1 3
Microsyst Technol
DOI 10.1007/s00542-015-2716-z
TECHNICAL PAPER
Design and performance analysis of capacitive micromachined
ultrasonic transducer (CMUT) array for underwater imaging
Rui Zhang
1
· Chenyang Xue
1
· Changde He
1
· Yongmei Zhang
2
·
Jinlong Song
1
· Wendong Zhang
1
Received: 9 June 2015 / Accepted: 29 October 2015
© Springer-Verlag Berlin Heidelberg 2015
present, piezoelectric micromachined ultrasonic trans-
ducers (PMUTs) occupy the leading position in the ultra-
sonic transducer field. However, the acoustic impedance of
PMUTs (10–30 MRayl) is higher than that of air and other
fluid media, which can limit the performance of PMUT in
underwater application. Although surface matching lay-
ers are usually required to overcome this problem, it can-
not be denied that the selection and fabrication of match-
ing layers increase the complexity and cost of transducer
manufacture (Jia et al. 2005; Oralkan et al. 2002). Recently,
CMUTs have been developed as a promising candidate for
ultrasound transducer arrays for underwater application.
Compared to PMUTs, the ultrasonic emission source of a
CMUT is a fairly thin membrane, leading to lower imped-
ance and better matching with the acoustic impedance of
air and other fluid media without adding a surface match-
ing layer (Wang et al. 2014). CMUTs also provide large
immersion bandwidth and high electromechanical coef-
ficient, which would improve the image quality (Oralkan
2004). In addition, other advantages like its high directiv-
ity, wide working temperature range, low-cost batch fabri-
cation, ease of integrate with front-end electronic circuits
make CMUTs as strong candidate for different ultrasound
applications (Oralkan et al. 2002; Emadi and Buchanan
2013; Jeong et al. 2013; Salim et al. 2012; Cheng 2008).
However, the performances of CMUTs have to been further
improved untiled it can truly replace PMUTs.
The performances of an ultrasonic transducer or array,
including bandwidth, sensitivity, directivity and output
pressure are directly related to the resulting imaging qual-
ity (Zhou et al. 2005; Oralkan et al. 2002; Park et al. 2010).
As a response of the performance improvement needs, a
Receipt &Transmission CMUT array with higher directiv-
ity and broader bandwidth for underwater imaging has been
optimized designed and performance analyzed in this work.
Abstract In this paper, a Receipt & Transmission CMUT
array has been developed for underwater imaging purposes.
To guide the array design more intuitively, directivity fuc-
tions of CMUT array are deduced in accordance with its
structure feature. According to the simulation results, the
optimized CMUT array configuration is selected. Through
employing a Si-SOI bonding technique, the CMUT array
has been fabricated. Finally, the underwater imaging sys-
tem design and performance testing are completed. The
−6 dB center frequency is centered at 460 kHz and has a
relative bandwidth of 130 %. The −3 dB main beam width
is about 4°. These values imply that the designed CMUT
array has wide bandwidth and fine directivity. Using sector
scanning and echo processing, obvious position and image
of the obstacles has been reconstructed. This further dem-
onstrates that CMUT array presented in this paper can be
of great benefit in underwater detection systems.
1 Introduction
An ultrasonic transducer or array is a core component to
achieve ultrasonic imaging. Recently, with the develop-
ment of micromechanical systems, people have paid closer
attention to ultrasonic transducers based on MEMS. At
* Wendong Zhang
wd_zhangnuc@163.com
1
National Key Laboratory for Electronic Measurement
Technology, Key Laboratory of Instrumentation Science
and Dynamic Measurement (North University of China),
Ministry of Education, North University of China,
Taiyuan 030051, China
2
School of Computer Science, North China University
of Technology, Beijing 100144, China
