I have to realize an ultrasonic circuit for revealing defects in materials. Can u suggest me any book or link where I can learn how to design the schematic?
Typical ultrasonic systems for use in air work usually work at around 40KHz. That may be OK as a demonstration of the principle in large objects, but you likely need to use much higher frequencies for short range detection of small flaws in metal fabrications.
The possible flaw size and distance resolution of such a system are proportional to the wavelength of the ultrasonic signal in the medium it is propagating through.
eg. Some ultrasonic medical imaging systems use 5 MHz, to give very fine resolution.