Second harmonic leakage suppression by notching

Harmonic imaging offers better contrast resolution than conventional B-mode image. However, in ultrasonic array imaging system, the transmitting source contributes not only the fundamental harmonic but also the other harmonics. It is shown theoretically and experimentally that the interference of the transmitting-leaked second harmonic signal to the object generated second harmonic signal can be reduced by array notching. To do this, the transmitting beamwidth is set to be wider than the second harmonic receiving beamwidth such that the receiving beam can be steered into the first notch of the leaked harmonic beam. Different degrees of leakage suppression can be achieved by adjusting the ratio of the number of receiving elements to the number of transmitting elements and angle difference between transmitting and receiving beam