Download or read book Capacitive Micromachined Ultrasonic Transducer arrays for blood flow ultrasound Doppler and photoacoustic imaging applications written by Mengli Wang and published by . This book was released on 2010 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 Real time Volumetric Ultrasound Imaging with Capacitive Micromachined Ultrasonic Transducer CMUT Probes written by Jung Woo Choe and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In ultrasound imaging, an array of ultrasonic transducers is used to generate ultrasound beams and obtain the echo data reflected by the imaging targets. The echo data are sent to a back-end imaging system and processed for image reconstruction. Currently, most of the commercial ultrasound probes in the market are made of piezoelectric transducer arrays. Capacitive micromachined ultrasonic transducers (CMUTs) are another type of transducers which emerged as an alternative to piezoelectric transducers. Being fabricated using standard micromachining processes, they have advantages in fabricating transducer arrays with arbitrary geometry or many transducer elements, as well as in integrating them with a supporting front-end electronics. 2-D transducer arrays enable volumetric imaging without mechanically scanning the probe. However, a 2-D transducer array consists of a large number of transducer elements, which increases the imaging system complexity and the data processing time. To eliminate these issues, at the expense of degraded image quality, a sparse 2-D array with fewer transducer elements can be used in volumetric imaging. The first part of this dissertation describes an optimization method to find a sparse array configuration that provides optimal image quality with limited number of transducer elements. Among the various array shapes we can implement using CMUT fabrication technologies, the ring geometry is particularly attractive in many applications including intracardiac and intravascular applications. A ring transducer array, which is a type of 2-D sparse array, enables volumetric imaging with much fewer transducer elements compared to a fully populated 2-D array. To find the optimal imaging scheme for real-time imaging with a ring array, various imaging options were investigated and compared in both simulations and experiments. Commercial ultrasound imaging systems are mainly designed for probes with standard geometry and conventional imaging techniques. Therefore, they are not readily accessible for probes with non-standard geometry, such as a ring array. In addition, it is difficult to use them with non-conventional imaging schemes that may be ideal for non-standard array geometries. For real-time volumetric imaging with various types of CMUT arrays, a flexible imaging system that works with arbitrary probe geometry and various imaging schemes including non-conventional imaging techniques was designed and implemented. The raw data obtained by the custom imaging system are transferred to a host PC, and then processed for real-time image reconstruction by custom imaging software. The custom imaging software was first developed on a multi-core CPU platform, and then on a graphics processing unit (GPU) platform for better real-time imaging performance and more functionalities, such as real-time volume rendering and dual-mode imaging with both photoacoustic and ultrasound images. Using the custom imaging system and software, real-time imaging was demonstrated for various types of CMUT probes and imaging schemes. The imaging results presented in this dissertation show successful demonstration of real-time imaging for 1-D, rectangular, and annular CMUT arrays with various imaging phantoms.

Download or read book Materials and Failures in MEMS and NEMS written by Atul Tiwari and published by John Wiley & Sons. This book was released on 2015-09-11 with total page 435 pages. Available in PDF, EPUB and Kindle. Book excerpt: The fabrication of MEMS has been predominately achieved by etching the polysilicon material. However, new materials are in large demands that could overcome the hurdles in fabrication or manufacturing process. Although, an enormous amount of work being accomplished in the area, most of the information is treated as confidential or privileged. It is extremely hard to find the meaningful information for the new or related developments. This book is collection of chapters written by experts in MEMS and NEMS technology. Chapters are contributed on the development of new MEMS and NEMS materials as well as on the properties of these devices. Important properties such as residual stresses and buckling behavior in the devices are discussed as separate chapters. Various models have been included in the chapters that studies the mode and mechanism of failure of the MEMS and NEMS. This book is meant for the graduate students, research scholars and engineers who are involved in the research and developments of advanced MEMS and NEMS for a wide variety of applications. Critical information has been included for the readers that will help them in gaining precise control over dimensional stability, quality, reliability, productivity and maintenance in MEMS and NEMS. No such book is available in the market that addresses the developments and failures in these advanced devices.

