Underwater object detection using capacitive micromachined ultrasonic transducers (CMUTs)

Underwater object detection is one of the most challenging research topics in computer vision technology. The complex underwater environment makes underwater images suffer from high noise, low visibility, blurred edges, low contrast and color deviation, which brings significant challenges to underwater object detection tasks. In underwater object detection tasks, traditional object detection methods often perform poorly in terms of accuracy and generalization capabilities. Underwater object detection requires accurate, stable, generalizable, real-time and lightweight detection models, for which many researchers have proposed various underwater object detection techniques based on deep learning. Although many outstanding results have been achieved on underwater object detection over the years, the research status of underwater object detection techniques are still lack of unified induction, and some existing problems need to be further probed from the latest perspective. In addition, previous reviews lack analysis on the relationship between underwater image enhancement and object detection. Therefore, this paper provides a comprehensive review of the current research challenges, future development trends, and potential applications of underwater object detection techniques. More importantly, this paper has explored the internal relationship between underwater image enhancement and object detection, and analyzed the possible implementation manners of underwater image enhancement in the object detection task in order to further enhance its benefits. The experiments show the performances of current underwater image enhancement and state-of-the-art object detection algorithms, point out their limitations, and indicate that there is not a strict positive correlation between underwater image enhancement and the accuracy improvement of object detection. The domain shift caused by underwater image enhancement cannot be ignored. This paper can be regarded as a guide for future works on underwater object detection.

Capacitive micromachined ultrasonic transducer (CMUT) is an ultrasonic transducer based on the microelectromechanical system (MEMS). Wideband CMUT has good application prospects in ultrasonic imaging, ultrasonic identification, flow measurement, and nondestructive testing due to its excellent characteristics. This paper studies the method of increasing the bandwidth of the CMUT, proposes the structure of the wideband CMUT with a hybrid cell structure, and analyzes the design principles and characteristics of the wideband CMUT structure. By changing the cell spacing and the number of cells of different sizes composing the CMUT, we analyze the simulation of the effect of the spacing and number on the CMUT bandwidth, thereby optimizing the bandwidth characteristics of the CMUT. Next, the selection principle of the main structural parameters of the wideband CMUT is analyzed. According to the proposed principle, the CMUT in the air and water are designed and simulated. The results prove that both the air and water CMUT meet the design requirements. The design rules obtained in this paper can provide theoretical guidance for the selection of the main structural parameters of the wideband CMUT.

This study presents the primary design, fabrication process and device measurement of a Capacitive Micromachined Ultrasonic Transducer (CMUT) for underwater acoustic imaging. Theoretical analysis and computer simulations of the CMUT are performed. The CMUT fabrication uses the full surface micromachining techniques of the Micro Electro Mechanical System (MEMS). These techniques are Low Pressure Chemical Vapor Deposition (LPCVD), photolithography, Reactive Ion Etching System (RIE) dry etching, sacrificial layer wet etching, metal thermal evaporation coating and Plasma‐Enhanced Chemical Vapor Deposition (PECVD). Several important issues regarding fabrication are discussed. The measured input impedance of the CMUT is in agreement with the theoretical prediction. The received signal has a 35 dB signal‐to‐noise ratio indicating that practical applications of the immersion CMUT are feasible and that the radiation pattern measurement of the CMUT array has good beamforming characteristics for underwater imaging.

Piezoelectric transducers have long dominated ultrasonic transducer technology, but capacitive micro-machined ultrasound transducers (cMUTs) have emerged as an alternative. Features of cMUT devices are wide bandwidth, ability to use silicon MEMS fabrication methods to produce large arrays and potential for integration with supporting electronic circuits. cMUT technology can potentially produce the type of integrated sensor array to enable advanced 3-D imaging. A major challenge to achieve this goal is the packaging of a large array of cMUT die. To accomplish this we use a high density Teflon interposer called HyperBGA® technology, produced by Endicott Interconnect (EI) to design a modular package in which the sensor cMUT array is on the topside and the supporting electronics on the backside. A trenched cMUT device having a pillar is flip chip attached to the HyperBGA substrate with a die-to-die spacing less than 100 um. Each cMUT device has 256 I/O pads with a pitch of 185 um. The packaging challenges to design and build this type of advanced sensor array will be presented.

