Question

for 1 of my projects , i need to produce ultra sonic sound , hw can i produce it the easiest way ?

Answer 1

I recommend to buy a factory-made ultrasonic transducer:
http://www.google.fi/search?q=ultrasonic+transmitter+ebay
They are not expensive.

Answer 2

Most computers (sound cards) wont be able to produce ultrasonic frequencies, but depending on the specific frequency, you may get lucky and be able to make it straight off your computer.

Answer 3

get yourself one of those plastic spiders, and some fishing line. And if your married, you might need to secretly volunteer the participation of your husband .... if your not married, you might have to get married; that in andof itself should produce them :)