Download or read book Volumetric Ultrasound Imaging Systems Using Capacitive Micromachined Ultrasonic Transducer CMUT Arrays written by Anshuman Bhuyan and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Medical imaging has become very important in the proper diagnosis of a disease. It has eliminated the need for invasive surgery for evaluation purposes, which can be painful to the patient. There are many modes of medical imaging, ultrasound being one of the most common. Ultrasound imaging provides various advantages compared to other modes that make it very attractive for diagnostic purposes. Conventional ultrasound systems provide real-time 2-D images of the human anatomy and have been used for decades. However, 4-D ultrasound imaging is becoming increasingly popular due to the additional information it provides over conventional 2-D imaging. It makes the imaging procedure less susceptible to the errors of the sonographer and 2-D image slices can be taken at various orientations with respect to the imaging probe allowing convenient offline analysis by the doctor. There are however, several challenges in building such a system. This is because of the requirement of the frontend electronics (typically consisting of LNAs) needing to be very close to the transducer array and the large number of elements that need to be interfaced to the backend system. Also, imaging a volume space requires image processing of a very large dataset that could eventually limit the imaging volume rate. The first part of this dissertation describes a 4-D ultrasound imaging system using Capacitive Micromachined Ultrasonic Transducer (CMUT) technology. Use of CMUTs enables us to address most of the challenges in building such a 4-D ultrasound system. Integrated circuits (IC) with a transmit beamformer and receive signal conditioning circuit were designed and fabricated, and were integrated tightly with the transducer array using flip-chip bonding technology. Different techniques of integration are demonstrated, and the choice between them is dictated by the targeted application. Multi-beam transmit functionality is incorporated in the IC that addresses the issue of limited imaging volume rate in a 4-D ultrasound system. Imaging experiments are presented that illustrate a true real-time volumetric imaging capability of the system. Two other ultrasound systems are also described. One is an extension of the work presented in the first part by incorporating capabilities of therapy using High Intensity Focused Ultrasound (HIFU), in the same 4-D ultrasound imaging system. This would allow physicians to use the same probe for imaging as well as therapy. This system uses an IC similar in design to that used for developing the 4-D ultrasound imaging system. It also consists of a switch network to allow external pulsers to provide a continuous wave sinusoidal excitation to the CMUT transducer. A new high-voltage switch circuit design is presented that is used in the switch network. Finally, a wearable ultrasound probe is presented that is capable of performing 2-D imaging in real-time. Such a probe is useful for applications that require constant or periodic monitoring of body functions and therefore can be worn by the patient at all times. Again, ICs were designed and integrated closely to a 1-D CMUT array. The assembly process is described and imaging results are presented.

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 Transparent Transducers and Fast Electronics for Next generation Ultrasound and Photoacoustic Imaging written by Afshin Kashani Ilkhechi and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Most ultrasound transducers are opaque. Transparent transducers could lead to novel applications, including combined optical and ultrasound imaging, photoacoustic imaging and other multi-modality systems. This thesis introduces transparent capacitive micromachined ultrasound transducers and demonstrates their use for some of these novel applications. Our long-term objective is to develop 2D row-column arrays for 3D ultrasound, photoacoustic, and optical imaging. The achievement of this long-term objective requires stepwise innovation. We first demonstrate 1D array transparent CMUTs, then overcome optical and electrical material property challenges to fabricate the first-ever transparent linear arrays. We demonstrate these arrays for photoacoustic imaging and combined ultrasound and optical imaging. We additionally take steps toward mitigation of dielectric charging problems in these CMUTs using novel thin-film processes. As a step towards 3D \& 4D imaging with row-column arrays, we first design and fabricate needed fast bias-switching electronics and demonstrate their use with non-transparent row-column arrays. Finally, we outline a roadmap for achieving transparent 2D arrays and postulate their future utility for next-generation 3D multi-modal imaging.

