Energy and thermal distribution under the skin during ultrasound power transfer

Energy distribution under the human skin during ultrasound power transfer using a 15×15 MEMS transducer array with 2.2 MHz driving frequency is presented in this paper. When the surface pressure of the array element is 96 kPa, intensity at 2 mm under the skin is 0.96 W/cm²; intensity increases to 24 W/cm² when the surface pressure increases to 0.48 MPa. In other words, the simulation results show that the larger the surface pressure, the larger the intensity. The simulated and the measured power density values at 7 mm in the vertical direction of the transducer surface in degassed water are 96.72 mW/cm² and 94.08 mW/cm², respectively. Temperature change due to ultrasound radiation on the skin is discussed, and the feasibility of ultrasonic power transfer for implantable medical devices specially implanted just underneath the skin is presented.