Transducer characterization by sound field measurements

The paper discusses different methods for characterizing an ultrasonic transducer by sound field measurements and introduces a novel easy-to-implement method besides the commonly known point reflector and hydrophone measurement methods. The characterization methods that are presented are particularly suited to measuring the actual transducer element size and determining fabrication details and asymmetries, where the necessary information is derived from the position of the ultrasonic focus and the structure of the sound field. The procedure is discussed on the basis of the following practical problems: measurement of the acoustically relevant element size of a planar 3-MHz annular array made of lead zirconate titanate (PZT) using a single point reflector; visualization of inaccuracies, asymmetries, and fabrication details for different setups with transducer frequencies between 3 and 50 MHz; determination of the element sizes of the single elements of a spherically curved 9-MHz sparse annular array and examination of the transducer´s focusing characteristics in a fluid containing scattering particles; and determination of the focus position of a 9-MHz single-element transducer with acoustic lens and comparison between two lens materials.