Passive ultrasonic communication link for deep-tissue sensor implants

Wireless communication is critical for non-invasive in situ monitoring of vital signs in deep tissues. Electromagnetic-wave-based communication methods suffer from high attenuation and limited penetration in biological tissues. Wireless ultrasonic links can solve these shortcomings but typically require highly customized and complex designs for the implant electronics or rely on physical changes in implanted metamaterials. Here, we report a wireless, passive, frequency-based, and electronics-free ultrasonic communication method for deep-tissue sensor implants. The device consists of a piezoelectric crystal used as the ultrasonic antenna with a simplified design and can be integrated with any capacitive implantable sensor. We demonstrate the applicability of the passive communication method using a commercial pressure sensor at a depth of 5 cm, revealing a sensitivity of 5.83 pF/kPa below 20 kPa.