@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} }