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A capacitive micromachined ultrasonic transducer used for underwater remote imaging is designed, fabricated and tested in this paper. In the structure, silicon dioxide insulating layer is inserted between the top electrode and the vibrating film to prevent ohmic contact. The transducer is mainly used in a long distance test of underwater environmen...
Citations
... CMUTs exhibit high sensitivity, increased resolution, and wide bandwidth (66). These arrays enable smaller inter-element spacing for improved spatial resolution and reduction of motion artifacts. ...
Tissue elasticity remains an essential biomarker of health and is indicative of irregularities such as tumors or infection. The timely detection of such abnormalities is crucial for the prevention of disease progression and complications that arise from late-stage illnesses. However, at both the bedside and the operating table, there is a distinct lack of tactile feedback for deep-seated tissue. As surgical techniques advance toward remote or minimally invasive options to reduce infection risk and hasten healing time, surgeons lose the ability to manually palpate tissue. Furthermore, palpation of deep structures results in decreased accuracy, with the additional barrier of needing years of experience for adequate confidence of diagnoses. This review delves into the current modalities used to fulfill the clinical need of quantifying physical touch. It covers research efforts involving tactile sensing for remote or minimally invasive surgeries, as well as the potential of ultrasound elastography to further this field with non-invasive real-time imaging of the organ’s biomechanical properties. Elastography monitors tissue response to acoustic or mechanical energy and reconstructs an image representative of the elastic profile in the region of interest. This intuitive visualization of tissue elasticity surpasses the tactile information provided by sensors currently used to augment or supplement manual palpation. Focusing on common ultrasound elastography modalities, we evaluate various sensing mechanisms used for measuring tactile information and describe their emerging use in clinical settings where palpation is insufficient or restricted. With the ongoing advancements in ultrasound technology, particularly the emergence of micromachined ultrasound transducers, these devices hold great potential in facilitating early detection of tissue abnormalities and providing an objective measure of patient health.
... Compared with traditional bulk ultrasonic transducers, MUTs have the advantages of small size, light weight, low power consumption, high reliability, easy frequency control, high sensitivity, and easy integration with circuits [8,9]. MUTs can be divided into two types: capacitive micromachined ultrasonic transducers (CMUTs) [10][11][12][13], and piezoelectric micromachined ultrasonic transducers (PMUTs) [14][15][16]. Compared with CMUTs, PMUTs have the advantages of being compatible with CMOS [17,18], low driving voltage, and easy arrayment. ...
Ultrasound is widely used in industry and the agricultural, biomedical, military, and other fields. As key components in ultrasonic applications, the characteristic parameters of ultrasonic transducers fundamentally determine the performance of ultrasonic systems. High-frequency ultrasonic transducers are small in size and require high precision, which puts forward higher requirements for sensor design, material selection, and processing methods. In this paper, a three-dimensional model of a high-frequency piezoelectric micromachined ultrasonic transducer (PMUT) is established based on the finite element method (FEM). This 3D model consists of a substrate, a silicon device layer, and a molybdenum-aluminum nitride-molybdenum (Mo-AlN-Mo) sandwich piezoelectric layer. The effect of the shape of the transducer’s vibrating membrane on the transmission performance was studied. Through a discussion of the parametric scanning of the key dimensions of the diaphragms of the three structures, it was concluded that the fundamental resonance frequency of the hexagonal diaphragm was higher than that of the circle and the square under the same size. Compared with the circular diaphragm, the sensitivity of the square diaphragm increased by 8.5%, and the sensitivity of the hexagonal diaphragm increased by 10.7%. The maximum emission sound-pressure level of the hexagonal diaphragm was 6.6 times higher than that of the circular diaphragm. The finite element results show that the hexagonal diaphragm design has great advantages for improving the transmission performance of the high-frequency PMUT.
... Compared with conventional bulk ultrasound transducers made with piezoelectric ceramics, micromachined ultrasonic transducers (MUTs) based on thin films can provide more advanced array design, lower power consumption, and better acoustic coupling [1][2][3][4][5]. Notably, MUTs can be manufactured in various shapes and designs, e.g., annular [6], dome-shaped [7], and hexagon-shaped [8] arrays. ...
... To produce an ultrasound beam, the deflection of the top electrode membrane is achieved electrostatically. However, this cMUT, which requires a high DC bias voltage (>100 V), has limited applications because of safety issues [5,12]. Recently, a cMUT using a low input voltage has been developed [13], but still the DC bias limits the portability of the cMUT array for the biometric application. ...
