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Fraunhofer fabricates ultrasonic transducers with MEMS

Posted: 12 Jun 2014 ?? ?Print Version ?Bookmark and Share

Keywords:ultrasonic? sensor? CMUT? transducer?

Fraunhofer Institute for Photonic Microsystems (IPMS) researchers have built Capacitive Ultrasonic Micromachined Transducers (CMUTs) using MEMSa class of devices that can send and receive ultrasound in an energy efficient manner, as well as provide miniaturisation capabilities.

Ultrasonic imaging enables the contactless detection of objects with millimetric precision for a wide variety of materials regardless of their state, form and colour, and in practically any environment.

Whilst today's ultrasonic transducers are typically manufactured using piezoelectric materials, new MEMS alternatives are under development, offering greater sensitivity and broader frequency ranges than the established piezo-based transducers, according to Dr. Anartz Unamuno, manager of the CMUT (Capacitive Ultrasonic Micromachined Transducers) activities at Fraunhofer IPMS.

Using wafer bonding processes, these MEMS ultrasonic transducers also have a strong potential for monolithic integration with CMOS ASICs, paving the way to very compact and more rugged systems hosting all the necessary driver circuitry underneath the micromechanical structure.

The basic MEMS structure found in these CMUTs consists of two opposing electrodes spaced apart by an insulating layer and a gap. One is static and the other is deflectable.


CMUT chip on a ceramic carrier. Source: Fraunhofer

"As an emitter, an electric signal is applied between the electrodes which deflects the movable electrode and generates an acoustic wave. The inverse energy transformation, acoustic to electric, is used with CMUTs to sense ultrasound waves," explained Unamuno in an introduction paper.

"Each individual plate can range between about 10um and 100um in diameter/edge. But these elements are usually grouped so that the active acoustic area is larger and therefore more acoustic power is available. This also ensures a better sensitivity," clarified Unamuno in an email exchange with EETimes Europe.

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