BACKGROUND:　Implantable　medical　sensors　for　monitoring　and　transmitting　physiological　signals　like　blood　glucose,　blood　oxygen,　electrocardiogram,　and　endoscopic　video　present　a　new　way　for　health　care　and　disease　prevention.　Nevertheless,　the　signals　transmitted　by　implantable　sensors　undergo　significant　attenuation　as　they　propagate　through　various　biological　tissue　layers.　OBJECTIVE:　This　paper　mainly　aims　to　investigate　the　power　loss　of　an　out-to-in　body　wireless　radio　frequency　link　at　2.45　GHz.　METHODS:　Two　simulation　models　including　the　single-layer　human　tissue　model　and　three-layer　human　tissue　model　were　established,　applying　the　finite　element　method　(FEM).　Two　experiments　using　physiological　saline　and　excised　porcine　tissue　were　conducted　to　measure　the　power　loss　of　a　wireless　radio　frequency　link　at　2.45　GHz.　Various　communication　distances　and　implantation　depths　were　investigated　in　our　study.　RESULTS:　The　results　from　our　measurements　show　that　each　2　cm　increase　in　implantation　depth　will　result　in　an　additional　power　loss　of　about　10　dB.　The　largest　difference　in　values　obtained　from　the　measurements　and　the　simulations　is　within　4　dB,　which　indicates　that　the　experiments　are　in　good　agreement　with　the　simulations.　CONCLUSIONS:　These　results　are　significant　for　the　estimate　of　how　electromagnetic　energy　changes　after　propagating　through　human　tissues,　which　can　be　used　as　a　reference　for　the　link　budget　of　transceivers　or　other　implantable　medical　devices.