This study investigates 10-kHz underwater electromagnetic communication using a half-sheath dipole antenna (HSDA) and evaluates propagation characteristics through electromagnetic field simulations. We examine the effects of the transmitting antenna orientation and a metallic air tank placed near the transmitter on communication performance. The results reveal that the propagation characteristics strongly depend on the antenna orientation, and that the reception performance improves when the air tank is arranged to act as a reflector.

Undersea communication is one of the key technologies of emerging sixth-generation (6G) mobile networks. Due to the strong propagation attenuation in undersea, low-frequency operation around 1 MHz is preferred for achieving practical communication distance. This paper will demonstrate the fabrication of normalmode helical antenna, NMHA working at $\text{1MHz}$ in seawater condition. Firstly, using the electromagnetic simulator FEKO, NMHA is simulated in a distilled water environment to achieve resonant point at 1 MHz, followed by simulating in seawater condition at 1 MHz. From the simulation, the efficiency gain of distilled water condition and seawater condition is obtained which are −9.26 dBi and −21.49 dBi. Secondly, the fabrication process is started based on the simulation model. Thirdly, the measurement process conducted and obtain impedance of $23.42 {\Omega}$ at 1 MHz.

Bedsores are irreversible tissue injuries caused by reduced blood flow in soft tissues due to localized pressure. Early intervention can shorten the treatment period. Therefore, this study aims to achieve non-contact early detection of bedsores using microwaves emitted from an antenna. This study reproduces bedsores on the sacral region of the high-definition human model and conducts analysis using a single-element patch antenna and a 2×2 patch array antenna in the 5.8 GHz band. The results confirm that (i) the peak value decreases as the bedsore moves away from the antenna; and (ii) using the array antenna improves the peak value and expands the detectable range of the bedsore.

The high permittivity and conductivity of the human body significantly affect antenna performance. In this paper, we investigated the radiation characteristics of UHF-band RFID tag antennas placed close to the human body, specifically the head and legs. Simulation results show that by optimizing the antenna length and designing it to resonate at a higher frequency in free space, impedance matching was improved, and gain was achieved even at close distances to the human body. These findings indicate that pre-shifting the resonant frequency was a practical approach for RFID tag antennas operating near the human body.

Undersea communication is a key component of emerging sixth-generation $(6 \mathrm{G})$ mobile networks. Due to the strong propagation attenuation in seawater, lowfrequency operation around 1 MHz is preferred for achieving practical communication distance. However, the large wavelength around 30 meters at 1 MHz, the antenna gain of a wearable antenna will be reduced. In this paper, a normal-mode helical antenna (NMHA) is employed as an efficient antenna. Firstly, self-resonant antenna structure is designed. Secondly, to increase the antenna gain, two elements folded, and three element folded structures are designed. Thirdly, for undersea use, antenna containing capsules is optimized. Then, antenna gain is evaluated through power density calculation. At antenna structure of single, double and triple folded cases, antenna gain of −24.44 dBi, −16.21 dBi, and −10.01 dBi are obtained respectively.

Undersea radio communication is currently being studied at many institutes. To overcome strong propagation attenuation, a low-frequency range around 1 MHz is suitable. Due to the wavelength being approximately 30 meters in seawater, antenna gain is significantly reduced when using wearable antennas. In this paper, a normal-mode helical antenna (NMHA) is proposed. The NMHA is enclosed by a capsule, and by filling with distilled water, improved antenna gain is achieved for underwater use. Antennas with lengths of 33.3 cm and 66.7 cm are designed using electromagnetic simulations. Based on propagation attenuation results, antenna gains of -23.07 dBi (33.3 cm case) and -18.77 dBi (66.7 cm case) are obtained. The power density data were also obtained.

