This disclosure provides systems and methods for sensing coupling of an ultrasound source to a target and for providing a constant average output of power from an ultrasound source. The systems and methods can include a frequency sweep function. The systems and methods can also include receiving reflected energy from an acoustic window and determining a feedback using the reflected energy. The systems and methods can also include comparing the feedback with a threshold level and using the comparison to determine if the ultrasound source is coupled with a target.
