A study on ultrasound link for wireless energy transmission dedicated to deeply implanted medical devices is presented. The selection of the frequency to avoid biological side effects (e. g., cavitations), the choice of the power amplifier to drive the external transducers and the design of the rectifier to maximize the energy extraction fromthe implanted transducer are described in details. The link efficiency is characterized in water using a phantom material for a transmitter-receiver distance of 105 mm, transducers active area of 30 mm x 96 mm and 5 mm x 10 mm, respectively, and a system efficiency of 1.6% is measured.