A system for wireless power transfer of micro-systems in-vivo implantable in small animals is presented. The described solution uses a servo-controlled transmitter moved under the animal moving space. The solution minimizes the power irradiation while enabling animal speeds up to 30 cm/s. An x-y movable magnetic coil transmits the required power with a level able to keep constant the received energy. A permanent magnet on board of the implantable micro-system and an array of magnetic sensors form a coil tracking system capable of an alignment accuracy as good as 1 cm. The power is transferred over the optimized remote powering link at 13.56 MHz. The received ac signal is converted to dc voltage with a passive full-wave integrated rectifier and the voltage regulator supplies 1.8 V for the implantable sensor system. Experimental measurement on a complete prototype verifies the system performance.