arXiv subjects

Eiichi Shoji

Publications and source records attributed to Eiichi Shoji.

3 recordsLinked to original sources

arXiv2026

Disaster Information Reachability of Medium-Wave AM Broadcasting as a Wide-Area Disaster Information Infrastructure: Lessons from the 2024 Noto Peninsula Earthquake

The 2024 Noto Peninsula Earthquake caused widespread power outages, communication failures, and road disruptions, and a tsunami warning was issued immediately after the earthquake, highlighting the importance of reliable disaster information transmission. The Noto Peninsula is surrounded by the sea on three sides and has limited transportation networks, making community isolation and securing reliable information transmission critical challenges. This study defines "Disaster Information Reachability" as the capacity to deliver necessary information to those who need it when they need it, and examines the role of medium-wave AM broadcasting from this perspective. In September 2024, the author conducted a mobile reception survey from Kanazawa to Suzu City and a fixed-point reception survey in Suzu City using commercially available radio receivers and passive radio receivers, including HOOPRA. Medium-wave stations in Niigata, Toyama, Akita, and Tokyo were clearly received, although the local NHK Kanazawa stations were affected by noise. The nationwide high-power NHK Radio 2 network, which was still operational at the time, was confirmed to provide a wide-area, multidirectional reception pathway through maritime propagation, demonstrating its critical significance as a redundant disaster information infrastructure. The fact that FM relay station damage was documented in subsequent policy materials, while medium-wave AM broadcasting received no explicit attention, suggests that its disaster information reachability remains insufficiently recognized. Medium-wave AM broadcasting, with its wide-area simultaneous broadcast capability, high-power coverage, and maritime propagation characteristics, functions effectively as a disaster information infrastructure in peninsular regions and warrants reassessment in preparation for large-scale disasters such as a Nankai Trough megaquake.

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arXiv2026

Subsurface Propagation Characteristics of Medium-Wave Electromagnetic Fields Revealed by Measurements in the Nanatsuo-guchi Quarry: Conceptual Framework of the Subground Wave and the Rainfall Model

This paper presents field observations of medium-wave (MW; 300 kHz-3 MHz) radio signals propagating in the subsurface rock environment of the Nanatsuo-guchi quarry, an underground Shakudani Ishi excavation site on Mt. Asuwayama in Fukui City, Japan. MW broadcast signals from a nearby local station (JOFG, 927 kHz, 5 kW), received mainly as a surface wave, and from a distant station (JOAB, 693 kHz, 500 kW), received via ionospheric reflection, were successfully received deep inside the quarry, whereas very-high-frequency frequency-modulated (FM) broadcast signals attenuated rapidly and became undetectable near the entrance. This contrasting behavior highlights the strong wavelength dependence of electromagnetic-wave propagation in subsurface environments. Two-axis rotation measurements were performed using loop antennas to analyze the arrival direction and angular dependence of the received signals. In addition to the horizontal magnetic field component (Hx), dominant near the ground surface, a vertical magnetic field component (Hz) was consistently observed inside the quarry. The relative contribution of Hz increased with depth and was accompanied by systematic variations in the apparent arrival direction. Inclination measurements further revealed a characteristic minimum in reception sensitivity near 40-50 degrees, suggesting a composite magnetic field structure involving both Hx and Hz. These observations cannot be fully explained by conventional surface-wave propagation models based on the Zenneck-Sommerfeld formulation, and instead suggest the formation of a characteristic electromagnetic field structure under subsurface boundary conditions. This study provides experimental evidence for previously unreported MW field behavior in underground spaces and offers new perspectives for subsurface communication and disaster-resilient information systems.

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arXiv2023

Significance of Medium-Wave AM Radio Broadcasting for Enhanced Disaster Resilience in Japan: A Case Study in the Kanto Region and Fukui using Nonpowered HOOPRA

On the occasion of centenary anniversary of the Great Kanto Earthquake and commencement of radio broadcasting in Japan, this study reiterates the paramount importance of medium-wave (MW) AM broadcasting in safeguarding public safety and security. Utilizing the electromagnetic principles of MW, the author has earlier developed hoop-shaped radio (HOOPRA), which is a battery-free sustainable radio receiver. This study aims to determine the maximum achievable reception distance with HOOPRA for broadcasts from public stations, such as Nihon Hoso Kyokai (NHK) JOFG (927 kHz, 5 kW) in Fukui, and NHK JOAK (594 kHz, 300 kW), and JOAB (693 kHz, 500 kW), in the Kanto region. The significance of the findings in this study is that approximately 38 million individuals in the Kanto region, residing within an 80 km radius of JOAK or JOAB, can access broadcasts using only the energy of radio waves with HOOPRA. Additionally, ~0.4 million people in Fukui, within a 15 km radius of JOFG, can potentially be recipients of the broadcast. Given that most transmitting stations operate at 5 kW nationwide, HOOPRA can be effectively utilized within a 15 km radius of each station. Moreover, these outcomes validate the efficacy of HOOPRA as a radio receiver and provide valuable insights into the global potential applicability of MW AM radios. Furthermore, the current investigation underscores the need to reevaluate the significance of terrestrial MW broadcasting as a vital source of emergency information, especially in the event of anticipated natural disasters, such as the predicted Nankai Trough Earthquake.

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