During transmission the speed of ultrasound pulses gradually reduces due to their energy loss. So, calculating the detecting depth with fixed transmitting speed may distort two dimensional images due to the reduction of pulse speed. Correcting TOF error will rectify the depth registration and improve the quality of images.The thickness of activated piezoelectric materials decides the size and quantity of ultrasound pulses, which is related to its penetrating ability. So, increasing thickness of activated piezoelectric materials will increase the quantity of ultrasound pulses, which increase their penetrating depth.Moving objects change the speed of reflected ultrasound pulses. The forward moving objects increase reflected speed and reversely moving objects decrease reflected speed, which change their TOF. Therefore TOF shift can be used to calculate the velocity of moving objects in the continuous and pulse wave and color ultrasound, and correct aliasing of pulse and color ultrasound.
