As the population ages and with the advancements in medical technology, the number of patients using implanted electronic devices, such as artificial pacemakers and defibrillators, is increasing worldwide. Currently, the batteries of body-implanted devices are replaced by an incision surgery, which may lead to health complications. Accordingly, a new charging technique by wireless energy transfer is emerging that can also be used to charge the batteries of underwater devices, such as sensors, that are used for monitoring the conditions of submarine cables.
source https://www.lifetechnology.com/blogs/life-technology-technology-news/charging-underwater-and-body-implanted-electronic-devices-using-ultrasonic-waves
