Annular multifrequency piezoelectric array for enhanced wideband ultrasonic response

This paper presents the main results of a research carried out to achieve ultrasonic piezoelectric transducers with a bandwidth larger than that of present devices. The design is based on a kerfless multifrequency annular array, which is machined out of a 1-3 connectivity piezocomposite disk. The elements of the array are designed so that they present a different resonant frequency and the individual frequency bands of the elements overlap to furnish an overall response that approximate to the sum of the individual responses. A two elements array is presented: a central disk and a external ring with centre frequencies of 0.55 and 0.25 MHz, respectively. The transducer is designed for water immersion and is tested in pulse-echo. Bandwidth of the final design extends from 0.19 MHz up to 0.98 MHz, with a 6dB relative bandwidth close to 130%.