Broad bandwidth air-coupled micromachined ultrasonic transducers for gas sensing

The present work aims to develop ultra-wide bandwidth air-coupled capacitive micromachined ultrasonic transducers (CMUTs) for binary gas mixture analysis. detection principle is based on time-of-flight (ToF) measurements, in order monitor ultrasound velocity variations. To perform such CMUTs were especially designed out of resonance mode, like a microphone. chosen membrane size 32 × µm2 and gap height 250 nm. frequency collapse voltage found at 8 MHz 58 V respectively. As mentioned, the exploited quasi-static operating very low band, from 1 1.5 frequencies. transducer impulse response was characterised, ?6 dB relative fractional (FBW) higher than 100% measured, enabling use CMUT targeted application. Additionally, measuring cell has been hold fabricated emitter receiver prototypes facing each other. volume inside kept lower 3 mL surface emitter/receiver 1.6 mm2. validate general proposed technique, two mixtures CO2/N2 H2/N2, with varying concentrations, have tested. results are promising measured limit (LOD) 0.3% CO2 N2 0.15% H2 N2.