title: Frequency Tuning of Collapse-Mode Capacitive Micromachined Ultrasonic Transducer.
abstract: The information in an ultrasound image depends on the frequency that is used. In a clinical examination it may therefore be beneficial to generate ultrasound images acquired at multiple frequencies, which is difficult to achieve with conventional transducers. Capacitive micromachined ultrasonic transducers (CMUTs) offer a frequency response that is tunable by the bias voltage. In this study we investigate this frequency tunability for ultrasonic imaging. We characterized a CMUT array operated at bias voltages up to three times higher than the collapse-voltage. All elements of the array were connected to a single transmit and receive channel through a bias circuit. We quantified the transmit-receive and transmit sensitivity as a function of frequency for a range of bias voltages. Impulse response measurements show that the center frequency is modifiable between 8.7MHz and 15.3MHz with an applied bias voltage of -50V to -170V. The maximum transmit sensitivity is 52kPa/V at a center frequency of 9.0MHz with an applied bias voltage of -105V. The -3dB transmit range in center frequency accessible with the variable bias voltage is 6.7-15.5MHz. This study shows that a collapse-mode CMUT can operate efficiently at multiple center frequencies when the driving pulse and the bias voltage are optimized. We demonstrate the usefulness of frequency tuning by comparing images at different optimal combinations of driving frequency and bias voltage, acquired by linearly moving the transducer across a tissue mimicking phantom.
authors: Philips Research, Royal Philips NV, Eindhoven, The Netherlands; Thorax Center Dept. of Biomedical Engineering, Erasmus MC, Rotterdam, The Netherlands. Electronic address: martin.pekar@philips.com.
authors: Martin
authors: M
authors: Pekař
authors: Philips Research, Royal Philips NV, Eindhoven, The Netherlands.
authors: Wendy U
authors: WU
authors: Dittmer
authors: Philips Research, Royal Philips NV, Eindhoven, The Netherlands.
authors: Nenad
authors: N
authors: Mihajlović
authors: Thorax Center Dept. of Biomedical Engineering, Erasmus MC, Rotterdam, The Netherlands.
authors: Gijs
authors: G
authors: van Soest
authors: Lab of Acoustical Wavefield Imaging, Dept. of Imaging Physics, Delft University of Technology, Delft, The Netherlands; Thorax Center Dept. of Biomedical Engineering, Erasmus MC, Rotterdam, The Netherlands.
authors: Nico
authors: N
authors: de Jong
keywords: CMUT; Capacitive micromachined ultrasonic transducer; Collapse mode; Deep-collapse mode; Frequency tuning; Imaging; Intracardiac; Multi-frequency; Ultrasound