Design, Fabrication and Characterization of a Hybrid Piezoelectric-CMUT Dual-Frequency Ultrasonic Transducer

Dual-frequency ultrasonic transducers, capable of operating over distinct frequency bands, may be conveniently used in different applications such as harmonic imaging. This paper presents the design and fabrication of a dual-frequency hybrid transducer prototype, consisting of a Capacitive Micromachined Ultrasound Transducer (CMUT) placed on top of a piezoelectric transducer stack. The low-frequency (LF) transducer, i.e. a PZT disk supported by a backing and matched using a quarter-wavelength layer, was designed for transmit (TX) and receive (RX) operation around 7 MHz in immersion, while the high-frequency (HF) transducer, i.e. a single-element Reverse-Fabricated CMUT, was designed for RX operation around 14 MHz. Finite Element Modeling (FEM) was used to investigate the behavior of the proposed hybrid transducer stack. A hybrid transducer prototype was then fabricated. Two additional transducer prototypes, i.e. a single-element piezoelectric and a single-element CMUT, were fabricated using the same materials. The three transducer prototypes were electrically and acoustically characterized. Characterization results were compared with simulations showing that the proposed hybrid transducer approach can be used to increase the RX frequency bandwidth, thus demonstrating its potential in nonlinear imaging applications.