Study Fluid-membrane Interaction With Micro Lamb Wave Sensor

Micro Lamb wave sensor is one of useful tools to study the membrane-fluid interaction, especially in interdisciplinary and not yet explored areas, such as gas sensing, aerodynamics, the multi-parameters decoupling and so on. This is because micro Lamb wave sensor holds high sensitivity, low losses and multi-modes. This thesis deals with the membrane-fluid interaction with micro Lamb wave sensor theoretically and experimentally. The details are described as follows:In theory, combinations of the potential function method and the boundary conditions at all interfaces are used to analyze the membrane-fluid interaction. There are several aspects of this problem can addressed, including the displacement, the stress, velocity dispersion curve, Poynting vector, group velocity, energy velocity and so on. In the case of micro Lamb wave sensor, the resonant modes can be excited and worked simultaneously with the traveling modes, as the membrane is width limited and not large enough comparing with the wavelength of Lamb waves. The established model can reveal the mode distributions in micro Lamb wave device clearly and accurately. These works provide insight into the understandings of the modes in micro Lamb wave device, which is useful for further experiments.The gases effects on the evanescent wave and leaky wave near the membrane-gas interface are studied. The relative frequency shifts in the low frequency range of the A0 mode (evanescent wave, EW) is rather important and the shape of the curve looks like'U'shape. In the high frequency range of this mode (leaky Lamb wave, LLW), the quality factor decreases rapidly when the Lamb wave phase velocity approaches the gas sound velocity. The S0 mode shows immune to gas loading, which can be used as reference mode. This provides theoretical and experimental works for related fields in gas sensing. The application of membrane-gas interaction in aerodynamics is investigated theoretically and experimentally. The interaction between the gas flow boundary layer and the acoustic sound field (EW and LLW) at the membrane-gas interface can give out the parameter in the gas flow. In the EW case, the thickness of the gas flow boundary layer and the penetration depth of the evanescent wave are the two factors determining the sensitivity. When the Lamb wave phase velocity approaches the gas sound velocity, the gas flow effect is clearly observed. In the LLW case, it is shown experimentally that the gas flow has not evident effects on Lamb wave's propagations.At the membrane-liquid interface, the effects of different physical parameters (density, sound velocity, viscosity, etc) on the modes'propagations are studied. The liquid ingredients and components can be indentified quantitatively. Combination of the relative frequency shifts of the A01 mode (low frequency of A0 mode) and the A03 mode (the third harmonic wave of the A01 mode), the density and the sound velocity of the liquid can be decoupled. With the determined density, the amplitude in the S0 mode can decouple the viscosity of the liquid.