Operation and sound field of an ultrasonic biplane-array

For ultrasonic non-destructive testing several types of transducers are available based on single-channel or multi-channel technology. Transducers with more than two individual elements are usually called arrays. These arrays can differ in geometry and arrangement of their individual elements, e.g. linear, matrix and annular geometry. The advantage of arrays in contrast to single element transducers is the ability to tilt and focus the sound beam to a desired region inside the specimen. The biplane phased array is a new possibility in NDE for combining the advantages of linear phased arrays, regarding low costs and high compatibility to existing phased array electronics with the goal of matrix arrays to get signal information from the evaluated specimen in all three dimensions. The biplane array consists of a piezoelectric sensor with a conventional line electrode structure on the top and a second perpendicular line electrode structure rotated by 90° on the bottom side of the piezo layer. By using appropriate excitation and control techniques the biplane array is able to perform a conventional sector scan in two spatial directions. Moreover it is also possible to excite or receive with one single element or a choice of adjacent elements which allows flexible 3-D reconstruction techniques. All these features go along with significantly less technological effort compared to 2-D matrix arrays where each single element needs to be electrically connected and a large number of individual channels needs to supported by the used ultrasonic hardware. The paper describes and visualizes the operation of a biplane array by calculating its spatio-temporal sound field. The numerical simulations are performed by the CEFIT-PSS technique, a powerful combination of the axisymmetric Elastodynamic Finite Integration Technique (EFIT) with transient Point Source Synthesis (PSS).