Download or read book Ultrasound Imaging Systems Using Capacitive Micromachined Ultrasonic Transducer CMUT Arrays with In Probe Electronic Circuits written by Jean Lunsford Sanders and published by . This book was released on 2021 with total page 107 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Interface Engineering of Capacitive Micromachined Ultrasonic Transducers for Medical Applications written by Der-Song Lin and published by . This book was released on 2011 with total page 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 A Dual mode Ultrasound System for Imaging and High Intensity Focused Ultrasound HIFU with a Single 2 D Capacitive Micromachined Ultrasonic Transducer CMUT Array written by Ji Hoon Jang and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Ultrasound imaging technology has many applications for the medical field and for the public. Thanks to ultrasound imaging, parents can meet their precious child even before the baby is born. In clinical applications, ultrasound is inexpensive, portable and reveals the structure and movement of organs in real time, allowing physicians to monitor the growth and physical development of a fetus. Because there is no ionizing radiation exposure to the patient, it is a very safe technology. In addition to diagnostic applications, ultrasound has been used for therapeutic treatment. High intensity focused ultrasound (HIFU) has been widely used to treat different types of tumors, including those of prostate, liver, breast, kidney, bone and pancreas because of its non-invasive and precise approach for tissue ablation. The basic concept of using HIFU is to focus continuous ultrasound at the focal point and a temperature increase beyond a certain point creates a lesion without damaging the surrounding tissue. For successful HIFU operation, it is important to have a reliable method for guidance and monitoring of the treatment such as ultrasound imaging. Most ultrasound image-guided HIFU systems need separate imaging and HIFU transducers, and require a cooling system due to properties of piezoelectric transducers such as narrow fractional bandwidth and self-heating. As an alternative, capacitive micromachined ultrasonic transducers (CMUTs) have a distinctive advantage over piezoelectric transducers in respect to self-heating and a wide fractional bandwidth. Thus, CMUTs are especially beneficial in dual-mode operations where a single transducer is used for both imaging and therapy. By taking advantage of this CMUT technology, I developed a compact dual-mode ultrasound system that can perform both ultrasound imaging and HIFU with a single 2-D CMUT array. A dual-mode ultrasound probe is equipped with a dual-mode application-specific integrated circuit (ASIC) and a 2-D 32x32-element CMUT array. The dual-mode ASIC consists of pulsers, transmit beamforming circuitry, and low-noise amplifiers for imaging mode and high voltage (HV) switches for HIFU mode. By turning HV switches on and off, the system can alternately operate imaging mode and HIFU mode on demand. A 2-D 32x32-element CMUT array was fabricated to have a center frequency of 5 MHz in immersion. Both ASIC and CMUT array were flip-chip bonded to a custom-designed flexible printed circuit board (flex PCB). After polydimethylsiloxane (PDMS) encapsulation, the acoustic performance of the probe was evaluated. I successfully demonstrated the imaging mode of the dual-mode probe using nylon wire phantom. Using HIFU mode, I measured 7.4 MPa peak-to-peak pressure at 8 mm focal depth. To get higher pressure for the ablation, high AC and DC voltage were used, and CMUT arrays got shorted due to the insulator breakdown. With this probe, obtaining high pressure levels needed for tissue ablation was problematic with CMUTs due to device failure at high voltages. Therefore, I re-optimized a CMUT design that can produce higher output pressure without breakdown or device failure. With CMUT simulation software, the design parameters of CMUT element were optimized with a gap height of 0.13 um and a top plate thickness of 1 um. After it was fabricated and integrated, the dual-mode probe was tested again in an acoustic setup. Compared with previous results, the device shows improved performance without device failure. The focused pressure at F-1 (8 mm) was measured to 16 MPa peak-to-peak. More importantly, most of the device can produce high pressure levels reliably without device failure. Using HIFU simulation software, the specification for HIFU ablation was explored if the dual-mode probe can ablate the tissue. It shows that even with 10 MPa peak-to-peak the dual-mode probe can create the lesion. An ablation test was successfully performed on HIFU phantom gel and ex-vivo tissue using HIFU mode of the dual-mode probe. Another important evaluation as a HIFU probe was the heating of the device. While CMUT array has very low self-heating, because of the power dissipation on HV switches of dual-mode ASIC, the ASIC was heated during HIFU mode. To reduce the heating of dual-mode ASIC, the copper heat sink rod, the chiller, and the water circulation heat sink were added to the system and it significantly reduced the heating. With the thermal management system, the probe was thermally stable around the body temperature during HIFU mode and imaging mode. Lastly, I successfully demonstrated ultrasound image-guided HIFU on HIFU phantom gel with guide wires by switching between imaging mode and HIFU mode using dual-mode ultrasound system. Our studies established a dual-mode HIFU system that will improve the non invasive ablation of tissue. This work of the dual mode system certainly shows the possibility of the new treatment application that was impossible to achieve using the conventional image-guided HIFU system.

