@inproceedings{KupnikHoVaithilingametal., author = {Kupnik, Mario and Ho, Min-Chieh and Vaithilingam, Srikant and Khuri-Yakub, Butrus T.}, title = {CMUTs for air coupled ultrasound with improved bandwidth}, series = {IEEE International Ultrasonics Symposium 2011, Orlando, Florida, USA, October 18-21, 2011}, booktitle = {IEEE International Ultrasonics Symposium 2011, Orlando, Florida, USA, October 18-21, 2011}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {978-1-4577-1252-4}, pages = {592 -- 595}, language = {en} } @inproceedings{ApteVaithilingamSariogluetal., author = {Apte, Nikhil and Vaithilingam, Srikant and Sarioglu, Ali Fatih and Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {Large area 1D CMUT phased arrays for multi-modality ultrasound imaging}, series = {IEEE International Ultrasonics Symposium 2011, Orlando, Florida, USA, October 18-21, 2011}, booktitle = {IEEE International Ultrasonics Symposium 2011, Orlando, Florida, USA, October 18-21, 2011}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {978-1-4577-1252-4}, pages = {612 -- 615}, language = {en} } @inproceedings{HoHoffmannUngeretal., author = {Ho, Min-Chieh and Hoffmann, Maik and Unger, Alexander and Park, Kwan Kyu and Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {CMUTs in Permanent Contact Operation for High Output Pressure}, series = {Proceedings, ASME 2015 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems and ASME 2015 13th International Conference on Nanochannels, Microchannels, and Minichannels}, booktitle = {Proceedings, ASME 2015 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems and ASME 2015 13th International Conference on Nanochannels, Microchannels, and Minichannels}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5690-1}, doi = {10.1115/IPACK2015-48733}, pages = {6}, language = {en} } @inproceedings{UngerHoffmannHoetal., author = {Unger, Alexander and Hoffmann, Maik and Ho, Min-Chieh and Park, Kwan Kyu and Khuri-Yakub, Butrus T. and Kupnik, Mario}, title = {Finite element analysis of mechanically amplified CMUTs}, series = {Proceedings, 2013 IEEE International Ultrasonics Symposium}, booktitle = {Proceedings, 2013 IEEE International Ultrasonics Symposium}, publisher = {IEEE}, doi = {10.1109/ULTSYM.2013.0074}, pages = {287 -- 290}, abstract = {We introduce the possibility of improving a single-cell capacitive micromachined ultrasonic transducer (CMUT) for air-coupled ultrasound by simply adding a hollow conical-shaped structure (horn) on top of the CMUT plate. The main objective is to improve both transmit and receive sensitivity by lowering the center-to-average displacement ratio, which for bending plate operated devices inherently is limited. In addition, for receive mode the force generated from the impinging sound pressure wave is concentrated to the center of the plate, resulting in larger signals and, in contrast to piston-shaped plates, the horn has the advantage of only moderately increasing the modal mass of the structure. By using finite element analysis and first sound pressure measurements of our modified CMUT, we demonstrate that this idea is feasible and promising for air-coupled CMUTs operating at frequencies below 150kHz, as it has been been proven to be successful for commercially available piezoelectric - driven bending plate devices as well.}, language = {en} } @inproceedings{HoffmannUngerHoetal., author = {Hoffmann, Maik and Unger, Alexander and Ho, Min-Chieh and Park, Kwan Kyu and Khuri-Yakub, Butrus T. and Kupnik, Mario}, title = {Volumetric characterization of ultrasonic transducers for gas flow metering}, series = {Proceedings, 2013 IEEE International Ultrasonics Symposium}, booktitle = {Proceedings, 2013 IEEE International Ultrasonics Symposium}, publisher = {IEEE}, doi = {10.1109/ULTSYM.2013.0336}, pages = {1315 -- 1318}, abstract = {The design of ultrasonic gas flowmeters requires a thorough three dimensional characterization of the acoustic sound field. For large pipe flowmeters, such as used for flare gas metering, the transducers are operated at frequencies ranging from 20 kHz up to 150 kHz. Thus, in this work we use a commercially available calibrated 1/8-inch microphone, mounted on a 3D positioning system for performing volumetric measurements in a volume of up to 1x1x1 m. By using proper corrections in terms of angular and free-field response of the microphone, the measurement system is efficient and delivers around 30000 measurements in about only eight hours. The data then is visualized in form of 3D figures or various slices to extract all relevant information. The system has been used to identify non-uniform velocity profiles in capacitive micromachined ultrasonic transducers (CMUTs), operating in permanent contact mode. Further, the system can be used to investigate the effect of various acoustic boundary conditions the transducers are facing when mounted inside transducer port cavities and it can be used for general model validation purpose.