Integration of electronics and mechanics in next generation ultrasound transducers in medical imaging.

Internationally several research groups work to develop CMUT, Capacitive Micromachined Ultrasound Transducers, for medical imaging purposes. In an ongoing NFR-project, SMiDA, at our department aiming at development of CMUT arrays for intravascular 3D imag ing at 30 MHz it has become clear that present mounting technologies are inadequate to mount such arrays. A high centre frequency and 3D capability of the imaging increases the difficulty of the problem. There are many different medical applications which ask for high frequencies. Assistance during surgery, intravascular imaging, skin imaging, and others will benefit from frequencies of perhaps as high as 50MHz. The main factors that make the mounting demanding is the high frequency combined with the 3D capability of the imaging. This requires connection to each transducer element in an arry with high pitch, 25 micrometers centre to centre spasing in two direction for the 30 MHz case. And further the acoustic requirements that has to be fulfilled at the same time to make the array function satisfactorily. These include damping of acoustic waves carried by the substrate that will interact with the CMUT array. Especially waves with phase velocities above the acoustic velocity in water will be harmfull and distort the response, but also slower waves with low losses may be harmfull. The project will be carried out in close cooperation with Dag T. Wang, at Sintef, Oslo. The Mina-lab there, which is well wquiped for silicon micromachining, will supply much o f the technology that is requierd during the project. Dag T. Wang will serve as a coadvicer for the PhD student. His CV is enclosed.