how to design transmitter circuit Ma40s4s ultrasound
Capacitance of MA40S4S (about 2.55 nF) affects output of the power stage. 

Consider using an IC with higher output current.

Or you can try a burst generator (mosfet + inductor) driven by the PWN signal. Example you can find on page 9 of AN4841: 12ZVL LIN Enabled Ultrasonic Distance Measurement.