In this paper, we propose a 3D undersea positioning system using VLF electromagnetic waves as a system to support divers’ activities in seawater and show results of a basic study for the proposed system in electromagnetic field simulations. Assuming that a transmitting antenna is attached to a diver, the antenna’s position in seawater is estimated using the Received Signal Strength (RSS [dB]) of multiple receiving antennas placed near the sea surface. To assist in the installation and retrieval of the proposed system, we propose a receiving antenna array that integrates twelve dipole antennas into a single receiver. Furthermore, we also propose a position estimation algorithm optimized for the proposed receiver. In the proposed algorithm, Support Vector Regression (SVR) was utilized to estimate the distance between the transmitting antenna and the receiver from the RSS. We confirmed that position estimation using the receiver was possible within a circle with an approximately 12 m radius centered on the receiver, demonstrating the viability of our proposed system for implementation.

The authors have investigated the feasibility of establishing a undersea electromagnetic communication system for maintenance and inspection of floating offshore wind turbines. Wireless communication in seawater is known to have a serious problem of high attenuation of electromagnetic waves. To solve this difficulty, the authors paid attention to undersea support structures and considered that the lower floating concrete tube could be used as a waveguide to reduce propagation loss. In this paper, using a scale model of the concrete tube, vinyl chloride pipe is immersed in simulated seawater, and the transmission characteristics between dipole antennas placed near the vinyl pipes were measured, confirming that the presence of the dielectric tube reduces the propagation loss between the dipole antennas.

Mobile communication devices have become widely used in various situations in our daily lives. Not only are our opportunities for exposure to radio waves increasing, but the exposure environment is also changing owing to developments in telecommunications technology. Conventional studies on radio wave exposure evaluation have focused on only a single frequency, and only a few studies have considered radio wave exposure at multiple frequencies, including the frequencies used in fifth-generation (5G) mobile communications. In this study, specific absorption rate (SAR) evaluations were conducted assuming the exposure of the human body to radio waves with multiple frequency components. To simulate the actual use of a smartphone, analytical models were created using a smartphone model as the electromagnetic wave source and a numerical human body model as the exposure target. In the case of multiple frequencies, SAR was calculated for each frequency component, and SARs were summed. In addition, by changing the power ratio of each frequency component to the total radiated power, the distribution of SAR and the shift in the peak spatial SAR(10g )(psSAR(10g)) were investigated. As a result, it was confirmed that the SAR distribution changes with the power ratio of each frequency component in the radio wave. In the case of radio waves with multiple frequency components, no specific power ratios were found to cause a significant increase in psSAR(10g).

Many smartphones use multiple frequencies of electromagnetic communication. In addition, smartphones are used in various applications not only for making calls. In this paper, we evaluate multi-frequency electromagnetic exposure in various usage conditions using numerical smart phone models and the numerical human body model.

Bedsores are injuries caused by prolonged pressure on the skin that obstructs blood flow. The more advanced the damage caused by bedsores, the longer the treatment period. In some cases, surgery may also be necessary. Early detection is therefore important. In our research, we are developing a noncontact pressure ulcer detection system using 10.5 GHz electromagnetic waves. In this paper, we propose a method for estimating the distance between the skin and the antenna, and then a method for setting a threshold value that enables the detection of bedsores corresponding to the difference in distances.

A meander line antenna (MLA) is well known for its compact size and efficient performance in terms of antenna efficiency, input resistance, and bandwidth. This study investigates MLA performance in human body environments, focusing on medical devices and wireless implants. Due to their small size, MLAs are ideal for use in biological tissues with complex and lossy properties. The study analyzes MLA behavior in fat and muscle tissues, considering key parameters such as conductivity, radiation efficiency, and self-resonance. Input resistance and Voltage Standing Wave Ratio (VSWR) are examined. The smallest antenna size of (14.9 x 4.1 x 0.1) mm(3) is achieved. Human body phantoms for fat and muscle tissues were successfully formulated and fabricated, with dielectric constants aligning with reference values. A Q factor of approximately 2 was obtained through VSWR characteristics and validated against theoretical calculations, showing a 92% agreement. MLA gains of -30 dBi and -40 dBi were recorded in fat and muscle phantoms, respectively. These findings enhance the understanding of MLA performance in human tissue environments, supporting the development of next-generation implanted technologies for clinical and therapeutic applications.