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 High Frequency Piezo Composite Micromachined Ultrasound Transducer Array Technology for Biomedical Imaging written by Xiaoning Jiang and published by . This book was released on 2017 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this monograph, the authors reports the current advancement in high frequency piezoelectric crystal micromachined ultrasound transducers and arrays and their biomedical applications. Piezoelectric ultrasound transducers operating at high frequencies (>20 MHz) are of increasing demand in recent years for medical imaging and biological particle manipulation involved therapy. The performances of transducers greatly rely on the properties of the piezoelectric materials and transduction structures, including piezoelectric coefficient (d), electromechanical coupling coefficient (k), dielectric permittivity (e) and acoustic impedance (Z). Piezo-composite structures are preferred because of their relatively high electromechanical coupling coefficient and low acoustic impedance. A number of piezo-composite techniques have been developed, namely "dice and fill," "tape-casting," "stack and bond," "interdigital phase bonding," "laser micromachining" and "micro-molding". However, these techniques are either difficult to achieve fine features or not suitable for manufacturing of high frequency ultrasound transducers (>20 MHz). The piezo-composite micromachined ultrasound transducers (PC-MUT) technique discovered over the last 10 years or so has demonstrated high performance high frequency piezo-composite ultrasound transducers. In this monograph, piezoelectric materials used for high frequency transducers is introduced first. Next, the benefits and theory of piezo composites is presented, followed by the design criteria and fabrication methods. Biomedical applications using piezo composites micromachined ultrasound transducers (PC-MUT) and arrays will also be reported, in comparison with other ultrasound transducer techniques. The final part of this monograph describes challenges and future perspectives of this technique for biomedical applications.

Download or read book Acoustical Imaging Using Capacitive Micromachined Ultrasonic Transducer Arrays written by Ömer Oralkan and published by . This book was released on 2004 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Design Fabrication and Characterization of Capacitive Micromachined Ultrasonic Transducers for Imaging Applications written by Andrew Stephan Logan and published by . This book was released on 2010 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt: Capacitive micromachined ultrasonic transducers (CMUTs) have proven themselves to be excellent candidates for medical ultrasonic imaging applications. The use of semiconductor fabrication techniques facilitates the fabrication of high quality arrays of uniform cells and elements, broad acoustic bandwidth, the potential to integrate the transducers with the necessary electronics, and the opportunity to exploit the benefits of batch fabrication. In this thesis, the design, fabrication and testing of one- and two-dimensional CMUT arrays using a novel wafer bonding process whereby the membrane and the insulation layer are both silicon nitride is reported. A user-grown insulating membrane layer avoids the need for expensive SOI wafers, permits optimization of the electrode size, and allows more freedom in selecting the membrane thickness, while also enjoying the benefits of wafer bonding fabrication. Using a row-column addressing scheme for an NxN two-dimensional array permits three-dimensional imaging with a large reduction in the complexity of the array when compared to a conventional 2D array with connections to all N2 elements. Only 2N connections are required and the image acquisition rate has the potential to be greatly increased. A simplification of the device at the imaging end will facilitate the integration of a three-dimensional imaging CMUT array into either an endoscope or catheter which is the ultimate purpose of this research project. To date, many sizes of transducers which operate at different frequencies have been successfully fabricated. Initial characterization in terms of resonant frequency and, transmission and reception in immersion has been performed on most of the device types. Extensive characterization has been performed with a linear 32 element array transducer and a 32x32 element row-column transducer. Two- and three-dimensional phased array imaging has been demonstrated.

