This study investigates the maximum achievable received power for an implantable receiver deeply implanted in the human body, considering both electric dipole and magnetic loop sources with millimeter-scale dimensions. The analysis incorporates safety constraints related to the specific absorption rate. A full-wave simulation approach is employed for the case study. The results demonstrate that the proposed method can be applied to high-frequency simulations, where a received power of 0.16 W is achievable at 1.3 GHz under SAR consideration.