A Reduction Method of Phantom Shell Effects for APD Extraction Using Negative Permittivity Material

This paper proposes a method to reduce phantom shell effects that occur during the absorbed power density (APD) derivation using a negative permittivity material (NPM). In this study, APD is examined as a primary parameter to assess the effectiveness of the proposed method, especially following the introduction of APD above 6 GHz, in accordance with 2020 ICNIRP guidelines. As the frequency increases, the impact of the phantom shell can affect APD measurement results. To investigate this, a dipole antenna operating in the 6~10 GHz frequency range was used as the radiation source. Therefore, this study proposes a method to reduce effects by using NPM. The selection of the NPM is achieved through input impedance calculations method. Simulation results indicate that before applying the proposed method, the APD difference between the presence and absence of the phantom shell ranged from 20.6% at 6 GHz (W/ shell = 100, W/o shell = 82.9 W/m²) to 69.3% at 10 GHz (W/ shell= 52.3, W/o shell= 30.9 W/m²). After applying the method, these differences reduced to 6.9% at 6 GHz (proposed method= 77.2, W/o shell= 82.9 W/m²) and 13.5% at 10 GHz (proposed method= 35.1, W/o shell= 30.9 W/m²). This study is the first to highlight the impact of phantom shell effects on APD, revealing potential overestimations in the 6-10 GHz range and suggesting that these effects may worsen at higher frequencies. The proposed method effectively addresses these issues within current standards while providing insights for future standards development in higher frequency bands.