Download or read book Simulation of a Capacitive Micromachined Ultrasonic Transducer with a Parylene Membrane and Graphene Electrodes written by David Sadat and published by . This book was released on 2012 with total page 113 pages. Available in PDF, EPUB and Kindle. Book excerpt: Medical ultrasound technology accounts for over half of all imaging tests performed worldwide. In comparison to other methods, ultrasonic imaging is more portable and lower cost, and is becoming more accessible to remote regions where traditionally no medical imaging can be done. However, conventional ultrasonic imaging systems still rely on expensive PZT-based ultrasound probes that limit broader applications. In addition, the resolution of PZT based transducers is low due to the limitation in hand-fabrication methods of the piezoelectric ceramics. Capacitive Micromachined Ultrasonic Transducers (CMUTs) appears as an alternative to the piezoelectric (PZT) ceramic based transducer for ultrasound medical imaging. CMUTs show better ultrasound transducer design for batch fabrication, higher axial resolution of images, lower fabrication costs of the elements, ease of fabricating large arrays of cells using MEMS fabrication, and the extremely important potential to monolithically integrate the 2D transducer arrays directly with IC circuits for real-time 3D imaging. Currently most efforts on CMUTs are silicon based. Problems with current silicon-based CMUT designs include low pressure transmission and high-temperature fabrication processes. The pressure output from the silicon based CMUTs cells during transmission are too low when compared to commercially available PZT transducers, resulting in relatively blurry ultrasound images. The fabrication of the silicon-based cells, although easier than PZT transducers, still suffers from inevitable high temperature process and require specialized and expensive equipment. Manufacturing at an elevated temperature hinders the capability of fabricating front end analog processing IC circuits, thus it is difficult to achieve true 3D/4D imaging. Therefore novel low temperature fabrication with a low cost nature is needed. A polymer (Parylene) based CMUTs transducer has been investigated recently at UCF and aims to overcome limitations posted from the silicon based counterparts. This thesis describes the numerical simulation work and proposed fabrication steps of the Parylene based CMUT. The issue of transducer cost and pressure transmission is addressed by proposing the use of low cost and low temperature Chemical Vapor Deposition (CVD) fabrication of Parylene-C as the structural membrane plus graphene for the membrane electrodes. This study focuses mainly on comparing traditional silicon-based CMUT designs against the Parylene-C/Graphene CMUT based transducer, by using MEMS modules in COMSOL. For a fair comparison, single CMUT cells are modeled and held at a constant diameter and the similar operational frequency at the structural center. The numerical CMUT model is characterized for: collapse voltage, membrane deflection profile, center frequency, peak output pressure transmission over the membrane surface, and the sensitivity to the change in electrode surface charge. This study took the unique approaches in defining sensitivity of the CMUT by calculating the membrane response and the change in the electrode surface charge due to an incoming pressure wave. Optimal design has been achieved based on the simulation results. In comparison to silicon based CMUTs, the Parylene/Graphene based CMUT transducer produces 55% more in volume displacement and more than 35% in pressure output. The thesis has also laid out the detailed fabrication processes of the Parylene/Graphene based CMUT transducers. Parylene/Graphene based ultrasonic transducers can find wide applications in both medical imaging and Non destructive evaluation (NDE).