Capacitive Micromachined Ultrasonic Transducers (CMUTs) are the prospective alternative to the traditional piezoelectric ultrasonic transducers. CMUTs are essentially parallel plate capacitors produced using Microelectromechanical Systems (MEMS) technology. The production of CMUTs is broken down into sacrificial underetching and wafer bonding methods. The sacrificial release-based techniques are complex and require several adjustments in terms of optimizing fabrication steps and material selections. Further, the sacrificial release-based processes need ultimate control over the gap height and membrane thickness. On the contrary, the wafer bonding fabrication processes are not only simpler than the sacrificial release methods but also provide a very good parametric control over the membrane thickness and gap height. Besides its advantages, the wafer bonding methods are very sensitive to contamination and surface roughness. The surface roughness problems are addressed by either using the costly Silicon-on-Insulator (SOI) wafers or by using complex Chemical Mechanical Polishing (CMP) method. This article presents a simple and economical CMUTs wafer bonding fabrication method. A thermocompression based metal bonded technique is adopted to successfully fabricate low frequency CMUTs to be used for underwater applications.

In this work, novel airborne capacitive micromachined ultrasonic transducers (CMUTs) based on a dual-backplate (DBP) technology are presented. In contrast to conventional CMUTs, these transducers use a three-electrode-based capacitive system, where the membrane is placed between two highly-perforated counter electrodes, enabling enlarged displacement amplitudes in electrostatic actuation and wide and tunable bandwidth due to a ventilated air cavity. Fabricated DBP-CMUT prototypes therefore show exceptionally high receive and transmit sensitivities of -34.5 dB(V/Pa) and 259 nm/V, respectively, in their 84 kHz resonance. The viscous dissipation introduced by ventilating the cavity results in a wide factional bandwidth (FBW) of 29%. An applicability of the developed CMUT for airborne ranging is demonstrated in pulse-echo based ranging measurements, where the distance of a sound reflecting metal plate can be clearly detected by a single CMUT operated in a transceiver mode.

Underwater object detection has a wide range of application scenarios. Due to the characteristics of underwater imaging, the research focus of object detection based on underwater images differs from that of general object detection algorithms. The detailed quality of underwater images can be improved effectively by using the certain image enhancement algorithm, which is helpful for human recognition of underwater objects and object detection using traditional algorithms. In recent years, research on underwater object detection algorithms based on deep learning has gradually become popular, but the influence of image enhancement algorithms on object detection based on deep learning has not yet been systematically studied. In this paper, the correlation between image enhancement and underwater object detection based on deep learning is studied. First, three methods based on image dehazing, UWCNN, and FUNIE-GAN are selected to enhance the images of the URPC dataset, Then, SSD algorithm is adopted to train and evaluate the URPC dataset and the three enhanced dataset respectively, finally, a statistical analysis of the correlation between the changes of image quality parameter after image enhancement and the object detection accuracy is carried out. Experiments show that the average object detection accuracy on the image-enhanced dataset has been improved to a certain extent, but different image quality parameter changes have no obvious statistical correlations to the final detection accuracy. The small increase in the final object detection accuracy may be the result of a combination of several factors.

Capacitive micromachined ultrasonic transducers (CMUTs) present advantages such as wide frequency bandwidth, which could be further developed for nonlinear imaging. However, the driving electrostatic force induces a nonlinear behavior of the CMUT, thus generating undesirable harmonic components in the generated acoustic signal. Consequently, the use of CMUT for harmonic imaging (with or without contrast agents) becomes challenging. This paper suggests 2 compensation approaches, linear and nonlinear methods, to cancel unwanted nonlinear components. Furthermore, nonlinear responses from contrast agent were evaluated using CMUT in transmit before and after compensation. The results were compared with those obtained using a PZT transducer in transmit. Results showed that CMUT nonlinear behavior is highly influenced by the excitation to bias voltage ratio. Measurements of output pressure very close to the CMUT surface allow the estimation of optimal parameters for each compensation approach. Both methods showed a harmonic reduction higher than 20 dB when one element or several elements are excited. In addition, the study demonstrates that nonlinear approach seems to be more efficient because it is shown to be less sensitive to interelement variability and further avoids fundamental component deterioration. The results from contrast agent measurements showed that the responses obtained using CMUT elements in transmit with compensation were similar to those from PZT transducer excitation. This experimental study demonstrates the opportunity to use CMUT with traditional harmonic contrast imaging techniques.