}, language = {en} } @inproceedings{HoParkEckhoffetal., author = {Ho, Min-Chieh and Park, Kwan Kyu and Eckhoff, Kristian and Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {Air-coupled CMUTs operating at ambient pressures ranging from 1 to 20 atm}, series = {Proceedings, 2013 IEEE International Ultrasonics Symposium}, booktitle = {Proceedings, 2013 IEEE International Ultrasonics Symposium}, publisher = {IEEE}, doi = {10.1109/ULTSYM.2013.0358}, pages = {1412 -- 1415}, abstract = {We present impedance and pitch-catch measurements of capacitive micromachined ultrasonic transducers (CMUTs) in permanent contact mode with improved mechanical strength that demonstrate functionality up to 20 atm ambient pressure. Changes in device design and fabrication are made to improve the mechanical strength of the CMUT plates, including using smaller deflection to thickness ratio (9 - 33\%), choosing better quality SOI wafers (bowing < 20 μm), and designing a much larger bonding area (300 - 700 μm overlap in radial direction) for each cell. As a result, all designs with 2000 μm radius, 65-μm-thick plates, 7.74 μm gap heights and with 300, 500, and 700 μm wide bonding area overlap for the plate, performed from 1 - 20 atm without a single failure. Despite larger bonding area, pitch-catch measurements with these CMUTs (700 μm bonding width biased at 250 Vdc still give received signal with good SNR even at 20 atm. Our results support that such CMUTs are reliable and efficient over a wide pressure range.}, language = {en} } @misc{SariogluKupnikVaithilingametal., author = {Sarioglu, Ali Fatih and Kupnik, Mario and Vaithilingam, Srikant and Khuri-Yakub, Butrus T.}, title = {Nanoscale topography of thermally-grown oxide films at right-angled convex corners of silicon}, series = {Journal of The Electrochemical Society}, volume = {159}, journal = {Journal of The Electrochemical Society}, number = {2}, issn = {0013-4651}, doi = {10.1149/2.005202jes}, pages = {79 -- 84}, language = {en} } @misc{KupnikKhuriYakub, author = {Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {Monolithic integrated CMUTs fabricated by low temperature wafer bonding}, abstract = {Low temperature wafer bonding (temperature of 450°C. or less) is employed to fabricate CMUTs on a wafer that already includes active electrical devices. The resulting structures are CMUT arrays integrated with active electronics by a low-temperature wafer bonding process.The use of a low-temperature process preserves the electronics during CMUT fabrication. With this approach, it is not necessary to make compromises in the CMUT or electronics designs, as is typical of the sacrificial release, such as low process control, poor design flexibility, low reproducibility, and reduced performance are avoided with the present approach. With this approach, a CMUT array can be provided with per-cell electrodes connected to the substrate integrated circuitry. This enables complete flexibility in electronically assigning the CMUT cells to CMUT array elements.}, language = {en} } @misc{LeeParkKupniketal., author = {Lee, Hyunjoo J. and Park, Kwan Kyu and Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {Functionalization layers for CO2 sensing using capacitive micromachined ultrasonic transducers}, series = {Sensors and Actuators B: Chemical}, journal = {Sensors and Actuators B: Chemical}, number = {174}, issn = {0925-4005}, pages = {87 -- 93}, abstract = {Sensing of carbon dioxide(CO2)using inexpensive, miniaturized,and highly sensitive sensors is of great interest for environmental and consumer applications. In this paper, we present four functionalization layers that are suitable for resonant sensors based on mass-loading for CO2 detection. We compare the volume sensitivities of these layers to CO2 and relative humidity (RH) by using a highly sensitive 50-MHz capacitive micromachined ultrasonic transducer (CMUT) as a resonant sensor. Among the four function-alization layers, the layer based on a guanidine polymer exhibits the highest volume sensitivity to CO2 of 1.0 ppm/Hz in N2 and 3.8 ppm/Hz in air (∼45\%RH). Furthermore, we report on other important characteristics of the guanidine polymer for sensing applications, including polymer saturation, regeneration, and repeatability.}, language = {en} } @misc{LeeParkKupniketal., author = {Lee, Hyunjoo J. and Park, Kwan Kyu and Kupnik, Mario and Melosh, Nicholas A. and Khuri-Yakub, Butrus T.}, title = {Mesoporous thin-film on highly sensitive resonant chemical sensors for relative humidity and CO2 detection}, series = {Analytical Chemistry}, volume = {84}, journal = {Analytical Chemistry}, number = {7}, issn = {1520-6882}, doi = {10.1021/ac300225c}, pages = {3063 -- 3066}, abstract = {Distributed sensing of gas-phase chemicals is a promising application for mesoporous materials when combined with highly sensitive miniaturized gas sensors. We present a direct application of a mesoporous silica thin film on a highly sensitive miniaturized resonant chemical sensor with a mass sensitivity at the zeptogram scale for relative humidity and CO2 detection. Using mesoporous silica thin-film, we report one of the lowest volume resolutions and a sensitive detection of 5.1 × 10-4\% RH/Hz to water vapor in N2, which is 70 times higher than a device with a nontemplated silica layer. In addition, a mesoporous thin-film that is functionalized with an amino-group is directly applied on the resonant sensor, which exhibits a volume sensitivity of 1.6 × 10-4\%/Hz and a volume resolution of 1.82 × 10-4\% to CO2 in N2.}, language = {en} }