Download or read book Capacitive Micromachined Ultrasonic Transducers with Vented Cavities written by Nikhil Apte and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Capacitive micromachined ultrasonic transducers (CMUTs) are increasingly seen as a better alternative than piezoelectric transducers for many ultrasound applications. Ultrasonic flow metering presents one such case where CMUTs are much better suited. Due to their lower mechanical impedance, CMUTs are more efficient at coupling sound into a fluid medium than piezoelectric transducers. Unlike piezoelectric transducers which suffer from depoling at temperatures above their Curie point, CMUTs can easily be used in higher temperatures. This should make CMUTs ideal candidates for ultrasonic flow metering in extreme environments such as those that exist in flare stacks, high temperature steam lines in industrial plants, etc. Despite these benefits, conventional CMUTs are not suited for the highly variable pressure conditions that many flowmeters have to operate under. CMUTs with vented or pressurized cavities can overcome this limitation. This dissertation presents the design and modeling for such CMUTs. A reliable fabrication process for CMUTs vented through the plate or through the substrate is also presented. The fluid squeeze film formed in the cavity between the CMUT plate and the substrate provides a way to control the bandwidth and sensitivity of such CMUTs. The dissertation presents CMUTs with bandwidth ranging from 1% to over 20% in air. These CMUTs were tested under a pressure of up to 20 bar and maintained good bandwidth and SNR. The dissertation also discusses the importance of packaging for CMUTs vented through the substrate and presents a way to utilize acoustic resonances in the package for maintaining a steady operating frequency under varying pressure. The wide bandwidth of such CMUTs can be utilized in many other application of ultrasound in air. The dissertation briefly discussed the application of these CMUTs for thermoacoustic imaging as well as for gesture sensing.

Download or read book Air coupled Capacitive Micromachined Ultrasonic Transducers Based on Annular Cell Geometry written by Shuai Na and published by . This book was released on 2017 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: Air-coupled ultrasound is gaining increasing industry momentum due to the demands and development of non-destructive evaluation (NDE) of aerospace composite materials. Currently, the micromachining technology has advanced such that vacuum cavities sealed by thin plates, known as Capacitive Micromachined Ultrasonic Transducers (CMUTs), can be fabricated through silicon micromachining processes in a low cost manner. Given the thin plates, a CMUT is able to vibrate with a low mechanical impedance and thus a high coupling efficiency with the ambient atmosphere. Nevertheless, air-coupled applications are still highly limited by the transmit power of air-coupled CMUTs. A circle is the routine geometry in most CMUT cell designs. Even though efforts have been put forward to address the limitations of circular design in terms of sensitivity, more investigation about other cell geometries is prudent. In this work, a novel air-coupled CMUT design with annular cell geometry is proposed. Finite element analysis and experimental studies demonstrated its significant improvement in transmit efficiency over the conventional circular-cell CMUTs. A lumped element model was constructed to facilitate a better understanding and provide an efficient design technique of the annular CMUT. Three optimization schemes were developed to optimize the transmit efficiency and achieve a reasonable comparison between the novel annular and conventional circular CMUT cells. Based on the lumped models, a design optimization flow chart was constructed to facilitate the analytical optimization of the three schemes. To further enhance the transmit power as well as offer depth focusing, a 9-element concentric annular-cell array was designed, fabricated, and characterized. A pillar-free etching process was developed to create the deep large-area cavities. The cross-talk between neighbouring cells and the plate-cracking phenomenon were discussed with suggestions for improvement being provided. This study provides a systematic framework for designing and studying annular-cell CMUTs and demonstrates their great potential in transmitting high-power ultrasound in air.

