A 20-40 MHz ultrasound transducer for intravascular harmonic imaging

Recent studies have suggested the feasibility of tissue harmonic imaging (THI) with intravascular ultrasound (IVUS). This paper describes the design, fabrication and characterization of a piezoelectric transducer optimized for tissue harmonic IVUS. Ideally, such a transducer should efficiently transmit a short acoustic pulse at the fundamental transmission frequency and should be sensitive to its second harmonic echo, for which we have chosen 20 MHz and 40 MHz, respectively. The intravascular application limits the transducer dimensions to 0.75 mm by 1 mm. The transducer comprises of a single piezoelectric layer design with additional passive layers for tuning and efficiency improvement, and the Krimholtz-Leedom-Matthaei (KLM) model was used to find iteratively optimal material properties of the different layers. Based on the optimized design a prototype of the transducer was built. The transducer was characterized by water-tank hydrophone measurements and pulse-echo measurements. These measurements showed the transducer to have two frequency bands around 20 MHz and 40 MHz with -6dB fractional bandwidths of 30% and 25%, and round-trip insertion losses of -19 dB and -34 dB, respectively.