Bedsores, also known as pressure ulcers, are localized skin and subcutaneous tissue injuries caused by reduced blood flow due to prolonged pressure. Early treatment of bedsores can shorten the duration of treatment. In this study, an antenna is placed between the bed and mattress, and a non-contact microwave method is used to detect bedsores at an early stage. In this paper, we first evaluated the bedsores multi-layer phantom to be used. We performed an analysis using a simple skin model with a single antenna element and experiments using an agar phantom. As a result, we confirmed that the experimental output results were similar to the analysis results, although there were some observation errors. We investigated the area in which bedsores can be detected with one antenna.

Hepatitis E virus (HEV) exists in two distinct forms: a non-enveloped form (neHEV), which is present in feces and bile, and a quasi-enveloped form (eHEV), found in circulating blood and culture supernatants. This study aimed to elucidate the roles of Ras-associated binding 13 (Rab13) and protein kinase A (PKA) in the entry mechanisms of both eHEV and neHEV, utilizing small interfering RNA (siRNA) and chemical inhibitors. The results demonstrated that the entry of both viral forms is dependent on Rab13 and PKA. Further investigation into the involvement of tight junction (TJ) proteins revealed that the targeted knockdown of zonula occludens-1 (ZO-1) significantly impaired the entry of both eHEV and neHEV. In addition, in ZO-1 knockout (KO) cells inoculated with either viral form, HEV RNA levels in culture supernatants did not increase, even up to 16 days post-inoculation. Notably, the absence of ZO-1 did not affect the adsorption efficiency of eHEV or neHEV, nor did it influence HEV RNA replication. In cell-to-cell spread assays, ZO-1 KO cells inoculated with eHEV showed a lack of expression of HEV ORF2 and ORF3 proteins. In contrast, neHEV-infected ZO-1 KO cells showed markedly reduced ORF2 and ORF3 protein expression within virus-infected foci, compared to non-targeting knockout (NC KO) cells. These findings underscore the crucial role of ZO-1 in facilitating eHEV entry and mediating the cell-to-cell spread of neHEV in infected cells.

The melting of sea ice due to global warming poses an environmental challenge. Sea ice is one of the critical elements make up the global environment. Therefore, understanding the thickness of sea ice indicates the progress of global warming. However, existing measurement methods are large-scale and irregular in measurement accuracy. In this study, we examined a method for measuring sea ice thickness, a small-scale and highly accurate measurement technique. In addition, we reexamined the relative permittivity of sea ice and analyzed countermeasures against sea ice melting around the contact area due to heat radiated from antennas installed on sea ice.

The proportion of persons over 65 years old is projected to increase worldwide between 2022 and 2050. The increasing burden on medical staff and the shortage of human resources are growing problems. Bedsores are injuries caused by prolonged pressure on the skin and stagnation of blood flow. The more the damage caused by bedsores progresses, the longer the treatment period becomes. Moreover, patients require surgery in some serious cases. Therefore, early detection is essential. In our research, we are developing a non-contact bedsore detection system using electromagnetic waves at 10.5GHz. In this paper, we extracted appropriate information from a scalogram and utilized it to detect the sizes of bedsores. In addition, experiments using a phantom were conducted to confirm the basic operation of the bedsore detection system. As a result, using the approximate curves and lines obtained from prior analysis data, it was possible to estimate the volume of each defected area, as well as combinations of the depth of the defected area and the length of the defected area. Moreover, the experiments showed that it was possible to detect bedsore presence and estimate their sizes, although the detection results had slight variations.

Utilizing the existing foundation of a floating wind power turbine in the ocean as the channel for radio wave communication from underwater to air is studied. It is demonstrated that the foundation can be a low-loss transmission line for radio propagation in the sea. Additionally, on the opposite side of the excitation source, fields decrease more slowly in the radial direction.