This study presents the fabrication and characterization of a piezoelectric micromachined ultrasonic transducer (pMUT; radius: 40 μm) using a patterned aluminum nitride (AlN) thin film as the active piezoelectric material. A 20 × 20 array of pMUTs using a 1 μm thick AlN thin film was designed and fabricated on a 2 × 2 mm2 footprint for a high fill factor. Based on the electrical impedance and phase of the pMUT array, the electromechanical coefficient was ~1.7% at the average resonant frequency of 2.82 MHz in air. Dynamic displacement of the pMUT surface was characterized by scanning laser Doppler vibrometry. The pressure output while immersed in water was 19.79 kPa when calculated based on the peak displacement at the resonant frequency. The proposed AlN pMUT array has potential applications in biomedical sensing for healthcare, medical imaging, and biometrics.
... Ultrasonic transducers have played a significant role in imaging (Zure and Chowdhury 2012;Jia et al. 2018;Zhang et al. 2016), in high intensity ultrasound therapies (Stedman et al. 2017), as chemical sensor (Boulmé et al. 2014) and in cortical bone assessment (Rekhi et al. 2017) besides in wireless power transfer (Zhang et al. 2012). The advancements in MEMS technology has enabled the batch fabrication of capacitive micro-machined ultrasonic transducers (CMUT) that have taken over its piezoelectric counterpart. ...
In the present work, nonlinear dynamic characteristics of hexagonal capacitive micromachined ultrasonic transducer (CMUT) devices are reported for the first time. The 10 × 10 arrays showed a central frequency of 1.713 MHz with a bandwidth of 65 kHz, indicating synchronous vibration of the cells. Single cells and array are analyzed for their resonant frequency, quality factor, pull-in and mode of operation. The experimental analysis shows the resonance frequency shifts in the nonlinear regime. Spring hardening and then transition to spring softening of the structure with DC bias is observed on membranes with varying thicknesses. The paper demonstrates experimentally the traits of a single hexagonal cell with frequency shift under squeeze film damping phenomenon. The resonance frequency of these devices was found to vary from 1.58 to 1.83 MHz and this is attributed to the variation in thickness of the membrane across the wafer which is validated by FEM simulation results.
... In receiving mode, the membrane vibrates as a result of the incoming ultrasonic waves, which changes the capacitance of the transducer and, in turn, produces an electric signal. A typical CMUT and its working principle is Initially produced for air-coupled ultrasonic applications, CMUTs, late on, have been adopted for immersion applications, such as medical ultrasonic imaging and underwater imaging [3,4,5,6]. CMUTs offer better axial resolution due to its broader fractional bandwidth when compared to piezoelectric devices [7,8]. Furthermore, unlike piezoelectric devices, the use of micro-fabrication technology makes the CMUTs fabrication process very simple and precise transducers can be fabricated in array form [9]. Also, adopting a low temperature fabrication technique makes it possible for the CMUTs to be integrated with Complementary Metal-Oxide-Semiconductor (CMOS) technology [10,11,12]. ...
Capacitive Micromachined Ultrasonic Transducers (CMUTs) are the potential alternatives for the conventional piezoelectric ultrasonic transducers. CMUTs have been under an extensive research and development since their first development in the mid- 1990s. Initially developed for air-coupled applications, CMUTs have shown far better acceptability in immersion-based applications (i.e. medical ultrasonic imaging, medical therapy, and underwater imaging) when compared to the piezoelectric ultrasonic transducers.
CMUTs are parallel-plate capacitors fabricated using the Micro Electro Mechanical Systems (MEMS) technology. Despite of the fact that various CMUT fabrication methods have been reported in the literature, there are still many challenges to address in CMUTs design and fabrication. Standard fabrication techniques are further sub-divided into the Sacrificial Layer Release Process and the Wafer Bonding methods. A number of complications are associated with these techniques, such as optimization of the design parameters, process complexity, sacrificial layer material with the corresponding etchant selection, wafer cost and selection. In particular, the sacrificial release methods consist of complex fabrication steps. Furthermore, structural parameters like gap height and radius have optimization issues during the sacrificial release process. On the other hand, the wafer bonding techniques for the CMUTs fabrication are simple and have a great control over the structure parameters in contrast to the sacrificial release methods. At the same time, the wafer-bonded CMUTs require very high quality wafer surface and have a very high contamination sensitivity. For this purpose, this dissertation aims to develop a simple, low cost and lower constraint thermocompression-based technique for the CMUT fabrication.
