New ultrasound devices for medical and materials imaging
Ultrasound devices, particularly those used by the medical field, are conventionally based on piezoelectric (pressure-electricity) transducers that produce ultrasonic sound waves, sense sound pressure variations returned as a result of properties of the material tested and produce an electric current proportional to the pressure. Micromachined ultrasonic transducers (MUTs) are a new generation of devices produced by micro-electro-mechanical systems (MEMS) manufacturing techniques and employ tiny membranes or films driven by either piezoelectric or capacitive actuation (pMUTs and cMUTs, respectively). cMUTs are suitable for fabrication in large arrays thus increasing the bandwidth (range of frequencies with which sound can be applied and sensed) compared to pMUTs. A broader bandwidth is typically associated with greater resolving power whereas narrower ranges typically have greater penetration. European researchers working on the Mustwin project developed five demonstrator devices using two types of pMUTs and two types of cMUTs, the former for NDT and the latter for affordable acoustic probes and higher frequency probes for use in health diagnostic systems. Researchers identified the thickness-mode pMUT (TM pMUT) as an innovative device for high frequency medical imaging. An important application is intravascular imaging, such as that employed during angioplasty where a tiny ultrasound wand is fed through a large vein in the groin up to the coronary arteries. The silicon nitride (SiN) cMUT demonstrated the most advanced technology of all five devices, increasing bandwidth while decreasing the time required for response to sound pressure changes. Mustwin project devices have the potential to reduce cost and increase reliability of ultrasound technology, with important implications for manufacturers of ultrasound equipment, the field of NDT and the medical diagnostic sector.
