Since the spread of the wearable systems and the implementation of the forthcoming 5G in many devices, the question about the assessment of the exposure in wearable typical usage to millimeter waves is crucial and timely. For such frequencies, the power absorption becomes strongly superficial and involves only the most superficial tissue of the human body, i.e., the skin. In literature there are some models able to describe the layered structure of the skin but, until now, there is no literature consensus on the skin model to employ in computational exposure assessment studies. For these reasons, the present work aimed to simulate four different models of the most superficial tissues with different degree of detail exposed to two wearable patch antennas at different frequencies i.e., 28 GHz and 39 GHz. This allows to investigate the impact that the choice of a layered model rather than the homogeneous one has on the exposure. Simulations were performed through the FDTD method, implemented in the Sim4life platform and the exposure was assessed with the absorbed power density averaged over 1 cm2 and 4 cm2 (Sab). The data showed that the homogeneous model underestimates the peak value of Sab obtained for multi-layer models in the stratum corneum (by 14% to 21% depending on the number of layers of the model and the frequency). This finding was confirmed by an analytical approach with two impinging plane wave TEM-polarized with normal incidence at 28 GHz and 39 GHz respectively. Conversely, there are no substantial differences in the exposure levels between the layered models

翻译：自可穿戴系统的普及以及即将到来的5G技术在众多设备中的部署以来，评估可穿戴典型使用场景下毫米波频段的暴露问题变得至关重要且具有时效性。在此频段，功率吸收呈现强烈的表面性，仅涉及人体最表浅的组织，即皮肤。文献中存在一些能够描述皮肤分层结构的模型，但迄今为止，关于计算暴露评估研究中应采用何种皮肤模型尚未达成共识。基于此，本研究模拟了四种不同细节程度的最表浅组织模型，这些模型暴露于两个不同频率（即28 GHz和39 GHz）的可穿戴贴片天线中。这有助于探究选择分层模型而非均匀模型对暴露评估结果的影响。模拟通过Sim4life平台中实现的FDTD方法进行，暴露评估采用1 cm²和4 cm²平均吸收功率密度（Sab）。数据显示，均匀模型低估了多层模型中角质层Sab的峰值（根据模型层数和频率的不同，低估幅度为14%至21%）。该发现通过解析方法得到证实：分别采用28 GHz和39 GHz法向入射的TEM极化平面波。相反，不同分层模型之间的暴露水平没有显著差异。