Capacitive micromachined ultrasonic transducers (CMUTs) have recently emerged as an alternative technology to piezoelectric transducers, offering advantages such as wide bandwidth, ease of fabricating large arrays and potential for integration with electronic circuits. In this paper, we present 2D and 3D pulse-echo imaging results using ID linear and 2D rectangular CMUT arrays, respectively. The aim of this paper is to demonstrate the viability of CMUTs for underwater acoustic imaging. For imaging experiments, we have fabricated ID and 2D CMUT arrays, and built an experimental setup allowing us to transmit and receive ultrasound signals from individual transducer elements. The image quality obtained shows that CMUTs are a strong alternative to conventional piezoelectric transducer arrays for the design of future generations of underwater acoustic imaging systems.

Capacitive micromachined ultrasonic transducers (CMUTs) have long been studied. Past research has shown that CMUTs indeed have remarkable features such as wide bandwidth and high efficiency. This paper introduces an inclusion to the CMUT technology that uses the wafer-bonding technique to fabricate membranes on silicon. This new technology enables the fabrication of large membranes with large gaps, and expands the frequency span of CMUTs to 10 kHz in the low end. CMUT devices with different frequency spans are fabricated using both technologies, and tested. Electromechanical coupling efficiency, k/sub T//sup 2/, value as high as 0.85 and fractional immersion bandwidth as wide as 175 % are measured.

Capacitive Micromachined Ultrasonic Transducers (CMUTs) have demonstrated great potential in ultrasonic imaging due to their wide bandwidth, high electromechanical coupling coefficient, flexible design, and ease of integration. However, traditional CMUT devices require high drive voltages, which may pose potential safety risks to humans and limit their widespread application in imaging fields. To address this issue, this study innovatively designs and fabricates a large-diameter (20 cm) CMUT annular array with low drive voltage (25 V DC and 15 V AC). Finite element simulation results show that the collapse voltage of the CMUT is 52 V. Devices fabricated using wafer bonding technology exhibit excellent linear I-V characteristics and a "U" shaped C-V curve. In air, the resonant frequency is 4.71 MHz; after PDMS electrical insulation encapsulation, the resonant frequency drops to 2.74 MHz when submerged in water. The fabricated CMUT elements exhibit a −6 dB bandwidth of 118%, a −6 dB beamwidth of 13°, and a receive sensitivity of −205 dB @2.5 MHz. The maximum normalized consistency error among the 64 array elements is 0.3. In the underwater imaging experiment, five targets with varying sizes, positions, and sound speeds embedded in a tissue-mimicking phantom were successfully reconstructed. The maximum radial error in the reconstructed target center positions was 5%. These results demonstrate that the designed low-voltage CMUT ring array possesses excellent imaging performance and significant potential for underwater ultrasound imaging applications.

Intravascular ultrasound (IVUS) is a burgeoning imaging technology that provides vital information for the diagnosis of coronary arterial diseases. A significant constituent that enables the IVUS system to attain high-resolution images is the ultrasound transducer, which acts as both a transmitter that sends acoustic waves and a detector that receives the returning signals. Being the most mature form of ultrasound transducer available in the market, piezoelectric transducers have dominated the field of biomedical imaging. However, there are some drawbacks associated with using the traditional piezoelectric ultrasound transducers such as difficulties in the fabrication of high-density arrays, which would aid in the acceleration of the imaging speed and alleviate motion artifact. The advent of microelectromechanical system (MEMS) technology has brought about the development of micromachined ultrasound transducers that would help to address this issue. Apart from the advantage of being able to be fabricated into arrays with lesser complications, the image quality of IVUS can be further enhanced with the easy integration of micromachined ultrasound transducers with complementary metal-oxide-semiconductor (CMOS). This would aid in the mitigation of parasitic capacitance, thereby improving the signal-to-noise. Currently, there are two commonly investigated micromachined ultrasound transducers, piezoelectric micromachined ultrasound transducers (PMUTs) and capacitive micromachined ultrasound transducers (CMUTs). Currently, PMUTs face a significant challenge where the fabricated PMUTs do not function as per their design. Thus, CMUTs with different array configurations have been developed for IVUS. In this paper, the different ultrasound transducers, including conventional-piezoelectric transducers, PMUTs and CMUTs, are reviewed, and a summary of the recent progress of CMUTs for IVUS is presented.

