Ghost suppressive ultrasonic measurement with a sparse phased array by using multiple frequencies

An ultrasonic measurement technique has been proposed for ghost suppression with a sparse phased array by using multiple frequencies. A sparse phased array with an inter-element spacing over a half wavelength causes large grating lobes resulting in ghosts. In the proposed method, the ghosts have been effectively suppressed by combining with a lower frequency measurement on the same array. This method has been applied to microfabricated piezoelectric ultrasonic sensors and ghost suppressive characteristics are demonstrated.