The proposed wafer bonding technique for the CMUT fabrication in the dissertation
uses Polymethyl methacrylate (PMMA) adhesive as an intermediate layer for the thermocompression wafer bonding. The advantages associated with the PMMA adhesive based wafer bonding over the other wafer bonding methods include low process temperature (usually 200 ◦C or less), high wafer surface defects and contamination tolerance, high surface energy and low bonding stresses. These factors will add cost effectiveness and simplicity to the CMUTs fabrication process. Furthermore, the achieved receive sensitivity with the reported CMUT is found comparable to the commercially available ultrasonic transducers
... Capacitive Micromachined Ultrasonic Transducers (CMUTs), a potential alternative for piezoelectric ultrasonic transducers, have been under extensive development since their introduction in the mid-1990s [1][2][3][4][5][6][7][8][9][10]. Initially developed for air-coupled applications, CMUTs have shown far better acceptability in immersion applications, including medical ultrasonic imaging, medical therapy, and underwater imaging [11][12][13][14][15]. ...
This article presents a new wafer-bonding fabrication technique for Capacitive Micromachined Ultrasonic Transducers (CMUTs) using polymethyl methacrylate (PMMA). The PMMA-based single-mask and single-dry-etch step-bonding device is much simpler, and reduces process steps and cost as compared to other wafer-bonding methods and sacrificial-layer processes. A low-temperature (< 180 ∘ C ) bonding process was carried out in a purpose-built bonding tool to minimize the involvement of expensive laboratory equipment. A single-element CMUT comprising 16 cells of 2.5 mm radius and 800 nm cavity was fabricated. The center frequency of the device was set to 200 kHz for underwater communication purposes. Characterization of the device was carried out in immersion, and results were subsequently validated with data from Finite Element Analysis (FEA). Results show the feasibility of the fabricated CMUTs as receivers for underwater applications.
The exploration of ocean depend heavily on effective underwater communication. There is significant promise in the study and development of high-performance sensors tailored specifically for underwater communications. This work presents a high-performance sensor utilizing a scandium-doped aluminum nitride (Sc
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N) piezoelectric micromachined ultrasonic transducers (PMUTs) array, specifically designed for underwater communications applications. The PMUTs array, which consists of 7×8 sensing cells with a feature size of 500 μm, is being developed on a silicon-on-insulator (SOI) piezoelectric platform. The PMUTs array is bonding with a preamplification circuit, and packaged together with a polyimethylsiloxane(PDMS) layer to provide good acoustic impedance matching to water. The packaged PMUTs array is fully characterized using an industry standard calibration instrument. Experimental results show that the PMUTs array exhibits electromechanical coupling factors of 2.24% in air and 3.56% in water, respectively. The PMUTs array is omni-directional after packaging with a minimum deviation of ± 0.5 dB at 1 kHz. The reported PMUTs array achieves a receiving sensitivity of -172 dB (re: 1 V/μPa) with a 40 dB gain. Notably, the acceleration sensitivity is approximately 21 dB lower than the acoustic pressure sensitivity. It achieves lower bit error rates (BER) compared to commercial transducers, thereby enhancing overall communication reliability and performance. The measured results show that the design of the PMUTs array for underwater communications sensor application compares favorably with advanced commercially available transducers and a good prospect in commercial application.
Acoustic transducers with graphene film have high sensitivity and wide bandwidth of frequency response as receivers. However, they exist in transmitting mode with low radiation performance. We propose an effective approach to enhance radiation performance of the graphene acoustic transducer by embedding a coil in insulating layer, and investigate the characteristics of graphene acoustic transducers by experiments. A graphene acoustic transducer is designed and fabricated. The highest receiving sensitivity of the transducer is -30dB. The output sound pressure level of the transducer is more than 3 dB on average in the range of 2∼16 kHz compared without a coil. And the sound pressure level increases by 6 dB on average in the range of 40∼45 kHz. These results demonstrate that the graphene transducer maintains high receiving performance, and also improves acoustic radiation performance, which greatly expands its application field.
In this article, we present a high-performance aluminum nitride (AlN)-based microelectromechanical system (MEMS) hydrophone sensor, in which the sensing cells are designed and arranged as an innovative honeycomb architecture for achieving large acoustic pressure sensitivity and high fill-factor. An 8 x 9 array of 360 μm in characteristic size, 0.92-MHz MEMS hydrophone sensor is developed based on an AlN-on-cavity silicon-on-insulator (CSOI) platform. The size of the MEMS hydrophone sensor is 3.2 mm x 3.2 mm. The MEMS hydrophone sensor and its preamplification circuit are integrated on a printed circuit board and packaged together with an acoustically transparent material, in order to meet the stringent requirements of underwater applications. The packaged MEMS hydrophone is fully characterized through using an industry-standard hydrophone calibration instrument. The MEMS hydrophone achieves an acoustic pressure sensitivity of -178 dB (re: 1 V/μPa), with a maximum nonlinearity of 0.1%, and a noise resolution of 58.7 dB (re: 1 μPa/√Hz). The measurement results show that the reported MEMS hydrophone sensor with bioinspired honeycomb structure is compared favorable with advanced commercially available bulky hydrophones.