The frequency bandwidth of CMUTs (capacitive micromachined ultrasonic transducers) is known as relatively broader than that of other ultrasonic transducers. To utilize the wide bandwidth characteristic of the CMUT arrays, in this paper, we report on coded excitation techniques in the CMUT array. Through simulations, STMF (Simultaneous Transmit Multiple-zone Focusing) based ultrasound imaging techniques using orthogonally frequency-divided chirp signals are investigated. In the simulations, the frequency divided sub-band chirps that have orthogonal property are designed within the frequency bandwidth of the CMUT arrays, and simultaneously fired on multiple ranges, in which each signal is focused at a different range, in one transmission event. This paper also presents ultrasound images through a modulation and demodulation process of orthogonal sub-band coded signals. Experiments on the chirp-coded excitation in CMUT arrays are reported in this paper as a feasibility study of the FDMA (frequency division multiple access) like STMF method. In the experiment, mixed two orthogonal chirp signals are simultaneously fired with the CMUT arrays and the received signals are successfully separated into two compressed signals.

The objective of the paper is to design a Microelectronic Mechanical Systems(MEMS) based Capacitive Micromachined Ultrasonic Transducer (CMUT) which has been found to be superior in terms of bandwidth, transduction efficiency and array fabrication as compared to conventional piezoelectric transducers. With the years CMUT has been shown with different element geometries and fabrication techniques, however the optimization techniques and the application areas for the device persist. In this paper CMUT is simulated in COMSOL with Square and Circular diaphragm. FEM analysis is being carried out considering the same area for both the geometries in 3D.CMUT dynamics have been modeled by combining the Electrostatic module, Solid Mechanics Module and Mesh modules in COMSOL. The distributed stress and electric field are measured as function of time. This gives the exact comparison for the Eigen frequency, pull in voltage, deflection with applied DC bias and deflection of the diaphragm with AC superimposed on DC considering the isotropic Silicon as the diaphragm material. This simulation work provides results for the researcher to conclude on the geometry of the device prior to fabrication.

A challenging and attractive task in computer vision is underwater object detection. Although object detection techniques have achieved good performance in general datasets, problems of low visibility and color bias in the complex underwater environment have led to generally poor image quality; besides this, problems with small targets and target aggregation have led to less extractable information, which makes it difficult to achieve satisfactory results. In past research of underwater object detection based on deep learning, most studies have mainly focused on improving detection accuracy by using large networks; the problem of marine underwater lightweight object detection has rarely gotten attention, which has resulted in a large model size and slow detection speed; as such the application of object detection technologies under marine environments needs better real-time and lightweight performance. In view of this, a lightweight underwater object detection method based on the MobileNet v2, You Only Look Once (YOLO) v4 algorithm and attentional feature fusion has been proposed to address this problem, to produce a harmonious balance between accuracy and speediness for target detection in marine environments. In our work, a combination of MobileNet v2 and depth-wise separable convolution is proposed to reduce the number of model parameters and the size of the model. The Modified Attentional Feature Fusion (AFFM) module aims to better fuse semantic and scale-inconsistent features and to improve accuracy. Experiments indicate that the proposed method obtained a mean average precision (mAP) of 81.67% and 92.65% on the PASCAL VOC dataset and the brackish dataset, respectively, and reached a processing speed of 44.22 frame per second (FPS) on the brackish dataset. Moreover, the number of model parameters and the model size were compressed to 16.76% and 19.53% of YOLO v4, respectively, which achieved a good tradeoff between time and accuracy for underwater object detection.