Capacitive Micromachined Ultrasonic Transducer arrays for blood flow ultrasound Doppler and photoacoustic imaging applications

The Capacitive Micromachined Ultrasonic Technology (CMUT) has emerged as a promising alternative to piezoelectric transducers in the medical ultrasound market since 1990s. Compared to piezoelectric technology, the MEMS based CMUT has advantages such as ease of fabrication, miniaturization and the potential to integrate with front-end electronic circuits. In addition, CMUT also promises low acoustic impedance and high immersion bandwidth. This thesis work has designed and fabricated a bossed membrane CMUT. This newly designed CMUT is characterized and compared with the planar membrane CMUT showing broader bandwidth and higher electromechanical coefficient.;Using this bossed CMUT array, an implantable ultrasound Doppler blood flow meter is developed to overcome the dilemma between the detection depth and the measurement resolution. Due to its miniature size, this tool can be implanted close to target vessels deep inside the tissue without introducing significant disruption to the tissue while still delivering a high resolution. The system has integrated the blood flow velocity and beam to flow angle measurement to achieve a higher resolution.;This paper also describes the design and preliminary experimental results of a novel photoacoustic imaging system which cascades a light source behind an infrared-transparent ultrasonic transducer array and illuminates the image target through the transducer chip. Preliminary imaging in the metal phantom using this cascaded photoacoustic imager is obtained. These results indicate that photoacoustic imaging using CMUT technology has a great potential as a diagnostic modality for breast cancer screening.