Download or read book High performance Micromachined Ultrasonic Transducers written by Guo-Lun Luo and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: With emerging micro-electromechanical system (MEMS) technology, MEMS ultrasonic transducers (MUTs) are demonstrated with the merits of smaller size, lighter weight, lower power consumption. Compared to conventional ultrasonic transducers, MUTs have better acoustic matching, CMOS compatibility, and array fabrications. This dissertation focuses on high-performance MUTs, from the perspectives of driving mechanism, structure design, material, array design, fabrication process, sealing and housing, achieving higher transmitting pressure output, higher receiving sensitivity and wider bandwidth. First, this study investigates piezoelectric MUTs (PMUTs) and capacitive MUTs (CMUTs) to propose a novel hybrid MUT (HMUT) with the highest figure of merits (FoM) of MUTs. The HMUT is developed to remain the advantages of both MUTs for higher performance. For airborne applications, the HMUT is made by a PZT PMUT with large amplitude as transmitter (TX), and a capacitive CMUT with high sensitivity, wide bandwidth, and low bias, as receiver (RX). The airborne PMUT is fabricated by a single-crystal PZT thin film with a high piezoelectric coefficient (e[subscript 31,f ~] 15 C/m2), enabling a high-pressure output of 108 dB SPL at 30 cm. The PZT PMUT with a dielectric constant ([epsilon]r = 308) as RX, shows the sensitivity of 1.9 mV/Pa, resulting in high signal-to-noise ratio (SNR) in the pulse-echo experiment, demonstrating 5-meter round-trip detectable distance. However, the PZT PMUT has generically high permittivity resulting in low receiving sensitivity, the narrow bandwidth (9%) due to high Q-factor, and TX/RX resonances mismatching, and mechanical nonlinearity. Here, we use a wide-bandwidth CMUT as a receiver to eliminate the resonances mismatching, and higher sensitivity can be achieved due to low permittivity ([epsilon]r~1). The CMUT receiver, formed by a vented diaphragm and a small gap of 2 [mu]m, and CMUT with air damping is designed and optimized to have sensitivity of 14 mV/Pa, bias voltage of 5V, and fraction bandwidth of 150% from the mechanical characterization, resulting in 7X of sensitivity and 15X of bandwidth improvement compared to the single-crystal PZT PMUT. Moreover, the 3D printed housing of airborne MUTs is designed and implemented to protect the fragile structure and provide good acoustic impedance matching with air, enabling -1.4 dB acoustic loss from the housing, -2 dB SNR in pulse-echo measurement. For immersion MUTs, we utilized surface micromachining to developed MUTs, enabling high fill-factor MUT arrays with larger active areas to increase efficiency, and the MUT cavities can be sealed in vacuum for immersion applications. First, we demonstrated an AlN PMUT array with 80% fill-factor, and the PMUT cavities were sealed in vacuum. The explicit pressure model for MUT arrays with various fill-factor, is investigated from the experiments. Moreover, the structure enhancement is demonstrated using this process, resulting in higher PMUT pressure output. Compared to fully clamped PMUTs, the sloped PMUT with a 2.5X Q-factor (2.5X) can create 3X displacement by shaping the sacrificial layer. The corrugated PMUT is also implemented to demonstrate piston-like motions with an increasing active area, showing 3.2X volume velocity. In addition, the sealing technique with acoustic coupling layer is demonstrated to increase the bandwidth for immersion. Using surface micromachining, the immersion HMUTs is discussed and proposed to have the fully monolithic PMUT/CMUT integration with high performance.

