ}$</tex> beam steering range provides broader coverage. However, when human body shadowing is considered, a ceiling-mounted Tx phased array antenna offers broader coverage. These results can be utilized in research for identifying and improving shadow areas in mmWave indoor environments.