Implantable closed-loop neuromodulation device

Described herein are implantable closed-loop neuromodulation devices, systems that includes such devices and an interrogator configured to emit ultrasonic waves that power the device, methods of using such devices and systems, and methods of modulating neural activity. The implantable device can include one or more curved members extending from a body. The curved members are configured to at least partially circumscribe a nerve, and include one or more electrode pads. The body includes an ultrasonic transducer configured to receive ultrasonic waves and convert energy from the ultrasonic waves into an electrical energy; and a computational circuit configured to receive a detection signal based on a detected electrophysiological signal, generate a stimulation signal based on the detection signal, and operate the electrode pads of to emit an electrical pulse to the nerve based on the stimulation signal.