What is the current consumed by Ultrasonic Sensors/Transducers (1-2MHz) to generate Ultrasound waves
Ultrasonic sensors are piezoelectric devices that generate charge when deformed.  They don't even need to be powered.  You'd use a high input impedance amplifier or a charge amplifier to measure the signal.  

They also deform when you apply a charge to generate ultrasound waves, but a "sensor" wouldn't necessarily be used in that mode.