Wireless communication is critical for the non-invasive in-situ monitoring of vital signs in deep tissues. Wireless ultrasonic links demonstrated so far solved the shortcomings of electromagnetic wave-based communication methods. However, they either 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, considerably simplifying the implant 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 with decent precision and accuracy.