This study relies on double-sided chips where capacitive Micromachined Ultrasonic Transducers (cMUT) are manufactured on both sides of a silicon substrate in order to perform galvanic isolation between two electrical circuits. The operating principle is based on the propagation of acoustic waves from one transducer to the other, providing a high level of electrical isolation. The work presented here focuses mainly on the assessment of the power efficiency, from an experimental and from a theoretical point of view. Encouraging power efficiency values were reached, showing a significant efficiency gain when taking advantage of the coupling with the substrate.