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UBC Theses and Dissertations

All-polymer flexural plate wave sensors Busch, John Robert


A novel all-polymer flexural plate wave (FPW) sensor from a piezoelectric polyvinylidene fluoride (PVDF) thin-film with poly-(3,4-ethylenedioxythiophene) poly- (styrenesulfonate) (PEDOT:PSS) interdigital transducer (IDT) electrodes has been fabricated and characterized. PVDF films are made piezoelectric by stretching and poling. X-ray diffraction measurements confirm the transition of the PVDF into its piezoelectric β-phase. Inks of PEDOT:PSS, dimethyl sulfoxide and Triton X-100 are deposited on the PVDF films by inkjet printing to produce the IDT patterns. The sensor operates using fundamental frequency, f0, detection of Lamb waves propagating through the PVDF film. Upon the application of a time-varying voltage signal to the input IDT, acoustic waves are generated and measured using a laser Doppler vibrometer, as well as through an electric signal at the output IDT. The output signal is amplified, filtered and processed using an analog to digital converter, digital signal processor and a computer program. The measured fundamental frequencies range from 330 to 1600 kHz for devices with 18 and 125 micron thick PVDF substrates and 800 and 400 micron acoustic wavelengths. These values for fundamental frequency are well predicted by the device geometry using Lamb wave theory. The effect of mass-loading was characterized by inkjet printing layers of polyvinyl alcohol on the sensors and measuring the resulting frequency shift. The devices demonstrate a frequency shift, Δf , to mass loading, m, with a measured resonance frequency mass sensitivity of Δf/(mf0) = -55.9 cm²/g. Temperature sensitivity was measured to be 1870 Hz/ C. Sensors were also coated with a sensing layer of polyvinyl acetate and its response to toluene and acetone vapour concentrations was characterized.

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