I bought dual element transducer with cable has dual BNC (2.25 MHz). I need any device could be connect with this cable to make an excitation to this transducer. I linked this cable with a function generator but no response
You need an ultrasonic "pulser/receiver" unit such as the one sold by Imaginant, http://www.jsrultrasonics.com/pr_dpr300.html.
This unit will send a high-voltage spike to the transducer causing the piezoelectric element in your transducer to vibrate at its resonance, which will generate your desired ultrasonic waves. The pulser/receiver allows the transducer to cycle between transmit and receive modes, i.e., the same transducer is used as a source and receiver. The pulser/receiver has a signal output to be connected to an oscilloscope or digitizer to view the received ultrasonic signal.