Grating Lobe Suppression Through Novel, Sparse Laser Induced Phased Array Design

Laser Induced Phased Array (LIPA) is a non-contact, couplant-free inspection technique providing high quality ultrasonic imaging. LIPAs use lasers for ultrasound generation and detection: ultrasonic beam forming is performed in post processing, using delay-and-sum algorithms, while the data acquisition is done by scanning the two lasers, offering a unique flexibility in array designs that are currently impossible to achieve with conventional transducer based phased arrays. When synthesizing a 2D LIPA, 3D imaging can be achieved. However, due to the mechanical scanning and the large number of elements required for 2D arrays, LIPAs acquisition is time consuming, limiting the potential of the technique. One approach to overcome this limitation is to reduce the number of array elements, however this can lead to the production of grating lobes, resulting in imaging artefacts. Grating lobes can be suppressed through careful LIPA design and this is explored in this study. Rapid array prototyping is demonstrated for synthesizing 3 arrays designs using the same experimental setup.