problem on implementation of the ultrasonic circuitry
Your ultrasonic Transducer driver circuit isn't doing a very good job. At most you are getting only a few milliwatts output to the transducer. Your circuit is applying 12 volts through a 2.2K resistor to the transducer, and your Q1 transistor is merely shorting out the Transducer.  

From viewing the data sheet on your transducer, it looks like a tiny loud speaker and not a Piezo device. But that is OK.  

Try the following push pull driver circuit.  I have tried to keep it simple, but you would need to come up with a PNP transistor (in addition to your existing NPN transistor).  

The V2 square wave is your 5 volt output from Arduino.  

Also, notice that I have shown the driver circuit using 5 volts, not 12 volts. Using this circuit, if you use 12 volts supply, the output doesn't get any more powerful, and just causes more heating in the transistors.   

EDIT 1  :  IMPORTANT :  Don't leave your output pin in the HIGH state.  This turns on transistor Q1 and causes sustained current in the Transducer.  To alleviate this, insert a 47uf capacitor in series with the transducer.  

EDIT 2 :  Changed schematic to include output capacitor.