Phased transducer array for acoustic energy harvesting inside an MRI machine

In this study, an array of piezoelectric speakers is used to focus acoustic energy on a single transducer that acts as a harvester. The transmitting transducers are located along a curve that fits inside the magnetic resonance interferometer (MRI) torus interior. The numerical results for the pressure fields generated by circular-shaped and parabolic-shaped phased transducer arrays are compared, and the optimal locations for the acoustic energy harvester are determined for both shapes. In a series of experiments, the pressure on the axis of a single standalone speaker and on the axis of the non-phased parabolic array was measured to verify the numerical model. The experimentally determined location of the pressure peak in front of the parabolic-shaped array is predicted numerically with 4% accuracy. An acoustic energy harvester is placed at the location of the pressure peak, and the optimal resistive load value is determined experimentally for maximum output power. Approximately 1 µW of electric power is dissipated on the load when 10 mW is consumed by the source array at its second resonant frequency of 16 kHz, resulting in the electric input-to-output efficiency of 10-4.