Download or read book Interface Engineering of Capacitive Micromachined Ultrasonic Transducers for Medical Applications written by Der-Song Lin and published by Stanford University. This book was released on 2011 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: Capacitive micromachined ultrasonic transducers (CMUTs), have been widely studied in academia and industry over the last decade. CMUTs provide many benefits over traditional piezoelectric transducers including improvement in performance through wide bandwidth, and ease of electronics integration, with the potential to batch fabricate very large 2D arrays with low-cost and high-yield. Though many aspects of CMUT technology have been studied over the years, packaging the CMUT into a fully practical system has not been thoroughly explored. Two important interfaces of packaging that this thesis explores are device encapsulation (the interface between CMUTs and patients) and full electronic integration of large scale 2D arrays (the interface between CMUTs and electronics). In the first part of the work, I investigate the requirements for the CMUT encapsulation. For medical usage, encapsulation is needed to electrically insulate the device, mechanically protect the device, and maintain transducer performance, especially the access of the ultrasound energy. While hermetic sealing can protect many other MEMS devices, CMUTs require mechanical interaction to a fluid, which makes fulfilling the previous criterion very challenging. The proposed solution is to use a viscoelastic material with the glass-transition-temperature lower than room temperature, such as Polydimethylsiloxane (PDMS), to preserve the CMUT static and dynamic performance. Experimental implementation of the encapsulated imaging CMUT arrays shows the device performance was maintained; 95 % of efficiency, 85% of the maximum output pressure, and 91% of the fractional bandwidth (FBW) can be preserved. A viscoelastic finite element model was also developed and shows the performance effects of the coating can be accurately predicted. Four designs, providing acoustic crosstalk suppression, flexible substrate, lens focusing, and blood flow monitoring using PDMS layer were also demonstrated. The second part of the work, presents contributions towards the electronic integration and packaging of large-area 2-D arrays. A very large 2D array is appealing for it can enable advanced novel imaging applications, such as a reconfigurable array, and a compression plate for breast cancer screening. With these goals in mind, I developed the first large-scale fully populated and integrated 2D CMUTs array with 32 by 192 elements. In this study, I demonstrate a flexible and reliable integration approach by successfully combining a simple UBM preparation technique and a CMUTs-interposer-ASICs sandwich design. The results show high shear strength of the UBM (26.5 g), 100% yield of the interconnections, and excellent CMUT resonance uniformity ([lowercase Sigma] = 0.02 MHz). As demonstrated, this allows for a large-scale assembly of a tile-able array by using an interposer. Interface engineering is crucial towards the development of CMUTs into a practical ultrasound system. With the advances in encapsulation technique with a viscoelastic polymer and the combination of the UBM technique to the TSV fabrication for electronics integration, a fully integrated CMUT system can be realized.

Download or read book Characterization of Multiple Moving Membrane Capacitive Micromachined Ultrasonic Transducer written by Md. Iftekharul Islam and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: A newly developed multiple moving membrane capacitive micromachined ultrasonic transducer (M3-CMUT) is fabricated and characterized in this thesis. Unlike the single vibrating membrane in the conventional capacitive micromachined ultrasonic transducer (CMUT), the novel design involves two deflectable membranes suspended over a fixed bottom electrode. In the presence of bias, both of the membranes deflect simultaneously, which results in a smaller cavity compared to a CMUT. To understand the basics of a capacitive transducer, an equivalent mass-spring-capacitor model of CMUT was reported. The results of this analytical model were used to develop the finite element models (FEM) of CMUT and more complex M3-CMUT in COMSOL Multiphysics software. The electromechanical analysis of these models was conducted to observe their operating conditions. Following the modeling and analysis, several single-cell, 1-D, and 2-D arrays of these devices were fabricated using PolyMUMPs technology, a sacrificial fabrication technique for the MEMS transducers. The electrical and acoustic characterizations of the fabricated devices were performed to measure the actual transducer properties. The measured data and the model results were found to be in good agreement. It was observed from the electrical impedance measurements that a higher membrane deflection was achieved in the double membrane device. The reduction in the cavity of M3-CMUT enhanced the sensitivity of the transducer. The acoustic characterization using a pitch-catch experimental setup demonstrated that the novel M3-CMUT could be used as an ultrasonic transducer. The velocity and attenuation of the acoustic waves, when the transducer used as both the transmitter and the receiver, were found to be very close to the theoretical value.

