Surface micromachined CMUTs for liquid phase sensing

Interdigitally arranged and integrated with the polymer microchannels capacitive micromachined ultrasound transducers (CMUT) were designed, fabricated and tested for transverse waves, preferably Scholte type waves, excitation and receive. CMUTs were used for verification of the finite element model dedicated to predict the ability of sensing the elasticity of tethered phospholipid bilayers in liquid environment. Also, the sensitivity of the transducer and microchannel assembly to the liquid properties was tested while recording in the real time the amplitude of the received Scholte type transverse wave. Mixtures of isopropyl alcohol (IPA) and water in fractions of 10:1, 20:1 and 50:1 was used for this test. Finite element analysis predicted that considerable sensitivity of the received Scholte wave amplitude to the tethered phospholipid bilayer elasticity change from 2 to 5 GPa can be expected. The real-time sensing of the liquid mixture concentration changes revealed that even 2% water content increase (50:1 mixture case) can be sensed as 100 mV transition of the Scholte wave amplitude. Greater concentration changes caused up to 700 mV transition of the received wave amplitude.