Showing papers by "Teruo Onishi published in 2022"
TL;DR: In this article , two approximate approaches, namely the array-theory approach and the equivalent-current approach, are investigated for radio frequency electromagnetic field compliance assessments of smart surfaces with different beams, sizes, and shapes.
Abstract: Smart surfaces as one of the promising enabling technologies for sixth-generation wireless communications (6G) are paving their way. In this article, aiming at radio frequency electromagnetic field compliance assessments of them, two approximate approaches, namely the array-theory approach and the equivalent-current approach, are investigated. Smart surfaces with different beams, sizes, and shapes are designed, assessed, and analyzed. The results are compared with those of a reference approach, which is based on full-wave simulations, in terms of assessment accuracy. On one hand, both the approximate approaches provide significant improvement in assessment time, which is quite useful for compliance assessments in exposure scenarios with large numbers of possible beam states. On the other hand, it is found that the assessment accuracy for the two approximate approaches depends intrinsically on system configurations. Specifically, for a circle-shaped smart surface with a diameter equaling 21 times of the element periodicity, except for extreme situations where scanning angle is far from broadside, overestimated front compliance distances with relative errors no more than 30% and 24% are obtained for the array-theory approach and the equivalent-current approach, respectively.
1 citations
TL;DR: In this paper , the authors used a personal exposure meter (ExpoM-RF) to measure the exposure of children to radiofrequency electromagnetic fields (RF-EMF) in the 700 MHz-5.8 GHz frequency range.
Abstract: The opportunities for exposure to radiofrequency electromagnetic fields (RF-EMF) among children are increasing. Children's exposure to RF-EMF in Japan was recorded using a personal exposure meter (ExpoM-RF), and factors associated with the exposure examined. A total of 101 children, aged 10-15 years old, participated in the prospective birth cohort "Hokkaido study". RF-EMF data were recorded in the 700 MHz-5.8 GHz frequency range for 3 days. The recorded data were summarized into six groups of frequency bands: downlink from mobile phone base stations (DL), uplink from mobile phones to a base station (UL), Wireless Local Area Network (LAN), terrestrial digital TV broadcasting (digital TV), 2.5 GHz and 3.5 GHz Time Division Duplex (TDD), 1.9 GHz TDD, and total (the summation of power density in all measured frequency bands). A questionnaire was used to document the internet environment (at home) and mobile phone usage. Personal RF-EMF exposure in Japanese children was lower than that reported in studies in Europe. The DL signals from mobile phone base stations were the most significant contributors to total exposure, while Wireless LAN and digital TV were only higher at home. The urban residence was consistently associated with increases in the four groups of frequency bands (DL, UL, digital TV, and TDD). TDD level has several associations with mobile phone usage (calls using mobile phones, video viewing, text message service, and online game). The association between inattention/hyperactivity subscale of the Strengths and Difficulties Questionnaire (SDQ) and higher Wireless LAN exposure at nighttime was also noted. Further studies with additional data will shed light on factors involved in RF-EMF exposure among Japanese children.