Can this ultrasonic emitter be DC driven?
Yes, it needs to be AC driven at it's nominal frequency (40kHz)   

You can just apply a square wave of this frequency to the base/gate of a transistor with emitter/source to ground and put the transducer from collector/drain to +V. You can also use an inductor in parallel with the capacitance of the transducer to form a tank for increased amplitude (see this previous question)  

You can use the PWM module for this to spare more time for your main loop, or a timer with interrupt, or if you are not using a microcontroller use a 555, or anything else capable of generating your square wave (or sine wave)