@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{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} } @inproceedings{HoKupnikParketal., author = {Ho, Min-Chieh and Kupnik, Mario and Park, Kwan Kyu and Eckhoff, Kristian and Khuri-Yakub, Butrus T.}, title = {Wide pressure range operation of air-coupled CMUTs}, series = {IEEE International Ultrasonics Symposium, Dresden, Germany, 7 - 10 October 2012}, booktitle = {IEEE International Ultrasonics Symposium, Dresden, Germany, 7 - 10 October 2012}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {978-1-4673-4561-3}, doi = {10.1109/ULTSYM.2012.0023}, pages = {93 -- 96}, abstract = {We present measurement results of capacitive micromachined ultrasonic transducers (CMUTs)in permanent contact mode over a wide pressure range(1 - 8 atm). The CMUT plates are in contact with the bottom of the cavities due to atmospheric pressure, even without any dc bias voltage. The electrical input impedance at various dc bias voltages are measured at elevated pressure to characterize individual devices. The open and short circuit resonant frequencies are extracted from the impedance data, and the acoustic performance of pairs of devices is evaluated by performing pitch-catch measurements. A frequency matching method is proposed and used to determine the optimal dc bias voltages for the transmitting and receiving CMUTs individually. Our electrical impedance results show good agreement with the finite element model results (modal and harmonic analysis performed with ANSYS) over the entire pressure range. Moreover, the pitch-catch measurement results validate the proposed frequency matching method for an optimal biasing scheme, and a received signal with good signal-to-noise ratio of 45 dB was observed at a pressure of 7 atm. In conclusion, the behavior of CMUTs in permanent contact mode can be predicted well with our FEA, and they are indeed a promising solution in providing ultrasonic transducers that can operate over a wide pressure range.}, language = {en} } @inproceedings{HoKupnikParketal., author = {Ho, Min-Chieh and Kupnik, Mario and Park, Kwan Kyu and Khuri-Yakub, Butrus T.}, title = {Long-term measurement results of pre-charged CMUTs with zero external bias operation}, series = {IEEE International Ultrasonics Symposium, Dresden, Germany, 7 - 10 October 2012}, booktitle = {IEEE International Ultrasonics Symposium, Dresden, Germany, 7 - 10 October 2012}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {978-1-4673-4561-3}, doi = {10.1109/ULTSYM.2012.0022}, pages = {89 -- 92}, abstract = {We present long-term measurement results (<1.5 years) of CMUTs, which have been pre-charged for zero external bias operation. The fabrication is based on a direct wafer bonding process with a thick-buried-oxide-layer, which allows the realization of only partially connected, donut-shaped bottom electrodes. The only partially connected bottom electrode has a central portion that is completely encapsulated by 3-μm-thick thermally-grown silicon dioxide, and, thus, electrically floating. The devices are pre-charged by applying a dc voltage higher than the pull-in voltage, which injects charges into the electrically floating portion and creates a sufficiently strong intrinsic electric field in the gap. Measurements of resonant frequency at various bias voltages show that the charges have completely remained in the floating portion for the last 19 months. We prove the zero-external-bias operations with the pre-charged CMUTs by measuring the electrical input impedance, the ac signal displacement, and pitch-catch measurements under zero external dc bias voltage. Our results show that pre-charging CMUTs is feasible, and that the devices are capable of long-term, zero external bias voltage operation.}, language = {en} } @inproceedings{HoKupnikVaithilingametal., author = {Ho, Min-Chieh and Kupnik, Mario and Vaithilingam, Srikant and Khuri-Yakub, Butrus T.}, title = {Fabrication and model validation for CMUTs operated in permanent contact mode}, 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 = {1016 -- 1019}, language = {en} } @inproceedings{HoKupnikKhuriYakub, author = {Ho, Min-Chieh and Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {FEA of CMUTs suitable for wide gas pressure range applications}, series = {2010 IEEE International Ultrasonics Symposium (IUS 2010), San Diego, California, USA, 11 - 14 October 2010, vol. 2}, booktitle = {2010 IEEE International Ultrasonics Symposium (IUS 2010), San Diego, California, USA, 11 - 14 October 2010, vol. 2}, publisher = {IEEE}, address = {Piscataway, NJ}, pages = {1234 -- 1237}, language = {en} } @inproceedings{YoonHoApteetal., author = {Yoon, Hyo-Seon and Ho, Min-Chieh and Apte, Nikhil and Cristman, Paul and Vaithilingam, Srikant and Kupnik, Mario and Butts-Pauly, Kim and Khuri-Yakub, Butrus T.}, title = {Fabrication of CMUT cells with gold center mass for higher output pressure}, series = {10th International Symposium on Therapeutic Ultrasound, ISTU 2010, Tokyo, Japan, 9 - 12 June 2010}, booktitle = {10th International Symposium on Therapeutic Ultrasound, ISTU 2010, Tokyo, Japan, 9 - 12 June 2010}, publisher = {American Inst. of Physics}, address = {Melville, NY}, isbn = {978-0-7354-0917-0}, pages = {183 -- 188}, language = {en} }