Abstract
Most works that address 2-D array ultrasonic transducers for underwater applications are about the geometry aspects of the array and beamforming techniques to make 3-D images. They look for techniques to reduce the number of elements from wide apertures, maintaining the side lobes and the grating lobes at acceptable levels, but not many details about the materials and fabrication processes are described. To overcome these gaps, this paper presents in detail the development of a 2-D array ultrasonic transducer prototype that can individually emit and receive ultrasonic pulses to make 3-D images of immersed reflectors within a volume of interest (VOI). It consists of a 4 × 4 matrix ultrasonic transducer with a central frequency of 480 kHz. Each element is a 5 mm sided square cut into a 1–3 piezocomposite. The center-to-center distance of two contiguous elements (pitch) was chosen to be greater than half wavelength, to increase the amplitude of emission and reception of signals with larger elements. Artifacts generated by grating lobes were avoided by restricting the field of view in the azimuth and elevation directions within 40° × 40° and applying the sign coherence factor (SCF) filter. Two types of backing layer materials were tested, one with air and another made of epoxy resin, on the transducers called T1 and T2, respectively. The pulse echoes measured with T1 had 2.6 dB higher amplitude than those measured with T2, and the bandwidths were 54% and 50% @ −6 dB, respectively, exciting the element with a single rectangular negative pulse. The 3-D images obtained with full matrix capture (FMC) data sets acquired of objects from 0.2 to 1.15 m motivate the development of a 2-D array transducer with more elements, to increase the angular resolution and the range.
Highlights
A 2-D array ultrasonic transducer can be used to generate 3-D images of underwater objects up to several meters away, even if they are immersed in water with low or no visibility conditions, which is not possible with underwater optical cameras [1,2,3,4]
Only a beam is emitted at a time, and many beams are necessary to make a 3-D image, so the focused emission may not be suitable for underwater images in real-time, because the objects are too far from the sonar, more than usual in the non-destructive evaluation and medical ultrasound images
A 2-D array ultrasonic transducer made of 1–3 piezocomposite elements was designed, constructed, and characterized
Summary
A 2-D array ultrasonic transducer can be used to generate 3-D images of underwater objects up to several meters away, even if they are immersed in water with low or no visibility conditions, which is not possible with underwater optical cameras [1,2,3,4]. In [1], the development of a 3-D sonar intended for volumetric images at deep-sea waters is presented It consists of a 32 × 32 array of 1–3 piezocomposite elements, which operates at the central frequency of 1 MHz. The center-to-center distance between two contiguous elements (pitch) is equal to 2 λ, resulting in a square aperture with sides of. The stress applied to the flex circuit in its bonding process is a critical task, as it determines the thickness of the epoxy layer and, the spurious capacitance Another approach design for reducing the number of elements in a 2-D array transducer while maintaining the wide aperture to improve the lateral resolution is the Fermat spiral [7,18].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