Download or read book Capacitive Micromachined Ultrasonic Transducers CMUTs for Therapeutic Applications written by Hyo-Seon Yoon and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: High-intensity focused ultrasound (HIFU) is a noninvasive method to treat a variety of diseases. Most of the HIFU machines in clinic typically consist of a piezoelectric transducer array and an imaging system for temperature monitoring and anatomical location guidance. One of the limitations of piezoelectric transducers is self-heating, which requires cooling systems to protect both transducers and patients. Capacitive micromachined ultrasonic transducers (CMUTs) are another type of transducers fabricated with silicon micromachining. CMUTs are promising candidates as therapeutic transducers, as they experience a lot less self-heating compared to piezoelectric transducers. This dissertation mainly focuses on describing the design, simulation, fabrication, characterization, and experimental results of CMUTs for HIFU applications. Single-element transducers are fabricated using local oxidation of silicon (LOCOS)-wafer-bonding process. The measurement part compares the self-heating of a PZT and a CMUT, and discusses the charging issue of CMUTs. Geometric focusing using multiple single-element CMUTs is also demonstrated. The fabrication of 1-D CMUT arrays to enhance the output pressure for HIFU applications is discussed. Higher output pressure of a CMUT cell can be achieved by adding one extra fabrication step to the existing fabrication process. Two-dimensional transducer arrays are required for electronic focusing and beam steering. An 8-channel continuous wave (CW) excitation system is developed to drive a 2-D CMUT array. This 8-channel system minimizes the system complexity without significant loss of focusing capability, compared to a full system with hundreds to thousands of channels. The first successful 2-D CMUT array fabricated using the thick-buried-oxide (BOX) process is presented. The breakdown issue of the insulation layer observed in the test stage is investigated as well. Another type of 2-D CMUT array fabricated using the sacrificial-release process is also tested for HIFU applications. Using the 8-channel CW excitation system, the 2-D CMUT array has proven to be able to produce enough output pressure for thermal ablation. This dissertation presents the result of ex-vivo experiments, which created thermal lesions on bovine tissue using a CMUT array for the first time.

Download or read book Row column Capacitive Micromachined Ultrasonic Transducers for Medical Imaging written by Albert I-Hsiang Chen and published by . This book was released on 2016 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ultrasound imaging plays an important role in modern medical diagnosis. Recent progress in real-time 3-D ultrasound imaging can offer critical information such as the accurate estimation of organ, cyst, or tumour volumes. However, compared to conventional 2-D ultrasound imaging, the large amount of data and circuit complexity found in 3-D ultrasound imaging results in very expensive systems. Therefore, a simplification scheme for 3-D ultrasound imaging technology is needed for a more wide-spread use and to advance clinical development of volumetric ultrasound. Row-column addressing 2-D array is one particular simplification scheme that requires only N + N addressing lines to activate each element in an N x N array. As a result, the fabrication, circuit, and processing complexity dramatically decrease. Capacitive micromachined ultrasonic transducer (CMUT) technology was chosen to fabricate the array as it offers micro-precision fabrication and a wide bandwidth, which make it an attractive transducer technology. The objective of this thesis is to investigate and demonstrate the imaging potential of row-column CMUT arrays for RT3D imaging. First, the motivation, physics, and modelling of both CMUTs and row-column arrays are described, followed by the demonstration of a customized row-column CMUT pseudo-real-time 3-D imaging system. One particular limitation about row-column arrays discovered as part of this dissertation work is the limited field-of-view of the row-column arrays' imaging performance. A curved row-column CMUT array was proposed to improve the field-of-view, and the resulting modelling of the acoustic field and simulated reconstructed image are presented. Furthermore, a new fabrication process was proposed to construct a curved row-column CMUT array. The resulting device was tested to demonstrate its flexibility to achieve the necessary curvature. Finally, a new wafer bonding process is introduced to tackle the next generation of RC-CMUT fabrication. Many of the new fabrication techniques reported in this work are useful for CMUT fabrication engineers. The analysis on row-column array also provides additional insights for 2-D array simplification research.