Meander Line Antenna (MLA) is widely employed in compact electronic devices, such as cellular phones and WLAN terminals, owing to its electrically small size. To facilitate practical antenna design, essential equations encompassing self-resonant structure, input resistance, antenna efficiency, and Q factor have been systematically developed. However, the prior self-resonant equations included only inductive reactance (XC), neglecting the capacitive reactance (XD) equation. This manuscript addresses this gap by introducing new design equations, presenting a newly derived XD equation and an improved Q factor expression. The inadequacies of the existing Q factor equation, reliant on the radius of a sphere encompassing the antenna, are addressed by proposing a more fitting expression that incorporates antenna structural parameters using the ratio of reactance to resistance. The overview of existing design equations sets the stage for the introduction of these newly developed equations. To assess the accuracy of electromagnetic (EM) simulation results, a comparative analysis is conducted between simulated and theoretically calculated input resistance values. The derivation of new reactance equations involves the development of XC equations based on electromagnetic theory. The XD equation is established by deriving the stored charge equation from electrical near-field distributions obtained through EM simulations. By applying the relationship between charge and capacitance, a new XD equation is obtained. Subsequently, a new self-resonant equation is derived, and the validity of the newly derived equations is confirmed through EM simulation results, ensuring their accuracy. Two MLA prototypes, with lengths of 0.05 and 0.1 wavelengths at 405 MHz, are fabricated and experimentally validated. Smith chart measurements confirm the self-resonant condition and input resistance. By correlating with the VSWR characteristics, the obtained Q factor of approximately 100 aligns successfully with the results from the reactance equation. The antenna gain is verified at -7.7 dBi and -3.5 dBi for antennas with lengths of 0.05 and 0.1 wavelengths, respectively. These findings establish the practical applicability of the proposed equations for antenna design and elucidate the performance of practical antennas.

We propose a novel method based on an inverse problem to design a single channel radio frequency (RF) receive coil for magnetic resonance imaging (MRI) with an optimized signal-to-noise ratio (SNR) for imaging the rat kidney. We identified a dedicated curved-surface coil design for use on the rat body surface utilizing inverse problem analysis using direct current calculation and quantitatively evaluated the indicators of coil performance using alternating current calculation. The proposed coil achieved increased SNR and signal intensity responses that were respectively 1.05- and 2-fold higher than those of conventional surface coils. In the future, we will fabricate a prototype coil and perform the MRI of the rat kidney to diagnose kidney diseases.

Acute hepatitis E was considered rare until reports emerged affirming the existence of hepatitis E virus (HEV) genotypes 3 and 4 infections in Japan in the early 2000s. Extensive studies by Japanese researchers have highlighted the pivotal role of pigs and wild animals, such as wild boars and deer, as reservoirs for HEV, linking them to zoonotic infections in Japan. Currently, when hepatitis occurs subsequent to the consumption of undercooked or grilled pork, wild boar meat, or offal (including pig liver and intestines), HEV infection should be considered. Following the approval of anti-HEV immunoglobulin A antibody as a diagnostic tool for hepatitis E by Japan's Health Insurance System in 2011, the annual number of diagnosed cases of HEV infection has surged. Notably, the occurrence of post-transfusion hepatitis E promoted nationwide screening of blood products for HEV using nucleic acid amplification tests since 2020. Furthermore, chronic hepatitis E has been observed in immunosuppressed individuals. Considering the significance of hepatitis E, heightened preventive measures are essential. The Japan Agency for Medical Research and Development Hepatitis A and E viruses (HAV and HEV) Study Group, which includes special virologists and hepatologists, held a virtual meeting on February 17, 2024. Discussions encompassed pathogenesis, transmission routes, diagnosis, complications, severity factors, and ongoing and prospective vaccination or treatments for hepatitis E. Rigorous assessment of referenced studies culminated in the formulation of recommendations, which are detailed within this review. This comprehensive review presents recent advancements in HEV research and Japanese clinical practice guidelines for HEV infection.