Introduction:
-Shear methods only probe small surface layer
-2nd coefficient of viscosity can only be probed with acoustics
-Inline measurements can be made
-Tubes avoid spurious diffraction (which take computational effort to correct for)
Theory:
-Based on viscous attenuation of pressure waves
Patent which becomes 2nd Paper:
Introduction:
-liquid properties can be probed
-inline acoustic microscope
-Target analytes do not need to be trapped on surface with coating which need refreshing once saturated
Theory:
Jie Xu et al.\cite{Xu_2017} derive an analytical model, as does Volghuber-Brunnmaier et al.\cite{Voglhuber_Brunnmaier_2013}. Both papers neglect mounting conditions, and ignore shear forces.
Volghuber-Brunnmaier identifies unexpected additional peaks in real data, this is likely not from axial or circumferential modes but rather imperfections in the piezo itself.
Jie Xu shows there is coupling between the axial and radial modes when the aspect ratio of the the diameter and length of a piezoelectric tube are close to unity. However our experiments show that damping of spurious modes can be achieved with different mounting conditions. Axial clamping can reduce axial modes and encasing the piezo tube in a coupled cylinder can reduce radial mode. In this way the dominant mode of short-fat tubes can be tubed depending on the specified application.
Long tubes only, arbitrary radius\cite{Lin_2012}
Finally, a series of mechanical and geometrical aspects, such as flatness and parallelism, have to be taken into account. \cite{Chac_n_2006}
Piezotubes saw increased interest in the 90's as intelligent structures\cite{Hashemi_2014}\cite{Rajapakse_1997}
Compound piezo tubes have been used as fluid property sensors\cite{Kielczynski_2007}