Download or read book Capacitive Micromachined Ultrasonic Transducers with Through wafer Interconnects written by Xuefeng Zhuang and published by . This book was released on 2008 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Capacitive Micromachined Ultrasonic Transducers for Therpaeutic sic Ultrasound written by Serena H. Wong and published by . This book was released on 2008 with total page 576 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Airborne Capacitive Micromachined Ultrasonic Transducers in Dual Backplate Technology written by Sebastian Anzinger and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Novel Applications of Capacitive Micromachined Ultrasonic Transducers written by and published by . This book was released on 2007 with total page 328 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Topical Review written by Jingkuang Chen and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Capacitive Micromachined Ultrasonic Transducers with Substrate embedded Springs written by Byung Chul Lee and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: After the first capacitive micromachined ultrasonic transducer (CMUT) was invented in 1994, it became one of the candidate technologies to advance the state-of-the-art of medical ultrasound imaging. Benefiting from its fabrication technique based on the semiconductor industry, CMUT technology has broadened the medical and therapeutic applications such as real-time volumetric ultrasound imaging, catheter-based forward-looking intravascular ultrasound (IVUS), photoacoustic imaging, high-intensity focused ultrasound (HIFU) and so on. In spite of many advantages, however, CMUT technology has been criticized with its relatively low transmit sensitivity (~10 kPa/V) or low average volume displacement efficiency (0.1 nm/V) as well as large drive and bias voltage requirements (in a range of a few hundreds of volts). In order to resolve these issues and open up new potential of clinical applications, this dissertation describes the design, fabrication, and system implementation of CMUTs with substrate-embedded springs, so-called post-CMUT (PCMUT). Since PCMUT structure resembles an ideal piston transducer, the improvements in performance mainly stem from the higher average displacement of the top plate for a given gap height. The overview of the first generation PCMUT is introduced and two main issues in simulation and fabrication aspects of the first generation PCMUT is discussed. To further improve the PCMUT device, a 3D finite element analysis (FEA) model of the PCMUT is demonstrated to predict the performance of the first generation PCMUT. In addition, the design guideline of the second generation PCMUT is proposed for achieving the maximum fractional bandwidth (100 %) as well as with the highest transmit sensitivity (~28 kPa/V). The second generation PCMUT is fabricated by using three combination MEMS processes: usage of two silicon-on-insulator (SOI) wafers, wafer bonding process, and wafer polishing process. The second generation PCMUT achieves high transmit sensitivity (~21 kPa/V) or large average volume displacement efficiency (1.1 nm/V) with a low bias voltage (55 V). Compared to a commercial piezoelectric transducer, the second generation PCMUT improves 2.75 times of the maximum output pressure and 5.25 times of the average volume displacement efficiency with respect to the same voltage. After fabrication and performance characterization of the second generation PCMUT, this dissertation demonstrates the feasibility of PCMUT to use it in medical imaging system by integrating PCMUT with a custom-built integrated circuit (IC). Photoacoustic imaging is also presented for one of its application examples.

Download or read book Minimally Invasive Capacitive Micromachined Ultrasonic Transducers Array for Biomedical Applications written by Xiaoyang Cheng and published by . This book was released on 2008 with total page 326 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advances in Capacitive Micromachined Ultrasonic Transducer CMUT Technologies written by James Stuart McIntosh and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A PolyMUMPs Capacitive Micromachined Ultrasonic Transducer written by Ming Cai and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Exploring Multiple mode Vibrations of Capacitive Micromachined Ultrasonic Transducers CMUTs written by Wei You and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Capacitive Micromachined Ultrasonic Transducers CMUTs Built with Wafer bonding Technology written by Yongli Huang and published by . This book was released on 2005 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book MEMS Technology for Biomedical Imaging Applications written by Qifa Zhou and published by MDPI. This book was released on 2019-10-23 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt: Biomedical imaging is the key technique and process to create informative images of the human body or other organic structures for clinical purposes or medical science. Micro-electro-mechanical systems (MEMS) technology has demonstrated enormous potential in biomedical imaging applications due to its outstanding advantages of, for instance, miniaturization, high speed, higher resolution, and convenience of batch fabrication. There are many advancements and breakthroughs developing in the academic community, and there are a few challenges raised accordingly upon the designs, structures, fabrication, integration, and applications of MEMS for all kinds of biomedical imaging. This Special Issue aims to collate and showcase research papers, short commutations, perspectives, and insightful review articles from esteemed colleagues that demonstrate: (1) original works on the topic of MEMS components or devices based on various kinds of mechanisms for biomedical imaging; and (2) new developments and potentials of applying MEMS technology of any kind in biomedical imaging. The objective of this special session is to provide insightful information regarding the technological advancements for the researchers in the community.