Browsing by Subject "Acoustic coupling"

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Open Access
Analysis of mutual acoustic coupling in CMUT arrays using an accurate lumped element nonlinear equivalent circuit model
(2012) Oğuz, H.Kağan; Atalar, Abdullah; Köymen, Hayrettin
We use an accurate nonlinear equivalent circuit model to analyze CMUT arrays with multiple cells, where every cell in the array is coupled to other cells at their acoustic terminals through a mutual radiation impedance matrix. We get results comparable to finite element analysis accuracy. Hence, the analysis of a large array becomes a circuit theory problem and can be scrutinized with circuit simulators. We study the mutual acoustic interactions that arise through the immersion medium due to the influence of the generated pressure field by each cell on the others. We compare the performance of different 1D cMUT arrays, where each element is half-wavelength wide and 10 and 20 wavelengths long at the resonance frequency of a single cell. © 2012 IEEE.
Open Access
MEMS based ultrasonic gas sensor with universal sensing capability
(2023-09) Erkan, Derin
Gas sensors are a critical technology for life safety, process control, and most recently air quality measurements. Currently utilized gas sensing technologies need to be tailored to each specific gas, using either a chemically reactive substrate or an optical detector sensitive to certain gas types, providing very good selectivity at the expense of flexibility. In contrast, acoustic sensors promise a potentially universal method of gas sensing with lower selectivity, by measuring the speed of sound in a resonant cavity and inferring the gas content. In this work, a proof of concept for a MEMS based acoustic gas sensor is proposed. A horizontal cavity allows for a compact design, compared to vertical designs shown in the literature. Fabrication is simplified compared to existing CMUT/PMUT designs by using electrically tunable in-plane resonators as transducers. Fabrication of the designed sensor is carried out using an in-house developed SOI-MEMS process, while acoustic cavities are fabricated from silicon. During operation, one resonator excites the cavity while the other resonator measures the response. Frequency sweeps of the resonators while varying the tuning allows full characterization of device response. Overlaying sweeps at different tuning parameters reveals the cavity response, while testing with no cavity rules out parasitic effects. Both speed of sound and quality factor are observed, which can be used to improve selectivity in gas mixtures. The proof of concept device is tested in ambient air, measuring the speed of sound in air as 342 m/s, consistent with the literature and with external measurements.