Development of a 2-D Array Ultrasonic Transducer for 3-D Imaging of Objects Immersed in Water

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.

Comparison of Three Linear Digital Filters Applied to Improve the Quality of the Measured Acoustic Field

“…Because the hydrophone was not calibrated, the measurements were normalized by the maximum amplitude of the field. The phased-array transducer used in this work is the same transducer used in [27] to make 3D acoustic images of objects immersed in water. The transducer consists of 16 squared elements with sides equal to 5 mm distributed in a 4 × 4 matrix, which can emit and receive ultrasound pulses individually.…”

“…The transducer consists of 16 squared elements with sides equal to 5 mm distributed in a 4 × 4 matrix, which can emit and receive ultrasound pulses individually. The center frequency of the transducer is 480 kHz and its −6 dB bandwidth is 50% [27]. Both the transducer and the hydrophone were built in our ultrasound laboratory.…”

Plasmon-enhanced optoacoustic transducer with Ecoflex thin film for broadband ultrasound generation using overdriven pulsed laser diode

“…Ultrasound allows biocompatible and contactless bioimaging and therapeutic applications such as ultrasound imaging, 1 high-intensity focused ultrasound treatment, 2 and ultrasonic drug delivery 3 . Conventional ultrasonic transducers often utilize piezoelectric (PZT) materials, which induce ultrasonic waves through mechanical vibration 4 .…”

Design of 2D Planar Sparse Binned Arrays Based on the Coarray Analysis

“…Progress in ultrasonic array manufacturing has allowed the commercialization of highly-populated apertures [ 1 , 2 ]. However, these high-density transducers are difficult to use due to limitations imposed by data acquisition systems.…”

“…On the other hand, there is an increasing interest in synthetic aperture imaging methods [ 2 , 4 , 5 ], where all signals corresponding to each pair of emission and reception elements in the array are independently acquired, and the focusing process is performed as a part of digital signal processing operations. These solutions can be implemented with a trade-off between parallel resources and acquisition time and, although there is lower SNR (Signal-to-Noise Ratio) when compared to phased-arrays, the complete set of signals is rich in information [ 6 , 7 ].…”