Abstract
A capacitive micromachined ultrasonic transducer structure for use in underwater imaging is designed, fabricated and tested in this paper. In this structure, a silicon dioxide insulation layer is inserted between the top electrodes and the vibration membrane to prevent ohmic contact. The capacitance-voltage (C-V) characteristic curve shows that the transducer offers suitable levels of hysteresis and repeatability performance. The −6 dB center frequency is 540 kHz and the transducer has a bandwidth of 840 kHz for a relative bandwidth of 155%. Underwater pressure of 143.43 Pa is achieved 1 m away from the capacitive micromachined ultrasonic transducer under 20 excitation. Two-dimensional underwater ultrasonic imaging, which is able to prove that a rectangular object is present underwater, is achieved. The results presented here indicate that our work will be highly beneficial for the establishment of an underwater ultrasonic imaging system.
Highlights
Underwater imaging has extensive applications, including underwater observation, differentiation between different objects and recreational underwater activities [1]
A highly-doped silicon wafer is used as the vibration membrane [19]
The measured distance (31.67 cm) between the two CMUTs can be obtained from the speed of ultrasonic propagation underwater (1480 m/s) by multiplying the time that the signal takes to travel from the transmitting CMUT to the receiving CMUT (2.14 × 10−4 s)
Summary
Underwater imaging has extensive applications, including underwater observation, differentiation between different objects and recreational underwater activities [1]. Advances in micro-fabrication technology have enabled fabrication of the capacitive micromachined ultrasonic transducer (CMUT), which with its wide bandwidth and design flexibility has emerged as a strong candidate to replace the aging PZT transducer technology [8,9,10] Other advantages such as their compatibility with integrated circuit (IC) fabrication technology, array configuration capabilities, good acoustic impedance matching with liquids and high operational efficiency have brought CMUTs one step closer to being the generation transducer technology [11,12,13] and as a result, underwater acoustic imaging using CMUTs is a technology that requires further study. In this work a CMUT with a bandwidth of 155% that requires 20 excitation and has a 540 kHz center frequency for use in underwater imaging has been designed, fabricated and tested
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