TY - CHAP A1 - Ho, Min-Chieh A1 - Hoffmann, Maik A1 - Unger, Alexander A1 - Park, Kwan Kyu A1 - Kupnik, Mario A1 - Khuri-Yakub, Butrus T. T1 - CMUTs in Permanent Contact Operation for High Output Pressure T2 - 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 Y1 - 2015 SN - 978-0-7918-5690-1 U6 - https://doi.org/10.1115/IPACK2015-48733 PB - ASME CY - New York, NY ER - TY - CHAP A1 - Unger, Alexander A1 - Hoffmann, Maik A1 - Ho, Min-Chieh A1 - Park, Kwan Kyu A1 - Khuri-Yakub, Butrus T. A1 - Kupnik, Mario T1 - Finite element analysis of mechanically amplified CMUTs T2 - Proceedings, 2013 IEEE International Ultrasonics Symposium N2 - 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. Y1 - 2013 U6 - https://doi.org/10.1109/ULTSYM.2013.0074 SP - 287 EP - 290 PB - IEEE ER - TY - CHAP A1 - Hoffmann, Maik A1 - Unger, Alexander A1 - Ho, Min-Chieh A1 - Park, Kwan Kyu A1 - Khuri-Yakub, Butrus T. A1 - Kupnik, Mario T1 - Volumetric characterization of ultrasonic transducers for gas flow metering T2 - Proceedings, 2013 IEEE International Ultrasonics Symposium N2 - 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. Y1 - 2013 U6 - https://doi.org/10.1109/ULTSYM.2013.0336 SP - 1315 EP - 1318 PB - IEEE ER - TY - CHAP A1 - Ho, Min-Chieh A1 - Park, Kwan Kyu A1 - Eckhoff, Kristian A1 - Kupnik, Mario A1 - Khuri-Yakub, Butrus T. T1 - Air-coupled CMUTs operating at ambient pressures ranging from 1 to 20 atm T2 - Proceedings, 2013 IEEE International Ultrasonics Symposium N2 - 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. Y1 - 2013 U6 - https://doi.org/10.1109/ULTSYM.2013.0358 SP - 1412 EP - 1415 PB - IEEE ER - TY - GEN A1 - Lee, Hyunjoo J. A1 - Park, Kwan Kyu A1 - Kupnik, Mario A1 - Khuri-Yakub, Butrus T. T1 - Functionalization layers for CO2 sensing using capacitive micromachined ultrasonic transducers T2 - Sensors and Actuators B: Chemical N2 - 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. Y1 - 2012 SN - 0925-4005 IS - 174 SP - 87 EP - 93 ER - TY - GEN A1 - Lee, Hyunjoo J. A1 - Park, Kwan Kyu A1 - Kupnik, Mario A1 - Melosh, Nicholas A. A1 - Khuri-Yakub, Butrus T. T1 - Mesoporous thin-film on highly sensitive resonant chemical sensors for relative humidity and CO2 detection T2 - Analytical Chemistry N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1021/ac300225c SN - 1520-6882 VL - 84 IS - 7 SP - 3063 EP - 3066 ER - TY - CHAP A1 - Ho, Min-Chieh A1 - Kupnik, Mario A1 - Park, Kwan Kyu A1 - Eckhoff, Kristian A1 - Khuri-Yakub, Butrus T. T1 - Wide pressure range operation of air-coupled CMUTs T2 - IEEE International Ultrasonics Symposium, Dresden, Germany, 7 - 10 October 2012 N2 - 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. Y1 - 2012 SN - 978-1-4673-4561-3 U6 - https://doi.org/10.1109/ULTSYM.2012.0023 SP - 93 EP - 96 PB - IEEE CY - Piscataway, NJ ER - TY - CHAP A1 - Ho, Min-Chieh A1 - Kupnik, Mario A1 - Park, Kwan Kyu A1 - Khuri-Yakub, Butrus T. T1 - Long-term measurement results of pre-charged CMUTs with zero external bias operation T2 - IEEE International Ultrasonics Symposium, Dresden, Germany, 7 - 10 October 2012 N2 - 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. Y1 - 2012 SN - 978-1-4673-4561-3 U6 - https://doi.org/10.1109/ULTSYM.2012.0022 SP - 89 EP - 92 PB - IEEE CY - Piscataway, NJ ER - TY - GEN A1 - Park, Kwan Kyu A1 - Lee, Hyunjoo J. A1 - Kupnik, Mario A1 - Oralkan, Ömer A1 - Ramseyer, Jean-Pierre A1 - Lang, Hans Peter A1 - Hegner, Martin A1 - Gerber, Christoph A1 - Khuri-Yakub, Butrus T. T1 - Capacitive micromachined ultrasonic transducer (CMUT) as a chemical sensor for DMMP detection T2 - Sensors and Actuators B: Chemical Y1 - 2011 U6 - https://doi.org/10.1016/j.snb.2011.09.036 SN - 0925-4005 VL - 160 IS - 1 SP - 1120 EP - 1127 ER - TY - GEN A1 - Park, Kwan Kyu A1 - Lee, Hyunjoo J. A1 - Kupnik, Mario A1 - Khuri-Yakub, Butrus T. T1 - Fabrication of capacitive micromachined ultrasonic transducers via local oxidation and direct wafer bonding T2 - Journal of Microelectromechanical Systems Y1 - 2011 U6 - https://doi.org/10.1109/JMEMS.2010.2093567 SN - 1941-0158 VL - 20 IS - 1 SP - 95 EP - 103 ER -