Dual frequency hybrid ultrasonic transducers - design and simulations

This paper studies a design concept of a dual frequency ultrasonic transducer, in which we use different technologies for each band. A hybrid structure consisting of a piezoelectric stack used for the lower frequency (LF) band and a Capacitive Micromachined Ultrasound Transducer (CMUT) array placed on the top surface used for the higher frequency (HF) band is demonstrated by Finite Element Method (FEM) simulations. Simulated results show that LF structure introduces ripples into the HF. Simulations also show that using an RTV lens on top of the device is sufficient to damp the vibrations from the CMUTs interfering to the LF band. An array to test the LF band of the design was fabricated and measured electrical impedances show a good correspondence to simulations. The work shows a potential of combining piezoelectric and MUTs technologies in ultrasound transducer design for use in medical applications.