These crystals undergo a sudden change in shape and resonate thus producing sound waves that are emitted outwardly, consequently the echoes sound waves hit the crystals producing yet another bout of electrical current.
The transducer probes vary in sizes and shape based on where they are being used, for example, there are those that are used on the external skin surfaces, those used in the internal sonography and those used in endoscopic scanning. This is determined majorly by the size of sound waves frequency required and the image resolution.