A piezoelectric element within an external ultrasonic transducer assembly can be used for wireless communication of data between an implantable device and the external ultrasonic transducer assembly such as using ultrasonic energy coupled to a flexible portion of a housing of the transducer assembly. The flexible portion can be configured to contact skin of a body containing the implantable device. The transducer assembly can be configured to respectively transmit or receive ultrasonic energy using at least partially overlapping respective ranges of resonant frequencies.
