Implications of a low stiffness substrate in lamb wave gas sensing applications

VOC detection using an all polymer flexural plate wave sensor

“…In both cases, the frequency decreases with increasing toluene vapor concentration, suggesting a primarily mass sensitive device. Over the linear range, the mass sensitivity of the PS coated sensors ranged from -80 cm 2 /g to -200 cm 2 /g while that of the PVAc coated sensors ranged from -240 cm 2 /g to -490 cm 2 /g [2].…”

“…For a mass sensing only FPW detector, the sensitivity of the device can be estimated with the inverse of the mass density of the substrate and polymer layer [2]. A device of this density and thickness has a predicted sensitivity of -120 cm2/g.…”

“…As detailed in [1], the wave velocity and frequency of the fundamental, antisymmetric mode of propagation for a flexural plate wave can be approximated using Kirchoff's plate equation for thin plates In a previous model, these variables were obtained from experimentation and literature [1,2]. Due to the lack of complete experimental mechanical data available on PVAc and PS in the presence of toluene vapor, mass density, thickness and Young's modulus are described using Flory-Huggins (FH) solution theory.…”

“…Concentration was adjusted by varying the relative flow rate of clean and toluene-saturated air while maintaining constant total flow. During operation, a custom chirp signal with a 160 kHz centre frequency and 300 Vpp amplitude was applied to the input of the sensor to generate FPWs in the substrate [1][2][3]. For these experiments, one sensor was coated in PVAc and PS and exposed over 3 different test sessions for each of the two layers.…”

“…PDVF flexural plate wave acoustic sensors have shown promise as inexpensive chemical detectors [1][2][3]. Due to the low stiffness of the substrate, these devices can measure analyte induced density, thickness, stress and elasticity changes in a polymer sensing layer.…”