Radio-frequency (RF) signal transmission is highly susceptible to environmental factors such as the properties of materials. This paper presents an analysis of an ultra-high frequency (UHF) radio-frequency identification (RFID) system under various conditions, primarily focusing on signal quality in the presence of different materials and fluid levels. Multiple scenarios are analyzed using Ansys High Frequency Structure Simulator (HFSS) software, which utilizes the finite element method (FEM) for analysis. Scattering parameters (S-parameters) are key metrics to assess RF signal quality. The study shows that RF signal absorption is significantly influenced by the relative position of RFID tags to the water level, and the amount of water further aggravates signal attenuation. Furthermore, there is a clear trend of scattering parameter minimum shifting as the water level arises. Additionally, signal absorption is also affected by the container material, both PVC plastic and aluminum containers are analyzed in this paper. The results show that metal materials effectively reduce RF signal attenuation caused by water inside containers. This study offers valuable insights for improving RFID system performance in smart refrigerators and other complex environments.

Smartphone can be used to operate IoT devices and access services such as smartphone game, but prolonged use cause gaming disorder. Gaming disorder was published as an international disease in 2022 by World Health Organization (WHO). Gaming disorder is a symptom of an inability to control the amount of time spent playing games daily. In recent years, the number of patients with gaming disorder has been increasing and there are not enough hospitals to treat them, so it is necessary to cure gaming disorder by oneself without visiting hospitals. Therefore, it is necessary to understand the stress that users are under while playing games, and to provide remedial measures such as encouraging rest within a reasonable range. Since this paper is an initial study, stress evaluation of users during smartphone game playing. To evaluate the stress using biometric information, we obtain temporal changes in radio wave intensity by reflecting radio waveform in the 2.4 GHz band to the chest, and pulse wave and respiration waveforms by signal processing, from which 17 parameters that are attributable to stress. From the one-month smartphone usage logs, 16 subjects with short average game time per month and 18 subjects with long average game time per month are extracted. Since it can be assumed that the stress state during game play differs between the groups with short and long average game time, comparison of the difference in variation during game play using stress-induced parameters and binary classification using machine learning to evaluate the user's stress state. Since this method uses two antennas in the 2.4GHz band, it will be possible to measure stress using smartphones in the future, contributing to the understanding of stress that is likely to be held unconsciously.

With increased sophistication, robots tend to become bigger and heavier as it requires greater processing power and complexity. However, the increase in size and weight of robots can reduce efficiency and mechanical flexibility. Therefore, the removal of wires inside robots is proposed to reduce them. Signals are to be wirelessly propagated via waveguide structures fitted inside the robotic structure. In this paper, we discuss an improved waveguide model to fit inside a robotic leg structure and bending via the incorporation of a rotary joint is also investigated electromagnetically. For comparison, both rectangular and circular waveguide models are designed. In conclusion, it is found that the rectangular waveguide model is optimal for the proposed system, which operates between 2.83 GHz to 3.76 GHz.

This study proposes a salvage transmission (ST) scheme for 5G networks using device-to-device (D2D) communication. In mobile networks, communication is disabled when issues emerge in the core network or base station of the operator. To address this problem, the proposed scheme provides mobile communication services via D2D communication to user equipment (UE) that cannot use cellular networks. The users of an operator that is unable to provide service due to communication failure transmit signal using D2D communication with the closest UE of another operator. This ST scheme enables the mitigation of communication failures. In addition, this study introduced the basic protocols of ST with Wi-Fi Direct (IEEE 802.11) and 5G networks. Furthermore, we verified the effectiveness of the ST scheme in the case of communication failures via a simulation study.

In modern robotics, one of the topics is to remove or reduce the cables inside the robot, which can improve flexibility, decrease the maintain demand, and make the robot easier to build up. Therefore, wireless communication would provide a solution that can replace these cables for the above issue. In this paper, we propose a hybrid Medium Access Control (MAC) scheme for different wireless sensors communication based on our previous work, the Orthogonal Frequency subcarrier-based Multiple Access (OFSMA) scheme. For general sensors, we use the OFSMA scheme to ensure URLLC standards. As for audio sensors and video sensors. There are many spaces inside the robot structure. We set a goal to transmit the signal directly through these small spaces as an internal waveguide to achieve wireless communication. Therefore, we design a model to simulate the realistic situation of robots using High-Frequency Simulation Software (HFSS) and find out the possibility of signal propagation directly through the robot.

Wireless power transmission via radio frequency (RF) attracts attention as a power source for small devices such as wireless sensor networks (WSN). Among these, the method using RF waves have the advantage that power can be transmitted over long distances about several meters. Because RF waves can transmit power from a single power supply over a wide area simultaneously. RF can also drive a wireless sensor network semi-permanently. However, simply transmitting radio waves will cause problems such as interference and reflection, then it will reduce efficiency. In this paper, we propose an efficient wireless power transmission scheme by controlling the phase using an all-pass filter (APF). APF is a filter that acts only on the phase of the signal and realizes interference mitigation by controlling the phase difference. Experimental results show that the application of APF to wireless power transfer increased the voltage across WSN devices.

This paper proposes a self-optimizing based energy-efficient scheme with a dynamic coverage expansion of femtocells in the macro-femto two-tier networks. High SINR and low power consumption can be benefited by coordinating downlink cross-tier interference and intra-interference with a neuron control based adaptive power adjustment when sleep mode is involved in the macro base station (MBS). Moreover, by allowing open access in the hybrid femtocells, more near-indoor macro user equipments (MUEs), especially located around the edge of the macrocell can be served by indoor femto access point (FAP), which results in MBS having more of a probability to maintain sleep mode when the traffic is low. Many related performances are evaluated with a comparison of utility-based power control (UBPC) scheme, the energy impact of both MBS and FAP can be largely improved with optimal transmit power, which means the sleep mode technology can be enhanced, as shown in the simulation.

This paper proposes a method for obtaining surface orientations of transparent objects using polarization in highlight. Since the highlight, the specular component of reflection light from objects, is observed only near the specular direction, it appears merely on limited parts on an object surface. In order to obtain orientations of a whole object surface, we employ a spherical extended light source. This paper reports its experimental apparatus, a shape recovery algorithm, and its performance evaluation.