Radio Frequency Electromagnetic Field Exposure Compliance Assessments of Smart Surfaces: Two Approximate Approaches

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.