Background::
Ultrasound is widely used in the applications of underwater imaging. Capacitive micromachined
ultrasonic transducer (CMUT) is a promising candidate to the traditional piezoelectric ultrasonic transducer. In underwater
ultrasound imaging, better resolutions can be achieved with a higher frequency ultrasound. Therefore, a CMUT array for
high-frequency ultrasound imaging is proposed in this work.
Methods::
Analytical methods are used to calculate the center frequency in water and the pull-in voltage for determining
the operating point of CMUT. Finite element method model was developed to finalize the design parameters. The CMUT
array was fabricated with a five-mask sacrificial release process.
Results::
The CMUT array owned an immersed center frequency of 2.6 MHz with a 6 dB fractional bandwidth of 123 %.
The pull-in voltage of the CMUT array was 85 V. An underwater imaging experiment was carried out with the target of
three steel wires.
Conclusion::
In this study, we have developed CMUT for high-frequency underwater imaging. The experiment showed
that the CMUT can detect the steel wires with the diameter of 100 μm and the axial resolution was 0.582 mm, which is
close to one wavelength of ultrasound in 2.6 MHz.
