Micromachined ultrasonic transducers

In this chapter the basic principles, the fabrication process, and some modelling approaches of the novel micromachined ultrasonic transducers (MUTs) are described. These transducers utilize the flex-tensional vibration of an array of micro membranes. They are usually called cMUT (capacitive Micromachined Ultrasonic Transducer) or pMUT (piezoelectric Micromachined Ultrasonic Transducer) depending on the actuation principle, electrostatic or piezoelectric. For water coupling applications both these kinds of transducers offer a better matching to the load compared with the typical piezoelectric transducers and therefore they have a larger intrinsic bandwidth. Here emphasis is given to the cMUTs because they have shown good electroacoustic characteristics, which parallel, or even exceed, those of conventional piezoelectric transducers. Good echographic images of internal organs of the human body have been obtained demonstrating the possibilities of this technology to be utilized in commercial 1D and 2D probes for medical applications. At present pMUTs are in a very early stage of development and the potential advantages over the cMUTs are still to be demonstrated.